Restart solar system - off grid system

[PerraS]

Hi,
this is my first post here. Thanks for a great forum with lots of knowledgeable people.

I have a 12 volt solar system with a Epever 4215bn charge controller, two luxor panels at 320W each and two 160ah gel batteries in parallel. The system is located at my cabin on a little island.

Unfortunately I left a load on and came back to fully drained batteries. The volatage is right now a little bit above 5 volts. Yes Im gonna invest in a low voltage cut off switch.

Conditions:
I have another fully charged battery on another system on the island which I can use. It's a 12v flooded lead acid battery wiht a capacity of maybe 75ah.
The gel batteries has now been left without charge for aproximately four mounths.

My question:
Is there anyway for me to jumpstart the charge controller with my fully charged extra battery so the charge controller can start charging the flat batteries? Its a sunny day here and it should be sunny tomorrow. If so How do I do that, provided I am able to revive the batteries?
I really want to avoid carrying the batteries down to the boat and take them home to charge them if possible.

Any imput would be appreciated.

Thanks in advace!
/Per

 

[Bbbbrass]

Edit: After thinking for a minute I noticed you said these have been drained for months. You will most likely just damage your good battery trying to save these. Take them back for scrap. Where are you located? If it doesn't get very cold, this could be a perfect chance for a salvage DIY lithium build.

Sure, just parallel them. Make sure you use super thick wires (like 2/0 jumper cables), and realize the batteries are most likely toast. To have a chance of saving some usable capacity, you need to try recharging very slowly, so it will most likely work best to take them with you and use a CC/CV power supply over several days/weeks. Also a good excuse to build a lithium pack! (and either way, install a LVC) Good luck!

 

[PerraS]

Thanks for your reply! By "just parallel them" you mean, parallel the fully charged battery with the existing two flat ones?

At what amp do you suggest I charge them at if I bring them home with me?

Yes a lithium pack would be lighter to carry if nothing else .

 

[Bbbbrass]

Yep, just put the good one in parallel with the bad one. I would do it one at a time, and would go low and slow. Like 5Amps. Seriously though, it is almost certain you won't get a good result, and may mess up you PB battery or system.

 

[wme]

I suffered a similar situation and ended up with 2 frozen (-31 degrees) FLA batteries, bulged cases and all.
I let them warm to 70 deg F over 2 days. Then using cargo straps and wood blocks I "debluged" the batteries. 2 more days of rest and then used this charger...https://www.ebay.com/itm/3144183383...NbmCVpLwGCxX76ETN8N/yG1Q==|tkp:Bk9SR-6Lmsv0YQ
The charger has an "repair" function. Charged at 3 amps for a day, the battery recovered enough so that the normal charge function at 10 amps would work. The batteries new are 225ah and I cycled the repaired batteries and got 200ah.
Future life span ????

 

[MichaelK]

Before you load them onto the boat, here is one more thing you could try. Wire the two batteries in series to make what would be a 24V string, and then hot-wire one of your 320W panels directly to the battery terminals. The series batteries will drag the voltage of your 320W panel down to what the batteries would want to charge at. That might actually be around 24V or so. Carefully monitor the voltage of this series string with a voltmeter, and disconnect the hot-wire once the voltage raises to 28-29V, assuming it goes up at all.

Once you've gotten at least some charge back in the batteries, break them back down into two parallel 12V strings, and see if they have enough voltage now to properly boot the controller. Let the controller continue to charge the parallel strings until the bank reaches full charge. At that point use the voltmeter again and determine how balanced the resting voltages of each battery is. If the resting voltage has gone back up to maybe 12.5V or so, you might just have saved them, but most likely they'll have permanently reduced capacity.

Though they may have suffered some permanent damage, you might just get enough usage out of them to give you time to shop for a better battery bank. If the hot-wire charge doesn't do anything, then yes, they really are toast, and start lugging them down to the boat dock.