Gas generator with only 20-24V output for charging 12V batteries

MarkAl

This is probably more a head space question sadly. Does anyone know of a manufacturer who combines a gasoline motor with a generator (or alternator) for about 20-24VDC output of maybe 500 Watts? I have no need for 120 VAC to run the trailer. I would like to as quickly as possible recharge my battery(s) in my 320 while dry camping. The bulk, noise and inefficiency of using an inverter AC source then reducing it so a charger can correctly charge the battery seems wrong. My simple system would be gas engine driving a generator/alternator and regulator to 20-24 V I would then simply connect it into my existing solar controllers already installed in the trailer. This would give me almost 25 amps into the battery. About 1 hour of running it would replace my normal 24 hour use in my 2021 if I'm too deep in the woods for solar. I might even think then about upgrading the Victrons to a higher output version.  Please don't answer with the TV  

I really don't want to drag around and put up with the sound of hours of conventional generator  (and external charger) use. I've got some trips lined up this summer deep in the woods for a week or so and I can't count on solar.

Horigan

Assuming such a generator exists, you still need to regulate the voltage/charging to the trailer battery.  You can't just apply 20V.  Max charging voltage for AGMs is 14.4V.

MarkAl

Nope, that's the great thing of sending the voltage into the solar panel input on my controllers. They manage the regulation both input and output to the battery. I use a PC 100 watt 20 VDC power supply now to keep the batteries fully charged in float mode. This system also allows me to pre-cool the refrigerator before trips without the bulky 120V connected or depleting the batteries.

Horigan

Got it.  My solar port does not have a controller between it and the battery.

Grumpy_G

A generator for this specific application does not exist as far as I can tell. If it does it's going to be an expensive specialty product and likely putting out 100s of amps. What off-grid users have done is couple a 24V one-wire alternator to an engine. 24V is very common in the heavy equipment world and one wire alternators do not require an external voltage regulator. If you're looking at 500W a weed whacker engine would be enough. However this would be a somewhat kludgy solution. 
Granted using an inverter generator to generate 120V AC just to convert back into low voltage DC is not the most efficient way of doing it but it is the most practical. There are small sub 1000W inverter generators and you could find a 24V DC power supply with enough amperage and call it a day. 
The other issue is that you might be over estimating how much charge current the solar controller can deliver into the batteries and in real world conditions 25A might not be possible. 

Horigan

I've created 24V power supplies using server power supplies.  These were to power lipo battery chargers for my RC hobby (helicopters).  First link below is the low cost method that I did using eBay HP power supplies.  Second link is an option for dedicated power supplies that can provide up to 1500W.  With this power supply coupled with a regular generator, you'd have what you need.

http://www.tjinguytech.com/my-projects/diy-24v-47a

https://www.progressiverc.com/collections/24-27v-supplies

MarkAl

In some other threads the standard converter in the 2021 320 seems to be debated based on the wire size to the battery. I've thought it was 10 amps max or approximately 136 Watts for charging from the 120 V input. Is this correct based on user experience? I know I can get more from my solar array (though practically not much). I've never looked when on AC as how long it took to charge didn't matter. Maybe I need to just add a higher AMP charger and connect to the "standard" generator at 120V. Sigh, so conventional.

Grumpy_G

The WFCO converter in the 320 is 35A so in theory it can charge at a decent rate. It behaves somewhat weird though, in my tests it starts off at over 20A but within a couple of minutes settles down to sub 10A. I think the fuse at the battery is 30A so the wiring is not the limiting factor.