Kids ride-on battery mod

I am trying to modify my kids electric ride-on and wanted to have the battery disconnect from the rest of the circuit (wiring harness) when I plug in a battery charger. I don’t want to have to open the toy every time to charge, so I thought relays might be the ticket.

I also may want to upgrade from a 12V to 24V system to speed it up and control it via PWM with a small arduino to keep from destroying the gears. Unfortunately, the charger for the LiFePO4 battery only supports 12V, so I thought that a series of relays could work to go from series to parallel when charging. Below is the schematic I was thinking about, but have very little knowledge of circuit design or the actual parts I would need.

Any help would be greatly appreciated!

Hello Fireman1224,
I wanted to bring your attention to other options on the web. Under the Resources tab we have Design & Integration Services also under the tools is the Reference design library. When you click it you will see under the Power Management, battery chargers you may find other options to help.

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I appreciate the quick response! After looking at the directed area, I see that what is there is quite similar to what I had already found. Most of what I’m finding are schematics for making a “smart” battery charger to prevent over charging and damaging the battery. I already have a NOCO Genius 10 charger to evaluate and maintain the status of the battery as well as facilitate relatively quick charging. My intention is to simply make a harness disconnect and, in the future, switch from series to parallel when I plug in the charger. I do think the Reference design library would work for other projects I may tinker on as I learn a little more!


As drawn, it would appear that both batteries are directly short-circuited when the relays are in the “normal” state. Probably not a good design to run with…

A general problem with this sort of approach is that the precise timing of mechanical relays can be a bit fuzzy, due to things like contacts sticking a bit and whatnot. It only takes about a microsecond worth of short-circuit time in a case like this to ignite an arc that’ll destroy or seriously damage the relay, so it’s a thing to be avoided.

When you go back to the drawing board, consider what DPDT relays might have to offer.

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I guess I messed up when I was moving things around to make it smaller…

Is this a better solution and would I benefit from the diodes added to the DPDT relay?

Thanks for the help!