question

sweyn avatar image
sweyn asked

Multiplus 12/800/35 to trickle charge Lead Acid starter battery.

Is it ok to use the 1A trickle charge output of the Multiplus to charge a lead acid starter battery when the main batteries house batteries are Lifepo4?

Multiplus-IIchargerstarter battery
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Are you using mains power (multiplus) to charge your batteries, or a solar array/mppt??
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sweyn avatar image sweyn klim8skeptic ·

The House Lithium batteries will be charged from either mains through the Multiplus, MPPT or DC-DC from the alternator/Starter battery.

The starter battery will be charged by the alternator, but I’d like to have the ability to trickle charge it from the Multiplus if possible.

Not sure if the 1A trickle charge will be a problem if the Multiplus is configured for lithiums through.

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It is probably best to read this thread.

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sweyn avatar image sweyn klim8skeptic ·
That thread doesn’t seem relevant?

I’m interested to know if it is ok to have both lithiums and lead acid charged from the same Multiplus due to their different charging voltages etc, not whether it will technically do it.

I know it will do it.

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I am much more risk averse..


My truck starter battery reads 12.6v, 36 hours after being fully charged, no load.

My Lifepo4 battery still reads 13.25v @ 87% Soc.

That is a whole lot of voltage differential that could allow energy to flow from a partially discharged Li battery, to a fully charged LA battery.

NOTE, there is some discussion as to whether the multi "switch" disables the trickle charge function.

Proceed with caution, and give feedback upon conclusion.

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sweyn avatar image sweyn klim8skeptic ·
When my engine is running, it currently gives well over 14V to the Lead Acid battery, regardless of state of charge.


I can’t see the difference?
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You want to trickle charge your start battery when the engine is running?
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luphi avatar image luphi klim8skeptic ·
What would happen, if one does?


Cheers,

luphi


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sweyn avatar image sweyn klim8skeptic ·
No, when the engine is running, the alternator will charge the starter battery.

I’m just pointing out that the starter battery is regularly charged by a high voltage even when full, and that doesn’t seem to be a problem.

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1 Answer
pwfarnell avatar image
pwfarnell answered ·

The trickle charger is taken off the main DC feed to the Multiplus. The Multiplus contains a current limiting circuit and a diode so it will always lift your starter battery to within 0.4 to 0.6V lower than your house battery because of the voltage drop. When full the battery will limit the current lower than 1A. If your house is at 13.25V, the trickle charge will keep the starter at circa 12.65 to 12.85V so OK for the starter battery long term, but there will be a small current draw from the house.

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