MPPT solar charge controller

Can I use a mppt charge controller connected on battery siode to a 12v battery and pv side connected to my 24v lifepo4 to charge the 12v battery from solar setup.

Does this have any negative conesequences?

An MPPT controller measures solar panel output vs voltage by putting a variable load on the panel and measuring the power at different loads, then it picks the best one. With solar panels as the load increases the voltage will drop towards zero after it hits its maximum power point...A battery will put out enough current to blow up the loading device in the MPPT controller when it runs it's load measuring cycle. Not adviseable to connect a battery instead of solar panels.

There was a post some time ago on the forum where someone was proposing to use a Victron SCC to do this. In theory the current limiting ability of the Victron should allow it to work. I can't remember if (s)he came back with the results. Personally I wouldn't do it. This isn't how SCCs are intended to be used and there are plenty that don't limit current to protect themselves and will let the magic smoke out.

A DC-DC charger is the right way to do it.

I personally would rewire a panel (or some panels) through a separate small controller to charge the 12v battery. There are too many variables to give real advice to you. Such as, are your solar panels 12v or 24v? If they are 24v then what I said I would do, would not work, as most controllers now read the panel voltage automatically and would set themselves to 24v with no 12v output. If ,however, you have 12v panels wired in series to give you the 24v system you have, two panels could be wired (completely isolated from all the others) in a parallel configuration to give you 12 volts for a small, cheap 12 volt controller to charge the 12 volt battery. I am completely assuming you have DIY experience with you solar system. If not leave it alone and get qualified assistance.

gnubie said:

There was a post some time ago on the forum where someone was proposing to use a Victron SCC to do this. In theory the current limiting ability of the Victron should allow it to work. I can't remember if (s)he came back with the results. Personally I wouldn't do it. This isn't how SCCs are intended to be used and there are plenty that don't limit current to protect themselves and will let the magic smoke out.

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That might have been me. I wanted to charge my LiFePO4 from something like a laptop power supply. The current limiting capability of either the MPPT or the power supply itself is critical here. I did get it to work by tailoring the Victron current setting to the power supply in question. It's actually working rather well with a Lenovo laptop charger and limiting the Victron to 9A. YMMV of course and if the MPPT can't self-limit you may pull too much current from your power source causing it to blow a fuse, overload, who knows... If you're going to be creative you better know how these things work.