Electronics > Power/Renewable Energy/EV's

DC DC Charger for alternator and lithium charging

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David Hess:

--- Quote from: WaldPinkler on July 14, 2021, 11:45:18 pm ---Normally problems with lithium and alternators are the low resistance causing the alternator regulator overheat and the BMS disconnecting suddenly when full.
--- End quote ---

Overheating of the alternator happens with lead acid batteries also if the lead acid battery is large enough or dead enough.  More than once I have diagnosed a bad alternator after someone jumped their car from a dead battery because the alternator burned out recharging the dead battery.  In principle the alternator should protect itself but but car stuff is cheap.

f4eru:

--- Quote ---Many alternators may cook themselves going straight to lithium due to their low resistance and alternator outputting at maximum
--- End quote ---

Very very simple solution :
replace or modify the regulation circuit of the alternator in order to achieve CC-CV regulation, and take input from the BMS (original is only CV)

No need for Pb batteries at all. Keep it simple and straightforward.

richard.cs:
Yes, standard alternators don't regulate current at all, they don't measure it. All that saves them from cooking most of the time is that the output impedance is high, the windings have a lot of leakage inductance and at high RPM they act as a pretty good current source. With constant high loads they can still die, but usually the battery gets full before the alternator catches fire.  :) Old cars with DC generators on the other hand do have regulators that measure and control for current because Zout is much lower and they're more like voltage sources. Generally more efficient too, but with the downside of lower speed range and lesser cooling.

f4eru:
A big beefy specialized TVS will protect against load dump.

WaldPinkler:
Great advice here. There's lot of confusing information out there regarding lithium change overs. Mostly from companies selling over priced DC-DC chargers. It really makes more sense with a CC-CV regulator to the lithium and a smaller DC-DC charger for the lead acid.

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