Solar panels not keeping batteries charged up. Need assistance to diagnose.

[spudboy]

Hi - I need the brains trust to assist with the best way to diagnose why my solar panels are not keeping my batteries up to charge in my camper, please.

The basic components involved are:
-6 x 100W ultra thin solar panels, connected in pairs, so feeding in as 3 separate inputs to the MPPT charger at around 30V under load
- A 30A GSL MPPT charger (Australian made)
- 3 x Optima D31M Blue Top batteries connected in parallel. They are 75AH / 900CCA. So 225AH in total.

We haven't used the camper for 3 months, so nothing is turned on (like fridge, lights, pump, whatever). It is stored outside in shady sun, so I was expecting that with practically nill usage it would only need a trickle to keep it topped up. The voltage alarm went off when it dropped to 11.2V, and the auto cut-out turned everything off.

The people who supplied the solar panels and the MPPT charger have been very helpful. They asked me to do some tests to try and work out if it is the batteries or the panels which are the issue. They don't think it is the MPPT charger. Because the batteries are about 3 or 4 (or 5?) years old, they are suspecting that one battery may be faulty of have some faulty cells.

I've started by fully charging the batteries from 3 240V chargers. It took over a day to get them back up to fully charged, from being at 11.2 volts!

This is what I did to test the batteries:
o Separated the 3 batteries
o Charged them all, using 3 battery chargers.
o After 3 or 4 hours I would 'rotate' the chargers to make sure each battery got charged with each different charger (they were different capacity chargers) and 2 chargers had an AGM setting but the 3rd one is old and only had one setting
o Let the batteries 'rest' for 4 hours
o Recorded the unloaded voltage
o Hooked up 3 identical LED spotlights to the batteries
o I measured the Amps on each light when I connected them (as I thought that might be relevant) and put these details onto the graph below for each light.
o Recorded the voltages on each battery over 20 hours

This is the result of the testing - a graph!:


Any thoughts on the goodness of these results? Was the test load (about 0.8A) sufficient for testing?

Next thing is to work out how to test the panels....

Thanks
David

[spudboy]

Here's a block diagram of how it is built:

[Blknight.aus]

ok the testing isnt really valid, you did your best but there is a better way.

hook all the batteries in parallel, plug the biggest charger into the bank and let it have at it..

you must hook up in a star configuration on the positive so you have one point that feeds all the batteries you can then measure the amps going into each battery. let them sit on the biggest charger you've got for 24 hours, then disconnect them from each other. Now repeat the 4 hour sit and then test the volts and amps into a known draw.

with the way you have charged the battery they may have not all come up the same.

Assuming they have all received the same basic charge profile then the green battery has at least one cell that is close to dead or 2 or more cells that are being lazy.

depending on how exactly your panels are wired up an inputted one just one panel not putting out charge will limit the whole arrays out put, in reality Id expect you to have to have at least one in each pair down to really cut you out but if half of each panel is shaded and you're wired like I think you are then you loose all of your charging ability.

what you need to measure on the batteries is

1. volts and amps while charging
2. volts once charging stops
3. volts after 4 hours
4. volts and amps while under load

you also want a slightly bigger load. 5-10 Amps will be closer to what you want bu t the rough rule of Thumb I use for a test load is 10% of the capacity of the battery. so 7.5A in your case and you should hit 10 hours worth of life.

[ozeraser]

A lot of solar panels don't work in partial shadow like monocrystaline, if a panel is in half shadow it can often stop producing.

Also a lot of chargers actually power themselves via the battery and if there is little to no power coming in, it will vampire the batteries. If your usage outweighs the incoming you will slowly flatten your batteries.

Just connect a single battery to the MPPT charger, measure the voltage across the battery when you expect it to be charging (full sun for a good test). If its less than 13.8 you have a bit of an issue. Amperage is a something to take note of but dont as most standard multimeters max out at 10A.

Disconnect the batteries to anything other than the MPPT charger, then test again.

Finally just start disconnecting panels as a single 100W panel should easily charge a battery over a few days (depending on the charger).

Next is to read the details on the back of the panel and then measure them in full sun, again however check what the amperage is from them as you could blow your meter.

Could you just take it to an auto electrician?

[Sitec]

Just thinking from a different perspective here.. I'd park the truck in a different location.. With the shade of the trees and the arrival of winter the light has been pretty average of late even without shade....

[spudboy]

Thanks for all those thoughts. Some answers in a random order....

Firstly the easy one - Simon:

I've parked the camper out in the full sun (even though I know it is low in the sky at this time of year) to see what input I am geting.

In the midday sun, with all 6 panels going into the 12V charger, I was getting 4.6A at 12.9 volts going in, which seems really low for 6 x 100W panels.

I've installed a 100A shunt to measure what is going in from the solar panels, and a digital meter.

[spudboy]

Then Dave:

The 12V company that sold me the gear asked me to separate the batteries, then charge, then measure, so that's why I did it that way. I can easily do it again with them joined together.

So the green battery could be a dud? It's only 0.1V different than the others. Which might be pulling down the other 2? It is getting on now. I was hoping it to not be a battery issue as 3 new ones are going to be about $1200

If it's a problem with the panels, that is better for me as they are under a 10 year warranty!

Following your comments, I've been charging it with my biggest charger, a 15A Ctek,with all 3 now joined together. It was pumping in 14.8A at 13.4V for a while, and then it went down to 4A at 14.1V. It is still charging and the Amps are going down bit by bit.

I will try the load test again over the weekend, using some bigger loads. I have some 50W 12V globes, so that'll draw 4A. Can't think of anything that draws 7A that I have 3 of! Guess I could use 6 50W globes instead of 3....

[spudboy]

Then OzEraser:

When the 3 batteries are low, the voltage creeps up slowly over the morning, from (say) 12.9 to 13.6V over a few hours. Even if it's nice and sunny.

I have another (separate) setup with the same MPPT controller, but a lot more panels and only 1 battery, and that starts out at 14.2V in the morning, for an hour or two, then drops back to 13.4V for the rest of the day.

I can disconnect the 'output' circuit easily, so no power can be used by the fridge or lights (not that they are on).

The details of the panels are:

Panel Type: Mono-crystalline

Code: ZM-9154

Maximum Power (Pmax) 100 watts

Open Circuit Voltage (Voc) 21.70 Volts

Open Circuit current (Isc) 6.10 Amps

Max Power Voltage 17.70 Volts

Maximum Power Current (Imp) 5.70A

Module Efficiency 21.30%

Normal Operating Cell Temp (NOCT) 48+-2*C



It's not so easy to take it to an auto electrician, as it's not registered at the moment...

[Blknight.aus]

to test your panels, hook a pair of your 50W bulbs in parralell to each panel and measure volts and amps in full sunlight.

to make 7.5A put 2 50w bulbs in series and then put that in paralell with a singe 50w bulb, its not perfect but its close enough.

given that your whole voltage range from fully charged to effectively flat is about 2v .1v is a 10% variance.

your amps from the panels and regulator will be lower now as you have charged the batteries from the mains. To test that properly you need to have either flat batteries or a dummy load that can draw the full output of the regulator.

[drivesafe]

Hi David and first off, your batteries should never have been allowed to get down to 11.2v and I assume were left there for some time.

It is quite OK to cycle Optima batteries down to 10.5v as long as they have been discharged down to 10.5v in a short time, like over a few days, NOT MONTHS, and are recharged shortly after being discharged down to 10.5v. ( no lower than 11.58v for all other batteries )

Any battery that is left with a terminal voltage of less than 12.35v or an SoC of 75%, will begin to sulphate.

Optimas are far less likely to sulphate as quickly as most other batteries but left for long periods, they will and I suspect yours have.

While your test is a basic one, it will give you a very reasonable indication of the condition and state of charge of your batteries.

From the data you posted up, I suspect your batteries are about 15 to 20% down on their full potential capacity.

If your batteries are suffering from the effects of sulphration, CONDITIONING charging of your batteries may recover some or even all of your lost capacity.

You can use any 2 ( or more ) stage charger. It must have a BULK and FLOAT stage and then you can try to recover lost capacity.

The best way to CONDITION charge a battery is to turn your battery charger on, and regardless of whether your batteries are fully charged or not, the battery charger will go BULK charge mode at first.

Then depending on how high a state of charge the batteries are in, the charger will eventually go into FLOAT mode.

It is the FLOAT mode part of the charge cycle that will VERY slowly recondition the battery.

Try to leave the battery charger on the batteries in FLOAT mode for around 8 to 10 hours and then turn the charge off for 10 or more hours, to allow the batteries to settle, and then continually repeat the cycle for a good few days.

After a number of CONDITIONING cycles, try repeating your discharge test you carried out above, and see if you have any improvement in battery capacity.