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[Keith]

Here's a crazy idea that might be of some interest. My DC/DC convertor failed recently and I noticed that everything else worked fine without it. No lights of course, and the ABS was disabled (as usual for my off road use). There was only one flaw, no brake light triggered regen. That was really annoying. I had to quickly relearn how to use the rear brake, serious business on steep downhill trails. Anyway, i wondered if it would be possible to get regen without any 12 volts at all. It is, here's how, I'm pretty sure, use at your own risk. I may do this this myself, undecided so far.

[BrianTRice@gmail.com]

Neat. Although at that point, you may as well just shunt your own switching power supply...

[Keith]

The regen power supply needs to  be isolated from the high voltage. 9V battery is sleazy but should last for months, 7-10 hours of braking time anyway. But if you wanted a brake light to keep from getting rear ended by your buddy on the trail, this version might be better. $30 converter. https://www.mouser.com/ProductDetail/MEAN-WELL/RSD-30H-12/
or $40 but much smaller and has enable input http://www.mouser.com/ds/2/75/SPEC-ECLB40W-110-V11-1114358.pdf

[BrianTRice@gmail.com]

See, there's an idea worth pursuing just to have a separate always-on power supply (useful for maybe a tracking/security device or other onboard computer).

[Keith]

Here's a third version, this is what I'm going to actually do. I got rid of the relay but kept the battery. If I get tired of replacing the battery I'll get a DC converter instead. This circuit does what I want, one switch makes it off road ready with no lights or ABS but regen braking still working. Zener diode activates the brake light when 12V is on, but keeps it off when running on battery voltage. Parts on the way.

BTW I now know that there is a 10uF capacitor across the MBB input as shown. It blew the fuse in my new multimeter! It's there to prevent stay triggering but means there is a current surge.

[Keith]

OK, I did it, installed, tested, it works. Regen braking with no 12VDC at all. Updated schematic to show detail of how it is really connected to the wiring. Diode under the headlight is not so easy, the rest connects to the harness right where the rear brake switch wires split off, neat. Fun fact, the ABS warning light is not on when the DC converter is off. We'll see how long the 9V battery lasts.