Run water heater from inverter?

[Amnesia II]

I have a Prosine 2000 inverter putting out 120v. The water heater is 120v but is only set up to run from shore power. The common bus bar is shortened so as not to include the water heater and battery charger.

Surely, it's within the capacity of the Prosine to run the water heater?

I have an 850 ah battery bank and 600w solar.



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[Rustic Charm]

Originally Posted by Amnesia II

I have a Prosine 2000 inverter putting out 120v. The water heater is 120v but is only set up to run from shore power. The common bus bar is shortened so as not to include the water heater and battery charger.

Surely, it's within the capacity of the Prosine to run the water heater?

I have an 850 ah battery bank and 600w solar.

Sent from my iPad using Cruisers Sailing Forum

Gee, I would think you will drain your bank quick smart doing that.

[FlyingCloud1937]

Shirley,

it's with-in the inverter capacity.

butt,

is it with in the battery capacity?

YEP.

but is it with-in the charge capacity?

DOUBT it!

Lloyd

Originally Posted by Amnesia II

I have a Prosine 2000 inverter putting out 120v. The water heater is 120v but is only set up to run from shore power. The common bus bar is shortened so as not to include the water heater and battery charger.

Surely, it's within the capacity of the Prosine to run the water heater?

I have an 850 ah battery bank and 600w solar.



Sent from my iPad using Cruisers Sailing Forum

[nhschneider]

We have a 20-liter water heater with an 850-watt, 120-volt element and we run it off our inverter all the time. We don't leave the inverter on any longer than it takes to heat a tankful of water - about 20 minutes - and we curse ourselves if we forget and leave it on longer. That might draw about 25 amps out of a 12-volt battery bank but that doesn't seem too unreasonable to us.

Fair winds and calm seas.

[Dockhead]

We have a 1500 watt immersion heater and (nominally) 3000 watt inverter. My school bus type alternator puts out about 2000 watts at cruising speed (while motoring, obviously).

I have used my inverter to power the immersion heater when the engine coolant loop was not working (air lock). Immersion heaters are pure resistant loads and no problem as long as they are within the capacity of the inverter and the alternator powering it.

I don't think it's a very good idea, however, to do this on a regular basis, especially if you have a car-type alternator, which is not made to power big loads on a continuous basis. It's much more efficient to heat the calorifier using waste heat from the engine.

I wouldn't run the immersion heater from batteries. Our fairly large battery bank contains about 3 to 4 kW/h of usable power. Heating up a tank of hot water requires at least 1 kW/h of power and would need more than the 1/3 to 1/4 of the bank's capacity implied by this, because of Peukert's factor. Why would you spend so much (if not all) of your battery power doing this? You would just need to charge again anyway. Maybe only if you want a shower just before you start motoring somewhere, but even in this situation, you are putting wear and tear on the batteries by cycling them hard like that. I just wouldn't do that. Maybe if you have just really abundant solar power.

[Amnesia II]

Thankyou all. I should mention I also have a 180amp alt, so it may well be reasonable to run the motor for 1/2 hr with the alt supporting the batteries and inverter.


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[rwidman]

Originally Posted by Amnesia II

I have a Prosine 2000 inverter putting out 120v. The water heater is 120v but is only set up to run from shore power. The common bus bar is shortened so as not to include the water heater and battery charger.

Surely, it's within the capacity of the Prosine to run the water heater?

I have an 850 ah battery bank and 600w solar.



Sent from my iPad using Cruisers Sailing Forum

Yep the battery bank and inverter could run the water heater for a few minutes. Possibly not long enough to get the water hot though.

If you are thinking of running the engine to produce electricity to charge the batteries to power the inverter to make 120 volts AC to run the water heater, why not just connect the water heater to the engine to use waste heat to heat the water? If the water heater doesn't have a built in heat exchanger (most marine water heaters do), consider replacing the water heater with one that can does.

[Tingum]

Does not sound like a good idea to me. Why not buy one of the solar adapters that screw into the drain location and plumb that into your engine cooling line?

[W3GAC]

In big round numbers... any load drawing around 1000w at 120v will draw 100 AMPS from your 12v battery bank on inverter power. Any 1500w load at 120v will draw about 125 AMPS from 12v while being powered from inverter, regardless of brand. That's just how ohms law works.

So if your water heat takes half an hour to come up to temp... your have pulled half those figures in 'watt-hours' from your battery. So if you had a fully charged single 100 A-hr battery you would be down to its recommended 'not to exceed' 50% capacity limit. If you had engine running and alternator putting in 30a or solar putting in 30A... just subtract the 30a from the load of 100a (or 125a) and redo the watt-hour math to figure watt- hour load on the battery.

You have to do what you have to do, but batteries only have so many discharge/ charge cycles. Using them up to heat water is the ultimate tough duty on them and their life expectancy. But again... you got to do what you got to do! If you ever change out the water heater, strongly suggest you replace with one that also supports heating via engine's wasted heat cooling system. Then while you are charging batteries/ moving to next anchorage you are automatically generating two days worth of normal hot water use. That's how most of us do it.


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[cwyckham]

Originally Posted by W3GAC

... strongly suggest you replace with one that also supports heating via engine's wasted heat cooling system. Then while you are charging batteries/ moving to next anchorage you are automatically generating two days worth of normal hot water use. That's how most of us do it.


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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.

[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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[rwidman]

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.

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.

[Lepke]

I have a power boat with room. It has a 50 gallon hot water heater and incinolet toilets. The inverter easily runs the heater (3500 watts) and toilets. I optionally can heat water with a diesel stove coil or the generators. The heater has additional added insulation so the hot water will last several days if not used. I have a galley switch so I can turn the heater on in anticipation of need. The inverter setup provides 2 legs of 120v or 240v ac from a 48v dc bank. Prior inverter was 12v based. Having 24v or 48v also means smaller cables, etc. Everything runs thru the inverter. On shore power the ac passes thru the inverter and charges the dc banks.
My batteries allow the use of ac for refrigerator, freezer, tv, lights and computer, for several days if not heating water. Also, when steaming I use the inverter for ac needs while a alternator keeps the batteries up. So I save running a generator.
I have been on the ocean a long time and know plumbing, electricity and so on. My boat is 73 years old, professionally converted from a USCG cutter to a Monk design. This is not a super yacht and I am not rich or even well off and rarely meet a boater with less money to spend. An inverter like mine is about $2500 and some changes to battery bank cables.
Also, at dockside, shutting off a house sized hot water when not being used saves about $30/month on 0.068/kwh power.

[44'cruisingcat]

Originally Posted by Amnesia II

I have a Prosine 2000 inverter putting out 120v. The water heater is 120v but is only set up to run from shore power. The common bus bar is shortened so as not to include the water heater and battery charger.

Surely, it's within the capacity of the Prosine to run the water heater?

I have an 850 ah battery bank and 600w solar.



Sent from my iPad using Cruisers Sailing Forum

Depends on the Wattage of the water heating element. Ours is 850 Watts and can be run off the 1500 Watt inverter.

It does take a lot out of the batteries though, I've only ever done it a few times, usually when motoring on a sunny day, and we have more power than we know what to do with.

[AnchorageGuy]

We've been cruising for 25 years and we have to have hot showers every day. Our 2500 watt inverter easily runs our hot water heater. It only takes about 15 minutes to get the water hot enough for a comfortable shower for both of us and enough for dishes. The key is to run no longer than necessary. So we don't forget, we use a kitchen timer when we turn on the water heater. Consider changing out the water heater to one that will heat off the engine coolant. We have always had this type and it saves time running off the inverter. Your battery bank is plenty sufficient. I'm sure you probably have a battery monitor to watch your power usage. Taking showers during the day when you have assist from the solar panels will also help. I see no problem at all with your set up. Chuck