I have a spare engine sitting around and i've been planning on building a 220V generator from it. I'll be using an old UPS device which uses two 12V batteries wired in series to make 24V and connect it to the car batteries.

The plan is to have the engine power two car alternators and each alternator connects to one battery separately from each other while the batteries are still connected in series.

Question is, will there be an issue for the alternators charging one battery each while they are connected in series ?

  • Yes, first draw yourself a diagram of what you explained and see what is wrong...
    – Solar Mike
    Jun 17, 2019 at 14:04

1 Answer 1


Usually, alternators have a negative ground.

This means both alternators want their negative terminals to be at the same potential. It may not be feasible to avoid this, as all metallic parts in car are typically grounded.

You need to find an alternator that doesn't have all of its metal parts grounded, or alternatively you need to isolate the metal parts somehow so that they can be at a different potential. Even then, the metal parts are large and it's easy to accidentally touch them and the true ground at the same time with e.g. a wrench, creating a huge potential for nasty accidents.

An alternative would be to find a 24V alternator. I bet that's the easiest way forward. As far as I know, some large vehicles use 24V electrical systems so there should be plenty of choices for a 24V alternator.

  • I would isolate the windings in one of the alternators, but future replacement would be an issue!! I have made a 24v start, 12v run system, but would not advise it...
    – Solar Mike
    Jun 17, 2019 at 14:22

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