12 v camper solar help

bundyroy · Member

12 v camper solar help

Bobdown · Guru

Hi Bundyroy,

I'm not an expert or anything, but have always been told and read that the batteries should be the same size.

Mppt are the best, but there is nothing wrong with Pwm, they work fine, just a unnecessary expense if you already have one.

My solar is always connected, best not to let the batteries run down too much, not below 11.5 V I think, but don't quote me on that.

Safe travels....Bob

bundyroy · Member

thanks mate

swamp · Senior Member

HI
Good solar size minimum for 2x135ah.
Technically the 100ah will not have the voltage curve the 135ah do . Eg as the batteries get close to full the charger will be artificially told to slow down 100ah full but 100ah into a 135ah battery is NOT FULL . People do it but it is less than ideal . Don`t forget the smaller battery would have reduced capacity if greater than 1 yo .

Peter_n_Margaret · Guru

Need some more information to advise.
1. What are the output specs of the 2 panels (voltage and amps)?
2. What is the capacity of the controller (make and model would be useful).

Batteries don't need to be the same size if they are connected in parallel, but they do need to have similar charge specs and be in similar condition if possible. Your power usage would seem to suggest that the 2 x 135Ah would be more than adequate to supply your needs with plenty in reserve.
Solar panels in parallel can also be different sizes, but it is best that their output voltages are very similar.

No problem leaving the solar panels connected to the batteries providing the solar controller is a reasonably good one and charges at conditions appropriate to the batteries.
Cheers,
peter

Jaahn · Guru

Hi bundyroy smile

I think you are asking a couple of different questions so I will seperate them.

Can I use the 2x135 AGM with the old 100 as well. Not sure how old it is but I would probably just charge the 100 and disconnect it normally but keep it charged if you need it or just take it out. It is a slightly different chemistry and is now a bit lower quality due to age.

Can I use the two different panels together OK. As Peter said it depends if the two max power voltages are close. Give us the specs off the back of the panels. You can work two different panels together normally if the MPV are similar, with no problems. If not, they will work but not as much output but will not damage the batteries. aww

Is it safe to leave the panels connected when not in use. Short answer is yes but ! If you have a good regulator which has 3 stages of charging, which finish in a float voltage stage it will be OK. You should also reset the stage voltages correct for your new batteries.

If you do not have a 3 stage reg with adjustable settings as a minimum, then I would say now is the time to buy one. What is the brand and type of the one you have. A mppt reg will give you a bit more but there are lots of fakes out there so read the threads on here.

Jaahn

T1 Terry · Guru

Properly connected there is no problem using different capacity batteries with basically the same chemistry. Simply daisy chain connected will kill perfectly good or even brand new batteries, so those that have had a system die and blame the mismatch of battery capacity are probably blaming the wrong thing for the cause of an early system failure.
Different size and even different voltage panels connected in parallel through a PWM controller will work fine. Even if one of the panels has a lower Vmp voltage than the others (marked on the label on the back of the panel) it will work the hardest when the battery voltage is at its lowest. The panel with the highest Vmp is the one that will do that last top up charging in very hot weather.
As far as leaving solar panels on a lead acid battery pack that is doing no work, make sure you can drop the float voltage to 13.6v or even 13.5v for a 12v battery. That will save the electrolyte boiling and the plates buckling. But when you are ready to use the battery pack again, a good long charge at 14.4v or 14.8v, depending on the type, this is to stir the electrolyte up and get the acid mixed back in with the water rather than staying in the lower part of each cell.

T1 Terry

-- Edited by T1 Terry on Sunday 10th of February 2019 11:49:48 PM

denmonkey · Senior Member

I leave my panels connected all the time but it wouldn't sit for that long without use.
I make sure to duck out to the van on weekends and turn a few lights or something on for a while just to apply some load to the battery to keep it in good health and to give the solar controller something to do.
I went with old house panels which have a higher voltage then the usual van/car variants thus an mppt controller was required to make use of that extra voltage.
mppt converts the extra voltage to current and the higher voltages means I can use smaller guage wires. I still err on the side of overkill though here.
The second hand market is flooded with these panels now and providing you're a little particular with the ones you pick up can be hard for a bargain in my opinion.
I know you already have your panels though.
I have an epever controller which whilst on the cheaper end of the market, still has a pretty good name.
I have the one but will be getting another for the car.
A mate also has 2 and is happy with his.
If you have the bucks, Victron is another name that has a good following but you will pay for it.

cheers brett