Here's the dinky
RVwiki entry on DIY converters and
my blog entries on the topic.
Assuming you have a 12v battery bank:
Stuff to acquire
An
MPPT charge controller with configurable settings (PWM won't work for this). For something like a flooded 2x 6v 200Ah deep cycle bank we are supposed to charge at a minimum of C/10, which would be 20A. But since this isn't my only charging method and having shore power
suggests I might be in one place for several hours I went with a 10A controller. Using a slower charge rate will really bring down the cost of this DIY converter. [If you are running AGM you might want to go 30-40A for a more forceful charge. They like that kind of thing, ya know. ]
Wire the controller up to your bank. Configure the setpoints the way you like.
A
24v power supply. This will be something like maybe 7.5-10A; remember the volts will roughly halve and amps double when the MPPT bucks down to battery voltage.
This can be a nice one like
the $50 meanwells (Sternwake's preferred manufacturer), or
a cheap $20 one that like Bay or amazon. Something like
this less expensive meanwell might be good.
Do look for an adjustable output votage pot (potentiometer, you turn it with a little screwdriver) so you can tweak the output. There are ones with LED voltage meters but I just set it with a multimeter and save the $10 difference. I run mine at 23v since that's what Genasun specified.
The normal
wires and stuff.
What to do
Pretend the power supply is a solar panel: the supply's output goes into the controller's PV input. Turn power on to the power supply. Behold the charge controller happily pumping 9.7A (conversion losses) into your underfed battery bank.
Have a beer and strut around. <-- this part is optional but I always do it
