tecnodave just pm'd that he posted his instructions re the dual voltage water heater at midniteforum.com Here is the link:
Here is what tecnodave says in his initial post on that thread, part numbers are in the posts which follow in the same thread:
"I have made a dual voltage water heater for my motorhome which is primarily solar at 24 volts but can also be powered by the generator or shore power at 120 volts with no voltage conversion or inverter involved.
What is hard to find is a water heater tank that has two standard 1" NPSM (national pipe straight thread mechanical --- the U.S. Standard for heater elements) threaded openings for elements in a small size form factor suitable for an RV.
I used a standard GE brand water heater 10 gallon heater about 17" tall and 13" dia which Had only one such opening.
I removed the 120 volt 1800 watt element and replaced with a 24 volt 600 watt Missouri Wind and Solar DC element . I removed the drain plug and used a Camco Manufacturing water heater conversion kit which is meant for RV propane gas water heaters as an after market 120 volt 1000 watt heater which can be used togather with the gas. It is a special element and adapter which installs through the 1/2 (or 3/4" with adapter) inch drain plug opening. There are two thermostats.....the original GE which controls the CAMCO element.....and a DC one from Missouri Wind And Solar which controls the DC element. There are two complete separate circuits for the AC and DC sides.
Every thing is off the shelf 12 or 24 volt / 120 volt water heater........nobody markets such a thing but the parts are out there.
24 volt power is supplied by load circuit of Kid #1 and 120 volts only from generator but I could run both but no need.
"I did a bit of research on CAMCO to get these part numbers:
Kit is called water heater hybird conversion kit.......two are available
CAMCO Item # 11673. For 6 gallon heater. 425 watts at 120 volt
CAMCO item # 11773 For 10 gallon heater, 725 watts at 120 volts
These are not standard screw in elements......they are shipped with a compression fitting which installs into a 1/2 " or 3/4". NPT threaded opening, with the included adapter fitting it screwed into the G-E water heater with no problem.
Get these at CAMCO site on Amazon for the best price
I think that the 1000 watt one that I have is old stock and discontinued"
"I am still experimenting with this. Basic setup is load mode=battery, Function = PWM Divert,
Setup = offset -2, width -1----changing setup values will alter the balance with battery charging and diversion.
It takes some tinkering to achieve a balance of topping the batteries off and getting enough power for heating water. I have local coastal fog/cloud cover so I need to tinker this a lot to keep a balance. Some days I shut of diversion to be sure I get full charge. I am way over paneled to accommodate my variable coastal conditions, I live only 6 miles from that big pond------the Pacific Ocean.
Reprinted with permission.
For more discussion regarding the load diversion settings on the solar charge controller, see the continued discussion in the link above.