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/

[StirCrazy]

ewarnerusa wrote:

Chum lee wrote:
As previously hinted at, if you have a 2/3 way absorption type fridge, why not divert the excess power generated to that and save some propane? Clearly, if you have a 2 way fridge, you'll need an efficient inverter capable of generating at least +-500 watts on a duty cycle of at least 50%. Just keeping your 1500 watt PSW inverter online full time may be enough to waste enough excess power to solve your issue doing nothing else. IMO, 280 watts of solar wont be enough to run the fridge full time, but hey, it's a start. You'll be spending a lot of time doing load management.

Chum lee

A different take on this idea^^ I wonder if instead of a 12V water heater element I could explore a refrigerator 12V element? Is there harm in adding variable/inconsistent heat (less than the OEM 300 watt AC power element) to the ammonia in an absorption fridge? This is just a brainstorm, I definitely don't want to swap out the AC side of the fridge.

EDIT: I clearly don't know exactly how the ammonia is heated in an absorption fridge, just that this is part of the process. But first google search showed a promising success for a similar idea. This is a Dometic fridge, mine is Norcold. https://www.escapeforum.org/forums/f8/adding-12v-heating-element-to-rm2510-fridge-16224.html

my 3 way on 12V is 12 amps. thats a lot of power to be chucking out for the return on propane savings.. I can go probably between 1 and 2 months on just my fridge with a 20lb bottle, but as soon as your solar stops producing over the amprage for the 12v heater then you have to turn your fridge back to propane or you start eating battery capacity. Idealy you want somthing that you don't have to interact with in my opinion. the hot water element would be great, in my case the space heater would be good but in the summer you would have to be able to turn it off and you would still be not using all your potential when its hot... maybe a combanation of the water heater and space heater so you can use which ever one you want.

Steve

[ewarnerusa]

Chum lee wrote:
As previously hinted at, if you have a 2/3 way absorption type fridge, why not divert the excess power generated to that and save some propane? Clearly, if you have a 2 way fridge, you'll need an efficient inverter capable of generating at least +-500 watts on a duty cycle of at least 50%. Just keeping your 1500 watt PSW inverter online full time may be enough to waste enough excess power to solve your issue doing nothing else. IMO, 280 watts of solar wont be enough to run the fridge full time, but hey, it's a start. You'll be spending a lot of time doing load management.

Chum lee

A different take on this idea^^ I wonder if instead of a 12V water heater element I could explore a refrigerator 12V element? Is there harm in adding variable/inconsistent heat (less than the OEM 300 watt AC power element) to the ammonia in an absorption fridge? This is just a brainstorm, I definitely don't want to swap out the AC side of the fridge.

EDIT: I clearly don't know exactly how the ammonia is heated in an absorption fridge, just that this is part of the process. But first google search showed a promising success for a similar idea. This is a Dometic fridge, mine is Norcold. https://www.escapeforum.org/forums/f8/adding-12v-heating-element-to-rm2510-fridge-16224.html

[StirCrazy]

ewarnerusa wrote:
I like the space heater idea. Our typical camper use doesn't call for space heating during solar hours, but doing something like that would address a concern I have with my water heater idea. I feel I should have a thermostat control just in case the water is already at design temp. If the scenario is that the thermostat says no more heat allowed, then the diversion current has nowhere to go. The CC manual makes statements about making sure the diversion load can accept all diverted amps otherwise...something? That part requires more research. I think it dumps it back into the battery, which at this point doesn't need any more charging. Or maybe makes magic blue smoke??

ya we do a lot of spring / fall camping not freezing weather usaly but close to or just below freezing at night (wife won't go with me when its real cold haha) so somthing like THIS could use extra solar in the afternoon and just keep the chill out of the camper, maybe even keep it warm. that would have to be tried to find out I guess, but at 20ish bucks cdn it isnt that much of a deal breaker to try it.

Steve

[ewarnerusa]

I like the space heater idea. Our typical camper use doesn't call for space heating during solar hours, but doing something like that would address a concern I have with my water heater idea. I feel I should have a thermostat control just in case the water is already at design temp. If the scenario is that the thermostat says no more heat allowed, then the diversion current has nowhere to go. The CC manual makes statements about making sure the diversion load can accept all diverted amps otherwise...something? That part requires more research. I think it dumps it back into the battery, which at this point doesn't need any more charging. Or maybe makes magic blue smoke??

[StirCrazy]

ewarnerusa wrote:

StirCrazy wrote:
...People seem to get on this "we are waisting solar power when our batterys are full" kick every now and then. you are not waisting it, it is always being radiated and you can only waist somthing you have control over like a kitchen faucet left running for no reason. other wise we could say anyone who doesn't have a solar panel is waisting energy.

now personaly I think the idea of a deversion load is kinda neat and a 12V water heater eliment would be awsome to save a bit on propane, I have two issues though.

you are using a PWM controler so you are waisting solar energy by not having an efficient controler :B

second I am not sure of it will put out enough energy to make the element hot enough to keep it above the temp where it starts the burner up again, it might though...

First paragraph seems oddly nitpicky, in many situations the panels are able to harvest more energy than the immediate demand and to not utilize that capacity is wasting it. Let's call it wasting the capacity rather than wasting the current then.

PWM vs MPPT, yeah I get it. MPPT technology can squeeze out more amps in certain situations. But the PWM controller and 12V panels are a sunk cost from over 10 years ago.

This diversion current will never fully substitute the gas burner for primary water heating. But any electric heat input to the water can in theory offset the propane btus required to heat it up to the setpoint. I usually turn on the water heater first thing in the morning, off once breakfast duties are done, then on again for dinner duties followed by shutting off until the next day. This works for our boondocking style of camper use.

wasn't ment to be nit pickey but just my opinion, if you cant turn if off it cant be waisted as it then sends the energy into the enviorment, but ya I can agree to "waisting potential". in my case I over size just for a faster recharge, then it off setting electrical usage during the day so when I go to bed at night my batteries are always at 100%, but if I have a few bad solar days the over size will still be able to top off the batteries before the first sunny day is over.

ya I do agree that even if it isnt enough to meet your water heating needs it can reduce propane usage by keeping it warm longer.

Another idea that I have been looking at is a 200 watt ceramic 12V heater for space heating in the spring and fall thats only 600BTU but it is quiet and constant and costs 19 bucks, so I was thinking of trying it and seeing how it works. I just got to figure out how the "load" output works on my charger.. I am not sure it can handle the 10ish amp output... if I can find a MPPT with a diversion output that might be worth upgrading to. if I can off set the furnace that would be the biggest propane savings for me.

[ewarnerusa]

StirCrazy wrote:
...People seem to get on this "we are waisting solar power when our batterys are full" kick every now and then. you are not waisting it, it is always being radiated and you can only waist somthing you have control over like a kitchen faucet left running for no reason. other wise we could say anyone who doesn't have a solar panel is waisting energy.

now personaly I think the idea of a deversion load is kinda neat and a 12V water heater eliment would be awsome to save a bit on propane, I have two issues though.

you are using a PWM controler so you are waisting solar energy by not having an efficient controler :B

second I am not sure of it will put out enough energy to make the element hot enough to keep it above the temp where it starts the burner up again, it might though...

First paragraph seems oddly nitpicky, in many situations the panels are able to harvest more energy than the immediate demand and to not utilize that capacity is wasting it. Let's call it wasting the capacity rather than wasting the current then.

PWM vs MPPT, yeah I get it. MPPT technology can squeeze out more amps in certain situations. But the PWM controller and 12V panels are a sunk cost from over 10 years ago.

This diversion current will never fully substitute the gas burner for primary water heating. But any electric heat input to the water can in theory offset the propane btus required to heat it up to the setpoint. I usually turn on the water heater first thing in the morning, off once breakfast duties are done, then on again for dinner duties followed by shutting off until the next day. This works for our boondocking style of camper use.

[Boon_Docker]

"Isn't it 1 1/4"? I have not taken mine out and checked, just been googling.
https://www.dyersonline.com/atwood-domet........110v-1400w-screw-in-heating-element.html"

That is a strange size.
Atwood is typically 1/2 inch and Suburban is 3/4 inch.

[StirCrazy]

ewarnerusa wrote:

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.

People seem to get on this "we are waisting solar power when our batterys are full" kick every now and then. you are not waisting it, it is always being radiated and you can only waist somthing you have control over like a kitchen faucet left running for no reason. other wise we could say anyone who doesn't have a solar panel is waisting energy.

now personaly I think the idea of a deversion load is kinda neat and a 12V water heater eliment would be awsome to save a bit on propane, I have two issues though.

you are using a PWM controler so you are waisting solar energy by not having an efficient controler :B

second I am not sure of it will put out enough energy to make the element hot enough to keep it above the temp where it starts the burner up again, it might though...

[ewarnerusa]

Boon Docker wrote:

ewarnerusa wrote:

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

Yeah I don't think they're the right size for a swappable replacement of an RV water heater 120V element. But it says in loud all caps to not use on grid power as it will fry the element. It's a website for wind and solar and listed as a low voltage diversion load element, so seems like the perfect application if I can get it in the tank.

You are right.
The heater element is 1" NPT and an RV water heater is 3/4" NPT.

Isn't it 1 1/4"? I have not taken mine out and checked, just been googling.
https://www.dyersonline.com/atwood-dometic-water-heater-110v-1400w-screw-in-heating-element.html

[stevenal]

Maybe just use a Hott Rod. By my calculation, 450 W at 110 V works out to 26.9 ohms. At 12 V, this would be a bit over 5W. Not much, but it is something.

Before anyone objects to putting DC on an AC element, purely resistive loads don't care.

[Boon_Docker]

ewarnerusa wrote:

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

Yeah I don't think they're the right size for a swappable replacement of an RV water heater 120V element. But it says in loud all caps to not use on grid power as it will fry the element. It's a website for wind and solar and listed as a low voltage diversion load element, so seems like the perfect application if I can get it in the tank.

You are right.
The heater element is 1" NPT and an RV water heater is 3/4" NPT.

[AllegroD]

Deleted.

[ewarnerusa]

Chum lee wrote:
As previously hinted at, if you have a 2/3 way absorption type fridge, why not divert the excess power generated to that and save some propane? Clearly, if you have a 2 way fridge, you'll need an efficient inverter capable of generating at least +-500 watts on a duty cycle of at least 50%. Just keeping your 1500 watt PSW inverter online full time may be enough to waste enough excess power to solve your issue doing nothing else. IMO, 280 watts of solar wont be enough to run the fridge full time, but hey, it's a start. You'll be spending a lot of time doing load management.

Chum lee

Fridge draws 30 amps on DC side when I run it off of the inverter. Twice as much as my solar panels could provide during the most ideal of conditions. This has crossed my mind as something to do if I found myself with full batteries during peak solar harvest time while camping. But as you said, lots of load management to think of and it would draw from my batteries whenever duty cycle was on.

[Chum_lee]

As previously hinted at, if you have a 2/3 way absorption type fridge, why not divert the excess power generated to that and save some propane? Clearly, if you have a 2 way fridge, you'll need an efficient inverter capable of generating at least +-500 watts on a duty cycle of at least 50%. Just keeping your 1500 watt PSW inverter online full time may be enough to waste enough excess power to solve your issue doing nothing else. IMO, 280 watts of solar wont be enough to run the fridge full time, but hey, it's a start. You'll be spending a lot of time doing load management.

Chum lee

[ewarnerusa]

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

Yeah I don't think they're the right size for a swappable replacement of an RV water heater 120V element. But it says in loud all caps to not use on grid power as it will fry the element. It's a website for wind and solar and listed as a low voltage diversion load element, so seems like the perfect application if I can get it in the tank.