Making a custom LiFePO4 pack is rather trivial, but I am having a lot of trouble finding suitable inverter in India that would be compatible with lithium battery packs.
I currently have a microtek inverter (non pure sine, ~800VA I guess) + exide tall tubular 150AH battery that has aged quite a lot and needs replacement either way, I thought it would be a good opportunity to get pure sine and lifepo4 based setup instead because of several benefits.
I have some know how of custom battery packs and I am quite confident that I could make a 4s (or more) lifepo4 pack with prismatic cells and BMS but I really can’t find concrete information on inverters that would work with such battery, mostly there are two problems with using regular inverters:
typical inverters float charge when around full charge and that works for lead acid but is not at all ideal for lithium batteries.
and the inverter needs to have a configurable (or sane) low voltage cut off, i.e. before the BMS cuts off and messing up the whole system. A typical inverter assumes a dumb lead acid battery that would still have some charge left even if a few volts, enough to keep the logic part keep working but a BMS would have a hard cut off.
Any information, guidance etc would be really appreciated!
wouldn’t float charging at any voltage be an issue?
I don’t have any data to back up but my intuition says that:
BMS tries to dictate the safety behavior while charging
if an external charger is connected, at full charge, the BMS would just cut off the connection (at least momentarily)
would any regular inverter be able to cope with that?
Like at a very small scale I have noticed that a type c to 4s charger module would go haywire if connected after the BMS but worked fine if connected before the BMS in certain BMS boards, thus guessing something similar
The BMS only cuts off power in four or five situations, over voltage, under voltage, over current, over temperature and under temperature (at least for lifepo4 battery packs, these react slowly compared to lipo).
So long as the voltage outputted by the inverter is within 10V and 14.6V, the BMS doesn’t cut power.
And if power is cut, the inverter really doesn’t notice until it’s time to switch to battery power but the BMS would have auto recovered by then or almost immediately.
The details of what voltage is ideal for float/bulk/etc mainly has to do with prolonging battery life (one decade vs two decades).
First of all, hats off to you for doing so much research and providing the information thereof in that thread🙏🏼
I am very confused about which one to get, if what you say is true then I suddenly have a lot of options than I did before, even the ones you listed, almost all of them seem to have float voltage within the threshold for my purposes.
If I were to ask for your educated opinion, what would you recommended here?
Would it be okay to go with UTL or Genus inverter? they cost ~9-12k and are a bit more expensive than the regular branded ones but they seem to have a bit more flexibility ?
Both Genus and UTL are good choices but I’d confirm the voltage ranges again by requesting pdf manuals of the model from each company’s WhatsApp support.