temporary solution for lifepo charging

[racmaster]

hello, im using pv panels + mppt solar regulator to charge my lifepo battery. until now i had a gt1200 40A dc-dc charger used as a backup charger+balancer for the case the sun doesnt work. as there is december actually - that happens. sun doesnt work anymore .

getting to the problem, my gt1200 backup charger went smoking and doesnt work anymore. currently im solving the warranty issue with it.

until the warranty process will be closed, i need to wait. i dont want to buy new charger until then... instead of that im thinking about a solution, that can temporary charge my battery if the sun will be not enough.

so what i have available:
- lifepo 100ah 4s
- pwm solar regulator 20A
- mppt solar regulator 30A
- 2x pc psu`s used as a dc power source for gt1200 (same type, connected to parallel providing up to 40A - tested several times with gt1200) + petrol generator (AC230/2000w)
- several other pc psu`s of different specs
- alternator in my car about 100A
- simple balancer/cell voltage monitor connected to battery

do you see any possibility to make some temporary charger out of this stuff, that will put some Ah into lifepo without damaging anything, even if i have to sit and watch every cell voltage during the process...?

we are talking about solution, that will be used once, or maybe up to 3x until the warranty process will give me back my gt1200 charger or not and i will buy another as best practice working until now. so the temporary solution doesnt need to be really pretty.... just working.

[Sunking]

Nothing special needs to be done. LFP is compatible with Pb.

[racmaster]

does it mean, that its enough to start a car, disconnect pb car battery and connect lifepo instead, letting alternator do the job? just keeping eye on cell voltage for the case of unbalance and 1 cell runaway? as soon as required cell voltage will be reached, turn the car off and replace batteries?

[Sunking]

does it mean, that its enough to start a car, disconnect pb car battery and connect lifepo instead, letting alternator do the job?

You tell me. For about $800 to $1000 you can buy a LFP Starter battery replacement. Does not last any longer than a Pb starter battery, just cost 5 to 7 times more. Drop in replacement.

If it were me, and it is, last thing I want is any BMS as that is the number 1 root cause of battery failures/fires. Run the voltage at 13.8 volts and forget about it, the BMS will never be turned on or used.

[racmaster]

i dont have any bms installed on this LFP battery. im just trying to find temporary solution to charge it using the equipment (listed up there) until i will get get my charger from warranty process or buy new one....

[Ampster]

Perhaps SK didnt read your entire first post where you stated that you already had the LFP batteries. To answer your question you may want to monitor the voltage of your LFP batteries. As they approach 13.8 (3.45 per cell) you can check the voltage more frequently and disconnect the charging source if it goes beyond 13.8. In effect you become the Battery Monitoring System.

[racmaster]

yes i also supposed like he missed my target... regarding your answer - do you count with charging using car alternator, is it?

there could be one problem - disconnecting the lfp from alternator. what i found it could damage the alternator, as the LFP will take as much current as alternator may produce. so here we are talking about 100amps. disconnecting such a current could by some findings destroy alternator. is it true? any best practice?

[Ampster]

I am not knowledgeable about alternators but I have always been told to not disconnect an alternator under load. There must be a way to turn off the alternator before disconnecting?
I do know that 100Ahr LFP can easily take 100 Amps or more, so I would be careful.

[Mike90250]

Just insure the alternator is also driving other loads. Disconnecting the ONLY load is bad for an alternator Or get into the control line for the alternator and shut that down - if it's a standalone alternator.

[racmaster]

what do you mean by - get into the control line? thats an alternator in my car. what about simply turning the engine off before disconnecting battery(load)?

[Mike90250]

I didn't recall if you had a 2nd alternator installed, Alternators have a control wire that regulates the charge. Usually switching the ignition off is the way the control is turned off.

[bcroe]

Generally a car alt can be controlled by manipulating the voltage feedback input. But that is usually tied
directly to the battery voltage. The other input helps get it started (and drives the light). But once running
that input is not needed, and the alt will continue to output till the motor stops. Often an alt can start itself
with residual magnetism without that lead, at higher rpm. Bruce Roe

[Ampster]

....... what about simply turning the engine off before disconnecting battery(load)?

Yes, that is a simple solution. Perhaps not as elegant as figuring out the control wire specifications, but it works.

[racmaster]

thanx guys, thats sounds like a solution