I'm trying to find the best way to charge my 24v solar battery bank off my 12v bus system. The simple way seems to be a step-up converter and a diode, but I'm wondering if I can replace the diode with an isolator and make it possible to change the bus off the solar too? I'm still new to the nuance of voltage drop, would something like this work?


  • Welcome to Motor Vehicle Maintenance & Repair! I'm no expert, but if you have a transformer (you're calling a converter) which steps up from 12v to 24v, why would you need a diode or an isolater? Commented Feb 5, 2021 at 0:55
  • To stop the charge from flowing out of my solar bank? Voltage flows from high you low? Does the transformer prevent that? Commented Feb 7, 2021 at 7:02
  • Yes, the transformer does that. The only way it works is when it's energized, then the power will flow from the input to the output, which in this case is from low to high voltage. No need for a diode because a diode only allows electricity to flow from negative to positive and not in the reverse ... it really wouldn't do anything in this case because if it were to go from high to low voltage (for some reason), the electron flow would still be in the same direction. Commented Feb 7, 2021 at 15:12
  • @Paulster Transformers don't work on DC. That's why Edison had so much trouble inventing the lightbulb, in that age, the only way to have a constant current source was to use a transformer, which required AC, which would have required conceding to Tesla. Without a CC source, the bulb needed to self-regulate (i.e. be ohmic). Commented Feb 13, 2021 at 6:46

1 Answer 1


To charge a battery, you need a battery charger.

That's because the charger needs to do multi-stage charging that is correct for the battery type you are charging - lead-acid, lithium-xxxx, etc. so it doesn't

  • hydrolyze all the water out of a lead-acid wet cell
  • destroy a sealed lead-acid by hydrolyzing the electrolyte
  • set a lithium pack spectacularly on fire

They do, in fact, make battery chargers which input 12V and charge various 24V-range battery packs. They are rare and "boutique" so expect to mail order it and pay a lot.

However, you can do it with readily available commercial off-the-shelf parts: use any common 12V inverter to make 120V then use any common 24V battery charger to charge the larger pack.

If you are running an engine to get this power, the inverter -> 120V charger chain makes the most sense, because the 12-120-24 double-conversion efficiency losses are coming from fuel, and you can find those two components at nearly any truck stop anywhere.


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