Water Heater on Inverter

[TomC]

When we're boon docking, I typically run the generator in the morning to heat both water heaters, make coffee, and my wife to use the hair dryer. Then during the day, the water stays warm enough in the water heaters. Sometimes will run the generator at night also to build up the batteries for the evening. I do not have solar panels. Good Luck, TomC

[Jim Blackwood]

Yep, it's all about the wattage and whether or not you can harvest and store enough of them to cover all needs. Definitely interested in hearing how you make out. It seems that residential electric water heaters range from about 1200-4500 watts depending on the model and the voltage. So with your 1500w model at the lower end and a very health solar array you just might manage it. But obviously it's not a 1:1 relationship.

Jim

[richard5933]

I'm going to call the folks at Don Rowe today. That's where I bought the inverter. Unless they mention any potential problems, I'm going to rig it up for testing. I'll report my findings.

[chessie4905]

Seems a waste to put those loads on inverter and batteries to heat water??? Sure, it can be done, but why??? Turn on generator for half to an hour and go for a walk. You could also plumb the coil in the water heater to your generator.

[bevans6]

Presuming ( that's Assuming, but in a prior mode) that your heater is 120 VAC, your inverter is 120 VAC and 12VDC, your batteries are 790AH wet acid, in a 12 volt bank, and all else being equal...

You'll draw 1500W X 1.15 = 1,725 watts from the batteries for 20 minutes, or 1/3 hour, to heat your water.  1,725 @ 12.5 volts is 138 amps for 1/3 hour is 46 AH.   Your recovery rate from solar is 30 A/H, so you will recover in around 1.5 hours (not really, I think there is an efficiency thing I am missing, but you will recover if it's sunny out).  Maximum draw rate from the battery bank is going to be around 18% of the AH rating of the bank, so a somewhat aggressive load (in terms of a maximum load rate).  Average draw per cycle is around 6% of the capacity of the battery bank.  You could look up the load rate charts for your batteries to see where this load falls on their capacity, but those Trojans are a high spec battery.

In other words, maximum draw rate is very well accomodated by the battery bank (if fully charged), recovery from solar is well accomodated (if it's sunny), all loads and draw rates are well within range of the equipment noted, if all you do is run the water heater for 20 minutes a day.  If you look at a 5:1 ratio of run time VS recovery time, you can keep going indefinitely (as long as it's sunny), and realistically you can run the hot water heater several times a day in a single cycle mode (like for washing dishes in the evening, shower in the morning.

For me this is exactly why you have an inverter, a battery bank and some solar.  It's an application very well matched to a solution.  I'd do it.  I vote thumbs up!

Brian

[buswarrior]

Finally, some mathematics.

Thank you.

Happy coaching!
Buswarrior

[Jim Blackwood]

Yep, glad you ran the numbers on that.

Jim

[chessie4905]

Don't forget water pump, reefer, lights, vent fans, tv,etc.

[lostagain]

And a lot of days aren't sunny. Or sunny enough, like parked in the shade, or like up North anytime except May, June, July. Solar only isn't enough. I have solar panels on the roof of my bus and I like them. They are a nice complement to the whole system. But I could not get by without a generator.

JC

[richard5933]

And a lot of days aren't sunny. Or sunny enough, like parked in the shade, or like up North anytime except May, June, July. Solar only isn't enough. I have solar panels on the roof of my bus and I like them. They are a nice complement to the whole system. But I could not get by without a generator.

JC

I've got a generator, I just don't like using it. The way I look at it, if this works it gives me another option for making hot water. Solar can recharge, and so can driving to the next destination since we can charge at up to 70 amps while underway.

If need be, we have the generator.

[chessie4905]

How about a 50 foot piece of black garden hose with a mini circulator. Lay that out in the sun and it'll get really hot.

[Jim Blackwood]

You could also lay a loop or coil of tubing around your solar collectors. But that has the same issue of not being available at the hours when you might want to use it.

Jim

[richard5933]

Got it connected today. Wasn't too difficult since the transfer switch went into a kitchen cabinet which is directly above the water heater in the bay below.

When running in inverter, the inverter panel shows about 12.4 amps being pulled by the water heater. Victron battery monitor shows about 150 amps being pulled from the batteries.

The only problem might come from the temporary drop in voltage as things get evened out - battery monitor showed a drop to about 11.6 and then it crept back up towards 12 after a minute or so. The battery protect auto shutdown right now is set to shut things when voltage drops below a set point for more than 10 seconds. I'll have to keep an eye on that to see how things go.

My thought right now is that this will be a handy backup for making hot water if either we're on the road running the battery-to-battery charger (puts out up to 70 amps) or if we have solar actively running (up to about 30 amps output). Don't think I'd want to use this as our main method to heat water, at least until we get the additional solar installed that we plan to do at some point.

All that said, it cost nothing but 8 feet of wire and a switch that was sitting in my box taking up space. I'll give the new setup a trial run from cold tank to hot the next day we have the solar running to see how things go. I'm calling this project potentially successful.

[Geoff]

I dunno.  It wouldn't work for me.  I'm with Tom C on this one (and most of the time).

Geoff

[chessie4905]

If you have propane, you could use one of the tiny water heaters to assist heating the electric model. It doesn't  have much output, but could run a few hours to keep the temp up. They have an automatic shut off on some models. Home Depot, Lowes, and Camping World sell versions.