Charging a LIFEPO4 with a Lead Acid BMS?

nicoloks · Jul 20, 2022

Hi All,

I have a BMPro J35B BMS in my caravan which does not have a Lithium charge profile. To replace it with the model that does have a lithium charge profile would cost me over $1000AUD. I have checked the manual for the J35B and there is no mention of higher voltage desulphation or equalisation stages in its charge profile. No voltage above 14.4v is mentioned anywhere with a max charge current of 15A.

I am using a SRNE 40A MPPT (which does have a lithium profile) as my solar charge controller, however was looking to continue using my J35B for charging my LIFEPO4 battery when hooked up to mains power.

So many mixed messages coming from retailers around the impact of using a lead acid based charger on a LIFEPO4 battery. Given the 14.4v charge limit of the J35B is there anything in its charge profile that could potentially be harming my LIFEPO4 battery?

time2roll · Jul 20, 2022

Some would consider 14.4 on the high side of normal but should not present any issues. Also check the float voltage is closer to 13.2-13.4 if this function might be utilized for extended periods.

Verify the MPPT voltages. Some "lithium" profiles are not especially great.

Otherwise if the voltages are correct all will be fine.

nicoloks · Jul 20, 2022

Thanks for that, so sounds like retailers are just laying it down thick to try and get a sale. I did ask about the voltages, however never got a direct/suitable reply from any of them. Float voltage is 13.6v on my BMS. Think I'll stick with what I've got for now, only about $200 for a basic 22A AC-DC charger with Lithium profile.

midahar · Sep 19, 2022

nicoloks said:
Hi All,

I have a BMPro J35B BMS in my caravan which does not have a Lithium charge profile. To replace it with the model that does have a lithium charge profile would cost me over $1000AUD. I have checked the manual for the J35B and there is no mention of higher voltage desulphation or equalisation stages in its charge profile. No voltage above 14.4v is mentioned anywhere with a max charge current of 15A.

I am using a SRNE 40A MPPT (which does have a lithium profile) as my solar charge controller, however was looking to continue using my J35B for charging my LIFEPO4 battery when hooked up to mains power.

So many mixed messages coming from retailers around the impact of using a lead acid based charger on a LIFEPO4 battery. Given the 14.4v charge limit of the J35B is there anything in its charge profile that could potentially be harming my LIFEPO4 battery?

If if you're only charging at 14.4 I don't think you're going to hurt anything they expect 3.6 Volts for sale and that's what I'm given for sales that's what 14 4 volts is so it can't be overcharging it otherwise and a lead acid profile sometimes the charge in voltage goes up over 15 volts and then it holds it there for a long time which is not going to be good for which would be overcharging your lithium you have to have that hold on the lead acid batteries to Ram the the last little bit of charge in there but 14-4-volts is a safe number

mikefitz · Sep 20, 2022

Do you use the engine charging facility, aux input?
if this is the case some sort of current limit is needed in the charge path such as a battery to battery charger.
Charge at 14.4 and float at 13.6 are somewhat high in my view. but usable.
Depending on how the cells are balanced, the lithium battery protection may activate at 14.4 charge volts.

Mike

midahar · Sep 22, 2022

mikefitz said:
Do you use the engine charging facility, aux input?
if this is the case some sort of current limit is needed in the charge path such as a battery to battery charger.
Charge at 14.4 and float at 13.6 are somewhat high in my view. but usable.
Depending on how the cells are balanced, the lithium battery protection may activate at 14.4 charge volts.

Mike

I've considered putting a resistor in line to the lifep 04 which would lower the charging voltage

ocular · Nov 22, 2022

If you can be sure how the flooded lead profile behaves as you describe them you are in a safe zone. Redarc are probably the duck's nuts re DC DC chargers and do actually publish details of their BCDC chargers. In LiFePo4 mode they go to 14.5V and float at 13.6 and return to boost at 13.2/13.4
Never had one because are so expensive, but they are Aussie designed and made and the support guys on their forum know their stuff.
Your lead profile may or may not have a return to boost of 12.3V but with a LiFePO4 you are unlikely to get down there, and return to boost will happen when you stop and start vehicle. I would say go for it. And let us know. What LiFePo4 pack are you using?

ocular · Nov 22, 2022

here is the Redarc Profile for modes A,B,C and LiFePO4 for their BCDC chargers, wish others would follow and produce understandable profiles.

Charging a LIFEPO4 with a Lead Acid BMS?

nicoloks

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time2roll

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