Of course after the battery has reached the set voltages the unit reverts to PWM regulation anyway. The extra power available is not used at all.
Ah, that's what I thought. That would explain the "PWM + MPPT" claims of some vendors. I gather that some MPPT regulators can also boost a panel voltage that is lower than the battery voltage. I think these are described as "buck/boost" types.
T1 Terry said
12:04 PM Jan 8, 2019
Jaahn wrote:
Hi Dorian
Your search for knowledge is admirable I do not claim any expertise in this area other than my reading and ownership. I have said before that previous research has shown that lots or even most, of the cheap MPPT regulators are fakes. I have relied on other tests done in the past to compare some brands. But if you look at the size of the enclosures and the heat sinks for the units it is certainly obvious some units look and are sized like PWM regs. This applies IMHO to Australian retail offerings as well as Ebay.
For a MPPT reg to work well it needs two functions. First function which you are pursuing, it needs to be able to take input at a higher voltage than the battery and 'convert' that to battery voltage and increase the current proportionally. That is the current gain promised by MPPT regs, but is actually just the 'buck' regulator, not the MPPT part.
The second function that is not mentioned in most advertising or elaborated on, is the actual MPPT part of the control system. There must be a 'smart' controller which will periodically 'test' the input and out put against some parameters and adjust the output to get the maximum current. This IMHO, is what sorts out a good unit that tracks fast and has a good program to extract the maximum power from the panel under all conditions and sun exposure. Indeed it is called Maximum Power Point Tracking. A poor quality unit has a very slow and clunky adjustment to the continuous changes of input and battery condition. Indeed the cheap ones probably do almost nothing in this area to track the maximum power point, or even actually nothing at all.
Of course after the battery has reached the set voltages the unit reverts to PWM regulation anyway. The extra power available is not used at all.
Jaahn
Many of the mid range MPPT controllers use a ROM map and compare inputs to this topographical map to determine the best input voltage. It is not uncommon to see some MPPT controllers holding the input voltage at 16v, yet the true Vmp is down around 15v or less. This is the result of a limited range programmed into the ROM with 16v being the lower limit.
MPPT controllers that can perform both buck and boost function suitable for charging 12v batteries, AND, do it efficiently, are large and expensive, well beyond the average caravan set up. We use them in off grid house installs and there are some out there at very reasonable prices if you know what you are looking for as far as what to buy and what to avoid.
T1 Terry
Jaahn said
05:12 PM Jan 8, 2019
dorian wrote:
Jaahn wrote:
Of course after the battery has reached the set voltages the unit reverts to PWM regulation anyway. The extra power available is not used at all.
Ah, that's what I thought. That would explain the "PWM + MPPT" claims of some vendors. I gather that some MPPT regulators can also boost a panel voltage that is lower than the battery voltage. I think these are described as "buck/boost" types.
Hi Dorian
As far as the boost claim goes, Terry is probably correct, OK for bigger installs, but for smaller van type setups boosting the output of the panels when the voltage falls below the battery charge voltage is trying to boost SFA power anyway so any possible gain would go in the losses.
It may be useful, perhaps, if the panels you have are low cell count types, 30 or 32 cells and you have plenty of them. But why do that, because a MPPT reg can use higher voltage inputs, eg run them in series pairs instead or use 24V panels and normally get the extra power any time. When their panel voltage falls below the 12v charging voltage there is no power left to use, boosted or not
Jaahn
-- Edited by Jaahn on Tuesday 8th of January 2019 05:18:25 PM
dorian said
09:50 AM Jan 14, 2019
I've been trying to make sense of the Projecta range of solar controllers. AFAICT, there are no MPPT offerings in their range. In fact their web site makes no mention of the charging mode, except in some, but not all, instruction manuals.
But ... the recommendations on page 2 state that the "solar charge controller SC300D [is] suitable for use with solar charge controller part numbers SC320 & SC330", neither of which claims to support MPPT.
This begs the question, how are the "PV vol. and cur. values" measured in PWM mode? The example in the manual shows ...
PV voltage = 17.5V PV current = 15.2A
Battery voltage = 13.8V Battery current = 5.2A
Load voltage = 13.8V Load current = 10.0A
Does the PV output switch between 17.5V/0A and 13.8V/15.2A, in which case the battery current would be a peak reading rather than an average?
Edit: In retrospect, the current values only make sense if they are averages. The PV voltage must be the panel's open circuit voltage.
-- Edited by dorian on Monday 14th of January 2019 10:10:05 AM
T1 Terry said
01:39 PM Jan 14, 2019
My guess is those figures are the STC specs for the Vmp and short circuit current for a typical solar panel. The PWM solar controller simply connects the battery (big capacitor) to the solar panel until the target voltage is reached, then disconnects the solar panel, then reconnects when the voltage drops below the target voltage. Good quality controllers have an adjustable hysteresis between the off voltage and how many 1/10ths of a volt drop before it turns back on, the voltage is deemed to be the halfway point between the two voltages. With a 0.1v hysteresis and a meter with a 0.05v accuracy the voltage appears to remain constant, the current is the amount that can flow into the battery in the time the on pulse allows averaged over the sample period to make the reading something that can be easily read.
For those that like to see the real thing, a CRO will display just what is happening.
T1 Terry
DeBe said
03:57 PM Jan 14, 2019
This is whats on the Solar panel leads before the regulator. When its charging theres a steady voltage. When the battery is charged the regulator is pulsing ON/OFF to give an average voltage at the battery of 13.8V.
My guess is those figures are the STC specs for the Vmp and short circuit current for a typical solar panel.
Sorry, I should have posted the excerpt from the manual. The load current is constant, not pulsed (obviously), and the fact that panel current = battery current + load current would confirm that the figures are average values.
The screenshot shows a panel voltage of 14.7V at the regulator and 13.5V at the battery during charging. This voltage drop (1.2V) suggests that the MOSFETs have a much higher RDSon than specified in the datasheet. Maybe they are fakes?
-- Edited by dorian on Monday 14th of January 2019 07:54:18 PM
Jaahn said
09:28 PM Jan 14, 2019
Hi Dorian
I think that the figures may be just made up anyway.
But the meter section of the regulator is probably very crude and the voltages shown are less than accurate. To read PWM voltages and have sensible answers is not easy. Good quality meters which do this are expensive, so do not expect to get quality figures on the readout. As you asked are the voltages averages, or RMS or what !! Who normally cares ?
Even my moderately expensive multi meter gives different readings +to- compared to -to+, so you might be expecting too much. I spent quite a few years setting up test rigs for data logging. Getting reliable repeatable readings is not easy even with expensive gear . The system must be built right to get right answers, not a cheap chinese knockoff and a few 2nd rate resistors for the circuits. That would be considered OK for a solar controller readout. IMHO
The circuit boards are a bit second rate too. The copper thickness and width is marginal for the current specs in some I have looked at. Perhaps there is a voltage drop there from one terminal to the other. But where are the voltage tappings anyway ??
Jaahn
-- Edited by Jaahn on Monday 14th of January 2019 09:32:36 PM
The author of the "instructable" is an electrical engineer. He uses the terms "PWM" and "MPPT" in the same sense as the solar industry. To me it makes more sense to think of MPPT and PWM as "smart" and "dumb" PWM, respectively.
The author uses Hall effect sensors for current measurement:
Greater than 90% of all of you are killing your batteries from deficit/severe under charging, and following the manufactures recommendations are only making it worse. With a commercial charger you start charging in Bulk until you hit about 80% SOC, then switch to Absorb which lowers the voltage a bit, current slows down and tapers to 2% of C. (about 6 clock hours) then you switch to Float and your battery continues to charge overnight and becomes saturated and fully charged by morning. Well guess what? It is impossible for you to fully charge a lead acid battery on Solar unless properly oversized by design which you likely failed to do to start with. Even a properly designed system is going to come up short in winter months. There is just not enough Sun Hours in a Day to fully Saturate your battery. Battery manufactures are getting slammed with warranty claims from Renewable Energy users. The claims are a result of chronic under charging and sulfated batteries. Many manufactures have revised their charging procedures for RE users. They have done away with Bulk Absorb, and Float voltage Algorithms. Today they aim at Maximum Smoke. Trojan calls it a Daily Charge of 2.47 vpc which use to be roughly Equalize voltage levels. What they are doing is forcing your Charge Controller to operate in Bulk mode or Max Smoke from Sunrise to Sunset. Still may not get your batteries fully charged. But still significantly more power stored than setting the voltage to a lower value. So what do you do? Well what you should have been doing from the start. Use your Temperature Compensating Hydrometer to find the right voltage if there is one. For roughly 90% of you there is No Voltage High Enough you can set your controller to get the batteries fully charged up, because you do not have enough panel wattage to begin with. For those of you who find yourself in that situation, all you can do is limit the damage by cranking the voltage to MAX, and then every couple of day run the genny to get your batteries back to 100%.
T1 Terry said
03:41 PM Jan 15, 2019
The science of charging lead acid batteries via solar is definitely one of the "grey" sciences, I think they call it fuzzy logic these days. Basically there is always more than one correct answer but it can be argued as to whether that answer meets all conditions anyway. Lead acid battery charging using ripple free constant current and then constant voltage reducing as the battery nears 100% SOC to avoid heating and excessive gassing will take much longer than pulse charging to achieve the same result. Dr Jay Whitacre did quite a lot of research into this while at the Carnegie Mellon University but I'm not sure he released any papers on it, he very briefly mentions it in a talk to EV builders about LiFeP04 cells.
This is the same Dr Jay Whitacre that developed Aquion Salt Water battery with the backing of Bill Gates and many other major investors. Unfortunately it is now in Chinese hands after being bought for $9.2 million after a chapter 11 bankruptcy, yet more than $20 million went into developing the technology and bringing it to market. It just grew too fast and didn't have enough big pockets to finance it, the Chinese govt does so they bought it for a song.
T1 Terry
DeBe said
03:54 PM Jan 15, 2019
Since its imposible to use a hydrometer as suggested on sealed batterys. I purchased this unit on Ebay for $50, to check state of Health & internal resistance. I keep a record of what the readings are when purchased & fully charged. This then gives me some idea as to how good my batterys are. The 75Ah AGM is quite old & does not have a lot of usable capacity. The 120Ah AGM is only about 6mths old. The tester also can check altenator output & ripple, also cranking test.
In your quest, you certainly should look at the new post Custom 6x20 watts solar setup with MPPT. A very neat setup and he has given screen shots of his monitor which show the panel outputs and the battery inputs for the Victron MPPT regulator. Very instructive to see how they all work under different condition of battery voltage and various sun power input. He is getting full power + out of his small system with a quality MPPT reg.
Jaahn
PS thanks also to DeBe for very instructive inputs to this thread with real workbench pictures and dismantled regs.
-- Edited by Jaahn on Wednesday 16th of January 2019 09:28:17 AM
dorian said
11:22 AM Jan 16, 2019
Thanks, I did see that thread.
The Victron web site is very impressive. I found the following document to be a very good read:
According to the white-paper, the best arrangement for multiple panels is series rather than parallel (in MPPT mode). The benefits are lower IR power losses in the cable runs, and greater usable panel voltage under low irradiance conditions. I see that there is another discussion about connecting two controllers to the same battery, either PWM or MPPT. ISTM that those people who are using two MMPT controllers with two panels might be better off wiring the panels in series and going with a single MPPT controller.
T1 Terry said
03:14 PM Jan 16, 2019
dorian wrote:
Thanks, I did see that thread.
The Victron web site is very impressive. I found the following document to be a very good read:
According to the white-paper, the best arrangement for multiple panels is series rather than parallel (in MPPT mode). The benefits are lower IR power losses in the cable runs, and greater usable panel voltage under low irradiance conditions. I see that there is another discussion about connecting two controllers to the same battery, either PWM or MPPT. ISTM that those people who are using two MMPT controllers with two panels might be better off wiring the panels in series and going with a single MPPT controller.
The problem there is the total open circuit voltage. No point in getting an MPPT controller that can handle more than 120vdc, WA I believe it is as low as 115vdc unless you are a licenced electrician within the state you are doing the job or and testing or rectification work on the system. This means unless the licenced sparkie is licenced in every state, they can not work on their own solar set up unless they are at home
The average 12v nom. panel has a 20vdc open circuit voltage, so 5 panels in series is about the max, so unless the custom 6 x 20w panels have an open circuit voltage less than 20vdc, the person working on the system must have a full electrician's licence within that state, even though the system is only 120w.
Crazy yes, but them is the rules. If anyone gets injured or dies due to a heart problem while they are in contact with any part of a building that can come into contact with the system and it is found that the system open circuit voltage could show greater than the threshold that the licencing requirements and it wasn't connected and certified by a licenced electrician, the person that did the work, any person after that that did any work on the system and the owner of the system could find themselves fronting a "please explain why you should not be tried from manslaughter" type situation.
I have no idea how far the long arm of the law reaches as far as supplying equipment that could be used to build such a system or advice given to someone regarding building such a system, but it does fall into same category as giving advice on 240vac wiring and how to do it or fix it
T1 Terry
DeBe said
05:50 PM Jan 16, 2019
Don't see a problem with high voltage if you read what the person has done. If you read the thread he has set it up with 3 lots of 2 panels inseries giving 32.5V into the regulator.
Jaahn said
06:23 PM Jan 16, 2019
DeBe wrote:
Don't see a problem with high voltage if you read what the person has done. If you read the thread he has set it up with 3 lots of 2 panels inseries giving 32.5V into the regulator.
Hi Debe
Correct. Terry should have looked at the posting.
To make a comment on the series use of panels. Quite some time back when I was researching regulators, PWM and MPPT, I came across some testing of the concepts. I have not seen it since but it made sense at the time. While there are benefits in putting lots of panels in series, mainly the lower resistance losses or the reduced copper cost, on a small installation like a van or MH this is just small beer really. The extra charging from the higher voltage at low solar insolation is almost nothing due to the low power available at that time anyway.
In that testing I recalled that the maximum efficiency of the MPPT system was when the input voltage was not too far above the battery voltage, perhaps (by memory) +30-50%. This involved less conversion losses in the electronics. The recommendation was to use about double the nominal panel voltage by using two panels in series. That is what I have done and been happy with the results. I note that is what has been done in the 6x20W solar setup, AND he has shown how well it works. No high voltages to worry about either ! Victron also says that !
I have found that the long leads do need to be generous size to get the best output. But the cable cost is a one off to get double the gauge for not much more cost. When I had portable panels I had long cables to make it easy to chase the sun if I was in a bad spot. Who put those bloody trees there ????
Jaahn
PS 6x20W panels could use another configuration to limit the losses from long leads. 2 strings of 3 panels in series. Just saying for other people who want ideas.
-- Edited by Jaahn on Wednesday 16th of January 2019 06:30:39 PM
-- Edited by Jaahn on Thursday 17th of January 2019 08:51:24 AM
dorian said
07:56 AM Jan 17, 2019
Jaahn wrote:
Correct. Terry should have looked at the posting.
I think I confused the issue with my use of the word "multiple". In any case I found Terry's explanation to be informative.
(I would also like to thank DeBe for the PCB photos and CRO screenshots)
-- Edited by dorian on Thursday 17th of January 2019 09:16:13 AM
dorian said
10:14 AM Jan 17, 2019
I've been reading about PV panel materials. Wikipedia states that GaAs panels are the most efficient, but also relatively expensive. In an attempt to find out just how expensive they are, I found this:
It is rated for 200W and is 1320mm x 992mm. That's 153W / sq m.
The difference in power output is only about 8%.
T1 Terry said
02:22 PM Jan 17, 2019
If you look at my post and the highlighted line from the Victron Whit paper
"quote: might be better off wiring the panels in series and going with a single MPPT controller." That was the item I was referring to and why it was highlighted. The example of the 6 x 20w panels was just to point out that solar capacity had nothing to do with the rules regarding the need for a licenced electrician the handle all parts of the solar side including the controller installation, it is the series string voltage.
There are completely different issues with series parallel connections regarding shade effect. Much of it can be mitigated by the way it is wired, but the issues still remain
T1 Terry
T1 Terry said
02:36 PM Jan 17, 2019
dorian wrote:
I've been reading about PV panel materials. Wikipedia states that GaAs panels are the most efficient, but also relatively expensive. In an attempt to find out just how expensive they are, I found this:
It is rated for 200W and is 1320mm x 992mm. That's 153W / sq m.
The difference in power output is only about 8%.
The real difference between panel designs and output does not show up by comparing STC results, they actually reflect just about nothing of how the solar panels will function when out in the Australian mid day sun.
The fact most RV panels are flat mounted on the RV roof with very poor heat transfer away from the back face of the panel (because there is a trapped air pocket there) means true testing needs to be with the panel temp above 60*C and the ambient temp more like the temp likely to be found in free camp site throughout Australia. Even the NOCT results are with a panel temp of 45*C an ambient temp of 20*C, can you see that occurring anywhere in an Australian summer?
We do have an Australian solar panel manufacturer, Tindo, check out what type of panels they build and ask why that technology and not the other, the engineers answers will give you a good insight into why papers written in Europe have very little relevance in Australian conditions.
t1 terry
Baz421 said
05:03 PM Jan 18, 2019
Hi
a lot of this is over my head but I a question now please,,, based on previous,,,,
Is the Victron MPPT 75 15 controller a genuine MPPT or PWM in disguise?
Cheers Baz
Jaahn said
06:02 PM Jan 18, 2019
Baz421 wrote:
Hi
a lot of this is over my head but I a question now please,,, based on previous,,,,
Is the Victron MPPT 75 15 controller a genuine MPPT or PWM in disguise?
Cheers Baz
Hi Baz
Victron make good gear and they perform as they claim. So a genuine MPPT unit.
My disclaimer: I own one and some inverters.
Jaahn
Baz421 said
06:07 PM Jan 18, 2019
Jaahn wrote:
Baz421 wrote:
Hi
a lot of this is over my head but I a question now please,,, based on previous,,,,
Is the Victron MPPT 75 15 controller a genuine MPPT or PWM in disguise?
Cheers Baz
Hi Baz
Victron make good gear and they perform as they claim. So a genuine MPPT unit.
My disclaimer: I own one and some inverters.
Jaahn
Thanks Jaahn Appreciate your posts over many years. Cheers baz
dorian said
07:17 PM Jan 18, 2019
I should have looked more closely. The Alibaba panel lists GaAs under Specifications but Polycrystalline Silicon under Quick Details. I guess that explains the unremarkable 17% efficiency figure.
Not only is Alta's power output impressive, but the temperature coefficient is -0.09% per deg C. The Tindo panel has a corresponding coefficient of -0.41% per deg C. This means that for a roof temperature of 65C, a 200W GaAs panel would lose about 3.6% or 7W whereas the monocrystalline panel would lose 16.4% or 33W.
It is unrealistic to expect the $112 item to perform as well as the $1500 item, just because they both have the name Victron on them, it really is a case of getting what you paid for .....
T1 Terry
T1 Terry said
05:00 PM Jan 19, 2019
Hi Dorian, have they actually got these cells into a commercially available panel format yet? I was reading about a quad junction cell that had achieved very impressive conversion figures but I haven't seen any mention as to whether it scaled up to a marketable product yet.
Ah, that's what I thought. That would explain the "PWM + MPPT" claims of some vendors. I gather that some MPPT regulators can also boost a panel voltage that is lower than the battery voltage. I think these are described as "buck/boost" types.
Many of the mid range MPPT controllers use a ROM map and compare inputs to this topographical map to determine the best input voltage. It is not uncommon to see some MPPT controllers holding the input voltage at 16v, yet the true Vmp is down around 15v or less. This is the result of a limited range programmed into the ROM with 16v being the lower limit.
MPPT controllers that can perform both buck and boost function suitable for charging 12v batteries, AND, do it efficiently, are large and expensive, well beyond the average caravan set up. We use them in off grid house installs and there are some out there at very reasonable prices if you know what you are looking for as far as what to buy and what to avoid.
T1 Terry
Hi Dorian
As far as the boost claim goes, Terry is probably correct, OK for bigger installs, but for smaller van type setups boosting the output of the panels when the voltage falls below the battery charge voltage is trying to boost SFA power anyway so any possible gain would go in the losses.
It may be useful, perhaps, if the panels you have are low cell count types, 30 or 32 cells and you have plenty of them. But why do that, because a MPPT reg can use higher voltage inputs, eg run them in series pairs instead or use 24V panels and normally get the extra power any time. When their panel voltage falls below the 12v charging voltage there is no power left to use, boosted or not
Jaahn
-- Edited by Jaahn on Tuesday 8th of January 2019 05:18:25 PM
I've been trying to make sense of the Projecta range of solar controllers. AFAICT, there are no MPPT offerings in their range. In fact their web site makes no mention of the charging mode, except in some, but not all, instruction manuals.
Here is a 60A unit:
https://www.projecta.com.au/solar-panels-controllers-products/autautomatic-1224v-60a-4-stage-solar-charge-smart-controller
In this example the manual does refer to PWM technology, but there is no mention of it on the product page:
https://www.projecta.com.au/s/SC220-245-260-Instruction-Manual.pdf
Similarly, there is no mention of PWM or MPPT on the product page for the SC330D, or in its product manual:
https://www.projecta.com.au/solar-panels-controllers-products/automatic-1224v-30a-4-stage-solar-charge-premium-controller-with-remote-control
https://www.projecta.com.au/s/SC320-330-Instruction-manual-brx5.pdf
However, there is an indirect reference to "Mode:PWM/MPPT" in the "Real-time monitoring" flowchart in the manual for the remote control unit:
https://www.projecta.com.au/s/SC300D-Instruction-manual-93yp.pdf
But ... the recommendations on page 2 state that the "solar charge controller SC300D [is] suitable for use with solar charge controller part numbers SC320 & SC330", neither of which claims to support MPPT.
This begs the question, how are the "PV vol. and cur. values" measured in PWM mode? The example in the manual shows ...
PV voltage = 17.5V
PV current = 15.2A
Battery voltage = 13.8V
Battery current = 5.2A
Load voltage = 13.8V
Load current = 10.0A
Does the PV output switch between 17.5V/0A and 13.8V/15.2A, in which case the battery current would be a peak reading rather than an average?
Edit: In retrospect, the current values only make sense if they are averages. The PV voltage must be the panel's open circuit voltage.
-- Edited by dorian on Monday 14th of January 2019 10:10:05 AM
For those that like to see the real thing, a CRO will display just what is happening.
T1 Terry
This is whats on the Solar panel leads before the regulator. When its charging theres a steady voltage. When the battery is charged the regulator is pulsing ON/OFF to give an average voltage at the battery of 13.8V.
Sorry, I should have posted the excerpt from the manual. The load current is constant, not pulsed (obviously), and the fact that panel current = battery current + load current would confirm that the figures are average values.
The screenshot shows a panel voltage of 14.7V at the regulator and 13.5V at the battery during charging. This voltage drop (1.2V) suggests that the MOSFETs have a much higher RDSon than specified in the datasheet.
Maybe they are fakes?
-- Edited by dorian on Monday 14th of January 2019 07:54:18 PM
Hi Dorian
I think that the figures may be just made up anyway.
But the meter section of the regulator is probably very crude and the voltages shown are less than accurate. To read PWM voltages and have sensible answers is not easy. Good quality meters which do this are expensive, so do not expect to get quality figures on the readout. As you asked are the voltages averages, or RMS or what !! Who normally cares ?
Even my moderately expensive multi meter gives different readings +to- compared to -to+, so you might be expecting too much. I spent quite a few years setting up test rigs for data logging. Getting reliable repeatable readings is not easy even with expensive gear . The system must be built right to get right answers, not a cheap chinese knockoff and a few 2nd rate resistors for the circuits. That would be considered OK for a solar controller readout. IMHO
The circuit boards are a bit second rate too. The copper thickness and width is marginal for the current specs in some I have looked at. Perhaps there is a voltage drop there from one terminal to the other. But where are the voltage tappings anyway ??
Jaahn
-- Edited by Jaahn on Monday 14th of January 2019 09:32:36 PM
Same on the outside, but different on the inside:
https://www.amazon.com/gp/product/B01MU0WMGT/
The one with "less components" appears to have an extra MOSFET (4 versus 3).
The microprocessor is an STM 8:
https://www.st.com/en/microcontrollers/stm8-8-bit-mcus.html?querycriteria=productId=SC1244
It has a 12-bit ADC, so I would think that the voltage and current readings would be very accurate.
-- Edited by dorian on Tuesday 15th of January 2019 07:44:44 AM
Here is an MPPT controller:
https://www.amazon.com/ALLPOWERS-Input-Solar-Charge-Controller/dp/B07H3NY9J7
This is what they are comparing it against:
https://www.instructables.com/id/ARDUINO-SOLAR-CHARGE-CONTROLLER-Version-30/
https://cdn.instructables.com/ORIG/F76/5DJ1/IEOP45ZK/F765DJ1IEOP45ZK.pdf (circuit diagram)
The author of the "instructable" is an electrical engineer. He uses the terms "PWM" and "MPPT" in the same sense as the solar industry. To me it makes more sense to think of MPPT and PWM as "smart" and "dumb" PWM, respectively.
The author uses Hall effect sensors for current measurement:
https://www.allegromicro.com/~/media/Files/Datasheets/ACS712-Datasheet.ashx?la=en&hash=36988234DAD64352493E4A4686E6C3A927F4D7AC
These have a 1.2 mOhm resistance between the current carrying pins. That's got to be much better than a discrete power resistor.
-- Edited by dorian on Tuesday 15th of January 2019 01:25:20 PM
The more I read, the more confused I become.
https://www.solarpaneltalk.com/forum/off-grid-solar/batteries-energy-storage/19316-are-you-killing-your-batteries
This is the same Dr Jay Whitacre that developed Aquion Salt Water battery with the backing of Bill Gates and many other major investors. Unfortunately it is now in Chinese hands after being bought for $9.2 million after a chapter 11 bankruptcy, yet more than $20 million went into developing the technology and bringing it to market. It just grew too fast and didn't have enough big pockets to finance it, the Chinese govt does so they bought it for a song.
T1 Terry
Since its imposible to use a hydrometer as suggested on sealed batterys. I purchased this unit on Ebay for $50, to check state of Health & internal resistance. I keep a record of what the readings are when purchased & fully charged. This then gives me some idea as to how good my batterys are. The 75Ah AGM is quite old & does not have a lot of usable capacity. The 120Ah AGM is only about 6mths old. The tester also can check altenator output & ripple, also cranking test.
These datasheets confirm that the internal resistance should be around 3 milliohms:
http://web.archive.org/web/20170326053149/http://www.power-sonic.com/images/powersonic/sla_batteries/ps_psg_series/12volt/PS-121400FR_11_Feb_21.pdf
http://web.archive.org/web/20170328003747/http://www.power-sonic.com/images/powersonic/sla_batteries/pg_series/PG-12V200_11_Jan_12.pdf
http://web.archive.org/web/20170328003747/http://www.power-sonic.com/images/powersonic/sla_batteries/pg_series/PG-12V200_11_Jan_12.pdf
This is a comprehensive tech manual for SLA batteries:
http://www.power-sonic.com/wp-content/uploads/2018/12/Technical-Manual.pdf
Hi Dorian
In your quest, you certainly should look at the new post Custom 6x20 watts solar setup with MPPT. A very neat setup and he has given screen shots of his monitor which show the panel outputs and the battery inputs for the Victron MPPT regulator. Very instructive to see how they all work under different condition of battery voltage and various sun power input. He is getting full power + out of his small system with a quality MPPT reg.
Jaahn
PS thanks also to DeBe for very instructive inputs to this thread with real workbench pictures and dismantled regs.
-- Edited by Jaahn on Wednesday 16th of January 2019 09:28:17 AM
Thanks, I did see that thread.
The Victron web site is very impressive. I found the following document to be a very good read:
https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf
According to the white-paper, the best arrangement for multiple panels is series rather than parallel (in MPPT mode). The benefits are lower IR power losses in the cable runs, and greater usable panel voltage under low irradiance conditions. I see that there is another discussion about connecting two controllers to the same battery, either PWM or MPPT. ISTM that those people who are using two MMPT controllers with two panels might be better off wiring the panels in series and going with a single MPPT controller.
The problem there is the total open circuit voltage. No point in getting an MPPT controller that can handle more than 120vdc, WA I believe it is as low as 115vdc unless you are a licenced electrician within the state you are doing the job or and testing or rectification work on the system. This means unless the licenced sparkie is licenced in every state, they can not work on their own solar set up unless they are at home
The average 12v nom. panel has a 20vdc open circuit voltage, so 5 panels in series is about the max, so unless the custom 6 x 20w panels have an open circuit voltage less than 20vdc, the person working on the system must have a full electrician's licence within that state, even though the system is only 120w.
Crazy yes, but them is the rules. If anyone gets injured or dies due to a heart problem while they are in contact with any part of a building that can come into contact with the system and it is found that the system open circuit voltage could show greater than the threshold that the licencing requirements and it wasn't connected and certified by a licenced electrician, the person that did the work, any person after that that did any work on the system and the owner of the system could find themselves fronting a "please explain why you should not be tried from manslaughter" type situation.
I have no idea how far the long arm of the law reaches as far as supplying equipment that could be used to build such a system or advice given to someone regarding building such a system, but it does fall into same category as giving advice on 240vac wiring and how to do it or fix it
T1 Terry
Hi Debe
Correct. Terry should have looked at the posting.
To make a comment on the series use of panels. Quite some time back when I was researching regulators, PWM and MPPT, I came across some testing of the concepts. I have not seen it since but it made sense at the time. While there are benefits in putting lots of panels in series, mainly the lower resistance losses or the reduced copper cost, on a small installation like a van or MH this is just small beer really. The extra charging from the higher voltage at low solar insolation is almost nothing due to the low power available at that time anyway.
In that testing I recalled that the maximum efficiency of the MPPT system was when the input voltage was not too far above the battery voltage, perhaps (by memory) +30-50%. This involved less conversion losses in the electronics. The recommendation was to use about double the nominal panel voltage by using two panels in series. That is what I have done and been happy with the results. I note that is what has been done in the 6x20W solar setup, AND he has shown how well it works.
No high voltages to worry about either ! Victron also says that !
I have found that the long leads do need to be generous size to get the best output. But the cable cost is a one off to get double the gauge for not much more cost. When I had portable panels I had long cables to make it easy to chase the sun if I was in a bad spot. Who put those bloody trees there ????
Jaahn
PS 6x20W panels could use another configuration to limit the losses from long leads. 2 strings of 3 panels in series. Just saying for other people who want ideas.
-- Edited by Jaahn on Wednesday 16th of January 2019 06:30:39 PM
-- Edited by Jaahn on Thursday 17th of January 2019 08:51:24 AM
I think I confused the issue with my use of the word "multiple". In any case I found Terry's explanation to be informative.
(I would also like to thank DeBe for the PCB photos and CRO screenshots)
Does anyone use a coulomb counter (coulometer)?
https://www.alibaba.com/product-detail/TK15-Battery-Coulometer-Digital-LiFePO4-Lead_60783207248.html
http://powerampdesign.net/images/PBV-R005-1.pdf (PBV precision current sense resistor datasheet)
https://www.alibaba.com/product-detail/TR16-Battery-coulomb-meter-Coulometer-Digital_60749751136.html
-- Edited by dorian on Thursday 17th of January 2019 09:16:13 AM
I've been reading about PV panel materials. Wikipedia states that GaAs panels are the most efficient, but also relatively expensive. In an attempt to find out just how expensive they are, I found this:
https://www.alibaba.com/product-detail/Gallium-arsenide-solar-cells-made-transparent_60808115115.html
The panel is rated for 320W and its dimensions are 1960 x 992 mm. That's 165W / sq m.
Here is a polycrystalline panel:
http://www.centsys.co.za/upload/CENTSYS%20Documentation/0_07_B_0133%20200W%20Solar%20Panel%20Specifications%20sheet-29062015-NG.pdf
It is rated for 200W and is 1320mm x 992mm. That's 153W / sq m.
The difference in power output is only about 8%.
If you look at my post and the highlighted line from the Victron Whit paper
"quote: might be better off wiring the panels in series and going with a single MPPT controller." That was the item I was referring to and why it was highlighted. The example of the 6 x 20w panels was just to point out that solar capacity had nothing to do with the rules regarding the need for a licenced electrician the handle all parts of the solar side including the controller installation, it is the series string voltage.
There are completely different issues with series parallel connections regarding shade effect. Much of it can be mitigated by the way it is wired, but the issues still remain
T1 Terry
The real difference between panel designs and output does not show up by comparing STC results, they actually reflect just about nothing of how the solar panels will function when out in the Australian mid day sun.
The fact most RV panels are flat mounted on the RV roof with very poor heat transfer away from the back face of the panel (because there is a trapped air pocket there) means true testing needs to be with the panel temp above 60*C and the ambient temp more like the temp likely to be found in free camp site throughout Australia. Even the NOCT results are with a panel temp of 45*C an ambient temp of 20*C, can you see that occurring anywhere in an Australian summer?
We do have an Australian solar panel manufacturer, Tindo, check out what type of panels they build and ask why that technology and not the other, the engineers answers will give you a good insight into why papers written in Europe have very little relevance in Australian conditions.
t1 terry
Hi
a lot of this is over my head but I a question now please,,, based on previous,,,,
Is the Victron MPPT 75 15 controller a genuine MPPT or PWM in disguise?
Cheers Baz
Hi Baz
Victron make good gear and they perform as they claim. So a genuine MPPT unit.
My disclaimer: I own one and some inverters.
Jaahn
Thanks Jaahn Appreciate your posts over many years. Cheers baz
I should have looked more closely. The Alibaba panel lists GaAs under Specifications but Polycrystalline Silicon under Quick Details. I guess that explains the unremarkable 17% efficiency figure.
Here is the datasheet for a monocrystalline silicon Tindo panel (17.1 - 18.0% efficiency):
http://www.tindosolar.com.au/wp-content/uploads/2018/05/300W-Tindo-Karra-data-sheet.pdf
Here is an Alta Devices single-junction GaAs cell/panel (26% efficiency):
https://www.altadevices.com/wp-content/uploads/2018/04/Single-Junction-Tech-Brief.pdf
Not only is Alta's power output impressive, but the temperature coefficient is -0.09% per deg C. The Tindo panel has a corresponding coefficient of -0.41% per deg C. This means that for a roof temperature of 65C, a 200W GaAs panel would lose about 3.6% or 7W whereas the monocrystalline panel would lose 16.4% or 33W.
http://www.tindosolar.com.au/learn-more/temperature-coefficient/
The Victron 75/15 is a genuine MPPT controller but being one of their budget line products https://www.ebay.com.au/itm/Victron-Energy-Blue-Solar-12-24V-75-15-MPPT-Solar-Charge-Controller/271875497952?hash=item3f4d0adfe0:g:GXgAAOSwe2ZbtAJk:rk:2:pf:1&frcectupt=true it does not have the same sophistication as the much more expensive Victron SmartSolar range that are well over the $1,000 mark https://www.ebay.com.au/p/Victron-Energy-BlueSolar-12-48v-150-85-MPPT-Solar-Charge-Controller/3012076814?iid=162482181644&chn=ps
It is unrealistic to expect the $112 item to perform as well as the $1500 item, just because they both have the name Victron on them, it really is a case of getting what you paid for .....
T1 Terry
Hi Dorian, have they actually got these cells into a commercially available panel format yet? I was reading about a quad junction cell that had achieved very impressive conversion figures but I haven't seen any mention as to whether it scaled up to a marketable product yet.
T1 Terry