Feedback on 12V water heater element as solar diversion load

[ewarnerusa]

My solar charge controller has a diversion load feature where excess current can be diverted to a load once batteries are full. The manual discusses using a water heater element and this sounds like a clever way to do something with excess solar harvest that would otherwise be wasted. I recognize that this is not a primary method for heating the water, just a way to doing something rather than nothing with excess solar harvest. Does anyone do this and have feedback? I found an old thread posted by "msiminoff" with a cool project doing this with a custom element.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/25824208/srt/pa/pging/1/page/1
Otherwise, there are existing 12V heating elements that can do this.
https://windandsolar.com/9-3-8-inch-dual-power-submersible-water-heating-element/

[stevenal]

Those 12 V elements look like they are for home style water heaters, not RV.

[Tom_M1]

Bobbo wrote:
What I don't understand is why you feel the need "to do something with excess solar harvest that would otherwise be wasted." It's not as if you would have to go out and buy new "solar harvest" if you waste it. It seems to me that this is a solution in search of a problem.

It means that you would use less propane. Once your battery is fully charged you would then heat your water with the excess electricity. Seems like a great idea to me.

[pianotuna]

ewarnerusa,

Go for it!

I originally intended to use the battery bank to run the fridge for 12 hours before taking a trip.

I never got around to doing so--and the controller did not have a diversion load terminal.

[Grit_dog]

Sure it would probably work. Presume you never use any shore power with your water heater?

[ewarnerusa]

Bobbo wrote:
What I don't understand is why you feel the need "to do something with excess solar harvest that would otherwise be wasted." It's not as if you would have to go out and buy new "solar harvest" if you waste it. It seems to me that this is a solution in search of a problem.

Because wasting is...well...wasteful? Sure, this isn't a lot of wasted amps we're talking about and not worth buying a lot more stuff just to be "wasting" less. But a $25 heating element plus wiring and my time is play money if it works as described in the manual and/or as the thread I linked to. Rephrasing this, it an idea to offset a little bit of propane used for water heating when boondocking.

[Bobbo]

What I don't understand is why you feel the need "to do something with excess solar harvest that would otherwise be wasted." It's not as if you would have to go out and buy new "solar harvest" if you waste it. It seems to me that this is a solution in search of a problem.

[ewarnerusa]

Morningstar Tristar Solar Charge Controller manual
6.0 Diversion Charge Control
The TriStar’s third mode of operation is diversion load battery charge control. As the battery becomes fully charged, the TriStar will divert excess current from the battery to a dedicated diversion load. This diversion load must be large enough to absorb all the excess energy, but not too large to cause a controller overload condition.
6.1 Diversion Charge Control
In the diversion mode, the TriStar will use PWM charging regulation to divert excess current to an external load. As the battery becomes fully charged, the FET switches are closed for longer periods of time to direct more current to the diversion load. As the battery charges, the diversion duty cycle will increase. When fully charged, all the source energy will flow into the diversion load if there are no other loads. The generating source is typically a wind or hydro generator. Some solar systems also use diversion to heat water rather than open the solar array and lose the energy.

[ewarnerusa]

FLY 4 FUN wrote:
I would check what the load circuit is rated for as normally its a few LED lights, small 12v fan or plugging in USB ports for phones/tablet etc. I wouldn't think it could manage any sort of big load unless you had a pretty sizeable setup (think grid tie system on a house with 3000-4000W of solar.

Not a load circuit, a diversion load profile that switches the solar current between the batteries and diversion load depending on the SOC of the batteries and the charging profile. Batteries get the priority, diversion load gets what's left.

[ewarnerusa]

enblethen wrote:
Your second link smallest element is 300 watts. That is 25 amps roughly at 12 volts. Your 280 watts of solar will not be sufficient and will pull power from the batteries.

That's not the way the diversion load profile works. The current passed to the load is just from the solar side that can't be passed to the batteries because once their SOC doesn't accept it.

[enblethen]

Only way any setup like this would work is to route loads through the 12-volt distribution center.

[FLY_4_FUN]

I would check what the load circuit is rated for as normally its a few LED lights, small 12v fan or plugging in USB ports for phones/tablet etc. I wouldn't think it could manage any sort of big load unless you had a pretty sizeable setup (think grid tie system on a house with 3000-4000W of solar.

[enblethen]

Your second link smallest element is 300 watts. That is 25 amps roughly at 12 volts. Your 280 watts of solar will not be sufficient and will pull power from the batteries.