Run water heater via inverter?

[senormechanico]

We have an Isotemp 17 liter tank with a 1kw 120 volt AC element.
I hooked up a 12 volt DC wall wart type power supply across the thermostat contacts, so when the heater element hits the shutoff, the heater element is in series with the wall wart primary winding.
This gives an isolated 12 volt DC output from the wall wart which is connected to an automotive chime (keys are in the ignition!) alarm.
This tells me to turn off the inverter.
We have 320 watts of solar, lithium battery bank of 200aH, Aerogel insulation in the fridge, and the extra was applied to the stripped down hot water tank.
We never have to run the engine for anything but propulsion when there's no wind.

[Bash]

Originally Posted by senormechanico

We have an Isotemp 17 liter tank with a 1kw 120 volt AC element.
I hooked up a 12 volt DC wall wart type power supply across the thermostat contacts, so when the heater element hits the shutoff, the heater element is in series with the wall wart primary winding.
This gives an isolated 12 volt DC output from the wall wart which is connected to an automotive chime (keys are in the ignition!) alarm.
This tells me to turn off the inverter.
We have 320 watts of solar, lithium battery bank of 200aH, Aerogel insulation in the fridge, and the extra was applied to the stripped down hot water tank.
We never have to run the engine for anything but propulsion when there's no wind.

That's absolutely brilliant. I didn't realize Isotemp made a tank that small. How long does it take before the chime goes off usually?

[donradcliffe]

I agree with the point that you don't need really hot water for your showers. I prefer it when the water heater is at about 105 degrees, so all hot water is comfortable in the shower. When I have to add cold, the temperature goes up and down as the freshwater pump kicks on and off.

[senormechanico]

Originally Posted by Bash

That's absolutely brilliant. I didn't realize Isotemp made a tank that small. How long does it take before the chime goes off usually?

OOPS! It's a 17 liter Ardic.

The very first time I tried it was in March in the PNW.
The tank water temp measured 47 degrees f.
I turned on the inverter and timed it until shutoff.
Exactly one hour and one minute drawing 108 amps !
The water outlet temp was 173 degrees f.
That of course, was an early date in the year (roughly spring equinox) worst case scenario, and it took until the next afternoon to refill the batteries.
I dialed the thermostat back to about 160 f.

The reason I kept it high is that you can mix cold with it for showers etc, but you can store more btu's with increased temp.

The Aerogel is definitely the way to go for insulation.
I used the extra from the fridge build, wrapping 4 layers on the side and two layers on the ends.

During the summer, we run it every day and having used maybe a half tank for showers and dishes, it takes around 20 to 25 minutes.
Solar fills the batteries by the end of the day.

[Mark_S.]

I have a similar question. We have a 4KW DC diesel generator that we run everyday to recharge an 800 ah battery bank. We recently had to have it rebuilt and the mechanic said it would work best to run it for long periods (2 to 3 hours) with load on it. I don't want to sacrifice my batteries by discharging them to a low point just to get the generator to run harder to recharge them. This got me to thinking that I could connect our hot water heater to our 2000 watt inverter while the generator is running. Any thoughts on this strategy? I know it is inefficient, but it would give us hot water everyday, run the generator harder and keep the batteries in good shape. Would there be too much power going through the system to damage something? Thanks for any thoughts.

[deckofficer]

Originally Posted by senormechanico

We have an Isotemp 17 liter tank with a 1kw 120 volt AC element.
I hooked up a 12 volt DC wall wart type power supply across the thermostat contacts, so when the heater element hits the shutoff, the heater element is in series with the wall wart primary winding.
This gives an isolated 12 volt DC output from the wall wart which is connected to an automotive chime (keys are in the ignition!) alarm.
This tells me to turn off the inverter.
We have 320 watts of solar, lithium battery bank of 200aH, Aerogel insulation in the fridge, and the extra was applied to the stripped down hot water tank.
We never have to run the engine for anything but propulsion when there's no wind.

1000 watts is a good load. I'll bet one of the reasons your system works so seamlessly is your lithium battery bank. Unlike lead acid, when your batteries see a 1000 watt load, instead of pulling 90 amps as the lead acid battery has sagged to 11 volts, your lithium bank is pulling 75 amps at a non-sagging 13.2 volts.

[AnchorageGuy]

Originally Posted by Mark_S.

I have a similar question. We have a 4KW DC diesel generator that we run everyday to recharge an 800 ah battery bank. We recently had to have it rebuilt and the mechanic said it would work best to run it for long periods (2 to 3 hours) with load on it. I don't want to sacrifice my batteries by discharging them to a low point just to get the generator to run harder to recharge them. This got me to thinking that I could connect our hot water heater to our 2000 watt inverter while the generator is running. Any thoughts on this strategy? I know it is inefficient, but it would give us hot water everyday, run the generator harder and keep the batteries in good shape. Would there be too much power going through the system to damage something? Thanks for any thoughts.

Why not just run the water heater off the generator to produce a load?

[deckofficer]

Originally Posted by Waterwayguy

Why not just run the water heater off the generator to produce a load?

I think he said DC generator, probably dedicated to producing 275 amps at battery charging voltage.

[sailorchic34]

Originally Posted by Mark_S.

Would there be too much power going through the system to damage something? Thanks for any thoughts.

The typical marine water heater element is 1200 watts at 120V, last time I looked anyway. So provided not too much else was running on the inverter then it should be doable.

It would take about 1.25 hours to heat the typical 6 gallon water heater from cold to hot. Or about 5 gallons per hour of run time for a larger tank.

[sailinglegend]

Originally Posted by Mark_S.

We have a 4KW DC diesel generator that we run everyday to recharge an 800 ah battery bank. ...........could connect our hot water heater to our 2000 watt inverter while the generator is running......

We too have a 4KW DC diesel genny and a 2000 watt inverter, and a 1050 Ah battery bank. If you have the same FP DC genny as me that will give a max current of 280 amps then the 800 Ah batteries are enough load for the genny, especially if they are AGMs. You should only turn on the AC water heater as an extra load when the battery charging current is low enough so that the extra AC load of the water heater does not overload the genny. Try and keep its continuous load down to 200 amps to stop it getting too hot. It's infrequent running, or running for less than 1-2 hours that is its downfall.

We run our genny once every 7-10 days, never letting the batteries getting lower than 65%. If you need to run your genny every day (you don't say for how long?), then either you have a huge daily load, or your batteries are not getting anywhere near 100%, or your systems are telling you the batteries need charging when they don't. If you don't have enough solar then you should run the genny once every 3 weeks for as long as possible to get as close to 100% as possible. You must have an accurate way to measure when you have reached 100%.

[Mark_S.]

Originally Posted by Waterwayguy

Why not just run the water heater off the generator to produce a load?

The generator is DC and the water heater is AC. I think I need the inverter to get AC power to the water heater.

[mcarling]

Originally Posted by Mark_S.

The generator is DC and the water heater is AC. I think I need the inverter to get AC power to the water heater.

The water heater probably should work fine on AC or DC as long as the voltage is within parameters.

[AnchorageGuy]

Originally Posted by Mark_S.

The generator is DC and the water heater is AC. I think I need the inverter to get AC power to the water heater.

I guess I need to read more carefully. We do have a 2500 watt inverter and run the water heater from it occasionally but only the heater. It generally only takes about 15 minutes to heat the water enough for a shower. But it does pull down the batteries considerably. If you want a longer load time, then by all means leave it on longer. Chuck