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craigp avatar image
craigp asked

Charging Lithium batteries from alternator

some examples show lithium batteries being charged directly from alternator. others show lithium battery being charged via DC-DC converter. Which is the correct/ preferred method? I was under the impression Lithium batteries required specific charging profiles?

battery charging
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bathnm avatar image bathnm commented ·

Depends if the alternator is externally regulated and can have its output reduced as it get hot.

This is a good video to watch.

https://www.youtube.com/watch?v=jgoIocPgOug&vl=en-GB

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3 Answers
spirou avatar image
spirou answered ·

DC-DC unless you want to destroy both alternator and battery. Victron has a video somewhere on their blog you might want to look at.

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craigp avatar image craigp commented ·

Victron web site shows many example circuits of both ways. Seems strange to me. If DC-DC is the recommended method then why show circuit examples of direct connection to alternator???

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craigp avatar image
craigp answered ·

Is there no requirement for a DC-DC here?

How can an arrangement like this include a method to connect LIthium Battery to Starter battery for emergency start?

How can starter battery be charged by solar in a system with Smart BMS?


1591659348735.png (317.5 KiB)
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bathnm avatar image bathnm commented ·

If you are wanting to ensure the starter battery is kept topped up by the Solar, then yes a DC-DC with source on the lithium and destination on the starter would do that.

As a point of design, I would configure a relay into the ignition switch of the DC-DC. This would mean that when the engine is running the DC-DC is disabled. If the relay is NC and feeding a positive signal into the ignition switch of the DC-DC, when the engine ignition is on, the relay will open and the DC-DC will shut down.

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craigp avatar image
craigp answered ·

OK, I get that we need to limit current/ protect alternator. My confusion is in the actual charging of the battery. I have read that Lithium batteries need carefully configured charging profiles (absorbtion, float etc). It seems that with either the DC-DC solution or BMS 12/200 or Smart BMS 12/100 the lithium battery is just connected straight to whatever voltage the alternator is churning out. What am I missing here?

Also, what is the point of the Smart Solar controller charging via set profiles when the alternator is just punching our say 14.8 constantly at the same time?


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