[rmeador]

This post is about boats, but not sail boats, and it's about solar power electrical systems, so I hope it will be tolerated on this board. You folks have the most knowledge of self-contained and waterproof solar tech of any community I know of.

My friend has a cabin on a small lake, and he recently equipped it with solar panels. The cabin itself has 4 golf cart batteries in series-parallel (to power LED lighting, a water pump, and an inverter), and he also has 4 Group 27 deep cycle batteries that are used to power the electric outboard motors on his boats (this is where the boats come in!). Just to be clear, these batteries get taken out of the boats, hooked up to the charger, then put back in the boat when ready.

We're wondering the best way to split his solar power among these 5 banks. I did some quick googling and I couldn't find any solar charge controllers that have 5 bank outputs, and even the 4-bank ones couldn't handle the amperage such a system would require. If possible, he'd also like to be able to tie in a generator as a backup and have it capable of charging all 5 as well. I think he's willing to go down to 2 boat batteries, for a total of 3 banks charging simultaneously, if charging all of them at once proves impractical.

Thanks for your help, and I apologize if this strays too far from on-topic.

 

[MarkofSeaLife]

Not being an electrical wizard...

Just shove the wires onto anything thats a 12 v battery and the electricity will run like water till everything is filled up.

So if that series/parallel thing you are talking about is 12v you are set to go. If its 24 v and the boat batteries are 12 then you have more things to do.

 

[Maine Sail]

This post is about boats, but not sail boats, and it's about solar power electrical systems, so I hope it will be tolerated on this board. You folks have the most knowledge of self-contained and waterproof solar tech of any community I know of.

My friend has a cabin on a small lake, and he recently equipped it with solar panels. The cabin itself has 4 golf cart batteries in series-parallel (to power LED lighting, a water pump, and an inverter), and he also has 4 Group 27 deep cycle batteries that are used to power the electric outboard motors on his boats (this is where the boats come in!). Just to be clear, these batteries get taken out of the boats, hooked up to the charger, then put back in the boat when ready.

We're wondering the best way to split his solar power among these 5 banks. I did some quick googling and I couldn't find any solar charge controllers that have 5 bank outputs, and even the 4-bank ones couldn't handle the amperage such a system would require. If possible, he'd also like to be able to tie in a generator as a backup and have it capable of charging all 5 as well. I think he's willing to go down to 2 boat batteries, for a total of 3 banks charging simultaneously, if charging all of them at once proves impractical.

Thanks for your help, and I apologize if this strays too far from on-topic.

You don't say how big the array is?

There are many ways to skin the cat.

Send all charge current to the 4 6V batteries using one good controller and or battery charger. Wire an automatic combining relay (voltage sensitive relay) or battery to battery charger (Sterling, Echo Charger or Duo Charger) for the other 4 batteries. Wire the 4 batteries in parallel when you need to charge them, using pre-made jumpers and treat them like a single bank during charging. Unparallel them when not charging.

A 1/2/BOTH switch could do the same only manually. If the ACR or Echo type charger won't be used all the time you will want a way to disable it when the other batts are not connected.

About 80 ways to skin that cat but none that I would choose that include dual bank solar controllers....

 

[rmeador]

Thanks for your insight so far. I don't know the wattage of the solar off the top of my head, but I've asked my friend and should hear back soon -- I think it's around 250W.

Simply attaching the batteries to each other is not an option, as they will be in various states of charge and they will attempt to equalize with each other, which could result in massive currents, battery damage, releasing of explosive hydrogen gas, etc... I think I wasn't clear on one potentially important point -- these boat batteries are each for a different boat, they don't make up one bank in a single boat; as such they'll see different levels of discharge, and in fact some will be charging while others are being used. Basically, I don't want any battery to be charged off any other battery, only the solar charger. Given that the panels output trivial amounts of power when it's cloudy (or night ) I think some automated combining method is required. The echo-charge and similar might work if there was one between each battery, but then we have to educate the users (people staying at the cabin) that they have to plug the batteries in in a certain order and they'll charge in a certain order (I think?)

Maine Sail, why are you averse to multi-bank chargers?

Thanks!

 

[Maine Sail]

Simply attaching the batteries to each other is not an option, as they will be in various states of charge and they will attempt to equalize with each other, which could result in massive currents, battery damage, releasing of explosive hydrogen gas, etc...

Total myth... Yes there will be a short inrush from the higher voltage battery to the lower but as the voltages come closer together the movement of current slows to a crawl. These inrush current are of zero concern, cause zero damage and absolutely can not cause gassing....

I think I wasn't clear on one potentially important point -- these boat batteries are each for a different boat, they don't make up one bank in a single boat; as such they'll see different levels of discharge, and in fact some will be charging while others are being used. Basically, I don't want any battery to be charged off any other battery, only the solar charger. Given that the panels output trivial amounts of power when it's cloudy (or night ) I think some automated combining method is required. The echo-charge and similar might work if there was one between each battery, but then we have to educate the users (people staying at the cabin) that they have to plug the batteries in in a certain order and they'll charge in a certain order (I think?)

Maine Sail, why are you averse to multi-bank chargers?

Thanks!

Again you are buying into myths and fear mongering.

Facts:

* All the batteries need to be charged

* Regardless of individual battery SOC batteries can easily be wired in parallel and charged. It is done every single day in millions of batteries world wide..

I am not opposed to multi-output solar controllers other than no one makes a decent one. The best controllers made are single output.

A multi-output charger is only diodes in the output to prevent back feeding. All batteries get the identical single charge profile..