2 new installed LiFePo4 batteries for travel trailer, please check my discharge and charge measurements

[apw63]

Hello,
I just purchased and installed 2 new SOK 12v 100Ah heated LiFePo4 batteries. Batteries where purchased from @HighTechLab. My current system was installed by Lance and is by Go Power, PWM 30 Solar controller charger, 2 190 watt panels, 1500 watt inverter & battery monitor GP-BMK-50. The batteries are mounted one on each side of the trailer. They are connected in parallel with 2/0 welding cable. The cable from the inverter to the batteries is also 2/0 welding cable.

What I'm seeing during discharge is unequal discharge rates. When I'm using the inverter to draw a load I'm seeing on battery #1 -35 amps 13.07v and on battery #2 -28 amps 13.04v draw. The batteries show different SOC after inverter usage, battery #1 95%, battery #2 97%. This makes sense to me because one battery has a greater draw. I'm using a drip coffee maker as a load. After discharge is over and the panels start to deliver amps. The charge rates are are approximately the same + ~6 amps ~13.42v on both batteries. When i use my volt meter on the batteries the meter shows equal volts on each battery. I don't have a clamp on amp meter, maybe I should get?

Is this normal discharge behavior? Is this something I need to worry about? I'm new to LiFePo4 batteries. If I left out any information that would be helpful please let me know.

Thank you for any help/advice/experience

Andy

 

[NVS]

It would be better to mount them side by side. Current follows the path of least resistance. So which ever battery is closer to the inverter will have more current pulled from it.

 

[apw63]

It would be better to mount them side by side. Current follows the path of least resistance. So which ever battery is closer to the inverter will have more current pulled from it.

Thank you for the reply. To mount the batteries side by side could be a challenge. To address my question is it something I need to worry about? Will this damage the batteries over time?

Andy

 

[rmaddy]

How are the 2/0AWG cables actually being run?

The two wires connecting the two batteries together must be the same length as each other.

The positive wire from the inverter must go to one battery and the negative wire from the inverter must go to the other battery. You must not have the two inverter wires going to the same battery, especially with your overly distant two batteries.

Download the "Wiring Unlimited" guide and read chapter 3 for lots of great info on wiring up batteries in parallel.

Wiring Unlimited

Wiring Unlimited is a great resource that covers many many common topics and questions relevant to DIYers. It is a free E-book from Victron Written by Margreet Leeftink. Check it out! Download

diysolarforum.com

 

[apw63]

How are the 2/0AWG cables actually being run?

The two wires connecting the two batteries together must be the same length as each other.

The positive wire from the inverter must go to one battery and the negative wire from the inverter must go to the other battery. You must not have the two inverter wires going to the same battery, especially with your overly distant two batteries.

Download the "Wiring Unlimited" guide and read chapter 3 for lots of great info on wiring up batteries in parallel.

Wiring Unlimited

Wiring Unlimited is a great resource that covers many many common topics and questions relevant to DIYers. It is a free E-book from Victron Written by Margreet Leeftink. Check it out! Download

diysolarforum.com

Thank you for the reply and link, I’ll read it.

It’s hard to say exactly how the cables are run. The batteries are in battery boxes 1 on each side of the trailer. The boxes are located on the front sides of the trailer. The batteries in each box are terminated at posts built in to the box interior. The inverter is under the bed, which is also at the front of the trailer. The shunt is located under battery 2s location. The cables coming from the inverter run in the direction of the shunt, then enter the structure of the trailer. I have attached a floor plan for the trailer for reference.

 

[rmaddy]

The floor plan isn't really relevant. What matters is how the wires are actually connected. Do you have a schematic of the electrical system?

You will have issues until the two parallel batteries are connected with equal length wires and the power is being drawn from opposite batteries.

 

[apw63]

I just got off the phone with Dexter at Current Connected (HighTechLab). He had read this thread and does not have any concerns. The life of the batteries will not be effected. The difference in current could be down to the BMS in each battery. He said there can be up to a 3% error in the BMS readings. There could be as much a 6% error between the 2 batteries. He did say that the difference in cable length will play factor.

My system is not configured optimally but its what I have. Thank you all for the help you offered it was greatly appreciated! Thank you Dexter great product support and communication! I would recommend your company to anyone.

Andy

 

[hegear]

Hi, I am having a similar problem.

I have 2 sok 206amp hooked up to redarc manager 30 and 50dctodc. Using 2/0gauge wire. Both cables are same length to conect the 2 batteries. Negative cable is longer leading to inverter due to shunt. Running 2000watt Cotek.

I get both uneven discharge and charging. It doesn’t matter if it’s a large load or small. Trying to run induction. When pushing more power battery a pulls up to 120 while battery b pulls 20-40amps. Pushed furtheR both bat shut down. I switched the location of the 2 and batteries had same results. Batteries work well on there own. Currently bat b is hooked to positive and bay a to negative. Didn’t charge battery’s before install, checked voltage before though and they were within .1 of a volt so I thought they would be fine. Also I noticed on bat B when under load and not connected in parallel 100amps on cell 1 is .333 lower voltage than the others (see attached).

Called sok and they recommended I dishcharge both individually and recharge 2 times so I’m trying that now.

Any ideas bad bms or batteries, or do you think Sok’s idea will fix?

Stressing out as I leave in week for a six week trip. So trying to get sorted before I leave.

Thanks for any tips or suggestions.

 

[TacomaJoe]

I agree with SOK, get each battery charged fully individually and then tie them together. Look at your cell voltages when they are charged up to see how balanced they are.