Run water heater from inverter?

[leftbrainstuff]

Your water heater is one high duty cycle, high current load. I think you might drain the house bank. We have 675 Ahrs house bank and 280W solar which is probably a little small to heat hot water without punishing the batteries.

We heat our hot water from either shore power, generator coolant, engine coolant or with our espar water heater via an air to water heat exchanger.

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[leftbrainstuff]

Originally Posted by W3GAC

Yes. I just have a standard 5 gal Ratian w/o any extra insulation. We practice the Navy shower technique of low water sink & shower use. The engine has a 180 degree thermostat so the hot water is frightfully hot compared to home settings and only takes a crack of the hot valve to get normal temp shower/ KP water. And actually wrapping the hot water tank would likely extend the shelflife of the hot water perhaps to 3 and maybe even still usable to a 4th day if not diluted much by usage. Good idea I'll try it myself.

For washing dishes I put a little Dawn in about half cup of very hot water and use one of those brushes designed for dish washing (9" handle. Dawn seems to do a much better job cutting grease than the other dishwashing products we tried, even with cold water. Once all the stuff has been brushed off and temporarily stacked (still soapy) I use just a trickle of water to rinse the items one by one. You can clean up after a meal for four with 1/2 to 3/4 gal of water and practically no hot water. In the Caribbean we did that final cold water rinse over a pot to capture that soapy water to use again on mask/ snorkel... what ever else only needed cooler soapy water to work.


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Our water heater keeps water hot for a day or so.

Originally Posted by rwidman

My water is still hot the next morning after sitting 15 hours or more. I don't remember the brand of heater but it's whatever came on the boat, nothing special.

Like W3GAC's heater my water comes out the same temperature as the engine coolant so that can be 175 degrees or so. There should be a tempering valve but there isn't. We just know hot it is and use it accordingly.

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[senormechanico]

Originally Posted by cwyckham

Wow. You can keep your hot water hot (or warm) for more than a few hours? I think I need to find a way to insulate my tank better!

Oddly, that never occurred to me.

We use our 1500 watt inverter to heat water.
Besides rebuilding our fridge/freezer, we also reinsulated our water tank with this:


Aspen Aerogel Spaceloft Insulation Hydrophobic Mat per Linear Foot 5mm | eBay

Solar keeps everything on the boat running, watermaker, HAM, wifi computer ElectroScan, radar autopilot etc.

One 200 aH Lithium Phosphate battery bank for the whole boat including engine start.

It's all about BALANCE !

[Amnesia II]

Exactly, it's all about balance!

I'm encouraged and learning from all your posts that I can indeed heat the water by using the inverter.

So, if the 2000w inverter runs the 1500w heater element for 1/2 hour it's drawing 50amp/hr from the 850amp/hr battery bank, not such a huge drawdown.

The solar panels are very capable of producing 25amps per hour for 2 hours or more on a good day so I think that should cover it!
Currently the batteries are at full voltage by lunchtime so plenty of time to make up the extra 50amp/hr!

While sitting at anchor for a few days, I'd like to have hot water without having to start the motor or run the Honda generator.

I just need to get the 120v wiring changed and checked.


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[Rustic Charm]

Originally Posted by Amnesia II

The solar panels are very capable of producing 25amps per hour for 2 hours or more on a good day so I think that should cover it!

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Seriously? What size solar panels do you have that will give you 25amps an hour? I want some.

[AnchorageGuy]

Keep in mind that you only have 425 usable AH in that bank to keep from drawing down more than 50%. 50 AH will be about 12% of available AH. You will be using other power at the same time. But it is doable if you manage your usage. Chuck

[Amnesia II]

I have 3 x 200w panels over the Bimini, too heavy I know but I've had no issues in encountering persistent 40 knot gales!


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[Amnesia II]

Originally Posted by AnchorageGuy

Keep in mind that you only have 425 usable AH in that bank to keep from drawing down more than 50%. 50 AH will be about 12% of available AH. You will be using other power at the same time. But it is doable if you manage your usage. Chuck

I guess my intention is to be heating water during daytime sunshine when possible and when required the motor can be run to have the 180 amp alternator feed the battery bank( on just above idling puts out 75amps approx).


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[jeepbluetj]

Yaknow, somewhere I read about 12v heater elements. IIRC they're pretty small, like 400w or something. But that'd be a fantastic diversion load for folks with lots of solar. Once the batts are full, pump the solar into the WH.

[Rustic Charm]

Originally Posted by Amnesia II

I have 3 x 200w panels over the Bimini, too heavy I know but I've had no issues in encountering persistent 40 knot gales!


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I think your anticipated 25 A an hour is a bit optimistic then. In optimal circumstances I think you will get around 18A, but that's running at best.

BUT, me no electrical guru. All I really know is the stuff bites when you touch the end of a wire connected to the battery to your tongue.

[Amnesia II]

Originally Posted by Rustic Charm

I think your anticipated 25 A an hour is a bit optimistic then. In optimal circumstances I think you will get around 18A, but that's running at best.

BUT, me no electrical guru. All I really know is the stuff bites when you touch the end of a wire connected to the battery to your tongue.

Not so, 600w @ 12volts in theory = 50amps

I regularly see 36amps going to the batteries on a good overhead sunny day!


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[sailorboy1]

Originally Posted by Rustic Charm

I think your anticipated 25 A an hour is a bit optimistic then. In optimal circumstances I think you will get around 18A, but that's running at best.

BUT, me no electrical guru. All I really know is the stuff bites when you touch the end of a wire connected to the battery to your tongue.

I bet he can get close to 50 amps during good conditions and under load running an inverter to supply the water heater.

[twinboat]

Here is the math, 3 X 200 watt panels = 600 watt / 13.5 charging voltage = 44 amps.

About 5.5 hours a day = 242 ah per day.

Nice system, I have about the same and get the same kind of output.

It`s just math

[belizesailor]

Originally Posted by cwyckham

Wow. You can keep your hot water hot (or warm) for more than a few hours? I think I need to find a way to insulate my tank better!

Oddly, that never occurred to me.

Ive got a well insulated Isoterm tank that will keep water warm for hours. Have never collected data on its thermal performance, but have gotten warm water out of it after surprisignly long times.

Also has mixing valve at the outlet to blend hot/cold water. Dont need engine heated temps here in the tropics so blending down to "warm" is good and extends warm water supply.

[Amnesia II]

Originally Posted by twinboat

Here is the math, 3 X 200 watt panels = 600 watt / 13.5 charging voltage = 44 amps.

About 5.5 hours a day = 242 ah per day.

Nice system, I have about the same and get the same kind of output.

It`s just math

Quite right, I love the idea of the boat being totally self sufficient and not have to worry about how any lights are on or wondering if there's enough battery power to run the fridge, microwave and all the gizmos & gadgets.

So....just have to sort out the water heating, or the wiring configure.

Love those long lazy days on the anchor!


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