Dual alternators 12v and 24v

[lost1]

I am in the process of installing a second alternator in my camper. The truck has a 24 volt alternator for starting and all its electrical and the camper has a 12 volt alternator for charging its battery bank and running all the camper 12 volt fridge, AC, diesel heater fan, lighting etc.
My question are:
-1) Is it ok to use the truck chassis as a common ground for both the 12v and 24v systems? This would include both alternators and 12v camper accessories/appliances in addition to 24v truck electrical.

2) Can I use the 24v truck ignition switch to turn on (excite?) the 12v Alternator (it has an external voltage regulator with circuit for switched power) ? Or should I run a wire from the 12v battery with a toggle switch that I could turn on/off? Or some other option?

Thanks in advance for the inputs!

 

[Ozarker]

First I would not use that common ground as amps increase these circuits should be isolated, Secondly I would use the 12V battery and toggle switch, again keeping circuits isolated.

 

[1stDeuce]

There is nothing wrong with both voltage systems using the chassis for ground, just be aware that you are pulling more amperage through existing factory ground connection between the engine and frame, and you might want to upgrade it to handle more current.

Question or consideration... Rather than adding a 12v alternator for charging house batteries, is there some reason that you are not just using a DC-DC charger? Charging 12v with 24v DC-DC seems like a much better option than adding a second alternator at 12v, which will not be as effective as a DC-DC charger without significantly huge wire gauge between the alt and house batteries. A DC-DC charger near the batteries would be fine on much smaller gauge wire (twice the voltage means half the amperage) and would be able to charge the house batteries at full voltage without concern about voltage drop over distance...

For redundancy, you could then add a second 24v alternator, which would share the load with the factory alt to provide plenty of amperage for charging the house batteries...

If you do go with the 12v alt, using ignition to switch alt on should be fine, and that way you don't forget it and either run the house dead because you left the alternator energized with the truck off, or forget to engage charging and still have low batteries at the end of a day of driving.
I think you'll need to operate a 24v relay with the ignition and feed 12v to the alt/reg to switch it on though. If you just give the 12v regulator 24v to turn it on, not sure it'll be happy...

 

[Ozarker]

That is possible^!

Note all of the modifications, remember to do and not to do, and change wiring for additional amps.

If you want cheaper, simple, redundancy, safety, reliability and have fewer worries, keep circuits isolated.

 

[lost1]

Advice has been much appreciated. I installed a 130amp marine alternator with external (smart) voltage regulator. I am sharing the common ground and it seems to be ok. I put a lighted toggle switch to turn on the alternator but I think the ignition switch would be a better option with a relay and 12 volt power. I will look into that.
I wasn't sure if I could get the equivalent DC to DC charger that would put out the amps required to keep the (power hungry) AC and Fridge happy while still charging the 4 x 6 volt battery bank. Ultimately the alternator was a cheap option and it gives the option to charge my batteries if the trucks alternator decides to stop working. My 300 watt solar panel on the roof is really useless for charging due to my latitude, lack of sun and trees everywhere. I may double the wattage if I am feeling speedy...