Some of you may remember sometime back that I did a considerable amount of work re-doing our solar system. Replacing the two hose batteries from Gel to AGM, and then, having three 150w panels on the roof began a re hash. I replaced two solar controllers with one big one, ran new wiring to the controller to reduce the wire length and increased its size. The fitted all panels with blocking diodes that's for those again Terry and Tony.
Well all worked fine, and with ideal conditions supplies us with plenty of solar, but I had the nagging thought I had made a bo bo. It was also at that time there was a debate on here about PWM verses MPPT controllers, which I had begun to read, but it had involved into a huge argument so I didn't bother reading further, however as my reading of other documents continued, I have begun to realize that I should have fitted a MPPT controller and wired up all the panels in series.
Because we have a 12v fridge, our power is continuously being used, it is important the batteries are brought up to full charge each day, the problem that occurs is on overcast days, or really hot days with hot winds. It seems the MPPT will harvest more solar during low light conditions and when the panels get hot and the panel voltage drops. Preamble over!
My question is, do I still need to use the blocking diodes if the panels are wired in series, and if so how are the diodes wired into the circuit?
Whenarewethere said
11:40 AM Mar 4, 2019
My 6 x 20 watt panels are 2 panels in series, 3 sets in parallel. No diodes anywhere. I have tried shadowing 1 or 2 sets & the amps input to the controller goes down by a 1/3 or 2/3. Output seems to be a bit better depending on battery voltage.
Large panels may be a different situation & may need diodes. But I am no expert.
T1 Terry said
12:30 PM Mar 4, 2019
I'll put forward an argument that the MPPT controller can produce more battery charging output than a good quality PWM controller with the correct wiring.
The first argument is based around the amount of electronics involved in an MPPT controller compared to a PWM controller. There is no such thing as an electronic component that is 100% efficient, they all have losses in the form of electrical energy being converted to heat energy. The proof is the comparative size of the heat sink between the two types for a given output. A PWM controller does not require a fan, yet many MPPT controllers do require at least one fan and will shut down if it stops working to protect itself against thermal stress.
If the MPPT controller wastes more electrical energy as heat compared to a PWM controller, how can it possibly produce more electrical output in poor light conditions?
The next argument involves total solar harvest for the day. It is an established fact a PWM controller will start to produce and electrical output before an MPPT controller with the same amount of solar input and will still be producing output after the MPPT controller has stopped producing a useable output. This is because the MPPT controller requires energy to actually do anything, if that energy requirement is equal to the energy harvested from the solar the MPPT controller will still be functioning but not actually putting anything out at a level worth mentioning. Anything less than 0.5 amp is not a useful amount of energy when it comes to lead acid battery charging.
The next argument is in regards to safe working voltages and the capability of the MPPT controller to hand the open circuit voltages of a series array. There is no value in a controller that can handle 150vdc open circuit voltage if you have to pay a solar installer to do all the work as well as any maintenance work required. This limits the number of panels that can be connected in a single string. Connecting series strings in parallel to feed the one controller means any shading on any single panel in each series string will result in the loss of output from that section. This is because the voltage from that section will now be less than the voltage from the other series sections connected in parallel to the same controller. The higher output series strings will simply block and output from the lower voltage string because voltage wins that fight every time.
The last argument I'll put forward at the moment is the requirement for even more diodes in the system. Not only blocking diodes are required but bypass diodes as well to prevent turning an even slightly shaded panel into a heater and wasting the electrical energy produced by the other panels in the string.
So, will an MPPT controller really improve your useable output from the controller? Simply harvesting more solar does not mean you will get more useable electrical input into the system.
T1 Terry
Jaahn said
01:38 PM Mar 4, 2019
Hi Iana
This is my opinion on your setup. It is what I would do ! and indeed I do.
I do not know what the specs of your panels are. However I would not put the panels in series but leave them in parallel. This means there is a better result if there is any shading. One panel can drop out and you just loose that panel. With series it is more complicated. Series has some saving due to the cable losses being reduced, but you can improve the cable to a bigger size for parallel at a modest one-off cost to a common join point on the roof. Always worth the cost for improved output in MPPT mode IMHO.
The MPPT reg will increase the output by about the same amount in parallel or series in normal condition Under some odd conditions there will be less for sure. Not significent in my opinion overall. The MPPT reg increase will certainly be best at low battery voltages. The extra is probably only 15% overall and perhaps up to 25% in the right conditions for short times. At low sun times the extra for series usually is not very much. The PWM reg will not harvest the voltage above the battery voltage at any time so having well matched panels is then important.
I do not intend to discuss with other people the pros and cons as it has been over argued here. I suggest people only address your specific situation and nothing else. IMHO.
If you want more output in poor conditions making a panel or more, mobile so you can chase the sun may be more productive. Or tilting the panels in hot weather cools them much better than flat on the roof.
Jaahn
-- Edited by Jaahn on Monday 4th of March 2019 01:55:13 PM
iana said
02:06 PM Mar 4, 2019
Struooooth, Bloody Hell and all that!, and it will be all on again, I really don't want that.
T1 Terry wrote:
I'll put forward an argument that the MPPT controller can produce more battery charging output than a good quality PWM controller with the correct wiring.
The first argument is based around the amount of electronics involved in an MPPT controller compared to a PWM controller. There is no such thing as an electronic component that is 100% efficient, they all have losses in the form of electrical energy being converted to heat energy. The proof is the comparative size of the heat sink between the two types for a given output. A PWM controller does not require a fan, yet many MPPT controllers do require at least one fan and will shut down if it stops working to protect itself against thermal stress. If the MPPT controller wastes more electrical energy as heat compared to a PWM controller, how can it possibly produce more electrical output in poor light conditions?
Both the controllers I have been looking at do not have fans, but your argument is valid. Its a bit like chewing a tough steak, is the energy used to chew the steak going to be more than the energy one can extract from the steak, and chewing would also produce heat. However from what I have read, being able to convert voltage into amps meant capturing power that was otherwise lost.
The next argument involves total solar harvest for the day. It is an established fact a PWM controller will start to produce and electrical output before an MPPT controller with the same amount of solar input and will still be producing output after the MPPT controller has stopped producing a useable output. This is because the MPPT controller requires energy to actually do anything, if that energy requirement is equal to the energy harvested from the solar the MPPT controller will still be functioning but not actually putting anything out at a level worth mentioning. Anything less than 0.5 amp is not a useful amount of energy when it comes to lead acid battery charging.
The problem I had with the solar panels being hot, was the voltage dropped down to 13v, so with the PWN controller, the batteries would never reach full charge until ambient temperature dropped, however by using a MPPT controller, with panels in series, the input voltage was high, regardless of the panel voltages dropping. The information I have read say that the MPPT controller will start or be harvesting more solar in poor light conditions.
The next argument is in regards to safe working voltages and the capability of the MPPT controller to hand the open circuit voltages of a series array. There is no value in a controller that can handle 150vdc open circuit voltage if you have to pay a solar installer to do all the work as well as any maintenance work required. This limits the number of panels that can be connected in a single string. Connecting series strings in parallel to feed the one controller means any shading on any single panel in each series string will result in the loss of output from that section. This is because the voltage from that section will now be less than the voltage from the other series sections connected in parallel to the same controller. The higher output series strings will simply block and output from the lower voltage string because voltage wins that fight every time.
At what point does "Low Voltage" become "High Voltage" i.e. 3x panels in series = 54v. The rest of your statement does not create enthusiasm for me on the issue.
The last argument I'll put forward at the moment is the requirement for even more diodes in the system. Not only blocking diodes are required but bypass diodes as well to prevent turning an even slightly shaded panel into a heater and wasting the electrical energy produced by the other panels in the string.
This can be done, I have seen examples of circuits having those diodes.
So, will an MPPT controller really improve your useable output from the controller? Simply harvesting more solar does not mean you will get more useable electrical input into the system.
T1 Terry
A hi ambient temperature seems to have the most power usage, the fridge goes continuously, and we have fans going to make up for lack of air-con. The plan was to get a portable panel and use it on an angle in the mornings, but that involves more weight on the rig, when I know we are sailing close to the wind weight wise, it seemed by changing the controller, we could gain more power with no weight gain. On the other hand I have the system wired up for this, and I am looking at a fairly major re-vamp again.
The PMN controller is a Projecta SC45 (45 Amps), so I assume that it is of reasonable quality.
Open to any suggestions, but no argument, you all be good now.
Whenarewethere said
02:35 PM Mar 4, 2019
Looking at this from the other end, how much does your fridge draw typically, & also in hot weather, over a 24 hour period.
I am consuming about 15 to 18AH per 24 hours with 78AH of batteries. I would like a bit more battery capacity but finding a space is an issue.
Jaahn said
06:20 PM Mar 4, 2019
Hi Iana
What are the specs of your panels. If you are having trouble in very hot weather they may not be 36 cell panels and the max power voltage may be too low !! If so the MPPT reg will not give much advantage. So please give the specs off the back of the panels so we can help. Are they all the same specs or different.
Jaahn
iana said
06:34 PM Mar 4, 2019
Coast to Coast 150W Mono-crystalline solar module. No.of cells 36, max power output (pm) 150W, Output tolerance 0/+3%, Open circuit voltage (Voc) 22.40V, Short Circuit current (Isc) 8.66A, Max power voltage (Vpm) 18.10V, no. of diodes 2, series Fuse rating 10A, max system voltage 1000VDC, Testing condition AM1.5, 1000W/m2, 25 degrees C. Three of these panels.
The day in question was a real hum dinger, 40" hot northerly wind.
But the main thing is we won't have enough power in the winter with shorter days and the sun lower on the horizon.
Bagmaker said
07:37 PM Mar 4, 2019
And their voltages dropped to 13 when hot?
Jaahn said
10:00 AM Mar 5, 2019
iana wrote:
Coast to Coast 150W Mono-crystalline solar module. No.of cells 36, max power output (pm) 150W, Output tolerance 0/+3%, Open circuit voltage (Voc) 22.40V, Short Circuit current (Isc) 8.66A, Max power voltage (Vpm) 18.10V, no. of diodes 2, series Fuse rating 10A, max system voltage 1000VDC, Testing condition AM1.5, 1000W/m2, 25 degrees C. Three of these panels. The day in question was a real hum dinger, 40" hot northerly wind. But the main thing is we won't have enough power in the winter with shorter days and the sun lower on the horizon.
Hi Iana
Those panels look OK and should do the job. I have never been in a situation where I have seen my panel voltage drop to 13V or indeed when it will not bring the battery up to full charge voltage in full sun so I cannot comment on that.
However you are obviously short of solar power generally. I do not believe that fitting a MPPT reg will be the saviour you need. It will only give you about 15% more, ie about 70W extra normally overall. And it will not do much in the extreme heat unless you have the panels wired in series but the power from them will still be seriously reduced at 13V each. You really need another panel at least ie 33% more. I cannot help you with the extra weight problem.
But as whenarewethere suggests you could look at the other side and see what you can do about your consumption. The fridge is always the killer. Can you add insulation to it and a cooling fan for the heat rejection side, this might be worth trying. Even a heat shield on the outside with a gap, to shield the fridge area from the direct sun and heat.
Cheers Jaahn
-- Edited by Jaahn on Tuesday 5th of March 2019 10:09:34 AM
iana said
02:06 PM Mar 5, 2019
Yes agree the fridge is the killer, it is a compressor fridge.
1/ Can I add insulation to it ? Its a tight fit, I really don't see how you could insulate it further. If would also mean removing the fridge to do any work to it.
2/ Adding a cooling fan to the heat rejection side, it already has a fan across the face of the condenser, but rather than channeling the air up vertically, the compressor unit and condenser are mounted horizontaly, maybe an extra fan could be mounted in the bottom vent to aid vertical movement of the air.
3/ The wall separating the fridge from the outside is foam sandwich. The awning which is also on that side is usually extended.
I have worked out that when the fridge is working normaly, i.e. in cooler ambient temperatures, it goes for 5 minutes for every hour, drawing 7.5 amps. However when ambient temeratures are high i.e. 38'C, the compressor seems to be on almost continously, while holding its temperature, me thinks it is struggling to condense the refridgerant back to a liquid. And no I have not sat there and timed its operation in this case.
I guess this means under the best conditions the fridge is consuming 180 amp hours over a 24hr period, the batteries having a combine capacity of 220ah.
-- Edited by iana on Tuesday 5th of March 2019 02:14:26 PM
T1 Terry said
02:48 PM Mar 5, 2019
Something to keep in mind when connecting panels in parallel to an MPPT controller. The solar output voltage when loaded must be greater than the battery voltage seen on the output side of the MPPT controller or it will not turn on or stay switched on. In general the solar voltage must reach a point 5vdc higher than the voltage sensed at the controllers battery side before it will turn on and the solar voltage must remain roughly 2v higher than battery voltage seen at the controller for it to stay on.
It is often stated by MPPT controller owners they see 16vdc at the solar input side and 14. something on the output side. The assumption is the 16vdc is the optimum solar voltage but in reality it could well be the controller needs to hold the solar voltage higher than the sensed battery voltage so it will stay switched on. The optimum solar voltage could really be 15vdc or less but that would cause the MPPT controller to stop working, yet 15vdc will still charge a battery at 14.4v via a PWM controller at the maximum output the solar is capable of producing.
As can be seen on the Kyocera chart, as the panel heats up the voltage the maximum current available reduces quite significantly. If you look at the 75*C line you can see at the lower voltages the output is actually more than it is at 25*C and holds that until the point where the optimum voltage is reached. In this chart 75*C is the point a voltage higher than 13vdc would see a reduction in output current, if you draw a line down at the 16vdc point you will see the panel output is now about half the max output.
The other interesting thing is to do the maths of the actual max output of the 140w panel being tested at each panel temperature, at 25*C the output is roughly 8.5 amps x 17v = 144.5w, at 50*C using the same 8.5 amps x (the voltage has dropped to) 14.5v = 123w, at 75*C using the same 8.5 amps x 12.5v = 106w, yet it is still sold as a 140w panel.
Even at 50*C the panel max output voltage is only 14.5v but the output loss at 15v isn't that extreme so the voltage required to get the current to flow from the panel to the battery maybe not the the point where the most can be harvested, but it hasn't dropped that much so charging should still be ok.
Now look at what has happened at 75*C panel temperature, to get the same 15v required for charging the battery the max current is down to 6 amps, not the 8.5 amps that was available at 25*C.
The theoretical figure of 106 watts At 75*C in reality is 15v x 6 amps = 90w. At the 16v the MPPT controller would try to maintain so it would keep working the current drops even further to around 4 amp mark, 16v x 4 amps = 64w from the 140w panel, not even a 50% harvest.
Looking at those specs, if you want to go MPPT you will need to also switch to series connection, the panels can still put out there 106w each and the controller can easily maintain the higher solar voltage above battery voltage to keep itself operating. The comparison between 106w per panel theoretical, less the electrical energy used by the MPPT controller to convert 37.5v down to the required battery voltage and the 90w per panel via a PWM controller would be a good deal less than the theoretical 48w improvement, do you really think it's worth the expense and effort?
T1 Terry
Jaahn said
06:51 PM Mar 5, 2019
Iana
The ideal situation is to have the batteries getting quickly up to voltage in the morning, then the fridge(+fans etc) is running on the direct solar out put till that tapers off in the evening, so that the batteries just carry things overnight. Your batteries might do that OK if you had more solar panels. The full answer is in the details !
But if you are in need of another idea. My fridge seems to run much more if the thermostat is put up. I found when new it can run almost continuously turned up high, but settles to a more normal on/off cycle by turning it down a bit. Still seems cold enough.
Jaahn
daffyfrancis said
07:39 PM Mar 5, 2019
Hi,
I am not very technically minded but what brand & model of fridge do you have that is requiring so many amps or am I just misunderstanding your calculations?.
ie: if the compressor runs continously in hot weather do you mean it could use 7.5 x12 (12x5 minutes= 1 hour) =90 amps in 1 hour.
David
iana said
08:07 PM Mar 5, 2019
The fridge is a Waeco RPD 215, the fridge going full time was a figure of speech, as I also said I wasn't going to sit there all day waiting for the fridge to cycle. But this only happens on extreme days where the temperature in the shade is above 40'c. Otherwise it runs for say 5 minutes in each hour, I did sit up and time that, but temperatures were mild.
The thermostat is set to minimum temperature.
iana said
08:21 PM Mar 5, 2019
Jaahn wrote:
Iana
The ideal situation is to have the batteries getting quickly up to voltage in the morning, then the fridge(+fans etc) is running on the direct solar out put till that tapers off in the evening, so that the batteries just carry things overnight. Your batteries might do that OK if you had more solar panels. The full answer is in the details !
Jaahn
Being able to harvest the sun early in the morning was one of my aims, I have posted a thread on angling the panels early in the piece, and am still working on that. It was the mention on many articles that the mppt controller being smart would take advantage of the low light conditions.
Our ute has an auxiliary battery, feed from the vehicle charging system by a "Intervolt" DCDC charger, this charger has a 25amp mppt controller built in. I have made up an extension lead so the ute and the van can be connected. By turning the house batteries off, the system is isolated, and so the house batteries can be charged while the fridge etc is feed from the vehicle aux battery.
I shall drop the idea of changing the house controller to mppt because of advise received here, and fit a solar panel to the ute roof. This will mean that the house batteries can recharge without any power being drawn off them.
I am also in the process of constructing a low voltage switch/alarm that will cut the fridge out if voltages fall too low. I think this plan will do the job, I have to accept the extra weight of the additional solar panel.
Whenarewethere said
09:37 PM Mar 5, 2019
I looked up the specs on the fridge. It has a rated current of 7.5 amps at 12 volts, which is 1 amp more than my Waeco esky which has an actual maximum current of about 3.8 amps when running & often around 3.0 amps.
I think there is something else going on here. Have you got thick enough wires from the solar panels to the battery & is the controller near the battery. You don't need much of a voltage drop to make a meal of the setup.
iana said
08:40 AM Mar 6, 2019
I have just re-done all the wiring from the battery to the regulator, which included shortening the run, plus using heavy dia wire to avoid voltage drop. The wire from the panels is as the caravan manufacturer installed, which is quite a reasonable size, I can't do anything about that as the wires are through the roof sandwich and not movable.
The run of wire to the fridge from the Setec controller is quite long (about 7m, 14m there and back), and could have some voltage drop, it may be one of my jobs to shorten this in the future. The fridge motor seems to be able to run on quite a voltage variation according to the instruction book.
daffyfrancis said
09:29 AM Mar 6, 2019
iana wrote:
The fridge is a Waeco RPD 215, the fridge going full time was a figure of speech, as I also said I wasn't going to sit there all day waiting for the fridge to cycle. But this only happens on extreme days where the temperature in the shade is above 40'c. Otherwise it runs for say 5 minutes in each hour, I did sit up and time that, but temperatures were mild. The thermostat is set to minimum temperature.
I am easily confused but if your fridge mostly only runs for 5 minutes an hour would'nt its consumption only be around 7.5 amps /12 = 0.625amps in 1 hour & 0.625 x 24 =15amps per day? & the maximum it should use if it were to run continously all day would be 7.5 x 24 = 180 amps.
David
Whenarewethere said
11:27 AM Mar 6, 2019
I thought it was 15 amps per day. Based on the rated specs it should be closer to 15, maybe up to 20. On stinking hot days maybe 30 at most.
Have you checked voltage & current out of each panel, & going into the controller. Also voltage & current out of the controller & at the batteries.
I sat down for days with my esky in a hot 35° room & measured volts & amps, & estimated the average amps while the compressor was running, ranging from max 3.8 down to 2.5 amps. Round about 3.2 amps average while running. Also timed how long it cycled on & off. Tedious stuff, but I have a pretty good idea of what the fridge consumes.
Now I have the Victron data which pretty much tallies up with my numbers.
Have you dusted out the condenser. Mine was full of dust after only 6 months of use. Of that the fan would only be actually running about 1/6 of that time. Now I have a stronger fan & a dust filter, which I can wash regularly.
T1 Terry said
12:19 PM Mar 6, 2019
In hot weather we have recorded the consumption of a Waeco 215ltr fridge over a week to see just how well it coped with the heat and how much battery storage was required. On the days the inside temp of the converted bus reached in excess of 40*C the fridge/freezer drew 125 Ah per 24hrs, at a max of 35*C the draw was 85Ah but the nights were some what cooler as well so that would have helped. in winter it was only 68Ah with over night temps around 9*C and day time temps around 22*C.
The reason we did these tests was to get a comparison to using an inverter type 240vac fridge freezer to see if the added losses using a dedicated inverter just for the fridge/freezer was much greater than the equivalent dedicated 12v model.
T1 Terry
iana said
01:13 PM Mar 6, 2019
David you are so correct, so 15amp hours over a period of 24hr period on a cooler day, and Terrys figures would coincide with the fridge running on a hot day over 24hrs, i.e. nearly running continuously. Anyway hasn't the thread wandered a bit?
Jaahn said
04:16 PM Mar 6, 2019
iana wrote:
David you are so correct, so 15amp hours over a period of 24hr period on a cooler day, and Terrys figures would coincide with the fridge running on a hot day over 24hrs, i.e. nearly running continuously. Anyway hasn't the thread wandered a bit?
Iana, it is your thread so just get it back where you want it
Just a comment to help others reading this thread who may be getting confused on the electrical units. The writers all seem to understand the subject well but not all the units used are correct. Not trying to be critical but to be helpful, as this is a good example of them. The amps are a flow of electricity at any instant, the quantity of electricity used is the flow(amps), for some time(hours). So the correct unit is an amp hour(Ahr), for the quantity used by the fridge in a day or the quanity stored in a battery, or generated by the panels in a day. Electricky !!
Cheers jaahn
-- Edited by Jaahn on Wednesday 6th of March 2019 04:22:47 PM
Whenarewethere said
05:15 PM Mar 6, 2019
I questioned the voltage & amps at start & end of every wire because the rated amps of your fridge is only about 15% more than my fridge. In 35° temperature my fridge is pretty efficient. 40° is a lot more stress on the fridge but I don't feel the amps should be out of hand if everything thing else is working properly. I honestly feel something in the setup is not working as well as it should.
Link to testing my fridge which may be of some use https://thegreynomads.activeboard.com/t65059593/extra-fridge-insulation-wattage-test/
Our home fridge is prehistoric & we should change it. It has a condenser at the back. A decade ago I covered the body of the fridge & the doors & underneath which was a challenge in a few layers of Kingspan Air-cell (building bubble wrap) & the fridge's power consumption dropped by 30%. All thoroughly tested via my UPS over many days to get a good average power consumption.
T1 Terry said
12:01 PM Mar 7, 2019
The direction may have wandered from using a different controller and expecting that to solve the problem to looking at the cause of the problem in the first place. Always better to fix the cause than attempt to cover it up.
Insufficient solar harvest to cover the loads is a symptom, excess draw from the fridge appears to be the major cause of the problem. This means either the symptom is treated by increasing the total solar harvest area available, or the cause is treated so the harvest available now will be sufficient.
More solar is probably the easiest over all, but that still doesn't sort the fridge in hot conditions not coping problem. That one is a lot more difficult. The fridge problem is based on a fridge design that could not do the required job much above 32*C. The engineers that designed it consider that to be an extreme temperature and that is common belief among engineers outside Australia. You might be able to improve the sub standard insulation if the fridge has an external condenser grille/radiator, but if it is inside the walls of the fridge like modern refrigerators that will stop the thing from being able to reject the heat it is attempting to pull out of the cabinet. The major problem is the whole design is under sized, the evaporator can not absorb enough heat from inside the cabinet, the condenser can not eject enough of the heat and the compressor is not up to the job.
The first thing is to ensure the fridge has the best operating conditions available, like a pathway for the heat to exit above the fridge. Ideally this would be through the roof, but if this is not possible then the outside vent must be above the top of the fridge and it must have fan assistance to pull the hot air outside and away from the fridge cabinet.
The next thing is to ensure there is a path for cold air to enter all around the base of the fridge so it can carry the heat away and outside. This path needs to include the walls of the fridge because you need to keep them cool no matter what insulation is used. Much easier to not have the heat there trying to enter the fridge than adding layers to slow its enter.
The long term fix is to use a fridge/freezer that was designed for Australia's harsh climate and extensively tested to make sure it is up to the task. The Australian standards offer this proof of performance and will only award those models that can pass the test. There are no low voltage fridges with these Australian standards certification that I know of, but I'd be happy to be corrected if I have that wrong.
All 240vac household fridges with a star rating have had to pass this test first. Ask anyone who has installed an inverter technology household fridge and see what they think of it, the cost surprisingly low compared to a low voltage unit and the energy use is better than the low voltage units.
T1 Terry
Bagmaker said
12:59 PM Mar 7, 2019
T1 Terry wrote:
In hot weather we have recorded the consumption of a Waeco 215ltr fridge over a week to see just how well it coped with the heat and how much battery storage was required. On the days the inside temp of the converted bus reached in excess of 40*C the fridge/freezer drew 125 Ah per 24hrs, at a max of 35*C the draw was 85Ah but the nights were some what cooler as well so that would have helped. in winter it was only 68Ah with over night temps around 9*C and day time temps around 22*C. The reason we did these tests was to get a comparison to using an inverter type 240vac fridge freezer to see if the added losses using a dedicated inverter just for the fridge/freezer was much greater than the equivalent dedicated 12v model.
T1 Terry
So what did you find, essentially?
Just out of interest -as I could never go back to a camping style fridge, unless it had an icemaker and chilled water dispenser in the front (and they halved the price)
T1 Terry said
02:54 PM Mar 7, 2019
Bagmaker wrote:
T1 Terry wrote:
In hot weather we have recorded the consumption of a Waeco 215ltr fridge over a week to see just how well it coped with the heat and how much battery storage was required. On the days the inside temp of the converted bus reached in excess of 40*C the fridge/freezer drew 125 Ah per 24hrs, at a max of 35*C the draw was 85Ah but the nights were some what cooler as well so that would have helped. in winter it was only 68Ah with over night temps around 9*C and day time temps around 22*C. The reason we did these tests was to get a comparison to using an inverter type 240vac fridge freezer to see if the added losses using a dedicated inverter just for the fridge/freezer was much greater than the equivalent dedicated 12v model.
T1 Terry
So what did you find, essentially?
Just out of interest -as I could never go back to a camping style fridge, unless it had an icemaker and chilled water dispenser in the front (and they halved the price)
The highest we recorded for a number of different brand 255ltr to 300ltr fridge freezers was 85Ah including the inverter, the average summer weather was 68Ah and winter down around the 50Ah. They have all improved since then as that was back in 2015 and the star ratings on these type of appliances has gone up to the extent they needed to revise the star levels because they were all better than 5 stars on the old scale. I think a fridge/freezer that scored a 2.5 to 3 star rating only reaches a 1 to 1.5 star rating on the newer scale where just about all models these days are between 3 stars and 4.5 stars.
T1 Terry
Farmhat said
01:29 AM Mar 8, 2019
iana wrote: The plan was to get a portable panel and use it on an angle in the mornings, but that involves more weight on the rig, when I know we are sailing close to the wind weight wise, it seemed by changing the controller, we could gain more power with no weight gain.
The PMN controller is a Projecta SC45 (45 Amps), so I assume that it is of reasonable quality.
Open to any suggestions, but no argument, you all be good now.
Hi iana, portable panels don't have to be heavy. I have a 3 panel 150w that weighs less than 4kg, and have also used the Projecta and it did it's job well.
Joe.
T1 Terry said
09:45 AM Mar 8, 2019
When it comes to portable panels, there is cheap and heavy or light and not so cheap, as well as light and very expensive.
T1 Terry
markf said
11:28 AM Mar 8, 2019
T1 Terry wrote:
When it comes to portable panels, there is cheap and heavy or light and not so cheap, as well as light and very expensive.
T1 Terry
Cheap, Light and Good. Pick any two. eg Light and Good = not cheap, etc.
Some of you may remember sometime back that I did a considerable amount of work re-doing our solar system. Replacing the two hose batteries from Gel to AGM, and then, having three 150w panels on the roof began a re hash. I replaced two solar controllers with one big one, ran new wiring to the controller to reduce the wire length and increased its size. The fitted all panels with blocking diodes that's for those again Terry and Tony.
Well all worked fine, and with ideal conditions supplies us with plenty of solar, but I had the nagging thought I had made a bo bo. It was also at that time there was a debate on here about PWM verses MPPT controllers, which I had begun to read, but it had involved into a huge argument so I didn't bother reading further, however as my reading of other documents continued, I have begun to realize that I should have fitted a MPPT controller and wired up all the panels in series.
Because we have a 12v fridge, our power is continuously being used, it is important the batteries are brought up to full charge each day, the problem that occurs is on overcast days, or really hot days with hot winds. It seems the MPPT will harvest more solar during low light conditions and when the panels get hot and the panel voltage drops. Preamble over!
My question is, do I still need to use the blocking diodes if the panels are wired in series, and if so how are the diodes wired into the circuit?
My 6 x 20 watt panels are 2 panels in series, 3 sets in parallel. No diodes anywhere. I have tried shadowing 1 or 2 sets & the amps input to the controller goes down by a 1/3 or 2/3. Output seems to be a bit better depending on battery voltage.
Large panels may be a different situation & may need diodes. But I am no expert.
The first argument is based around the amount of electronics involved in an MPPT controller compared to a PWM controller. There is no such thing as an electronic component that is 100% efficient, they all have losses in the form of electrical energy being converted to heat energy. The proof is the comparative size of the heat sink between the two types for a given output. A PWM controller does not require a fan, yet many MPPT controllers do require at least one fan and will shut down if it stops working to protect itself against thermal stress.
If the MPPT controller wastes more electrical energy as heat compared to a PWM controller, how can it possibly produce more electrical output in poor light conditions?
The next argument involves total solar harvest for the day. It is an established fact a PWM controller will start to produce and electrical output before an MPPT controller with the same amount of solar input and will still be producing output after the MPPT controller has stopped producing a useable output. This is because the MPPT controller requires energy to actually do anything, if that energy requirement is equal to the energy harvested from the solar the MPPT controller will still be functioning but not actually putting anything out at a level worth mentioning. Anything less than 0.5 amp is not a useful amount of energy when it comes to lead acid battery charging.
The next argument is in regards to safe working voltages and the capability of the MPPT controller to hand the open circuit voltages of a series array. There is no value in a controller that can handle 150vdc open circuit voltage if you have to pay a solar installer to do all the work as well as any maintenance work required. This limits the number of panels that can be connected in a single string. Connecting series strings in parallel to feed the one controller means any shading on any single panel in each series string will result in the loss of output from that section. This is because the voltage from that section will now be less than the voltage from the other series sections connected in parallel to the same controller. The higher output series strings will simply block and output from the lower voltage string because voltage wins that fight every time.
The last argument I'll put forward at the moment is the requirement for even more diodes in the system. Not only blocking diodes are required but bypass diodes as well to prevent turning an even slightly shaded panel into a heater and wasting the electrical energy produced by the other panels in the string.
So, will an MPPT controller really improve your useable output from the controller? Simply harvesting more solar does not mean you will get more useable electrical input into the system.
T1 Terry
Hi Iana
This is my opinion on your setup. It is what I would do ! and indeed I do.
I do not know what the specs of your panels are. However I would not put the panels in series but leave them in parallel. This means there is a better result if there is any shading. One panel can drop out and you just loose that panel. With series it is more complicated. Series has some saving due to the cable losses being reduced, but you can improve the cable to a bigger size for parallel at a modest one-off cost to a common join point on the roof. Always worth the cost for improved output in MPPT mode IMHO.
The MPPT reg will increase the output by about the same amount in parallel or series in normal condition Under some odd conditions there will be less for sure. Not significent in my opinion overall. The MPPT reg increase will certainly be best at low battery voltages. The extra is probably only 15% overall and perhaps up to 25% in the right conditions for short times. At low sun times the extra for series usually is not very much. The PWM reg will not harvest the voltage above the battery voltage at any time so having well matched panels is then important.
I do not intend to discuss with other people the pros and cons as it has been over argued here. I suggest people only address your specific situation and nothing else. IMHO.
If you want more output in poor conditions making a panel or more, mobile so you can chase the sun may be more productive. Or tilting the panels in hot weather cools them much better than flat on the roof.
Jaahn
-- Edited by Jaahn on Monday 4th of March 2019 01:55:13 PM
A hi ambient temperature seems to have the most power usage, the fridge goes continuously, and we have fans going to make up for lack of air-con. The plan was to get a portable panel and use it on an angle in the mornings, but that involves more weight on the rig, when I know we are sailing close to the wind weight wise, it seemed by changing the controller, we could gain more power with no weight gain. On the other hand I have the system wired up for this, and I am looking at a fairly major re-vamp again.
The PMN controller is a Projecta SC45 (45 Amps), so I assume that it is of reasonable quality.
Open to any suggestions, but no argument, you all be good now.
Looking at this from the other end, how much does your fridge draw typically, & also in hot weather, over a 24 hour period.
I am consuming about 15 to 18AH per 24 hours with 78AH of batteries. I would like a bit more battery capacity but finding a space is an issue.
Hi Iana
What are the specs of your panels. If you are having trouble in very hot weather they may not be 36 cell panels and the max power voltage may be too low !! If so the MPPT reg will not give much advantage. So please give the specs off the back of the panels so we can help. Are they all the same specs or different.
Jaahn
The day in question was a real hum dinger, 40" hot northerly wind.
But the main thing is we won't have enough power in the winter with shorter days and the sun lower on the horizon.
Hi Iana
Those panels look OK and should do the job. I have never been in a situation where I have seen my panel voltage drop to 13V or indeed when it will not bring the battery up to full charge voltage in full sun
so I cannot comment on that.
However you are obviously short of solar power generally. I do not believe that fitting a MPPT reg will be the saviour you need. It will only give you about 15% more, ie about 70W extra normally overall. And it will not do much in the extreme heat unless you have the panels wired in series but the power from them will still be seriously reduced at 13V each. You really need another panel at least ie 33% more. I cannot help you with the extra weight problem.
But as whenarewethere suggests you could look at the other side and see what you can do about your consumption. The fridge is always the killer. Can you add insulation to it and a cooling fan for the heat rejection side, this might be worth trying. Even a heat shield on the outside with a gap, to shield the fridge area from the direct sun and heat.
Cheers Jaahn
-- Edited by Jaahn on Tuesday 5th of March 2019 10:09:34 AM
Yes agree the fridge is the killer, it is a compressor fridge.
1/ Can I add insulation to it ? Its a tight fit, I really don't see how you could insulate it further. If would also mean removing the fridge to do any work to it.
2/ Adding a cooling fan to the heat rejection side, it already has a fan across the face of the condenser, but rather than channeling the air up vertically, the compressor unit and condenser are mounted horizontaly, maybe an extra fan could be mounted in the bottom vent to aid vertical movement of the air.
3/ The wall separating the fridge from the outside is foam sandwich. The awning which is also on that side is usually extended.
I have worked out that when the fridge is working normaly, i.e. in cooler ambient temperatures, it goes for 5 minutes for every hour, drawing 7.5 amps. However when ambient temeratures are high i.e. 38'C, the compressor seems to be on almost continously, while holding its temperature, me thinks it is struggling to condense the refridgerant back to a liquid. And no I have not sat there and timed its operation in this case.
I guess this means under the best conditions the fridge is consuming 180 amp hours over a 24hr period, the batteries having a combine capacity of 220ah.
-- Edited by iana on Tuesday 5th of March 2019 02:14:26 PM
It is often stated by MPPT controller owners they see 16vdc at the solar input side and 14. something on the output side. The assumption is the 16vdc is the optimum solar voltage but in reality it could well be the controller needs to hold the solar voltage higher than the sensed battery voltage so it will stay switched on. The optimum solar voltage could really be 15vdc or less but that would cause the MPPT controller to stop working, yet 15vdc will still charge a battery at 14.4v via a PWM controller at the maximum output the solar is capable of producing.
As can be seen on the Kyocera chart, as the panel heats up the voltage the maximum current available reduces quite significantly. If you look at the 75*C line you can see at the lower voltages the output is actually more than it is at 25*C and holds that until the point where the optimum voltage is reached. In this chart 75*C is the point a voltage higher than 13vdc would see a reduction in output current, if you draw a line down at the 16vdc point you will see the panel output is now about half the max output.
The other interesting thing is to do the maths of the actual max output of the 140w panel being tested at each panel temperature, at 25*C the output is roughly 8.5 amps x 17v = 144.5w, at 50*C using the same 8.5 amps x (the voltage has dropped to) 14.5v = 123w, at 75*C using the same 8.5 amps x 12.5v = 106w, yet it is still sold as a 140w panel.
Even at 50*C the panel max output voltage is only 14.5v but the output loss at 15v isn't that extreme so the voltage required to get the current to flow from the panel to the battery maybe not the the point where the most can be harvested, but it hasn't dropped that much so charging should still be ok.
Now look at what has happened at 75*C panel temperature, to get the same 15v required for charging the battery the max current is down to 6 amps, not the 8.5 amps that was available at 25*C.
The theoretical figure of 106 watts At 75*C in reality is 15v x 6 amps = 90w. At the 16v the MPPT controller would try to maintain so it would keep working the current drops even further to around 4 amp mark, 16v x 4 amps = 64w from the 140w panel, not even a 50% harvest.
Looking at those specs, if you want to go MPPT you will need to also switch to series connection, the panels can still put out there 106w each and the controller can easily maintain the higher solar voltage above battery voltage to keep itself operating. The comparison between 106w per panel theoretical, less the electrical energy used by the MPPT controller to convert 37.5v down to the required battery voltage and the 90w per panel via a PWM controller would be a good deal less than the theoretical 48w improvement, do you really think it's worth the expense and effort?
T1 Terry
Iana
The ideal situation is to have the batteries getting quickly up to voltage in the morning, then the fridge(+fans etc) is running on the direct solar out put till that tapers off in the evening, so that the batteries just carry things overnight. Your batteries might do that OK if you had more solar panels. The full answer is in the details !
But if you are in need of another idea. My fridge seems to run much more if the thermostat is put up. I found when new it can run almost continuously turned up high, but settles to a more normal on/off cycle by turning it down a bit. Still seems cold enough.
Jaahn
Hi,
I am not very technically minded but what brand & model of fridge do you have that is requiring so many amps or am I just misunderstanding your calculations?.
ie: if the compressor runs continously in hot weather do you mean it could use 7.5 x12 (12x5 minutes= 1 hour) =90 amps in 1 hour.
David
The thermostat is set to minimum temperature.
Being able to harvest the sun early in the morning was one of my aims, I have posted a thread on angling the panels early in the piece, and am still working on that. It was the mention on many articles that the mppt controller being smart would take advantage of the low light conditions.
Our ute has an auxiliary battery, feed from the vehicle charging system by a "Intervolt" DCDC charger, this charger has a 25amp mppt controller built in. I have made up an extension lead so the ute and the van can be connected. By turning the house batteries off, the system is isolated, and so the house batteries can be charged while the fridge etc is feed from the vehicle aux battery.
I shall drop the idea of changing the house controller to mppt because of advise received here, and fit a solar panel to the ute roof. This will mean that the house batteries can recharge without any power being drawn off them.
I am also in the process of constructing a low voltage switch/alarm that will cut the fridge out if voltages fall too low. I think this plan will do the job, I have to accept the extra weight of the additional solar panel.
I looked up the specs on the fridge. It has a rated current of 7.5 amps at 12 volts, which is 1 amp more than my Waeco esky which has an actual maximum current of about 3.8 amps when running & often around 3.0 amps.
I think there is something else going on here. Have you got thick enough wires from the solar panels to the battery & is the controller near the battery. You don't need much of a voltage drop to make a meal of the setup.
The run of wire to the fridge from the Setec controller is quite long (about 7m, 14m there and back), and could have some voltage drop, it may be one of my jobs to shorten this in the future. The fridge motor seems to be able to run on quite a voltage variation according to the instruction book.
I am easily confused but if your fridge mostly only runs for 5 minutes an hour would'nt its consumption only be around 7.5 amps /12 = 0.625amps in 1 hour & 0.625 x 24 =15amps per day? & the maximum it should use if it were to run continously all day would be 7.5 x 24 = 180 amps.
David
I thought it was 15 amps per day. Based on the rated specs it should be closer to 15, maybe up to 20. On stinking hot days maybe 30 at most.
Have you checked voltage & current out of each panel, & going into the controller. Also voltage & current out of the controller & at the batteries.
I sat down for days with my esky in a hot 35° room & measured volts & amps, & estimated the average amps while the compressor was running, ranging from max 3.8 down to 2.5 amps. Round about 3.2 amps average while running. Also timed how long it cycled on & off. Tedious stuff, but I have a pretty good idea of what the fridge consumes.
Now I have the Victron data which pretty much tallies up with my numbers.
Have you dusted out the condenser. Mine was full of dust after only 6 months of use. Of that the fan would only be actually running about 1/6 of that time. Now I have a stronger fan & a dust filter, which I can wash regularly.
The reason we did these tests was to get a comparison to using an inverter type 240vac fridge freezer to see if the added losses using a dedicated inverter just for the fridge/freezer was much greater than the equivalent dedicated 12v model.
T1 Terry
Iana, it is your thread so just get it back where you want it
Just a comment to help others reading this thread who may be getting confused on the electrical units. The writers all seem to understand the subject well but not all the units used are correct. Not trying to be critical but to be helpful, as this is a good example of them. The amps are a flow of electricity at any instant, the quantity of electricity used is the flow(amps), for some time(hours). So the correct unit is an amp hour(Ahr), for the quantity used by the fridge in a day or the quanity stored in a battery, or generated by the panels in a day. Electricky !!
Cheers jaahn
-- Edited by Jaahn on Wednesday 6th of March 2019 04:22:47 PM
I questioned the voltage & amps at start & end of every wire because the rated amps of your fridge is only about 15% more than my fridge. In 35° temperature my fridge is pretty efficient. 40° is a lot more stress on the fridge but I don't feel the amps should be out of hand if everything thing else is working properly. I honestly feel something in the setup is not working as well as it should.
Link to testing my fridge which may be of some use https://thegreynomads.activeboard.com/t65059593/extra-fridge-insulation-wattage-test/
Our home fridge is prehistoric & we should change it. It has a condenser at the back. A decade ago I covered the body of the fridge & the doors & underneath which was a challenge in a few layers of Kingspan Air-cell (building bubble wrap) & the fridge's power consumption dropped by 30%. All thoroughly tested via my UPS over many days to get a good average power consumption.
Insufficient solar harvest to cover the loads is a symptom, excess draw from the fridge appears to be the major cause of the problem. This means either the symptom is treated by increasing the total solar harvest area available, or the cause is treated so the harvest available now will be sufficient.
More solar is probably the easiest over all, but that still doesn't sort the fridge in hot conditions not coping problem. That one is a lot more difficult. The fridge problem is based on a fridge design that could not do the required job much above 32*C. The engineers that designed it consider that to be an extreme temperature and that is common belief among engineers outside Australia. You might be able to improve the sub standard insulation if the fridge has an external condenser grille/radiator, but if it is inside the walls of the fridge like modern refrigerators that will stop the thing from being able to reject the heat it is attempting to pull out of the cabinet. The major problem is the whole design is under sized, the evaporator can not absorb enough heat from inside the cabinet, the condenser can not eject enough of the heat and the compressor is not up to the job.
The first thing is to ensure the fridge has the best operating conditions available, like a pathway for the heat to exit above the fridge. Ideally this would be through the roof, but if this is not possible then the outside vent must be above the top of the fridge and it must have fan assistance to pull the hot air outside and away from the fridge cabinet.
The next thing is to ensure there is a path for cold air to enter all around the base of the fridge so it can carry the heat away and outside. This path needs to include the walls of the fridge because you need to keep them cool no matter what insulation is used. Much easier to not have the heat there trying to enter the fridge than adding layers to slow its enter.
The long term fix is to use a fridge/freezer that was designed for Australia's harsh climate and extensively tested to make sure it is up to the task. The Australian standards offer this proof of performance and will only award those models that can pass the test. There are no low voltage fridges with these Australian standards certification that I know of, but I'd be happy to be corrected if I have that wrong.
All 240vac household fridges with a star rating have had to pass this test first. Ask anyone who has installed an inverter technology household fridge and see what they think of it, the cost surprisingly low compared to a low voltage unit and the energy use is better than the low voltage units.
T1 Terry
So what did you find, essentially?
Just out of interest -as I could never go back to a camping style fridge, unless it had an icemaker and chilled water dispenser in the front (and they halved the price)
The highest we recorded for a number of different brand 255ltr to 300ltr fridge freezers was 85Ah including the inverter, the average summer weather was 68Ah and winter down around the 50Ah. They have all improved since then as that was back in 2015 and the star ratings on these type of appliances has gone up to the extent they needed to revise the star levels because they were all better than 5 stars on the old scale. I think a fridge/freezer that scored a 2.5 to 3 star rating only reaches a 1 to 1.5 star rating on the newer scale where just about all models these days are between 3 stars and 4.5 stars.
T1 Terry
Hi iana, portable panels don't have to be heavy. I have a 3 panel 150w that weighs less than 4kg, and have also used the Projecta and it did it's job well.
Joe.
T1 Terry
Cheap, Light and Good. Pick any two. eg Light and Good = not cheap, etc.