Do 12v LFP in parallel "equalize"

[Flunkyboi]

Making progress on my 48v system. My plan, so far, has been to precharge all four of my new Dufume 12.8v 100ah individually. I'm using two panels (2P) and a Victron 100/50.

It has taken since Thursday, but I think they all topped off. I wired them all in parellel this evening. Zero sparks making connections (but I did use a bleed resistor to check before I bolted the cables)

I let it sit like that that an hour and checked voltage. 13.60v across the bank. I put the amp clamp on cables between each battery. There were slight differences in amp draw, but each less than an amp. I assume they are equalizing.

The next phase is to connect the 4P bank to the Victron/panels and let the Victron charge it all week.

Next weekend, the 48v battery balancer should be here. I'll then wire the bank in series and use the new EG4 3kw hybrid. My full array (6S-270vdc-2430w) will feed the EG4.

Does this plan sound OK?

 

[cs1234]

Do 12v LFP in parallel "equalize"

Not as much as one would like, due to the flat voltage curve. They will equalize in voltage, but the SOC could still be pretty different amongst them up near the top of the voltage range.

Next weekend, the 48v battery balancer should be here. I'll then wire the bank in series and use the new EG4 3kw hybrid. My full array (6S-270vdc-2430w) will feed the EG4.

I have balancers on my 12v to 48v series packs.. they are a must in my experience. However, they still aren't as good as a native 48v battery would be. If you aren't stressing them to the max, they will work ok though.

 

[Backyard]

Your best bet when paralleling batteries for the purpose of balancing them is to do several cycles on them. Just keeping them connected will do very little balancing unless there is a large difference between them.

 

[Flunkyboi]

Not as much as one would like, due to the flat voltage curve. They will equalize in voltage, but the SOC could still be pretty different amongst them up near the top of the voltage range.

I have balancers on my 12v to 48v series packs.. they are a must in my experience. However, they still aren't as good as a native 48v battery would be. If you aren't stressing them to the max, they will work ok though.

I don't know how to determine the state of charge. I'm new to battery power systems. Especially these weird LFP4 batteries. The paperwork that came with these batteries stated they could only ship them with a partial charge. I assumed charging them up my Victron and some panels was all I needed before seriesing them all to 48v.

 

[Flunkyboi]

Your best bet when paralleling batteries for the purpose of balancing them is to do several cycles on them. Just keeping them connected will do very little balancing unless there is a large difference between them.

I don't think there could have been a lot of difference in charge between them. I first parelleled two, but before making the final connection, I bridged a high wattage resistor and watched the clamp on ammeter. Saw no jump in amps above one amp. Three were less than a half amp. No sparking at all when I removed the resistor and bolted the leads down. Rinsed and repeated until all four were connected in parrellel.

You mentioned cycling them. Can I drain all four while they are wired together?

 

[cs1234]

I don't think there could have been a lot of difference in charge between them. I first parelleled two, but before making the final connection, I bridged a high wattage resistor and watched the clamp on ammeter. Saw no jump in amps above one amp. Three were less than a half amp. No sparking at all when I removed the resistor and bolted the leads down. Rinsed and repeated until all four were connected in parrellel.

You mentioned cycling them. Can I drain all four while they are wired together?

If they are close in voltage, they won't spark when you connect them in parallel.

 

[cs1234]

I don't know how to determine the state of charge. I'm new to battery power systems. Especially these weird LFP4 batteries. The paperwork that came with these batteries stated they could only ship them with a partial charge. I assumed charging them up my Victron and some panels was all I needed before seriesing them all to 48v.

If they don't have bluetooth, determining state of charge requires an external coulomb counter shunt. Your best bet was suggested somewhere a few posts up. Just connect them in parallel and charge and discharge that way for a while. If you are going to run them in series, put the balancer on there when you get it. Run it, but don't expect to get full amp hours out of the configuration from a 12v to 48v bank. They work, but not as well as a native 48v battery controlled by a BMS that is managing all the cells directly as a 48v battery.

 

[740GLE]

Even one you build the 48v pack, def pick up some 12v battery balancers, it’s pretty much a requirement.

If you dont, you’ll need to charge each one individually time from time to make sure each 12 battery is are staying balanced.

 

[Flunkyboi]

If they don't have bluetooth, determining state of charge requires an external coulomb counter shunt. Your best bet was suggested somewhere a few posts up. Just connect them in parallel and charge and discharge that way for a while. If you are going to run them in series, put the balancer on there when you get it. Run it, but don't expect to get full amp hours out of the configuration from a 12v to 48v bank. They work, but not as well as a native 48v battery controlled by a BMS that is managing all the cells directly as a 48v battery.

So I can "run them down" and then recharge in their current parellel configuration?

Now I have to figure out some sort of 12vdc load to do this. I don't have a 12 inverter. We'll, I do, but it's a dinky 150 w. That drain down will take forever.

 

[740GLE]

So I can "run them down" and then recharge in their current parellel configuration?

Now I have to figure out some sort of 12vdc load to do this. I don't have a 12 inverter. We'll, I do, but it's a dinky 150 w. That drain down will take forever.

Snap a picture of how you have them connected in parellel.

If you “cross connect” the charge it should be able to bring them all up to fully charged but if do it at a low current charging rate, 5a at most.

 

[Flunkyboi]

Snap a picture of how you have them connected in parellel.

If you “cross connect” the charge it should be able to bring them all up to fully charged but if do it at a low current charging rate, 5a at most.

I just have them charging at 30a. I can go out and throttle it back to 5a.

 

[Flunkyboi]

I drew this "wiring diagram" for parellel before cabling up and to keep things straight.

 

[Backyard]

I drew this "wiring diagram" for parellel before cabling up and to keep things straight.

That should work. Keep the charge rate slow so they have time to balance

 

[740GLE]

I drew this "wiring diagram" for parellel before cabling up and to keep things straight.

Nice, yeah that’s cross charging. Using the positive terminal on one end and the negative on the other end.

It’d also be worth while to take a multimeter reading of each terminal and verify they are all within 0.01v.

 

[Ampster]

I don't know how to determine the state of charge.

Voltage is only a good indicator of SOC at the top or bottom of the charge curve. As another poster said, if you charged them full that would be good indicator when charging but once the settle they are in the flat part of the curve. That is why someone suggested to cycle them in parallel.

 

[Flunkyboi]

Nice, yeah that’s cross charging. Using the positive terminal on one end and the negative on the other end.

It’d also be worth while to take a multimeter reading of each terminal and verify they are all within 0.01v.

Here is an actual photo of my temp cabling. I posted pic of diagram first because the batteries are not physically located as in the diagram, but the wiring is to my drawing. Yellow dots denote positive cables.

 

[Flunkyboi]

Voltage is only a good indicator of SOC at the top or bottom of the charge curve. As another poster said, if you charged them full that would be good indicator when charging but once the settle they are in the flat part of the curve. That is why someone suggested to cycle them in parallel.

I let them all sit, wired in parellel all night. Voltage for the whole bank was the same as last night...13.6v. I connected the Victron and PV right after. My max current setting on the Victron was throttled to 30a. The panels were not yet in direct sun, so the charge current was around 20ish amps. Charge voltage was 14.2. Victron showed "absorbtion" mode.

I went out to lower the output current to 5a, but the Victron was already putting out only a few amps. Still in absorbtion mode. I set max to 5a as suggested.

I'll leave it like that, then check each battery volts (with the cables off) later.

 

[740GLE]

I let them all sit, wired in parellel all night. Voltage for the whole bank was the same as last night...13.6v. I connected the Victron and PV right after. My max current setting on the Victron was throttled to 30a. The panels were not yet in direct sun, so the charge current was around 20ish amps. Charge voltage was 14.2. Victron showed "absorbtion" mode.

I went out to lower the output current to 5a, but the Victron was already putting out only a few amps. Still in absorbtion mode. I set max to 5a as suggested.

I'll leave it like that, then check each battery volts (with the cables off) later.

You’re on the right path. 14.2v is darn near 100%.

It’d be best to just double check with a multimeter each battery terminal is showing the same 14.2v

 

[Flunkyboi]

You’re on the right path. 14.2v is darn near 100%.

It’d be best to just double check with a multimeter each battery terminal is showing the same 14.2v

I will.

The wait on the equalizer is holding up my first 48v trial/use with the new EG4 hybrid 3kw. (That and I've not completed all my earth grounding on the array.) That should be done by Sat. My array framing is not metal. It is the roof on a wood structure. I've got to ground bond the frames on all six. That series circuit will be sending 270vdc to the EG4. I brushed 120vac once...was not a fan of that sensation. 270 would likely put your pecker in the wrecker, forever.

 

[Ampster]

270 would likely put your pecker in the wrecker, forever.

It is the Amps that kill. The problem with voltage on a roof or ladder is that the voltage may not kill you but falling off the roof or the ladder could easily kill you.

 

[Backyard]

It's actually kinda both. You need volts to deliver sufficient amps to do any damage

You can touch both terminals on a car battery and not get harmed yet it has more then enough amps to kill hundreds of people many time over. It's that it doesn't have sufficient voltage to push the required amps through a high resistance person

Ohms law and all....

 

[740GLE]

It's actually kinda both. You need volts to deliver sufficient amps to do any damage

You can touch both terminals on a car battery and not get harmed yet it has more then enough amps to kill hundreds of people many time over. It's that it doesn't have sufficient voltage to push the required amps through a high resistance person

Ohms law and all....

There’s always that one story of someone bare chested leading over a boat battery terminal in the hot sweaty sun reaching deep into the bilge and getting the 12v pace maker treatment.