Swapping out a 24V bank with a 12V bank temporarily, the safest way

Tyler702

Desert dweller, quiet prepper
Joined
Aug 20, 2020
Messages
163
I just received 4 of 8 200Ah cells. The other 4 are about a week away still. What I want to do is work on these 4 now. I'd like to attach them into my current system, and get them fully charged or close to it. (My benchtop ps is taking forever), so what I propose is to disconnect my current 24V batt bank, and quick swap out for these 4 cells, no bms at this point, and let my ample pv power bring them up quicker. My CC is epever tracer 4215bn. The way I see it, all I need to do is shut down PV input. Disconnect old batt pos and neg from the distribution block (see pic), and attach the new batt pos and neg bank in its place. Then basically adjust the CC settings for a 12V batt. Then turn on PV input, and let it charge up. My 24V inverter I'll have to turn off of course. I don't think I need to actually disconnect it, just turn it off? Once the new bank is at 14V, I'll terminate charging, shut down PV input, pull them off, and from there I can fine tune them with my bench top ps. I'll re-attach the original 24V bank, re-set my original 24V CC settings, turn back on pv input. now I have got my new 12V bank very close to fully charged in way over half the time it would've taken with my 60V 5A ps. Any unforseen issues with this? Is the order of shut down/disconnect /re-connect ok?
The only issue I see is I have my CC set to 24V instead of Auto, but I figure I can change it to auto prior to doing anything.
 

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Tyler702

Desert dweller, quiet prepper
Joined
Aug 20, 2020
Messages
163
Well, I don't have a 4s bms, nor do I need one. I've had this new pack on my PS off and on for the last few days doing a sloooow charge. (PS is set at 14V@ 4.5A..63W!) Pretty much for a few hrs when I get home from work so I can monitor it on the half hr. Direct metering each cell. Then I disconnect everything before bed, and upon checking in the morning, all 4 cells have rested to within good range:
3.310
3.310
3.311
3.309
As of last charge. So..
I understand that a bms is critical..but what I'm really going for is hooking this bank up to my existing system (4X250W panels 2S2P into my 40A mppt) and really giving this 12V bank a boost! I'm off the next 2 days, so believe me, I'll stand there with my fluke and meter the pack and each cell every 15 mins to ensure there's no runaway. I'm just wondering if the order at which I disconnect the 24v batt and attach the 12v batt is correct. Let's say I DO have a 4s bms. Is it as simple as removing my 8s bank, adjusting the CC settings to a 12V 200Ah and fire it up?
Essentially, my PS is taking way too long, and I've got all this sun here in Vegas that I could be using to bring this pack up quickly.
 

Wibla

Engineer
Joined
Jun 6, 2021
Messages
262
every 15 mins to ensure there's no runaway.
A lot can happen in the space of a few minutes.

Let's say I DO have a 4s bms. Is it as simple as removing my 8s bank, adjusting the CC settings to a 12V 200Ah and fire it up?
Yes.
Essentially, my PS is taking way too long, and I've got all this sun here in Vegas that I could be using to bring this pack up quickly.
Patience is a virtue ;)

I wonder if there isn't anyone in Vegas that could lend you a smaller 4S BMS for a few days, or sell you one.
 

Tyler702

Desert dweller, quiet prepper
Joined
Aug 20, 2020
Messages
163
Well, I went ahead and did it. Other than a nice spark when I attached the batt lugs to the distribution block, it seems to be going well. Set the CC to 14.0V charge limit. Its 9:30am here now, and I'm charging at about 200-450W. (It's spotty/overcast right now) Much better than the 63W my ps was giving, so I'm happy. This really speeds things along.. I'll be watching it diligently for the next few hrs. Especially once it hits the top end. Then I'll disconnect it, bring it inside and use my ps to fine tune that last little bit.
 
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