Dual Voltage Water Heater. 12/24/120volt

[SolarMusher]

I switch my systems around a lot and now I am using Trace C-40 controllers in diversion mode which is controlled by a relay from port 1 of the Classic which switches pots on the C-40......the C-40 has analog pots to set the charge set points and I have a patch panel with two sets of pots, one for Classic in control, one for standalone...usually set high as a dummy value so the C-40 does not operate unless controlled by the Classic..........patched into the C-40's..too complicated but I want the Classic to be the master of the system and the Kid as helper
Td

Dave, does your classic work with EA/WBjr on aux2 ? If yes, I would be curious to know what you did to make the C-40 absorb time to match the Classic EA abs time. I tried this with a tristar pwm but gave up and finally bought a CL lite to have another aux2 available in follow me to control my heater.
Thanks,
Erik

[russ_drinkwater]

Ah, well my place of abode is a long way from the confines of the redtape brigade!
If I want it I build it.
Can not see it changing in the next 50-100 years.
Too far away from civilization!
Was just an idea

[dgd]

... I would be curious to know what you did to make the C-40 absorb time to match the Classic EA abs time. I tried this with a tristar pwm but gave up and finally bought a CL lite to have another aux2 available in follow me to control my heater.

Just curious to know how the Tristar PWM controller was included as part of your system?
Did it have its own PV and charged the same battery bank as the Classic? Or were you trying to use it in some sort of diversion mode for water heating?

It appears that you wanted to align its transition from absorb to float with the Classic so that both floated at same time, a follow-me in effect?

Dgd

[SolarMusher]

Hey David,
Not really, I was thinking to use it as diversion for pwm heating only in order to keep my EA/WBjr on Aux2 but it was a bad idea.
To get it right, I should have used classic absorb on time only without EA and set the Tristar with the same parameters. So I gave up on Tristar and only used aux1 waste not for heating (not so bad). To make a short story, I bought a Lite to add some PV (it didn't work without input => resting) and get a better input in Fall/winter with short days. That way, I would also be able to use the Aux2 pwm from the Lite to heat some water in winter and change elements to heat faster.
And you know what...? I didn't have enough time to work on it and get it as I'd like  .
Erik

[1der]

It has been a while since I posted here but thought it was proper to provide an update on what I did and what I have learned about this effort.

Starting Components:
Ford E350 Camper Van application
Water Heater:  Isotherm SPA15 - 4 Gals, 750w AC element and capability for engine coolant circulation.
Solar: 300w LG NeON panel running through The KID controller
Battery Bank:  2x175w Alacatel AGM house linked with two Bosch Grp65 AGM Engine

The idea here was to utilize the solar divert ability of The KID to heat water once the batteries were up to charge.  Typical overnight battery usage would see us in float around 11am and the batteries would stay in float for the rest of the daylight hours.  It seemed to me this additional "free" solar power could be put to use heating water.

First was determining what water heater.  I chose the Isotemp SPA15 because it is stainless steel, can go to 160 degrees (has a mixing valve),  and extremely well insulated.  Also, a volume of water capacity as close to what I determined to be optimal for our usage and excess solar capacity to bring the water up to comfortable temperature.  I calculated 3 gals as perfect, but there are no 3 gal SS tanks around, at least that I could find.

Why 3 Gals?  I am an accountant by education and training but internally a frustrated engineer lurks,  haha.  I calculated about how many watts would be available from the solar panel after the batteries came up to charge.  I also calculated how many degrees of temperature rise that would give me per gallon.  So the intersection of watts available for how many hours and a temperature rise of around 60 degrees indicated 3 to 4 gals would be viable.  That is 3 to 4 gals of water could be heated in 3 to 4 hours of available solar electric generation.

Next in the calculations was the sizing of the 12v heating element to be the most efficient for expected use. A 12v-300 watt element requires 25 amps to be in its sweet spot.   I figured I had around 18 to 20 amps on a normal day from my 300W panel  but my refrigeration would use a few amps, so I figured around 14 to 16 amps available for water heating.  This pointed to a 200 watt element as the most desirable.  For the non engineers - resistance circuits for heating are not linear in nature.  One half the amps fed to a 300 watt element does not result in half the heat being generated.  It is closer to 1/4.  Thus the necessity to size the 12v heating element accordingly. ( A larger panel array would allow for a higher wattage element.)

The flange on the Isotherm heater does lend itself to a 1" NPT type fitting.  This required a loop element be custom made by Tempco.  Thank you to Dena at Tempco for working with me to get this custom element done!  The heater now has a 12VDC and a 120VAC heating element.  This works great.  If we are driving a long distance, I can flip the breaker on to heat the water with the 12 v element.  If the drive is shorter I can turn the inverter on and heat the water more quickly with the AC element.  Heating times are about 45 mins with the AC and about 3.5 hrs with the 12v.  This is getting the water up towards the thermostatically controlled 160 degree setting.

But back to the solar side when we are not driving- This also works well!  Keep in mind that this is a system to provide hot water for use later in the day and through the night and the next morning. Using the KID I have experimented with various settings under "Load" along with the finer settings for time, etc.  "PWM Divert" seems to be the best for unattended use.  The learning moment for me here was the KID does not divert a partial current to the diversion load.  I see it as : IF Battery is in Float, THEN divert 100% to Load, IF NOT in Float, THEN load gets nothing.  I originally thought it would divert "what was left", ie. what ever was left that the battery did not need.   No problem, it is what it is and it still works well.  The water is definitely hot after a couple of hours.

The other learning moment has to do with heating fluids in a tank.  Our tank sits horizontally and the elements are horizontal.  The thermostat probes live in a tube that projects horizontally well into the tank at about mid level.  At first I was very disappointed in the volume of hot water.  It seemed I only had a gallon or so before it would become cold.   I could not figure out why this was happening.  The water would heat up to the point it would trigger the pressure relief.   I thought there was a problem with the mixing valve.  Turns out when I reassembled the heater with the new element I inverted the AC element.  The AC element has a distinct bend in it, it is not straight.  Inverted the AC element now pointed towards the top of the tank and well above the thermostat sensor tube, and the 12 v element went pretty much straight in and was also above the thermostat tube.  Well, it turns out hot water rises just like hot air. While I was nearly boiling the water at the top of the tank, the thermostat would not reach shut off until the very, very hot water at the top of the tank was sufficient to work its way down to the thermostat level and anything below the thermostat was basically cold.

Once I realized what was causing the lack of hot water, I corrected the AC element orientation, so it was reaching nearly to the bottom of the tank, and made a bend in the DC element so it too, pointed towards the bottom of the tank. (See Pic 1)  Now the tank reaches near to the 160-degree temperature it was designed for.  With the mixing valve doing its thing, there is now plenty of hot water.  Each of the elements has its own thermostat, and using the “Load â€" Manual On” setting,  The KID becomes the switch allowing for the 12VDC element to simply be "on" if I am driving or even hooked up to shore power.  Otherwise, while on solar, PWM Direct is the setting.

All in all, it worked!  Functionally, it requires forethought to set the switches to have hot water, so it is certainly not ”on demand”.  But the whole system does what it was intended to do and it is really nice to have hot water available for washing and showers.