Using a mppt as a battery to battery charger.

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bstechnic asked Oct 17, '21

Using a mppt as a battery to battery charger.

Hello,

I was thinking if I could use a mppt (150v 35A ) connected to a 116V battery( input) to charge the 48V Home storage battery (output). At daylight I could connect pv panels and in the dark I could connect my 116V battery ( Zero electric motorcycle). What do you guys think?

Can the mppt handle this?

I guess that there us a constant draw of 35A. That for 2 hours.

I wouldn't do this every night, but in cases off longer bad weather and in winter. My home storage battery is 30Kwh and my motorcycle 13 Kwh. I would only drain 40 % so I can drive to work and charge the bike ( for free) again.

mppt charging

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Answer 1 · 2021-10-17T18:14:34Z

Mike Dorsett answered · Oct 17, 2021 at 06:14 PM

DON'T!! The MPPT's are designed for current limited sources, and a battery does not fit that category. Or, if you want to try it, do fit a breaker on the input that is rated well under (50%) of the maximum input current. The problem is that the MPPT search function will look for a power peak by taking more and more current from the source....

You need a converter configured for hydro or for battery use.....

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bstechnic commented · Oct 17, 2021 at 07:12 PM

Hello, i know its not designd for this, but maybe it can work. i cant find a battery charger that works from 116v dc. If i understand it correctly it will search for a power peak, but 35 A is maximum. In the manual you can add a overdimensioned solar aray but it will cut off at 35A. Why wiill the mppt dont do that with a battery source?

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Answer 2 · 2021-10-18T04:33:44Z

Mike Dorsett answered · Oct 18, 2021 at 04:33 AM

possibly it will, but it depends if you are willing to risk the charger. Even with an over dimensioned array, the source is still current limited. The thing to do would be to put in a trip (circuit breaker at 20A,) and then use the mppt in constant current mode - which requires programming one of the internal registers. If you can do this, it should work ok, but limit the current to below rating till you see how it works. The register is 0x2015 - see the VEdirect mppt protocol, and the current value needs to be written at least once a minute to keep it in this mode.

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