contra BiM
DRAFT
I’m not sure I see the value in the Li-Bim for charging LiFePO4 from alternators.
what I like
disconnection after charging
The Li-BiM is a kind of VSR, but disconnects at 13.4v when there is no charging occuring on the alternator side. This should avoid the “getting stuck closed” gotcha that affects VSRs with lead-specific voltage setpoints. I use a manual switch for breaking the circuit when required.
high voltage disconnect
The BiM disconnects when it detects >= 14.4v on the alternator side. Since it does not claim to charge fully1 I’d rather see HVD at ~14.0v.
what I dislike
periodic disconnect
The BiM connects for 15mins then disconnects for 20mins, repeat. This means we are charging ~43% at the max.
- how many setups could handle charging at X amps for 43% of the time but not sustained?
- is it better to thermal cycle the alternator rather than running it warmer?
- how good is it for the alternator to have a X amp cut-out every 35mins? I don’t think this is a big deal with a lead starter batt in the circuit, but still.
one hour limit
once the batteries have charged for one hour, the Li-BIM will isolate the batteries to prevent overcharging, and will only reconnect the batteries for charging if one of the batteries drops to approximately 80% charge, and the other is being charged.
What are the chances that a bank large enough to warrant a BiM would get a meaninful charged after an hour of driving (and ~26 minutes of charging)?
clockwork complexity
The internals are interesting but highly complex. Looks like a lot of stuff to fail.
cost
The 225A Li-Bim is ~$160, on the high side for a VSR.
conclusion
I think
- if your alternator can handle the demand then use a relay for 1/3rd the price.
- if your alternator can’t handle the demand then use a DC-DC charger or some other method to control current.