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zdubs avatar image
zdubs asked

Charging battery using load output

I just realized I have an aux battery factory installed in the vehicle that gets charged off the alternator on top of the primary starter battery. I also have standalone solar setup with its own battery that gets charged using the MPPT 75/15 and I would like to build in a redundant charging system and was hoping to hook the aux battery in to my standalone using the load output option on the charge controller. That way the alternator can charge the aux battery and my Deep Cycle battery can draw juice off the aux battery through the charge controller. Should I reverse that I have the aux battery hooked to the battery output and the deep cycle hooked to the load output?

Am I crazy and going to fry something?

MPPT Controllersbattery charging
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2 Answers
wkirby avatar image
wkirby answered ·

I wouldn't connect any batteries to the LOAD output of the charge controller. It is not designed for charging and does not have a charge profile to follow (Bulk, Absorb, Float). If you connect any battery to the load output it will most likely be overcharged and be killed quickly.

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Alexander Irion avatar image Alexander Irion commented ·
But when a DC-DC converter is used for charging a second battery, that converter could be connected to the MPPT load output, as long as it does not have a reverse current flow, right?
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ludo avatar image ludo commented ·
No, the second battery will not overcharge, as it is only connected to the first battery, not directly to any solar related voltage. I use this for charging my Starterbatterie, but ofc with a fuse and an 8a thermal current limiter.
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over-and-under-victron avatar image
over-and-under-victron answered ·

Looking to do the same thing....sort of. Did you end up doing this?


I want to power my van's stereo via the 100/20 load out. Since my house LFP bank sits around 13.2 there is zero chance it's going to overcharge my FLA start battery.


My concern is if I forget the load output is live and start the van. Will the 14.4V from the alternator damage the 100/20?

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warnings007 avatar image warnings007 commented ·
Same question you found an answer somewhere ?

You try ? It cause you any issue ?

MPPT have a direct connection between battery and load output it's right whatever the current flow ?
I think it's fine until we stay at the current limit of the MPPT no ?

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