I am currently running a small 24v emergency power solar system. I have a 40a MPPT charge controller with (4) 12v flooded lead-acid batteries in a 2S-2P configuration. I have a need for both 24v and 12v power during outages.

The 24v is obviously easy, but am having a problem getting a decent 12v buck converter to suit my power needs that doesn't cost an arm and a leg.

I was wondering if it would be possible to design a circuit that would take (2) 12v inputs and seamlessly switch between them constantly balancing the voltage on the two 12v banks, all the while outputting an uninterrupted high current (30+ amps) 12v output.

I know it's a lot to ask, and I realize the parts might cost more than a pre-made buck converter but I figured it would be worth a shot and I might learn something!

  • \$\begingroup\$ what's your 24v load? Have you considered a 4P system with a 12-24v boost converter? Define 'uninterrupted'. What variation is allowed on the nominal 12v output during switch-over events. 'Nominally none' would need something as complex as your 24-12v buck to approach. Can it dip to 10v? Can it peak to 18v? There is already an 11v to 15v tolerance on the supply input for most things that take 12v from batteries, can this device exceed those? \$\endgroup\$ – Neil_UK Jul 31 '19 at 5:53
  • \$\begingroup\$ The 24v load is two APC UPS units. These run a small server PC and some network equipment that have PoE IP cameras, phones and WAPs. \$\endgroup\$ – Jesse Dunn Jul 31 '19 at 17:10
  • \$\begingroup\$ As far as the "switch over" events, there would be none per-say. The circuit I'm looking for would be continuously switching keeping both 12v banks equalized. I'm also not sure what the optimal switching rate should be but I don't think it would need to be too rapid. \$\endgroup\$ – Jesse Dunn Jul 31 '19 at 17:16
  • \$\begingroup\$ The 12v output needs to supply an emergency power bus throughout my home which runs various LEDs and portable electronic charging equipment. As I'm not certain of the tolerance of all the RV/auto equipment on this bus, I don't think it would be wise to exceed 14v on this "12v" bus. \$\endgroup\$ – Jesse Dunn Jul 31 '19 at 17:17

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