trickle charging a system over winter - can it be done with mixed size batteries?

[sdal999]

Between April and August, we have a few 12V remote systems set up with solar panels. One powers lights and things in a caravan, there's two batteries and solar panels for two electric fences, and a final battery for running some other remote electrical monitoring devices. They're all set apart so can't all be run off one system, and we just use PWM charge controllers.

We usually just buy cheap 12V leisure batteries; we currently have two 70Ah, a 120Ah and a small 7Ah. The solar panels we have are a mixed bag too - 50W, 100W and two 110W.

Usually at least one of the batteries is dead by the time summer comes round again, so I was wondering about rigging up a system so the panels keep the batteries charged over winter, and stretch out their life a bit longer. How would I do this? Do I need to connect a single panel to each battery, or can I connect them in all to one through a single charge controller? should they be in series or parallel? Is it pointless anyway as lead-acid batteries are going to die after a couple of years no matter what I do?

 

[DThames]

I am not a lead acid expert but you can set up for them to be held at "float" voltage. They are charged only to counter the normal self discharge. It is best to have a charger that you can set so that it doesn't got to a boost full voltage charge each morning. So the value where it goes back to boost charge needed to be low enough that overnight the battery(s) do not drop to that level. If you have any load on them, that will make them drop a little. Ideally you would want to remove all loads so they just sit and the float change keeps them at that voltage. One charger and all batteries in parallel would work (unless a battery went bad and took the others with it). Note, I have an old car battery and an old mower battery on a small charger and small panel (for some lights in a shipping container). It goes to boost each day, 14.4v which is not ideal but better than just letting them discharge and die.

 

[MurphyGuy]

You can connect all the lead acid batteries together so long as they are all the same "type" of battery. I don't think you want to connect a flooded lead acid bat to an SLA one because they have different voltage specs.. but if they're all the same type, then it shouldn't be a problem.

You could probably find a solar powered trickle charger and connect your 50 watt panel to it to take care of all three batteries paralleled together.

 

[circus]

I'm assuming the panels are already charging the batteries in question. Perhaps a low voltage cutoff between the battery and load would protect against over draining the batteries.

 

[Geokilroy]

Don't forget about boil-off of battery fluid. I left my lead acid deep cycle in my motorhome with my solar still hooked up to keep the charge. After 2.5 months the fluid boiled out and ruined my battery. I live in Las Vegas and store my rig over the summer months. I only use it over the milder months due to the heat outside. When I was setting up in September the battery was dead. Would not take a charge. I popped open the covers and found the thing bone dry. Had to replace the battery. Luckily it was under a year old and was replaced free by Walmart.

 

[sdal999]

Thanks so much all - really helpful! I'm sure I will be back at some point with more questions..

 

[Wellbuilt]

I use a 20 amp morning star controller on my trailer I just use one 80 amp panel and the controller
just dose the rest . It float all winter dosent use much power .
The charger is 20 years old and just works
it will eq the battery’s every month .
I have 2 6volt golf cart battery they are going on year 7

 

[Rednecktek]

In a similar vein, I'm looking to do a bigger All-In-One system in the future, but the standby power on it is insane when I'm at sea for 8+ months a year. Could I parallel a simple PWM controller around the AIO so I can power off the AIO and keep the batteries topped up?