How to work out amps in battery.

Patto44 · Senior Member

How to work out amps in battery.

justcruisin01 · Guru

More than likely there are systems out there that I am not aware of but my solar regulator gives me a 30 day history in 24 hr intervills; that is total solar amps in/ load amps out/ max & min voltages of both solar & battery/ Float time( when batteries are fully charged).Â present amps in use/ present solar amps going in, state of charge ,eg boost/bulk ; absorbtion; & float; plus many other pieces of info.

This gives you a readout of how the system is performing.Its a bit hard to estimate how many amps are left because as the volts drop the amps being used increase.

JC

PeterD · Guru

If your solar regulator does not have a built in state of charge (SOC) monitor then you need to add something like this

bill12 · Guru

What brand reg do you have?I have a cm 30 which promised everything and gave nothing.Thanks, Bill

Patto44 · Senior Member

The solar regulator is a Powertech and shows last 2 days input apart from current volts and amps. My concern is if I leave the fridge on overnight it may discharge the batteries below 50% and damage them. The amps used by the fridge should not deplete the battery too much (about 50 amps overnight) however as stated in my first post the volts dropped from over 14 to 12.2 in a few hours when the sun set. I thought there may be a way of calculating SOC in amps. Patto

03_troopy · Guru

From their website, the fridge will draw an average of 2.5A over a period of 1 hour, running in an ambient temp of 32deg C in it's higher consumption mode. This equates to a consumption of 2.5AH. So your 2X100AH batteries, in theory, and without going into changes due to voltage drops etc, should be able to supply the fridges needs for 80 hours. ie 2 X 100AH/ 2.5AH. So to discharge the batteries to 50% you should be able to run the fridge for 40H. But that's in a perfect world, and changes in capacity with different current loads and dropping voltages would mean you'd get somewhat less than this. But the 2X100AH batteries should have no problem supplying the fridge overnight (10 Hours?) without depleting them past 50% charge.

jimricho · Guru

A discharge below 50% won't damage the batteries provided they are not left in this state for too long. Regular discharges below 50% will over time reduce the life of the batteries however, but there is no need to panic about the occasional discharge below this. Fully discharging will seriously shorten the life of the battery and will damage the battery if not recharged asap.

The better quality AGMs are a bit more tolerant to this treatment.

Plendo · Guru

Patto,

If you are considering puchasing batteries, ther are new battery tehnologies that woud be worth investigating, particulary LifePo4, which appears to be becoming viable. They are getting some very good write ups in the marine forums. High C ratings (both ways), high capaciy, low weight, and long lfe (thousands of cycles), they also read as if they hae overcome the early reliability issues.

PeterD · Guru

Patto44 wrote:
The solar regulator is a Powertech and shows last 2 days input apart from current volts and amps.

Is this the model of Powertech that you have? In that handbook it says "Monitors the state of charge of the battery" but there is nowhere in the rest of the instructions where it mentions SOC readout. The only way you will get that is to install a monitor like the one I gave the link to above.

The handbook makes mention of a "Deep Discharge Protection Voltage - 11.5/23.0V dc ±2%" - Depleting your batteries below 50% does not bugger them. You said you have AGM batteries. You can discharge them safely to 20% capacity on a regular basis, just don't leave them at that state of charge, charge them next day or two. That discharge protection of 11.5 V will protect your batteries if you have the regulator wired correctly with the house load being supplied from the output terminals.

You seem to be concerned by the battery voltage dropping from 14.4 to 13.6 V when you cease charging them. There is no concern with this. A battery will not take a charge unless the applied voltage is much higher than its resting voltage. The resting voltage of fully charged batteries is typically in the range of 12.7 to 12.9 V (the actual voltage is dependent on the chemical construction of the battery.) When you remove a charger from a fully charged battery the terminal voltage will drop from the output voltage of the charger to its resting voltage over a period of 2 - 8 hours even without any load. If you have a load on it the voltage will drop lower. The only way you can get a reasonable indication of your batteries state of charge with a volt meter is to let it rest for 4 - 8 hours without even the smallest current drain on it

Patto44 · Senior Member

Thanks for the input guys, it is much appreciated.

The controller is a Powertech MP3129 and as Peter indicated it only shows the PV amps being put in and PV & battery volts (plus today & last 2 days amps input). The SOC is indicated by a green or red light which relates to the voltage at the time.

I agree with Troopy that I should have several days without any further input from solar however the voltage gradually (over an hour or so) dropped to 12.2 and was still going down, so I disconnected the fridge. I did not realise it was OK to discharge below 50% overnight.

I have read the manual and I interpreted the over discharge protection was only if the power was connected to the 'load terminals' which in my case it is not. The installer (large company in Tuggerah NSW) said not to use the load terminals.

I will leave the fridge on tonight and see what volts I have in the morning. Not sure what do after that if it goes too low.

Thanks again,

Patto

-- Edited by Patto44 on Friday 15th of February 2013 02:45:36 PM

PeterD · Guru

Patto44 wrote:
I have read the manual and I interpreted the over discharge protection was only if the power was connected to the 'load terminals' which in my case it is not. The installer (large company in Tuggerah NSW) said not to use the load terminals.

If it is the mob on the Tuggerah straight who used to be located near Wyong station, I would not take too much credence in that advice. Those load terminals are there to protect your battery. Why did they say was the reason not to use them. I would locata any power hungry device like inverters close to the battery and cable them direct. However I would route the regular house wiring through the load terminals (even if that meant using heavier wiring due to much longer cable runs.)

Patto44 · Senior Member

Yes Peter, ... you picked the company that installed the solar. Will never go back there. Several problems that they never resolved. (all care but no responsibility)

The 'load' terminals on the controller are not being used. I feel that they may have felt it was to hard too re-route the house wiring. They wired the panels to the controller and then ran wiring to the existing power from the battery and spliced in (which was close by). I asked for a separate 12v 4mm wire to be run to near the controller to enable me to connect an inverter. This also was just spliced in to the existing wiring. I could have done that myself!!!!

I am using this 'separate' 12v outlet for the fridge.

Thanks for your interest; I am still learning about solar and getting a little disheartened. I want to run the fridge, small TV, vast set top box, and a couple of LED lights, so we can try free camping. Can't even run the fridge, so not looking good. It must be a battery problem as there is plenty of charge going in during the day.

Patto

-- Edited by Patto44 on Saturday 16th of February 2013 06:29:16 PM

briggspc · Senior Member

Well all I can say is that my car has a solar panel on the roof 80 watts charges a 100amh battery in the car and runs my engle fridge in freezer mode all day and nite every day and if no sun for 2 days start the gen.

my van has 2x90 watt solar panels runing into 2x110 amh batterys and runs my tv, vidio,sound,vast,all van lights and computers for about 5 hours every day and can do that for 3 days with little sun, after that just put the gen on for 5 or 6 hours, sorry for got about the 12 volt fan running all nite when hot.

Hope that helps.

allinone · Senior Member

Disclaimer: I no zip about anything so form your own conclusions....

If you have 4 panels and 2 batteries there would be on average plenty of daylight hours to recharge the batteries.
But is would seem to me that overnight you do not have sufficient charge to run all your equipment. IMHO if this was my setup I would need another 2 batteries or get bigger AH capacity ones, but then you get to the problem of is there enough charge to keep them full. Sort of like did the egg chicken come first debate.

There is a site that describes battery usability versus demand etc and links in the site may help you look at actual battery capacity. It is technical but is explained in some simple samples.

It may be of use time and time again....
http://www.batterystuff.com/kb/tools/peukert-s-law-a-nerds-attempt-to-explain-battery-capacity.html or
http://www.batterystuff.com/kb/tools/ac-to-dc-amperage-conversion-run-through-an-inverter.html

beiffe · Guru

I am sure that the LOAD terminals on your regulator are of a limited capacity only.

To get a proper SOC of your battery you really need to run a shunt and put all your load and charge through this shunt. Most regulators tell you the input but don't record the output so the SOC is useless.

Some expert may come in and elaborate as I am a elec dummy but I have a full solar setup and it was done by a person who does know solar and batteries and that is I believe his explanation of the load terminals.

I would be interested in the condition of your batteries. Have you tried to do a load test on your batteries. eg charge to what you think is full and then put a set load eg head light globe or heater element such as a coffee warmer in a large bucket etc so it does not get hot. Then time how long before your battery gets to the 12.2v on no load. So you have to take the load off

You stated that as soon as you took the charger off the batteries returned to 12,2v which to me tells me the batteries are stuffed.

I have used lithium batteries in my bus for over 20 months and they do have lots of advantages but not for someone who wants a drop in solution as there is a little work to learn how they work and there is no one in the market place who can tell you how and what to do.

We have done lots of experiments over many instals and varied setups, and believe we now have a dummy's setup guide but still there is stuff YOU have to do but in the end YOU know what is going on and how to fix whatever happens.

Best to get your batteries checked for their AH available before you spend any money and right off free camping as there are so many options out there to enjoy.

Regards
Brian

PeterD · Guru

beiffe wrote:
I am sure that the LOAD terminals on your regulator are of a limited capacity only.

To get a proper SOC of your battery you really need to run a shunt and put all your load and charge through this shunt. Most regulators tell you the input but don't record the output so the SOC is useless.

The load terminals are useful to carry a current up to the rating of the regulator. They are not designed to carry large loads like big inverters. However they should be used for your lighting and small power loads to protect your battery from things like compressor fridges over-discharging your battery. If you use it you can also get some readings of what is drawn from your batteries by the various lights and fridges (but not 3 way fridges.)

As I said above, that regulator does not does not give a true SOC reading of your batteries. Brian, you are correct in that second sentence. The monitor I gave the link to in my first reply does just what you were describing. Part of the kit is a current shunt that you install very close to the battery. If you install things correctly it measures all the current into and out of the battery. From these readings it calculates SOC. It even takes Peukerts law into consideration in its calculations.

Big Gorilla · Guru

You have 4 x 80 watt panels and 2 x 100 amp batteries. Should be more than enough to run your refrig. overnight. Most refs today have a low voltage cutout, meaning when the voltage reduces to 11.8 volts, the cutout will cut the power to the ref. Low voltage can cause the compressor to overheat and possibly burn out the windings,. Reduction to 12.2 volts overnight is not something to worry about. I am an electrician but I don't profess to be an expert on low voltage and solar installations. My suggestion is have the batteries checked. You don't mention how old batteries are, but they don't last forever. If I could offer a tip, check the water level in your batteries every week whilst on the road. Keep topped up with distilled water. Don't use tap water coz the minerals in the water will damage the plates inside. You can catch rain water in a plastic bucket or buy 4 liters at Supercheap or Auto Barn for around $5.00. This applies to your car battery also if you want long life from these batteries.

oldtrack123 · Guru

HI Patto

Lots of good advice on keeping check of battery SOC
But your present problem is either one or both batteies are stuffed

Have little "chargable" capacity due to age or excesive discharging,
The other possibilty is that one has a dead /shorted cell

In any case YOU should have a "LOW VOLTAGE CUT OUT" fitted AS close as possible to the batteries
[preferably set to cut out around around 11.75 to 12V]

PeterQ

Patto44 · Senior Member

According to the 'book' the low voltage cutout is set at 11.5 volts, which sounded a bit low as I have read that approx 11.9 volts is 'flat'.

After monitoring the readouts for several days now, they drop down rapidly (1 to 1.5 hrs) to about 12.7 (which is when the red light - SOC - comes on) and then stabilise at around 12.4 to 12.2 volts by the morning (6am before sunrise).

The fridge is an Evakool Fridgemate which also has a cutout in it if voltage drops (not sure what voltage).

Big G the batteries are AGM sealed and are about 5 years old.

I had them load tested and was told they are OK. They take a charge from solar panels quickly and reach 13.8 in a few hours each morning. I just feel that they are not holding the charge once the sun goes down and would not be confident to free camp using TV, lights and fridge etc. for any length of time (maybe 1 night should be OK).

Thanks

Patto

PeterD · Guru

Patto44 wrote:
I had them load tested and was told they are OK. They take a charge from solar panels quickly and reach 13.8 in a few hours each morning. I just feel that they are not holding the charge once the sun goes down and

I feel the reason they are not holding a chage is because you are using them. Disconnect your loads and check the voltage before the sun hits the panels in the morning (perhaps disconnect the panels after sunset just to be sure of no charge in the morning.)

oldtrack123 · Guru

Hi Patto
RE"I had them load tested and was told they are OK. They take a charge from solar panels quickly and reach 13.8 in a few hours each morning. I just feel that they are not holding the charge once the sun goes down and would not be confident to free camp using TV, lights and fridge etc. for any length of time (maybe 1 night should be OK"

If they only reach 13.8V & quickly, they are possably tnot f being FULLY charged

They should be charged to at least 14.2V & up to 14.7V, before going into float mode to around 13.2 13.7V
Actual recommended voltages can vary with makers.

It depends what the sort of " load test" 'was done
What was required was a capacity test& that TAKES TIME to do[ hours],, not quite the same as a load test which is just a quick test of current output!!

PeterQ

-- Edited by oldtrack123 on Saturday 23rd of February 2013 01:17:14 PM

Big Gorilla · Guru

Patto44 wrote:
According to the 'book' the low voltage cutout is set at 11.5 volts, which sounded a bit low as I have read that approx 11.9 volts is 'flat'.
After monitoring the readouts for several days now, they drop down rapidly (1 to 1.5 hrs) to about 12.7 (which is when the red light - SOC - comes on) and then stabilise at around 12.4 to 12.2 volts by the morning (6am before sunrise).
The fridge is an Evakool Fridgemate which also has a cutout in it if voltage drops (not sure what voltage).
Big G the batteries are AGM sealed and are about 5 years old.
I had them load tested and was told they are OK. They take a charge from solar panels quickly and reach 13.8 in a few hours each morning. I just feel that they are not holding the charge once the sun goes down and would not be confident to free camp using TV, lights and fridge etc. for any length of time (maybe 1 night should be OK).
Thanks
Patto

Thank you for mentioning a point I had overlooked. Yes, there are a lot of sealed batteries in use today and they dont or cant be topped up. Personally, I wouldnt worry too much about a voltage of 12.2 at sunrise. Take note of what current you are drawing after sundown, apart from the ref. Lights, inverter, TV, CD player, water pump, turn them off when not in use or if not required.. After dark, I run 1 or 2 lights, TV/DVD player and of course the ref. Until I go to sleep. The lowest my batteries dropped to one morning was 11.8volts so I was only a cats whisker away from losing the ref. However I have a solution to this low voltage problem that I will share with you.

I have a Motorhome, a thumbnail is below. My power supply comes from 3 sources, solar panels, a 240 volt charger when I am plugged into a power point, and thirdly from the engine alternator. Most Motorhomes are wired, or should be wired this way. Caravans are different in that most I have seen do not have the facility to charge the house batteries from the alternator under the bonnet.

If you believe your batteries are low, start the engine. The alternator will charge your house batteries. If you have a diesel, you can run the engine for a long period without the worry of overheating. Petrol engines must be monitored for overheating if you idle for a long period.

Only cable running between your car and caravan is 12 volt and powers tail lights, brake lights and flashers. If you cant do it yourself, have an auto electrician run a twin cable, minimum size to carry 30 amperes, but Id recommend 45 amps, from your car battery to the Battery Isolator for the house batteries. At the car battery, connect the red and black cable to positive and negative terminals. Run the cable under your car, securing it so it doesnt sag, to the tow bar. Fit a connector to each end so you can disconnect the cable when you want to unhook the car from the caravan. Then run the cable under the caravan to the battery box, connecting the red cable to the input side of the battery isolator and the black to negative terminal of one of the batteries. Problem solved. As you drive along your house batteries are being charged by solar and the alternator. Some will tell you that only one wire is required, a positive wire between the car battery and the battery isolator, that a negative is not required because the frame of the car and caravan acts as an earth or return wire. That is true up to a point but the earthing continuity between the car and caravan may not be satisfactory, particularly at the ball joint. By running a second negative between the batteries will eliminate any bad connections and insure the system is charging correctly.

I hope that information is helpful to those who tow a caravan.

oldtrack123 · Guru

Hi

Successful charging house /van batteries from a vehicle alternator is dependent on many factors

[1]The output voltage of the alternator, newer vehicles can have an putput voltage as low as 13.2V

That will not really charge a remote van battery

& a DC to DC charger is the only option

[2] the run length from the tug battery to the van battery causes voltage drop at the van battery making the alternator's output voltage even more critical

To minimize this voltage loss , the largest cable sizes possible should be used.

Cables sizes should be put in GAUGE ,current rating for auto cables has little meaning as does the quoted size [6mm is just the OVERAL dia,& has no relationship to CONDUCTOR size

Knowing the following :

[a]The alternator output voltage

run length from tug battery to van battery

[c] the other loads which may be running from the VAN battery while trying to charge from the alternator

Will allow a minimum recommended cable GAUGE to be advised

PeterQ

-- Edited by oldtrack123 on Sunday 24th of February 2013 11:17:26 AM