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Chargery 12v setup

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Dyotat100

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Oct 13, 2020
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What is the best way to run a 2-8s 300 amp chargery for a 12v setup? I have 8 280ah sells on the way and a chargery with 300 DCC. This is for my 5th wheel. I was told to go 24v but I have a lot of 12v to run. Plus I would have to use a 12v battery to start my 4000 w onan.

Thanks
 
What are you using for solar, inverter, converter?
 
I'm not familiar with the Aims ..... I'm planning to used independent inverter / converter in my setup and switch them on and off with low current relays instead of switching the DC side of things.
 
The Chargery BMS requires 15V/3A to operate and a 4S (12V) Battery doesn't cut it. That will require an external power supply or a step-up converter (I'm not comfortable with those personally). If you go with 24V you can run the BMS directly from the battery pack, then use a quality 24V to 12V Regulated Stepdown transformer to provide 12V for the 12V circuits (this ensures voltages stay at 12V and does not wander between 10-14V or more.

With regards to using the LFP bank as a starting power source for a Generator, I don't know how practical or wise that would be. In case of SHTF I believe it would be far more prudent to keep the Genset independent and have it's own battery for starting. Although, you could run a battery maintainer from the LFP bank to maintain the Genset battery.
 
I have tested my BMS8T which is in a 2P4S configuration with and without an external power supply .... it works fine both ways.

According to Jason, the only thing that may suffer if the battery gets to a very low SOC is that the alarm may be weak. I have tested mine down to inverter cut-off several times now and everything works fine.

Others have also tested a 4S configuration with successful results.
 
I agree with Bob. I run a BMS8T that is 3P4S. It does just fine running on the battery just fine to the cut off that
I choose. In fact, Jason on this site shared that down to 11 volts it works just fine. And to be honest, if it disconnected at that voltage I would be thankful. The only advantage that I can see would be an easier ability to turn the system off easier. But would add to another failure point.
 
I believe the 15V/3A is more related to having power available to drive two 12V Electro-Mech relays, with Energy Savers & SSR / DCC they certainly do not pull that much.
 
Steve_S said:
I believe the 15V/3A is more related to having power available to drive two 12V Electro-Mech relays, with Energy Savers & SSR / DCC they certainly do not pull that much.
Click to expand...
I'm not going to try to look it up right now ..... but Jason posted about this some time ago. He specifically said the reason was the alarm output.
 
Steve_S said:
I believe the 15V/3A is more related to having power available to drive two 12V Electro-Mech relays, with Energy Savers & SSR / DCC they certainly do not pull that much.
Click to expand...
I use the kilavac 500 amp contactors with the economizers. The problem I had was the inrush is 3.8 amps each it did not matter whether it was on battery or external.Two contractors dropped the output voltage (with two contactors) to 2 volts that in turn rebooted the BMS. It could deal with one. I solved the issue by using a micro mini relay on one contactor.
 
Bob B said:
I'm not going to try to look it up right now ..... but Jason posted about this some time ago. He specifically said the reason was the alarm output.
Click to expand...
"For 4S LiFe battery, when the total voltage is over 10V (2.5V / CELL), the BMS can be powered and work normally, but the Beeper sound will be less. LCD back light will be dark than at 12V.
So the 3.0V per cell UVP setting is suggested. so total battery voltage will be 12V at least."
 
grizzzman said:
"For 4S LiFe battery, when the total voltage is over 10V (2.5V / CELL), the BMS can be powered and work normally, but the Beeper sound will be less. LCD back light will be dark than at 12V.
So the 3.0V per cell UVP setting is suggested. so total battery voltage will be 12V at least."
Click to expand...
Yep, that's it .... guess my memory isn't completely shot. LOL But I did forget the part about the less bright LCD.
 
Thanks for all the input. Now I can go 4s if I decide to.

Next question is whats the best way to configure the cells for 12v? Could I set it up so I have 2 4s packs controlled by the 8s chargery? So it could balance each cell.
 
Ok thanks. It just shipped yesterday. Batteries haven't yet so im 30+ days out from building.
 
if use DCC, the drive voltage is 12V too, and the fan is powered by 12V too, so for 4S battery, if battery voltage is under 12V such as 11V, the BMS can work normally, but the fan speed will be slow too, but the speed should be enough. anything need to be tested in actual application.
 
I have a similar setup to what you're looking to do. I'm curious how yours ended up. Did you end up doing two separate 4s packs or did you put all 8 cells in one pack with a 2p4s configuration and a single bms?
 
I just finished top balancing my cells yesterday. I have to make buss bars. I'm going 2p4s. Might have them done today. Using copper bar.
 
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