Exciting 2nd Alternator for a DC2DC converter.

[larrylwill]

I am starting a new thread.
I have a 2nd alternator in my 2019 Roadtrek Simplicity. It has a voltstart with 2nd alternator. That alternator puts out 280 amps, but has NO balmar. I changed my batteries to 280 amp lifepo4. I installed a Renology DC2DC 60a converter so as not to shut off the BMS which is 150A. In order to charge the batteries I have to excite the 2nd alternator with a momentary 12v. Since it is a separate system from the starter battery, I have to figure a way to do it when I start the engine. A push button, wont work with the voltstart.

Here are my ideas.
1. A diode from the starter switch to the 2nd alternator output. So 12v is only supplied when the starter switch engages the starter.
2. A relay that engages with the starter cycle and times out in a second or 2.
3. A small (motorcycle battery) on the output of the 2nd alternator.
4. Possibly charging a 100uf or larger capacitor with a high value resistor like 10meg ohm with the cap hooked to the alternator output and the resistor hooked to 12v. I don't know yet if the cap would contain a large enough 12v pulse.

Any suggestions or other ideas.?

[Peder_y2k]

IMHO, I'd install a momentary-on lighted rocker switch. Press and hold for a moment AFTER the engine has started. Essentially the same as a push button switch. No diode needed if wired correctly with a proper fuse.