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  #1  
Old 05-19-2013
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Inverter for hot water tank

OK - I am asking this because I do not know. This is not a stupid question - teach me something.

I have an Irwin Citation 34 with a 2QM20 raw water cooled Yanmar and attached is an engine warmed hot water tank. The tank is also wired to shore power 120 V AC.

What would be the problem of using an inverter to make 120V AC while motoring to heat the tank water up?

Not all the time - just before we want showers.

Thanks

Rik
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Old 05-19-2013
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Re: Inverter for hot water tank

Nothing, so long as you have a large battery bank and a large alternator and are able to provide the 140 amps charging current to maintain the battery SOC.

(Assumes 1500 watt element and an inverter draw of 1500/12 x 1.1)

Bill
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Old 05-19-2013
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Re: Inverter for hot water tank

If you already have an engine coolant loop you will find the water is heated better that way then running the engine to keep the batteries up to support an inverter to heat water.

If you are going to do an upgrade at all I would add a heat exchanger and shift to fresh water cooling of the engine. This will prolong the life of your engine block and head and also increase the temperature of the water in your water heater.
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Old 05-20-2013
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Re: Inverter for hot water tank

OK - maybe I was not clear enough - sorry.

1 - it is a raw water cooled Yanmar 2QM20 engine so the water does not get very hot
2 - I do not want to use this while at anchor to heat the water
3 - I was only curious about using it while under way by power (we do get days when we have to motor - not wind or wind in the wrong direction) I though if it was viable we could have hotter water when we got to the anchorage to have our showers.

I do not want to install a heat exchanger because of the cost.

Thanks

rik
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Old 05-20-2013
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Re: Inverter for hot water tank

As Bill stated above unless you have an alt that can support the load or 85-90% of it you will be running a big deficit on your bank even with the engine running.

Even if we figure you have the 60A Yanmar alt, likely not, and we also "assume" it could actually run at 60A, which it won't, you are still losing 90A.

Bill likes to use 1.1 as an efficiency factor for a heater element/inverter and with some inverters this is true but I fudge on the side of caution and use a 1.2 efficiency multiplier...

1500W / 12V = 125A X 1.2 Eff Loss = 150A load - 60A Alt = 90A draw even with the engine running.. (this is a best case scenario)

In all likelihood a 60A Hitachi will be putting out under 30A when driven hard due to its internal regulator temp compensating and reducing the voltage to cool itself....
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Old 05-20-2013
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Re: Inverter for hot water tank

Again, Maine Sail to the rescue. Numbers I can understand.

Thanks mate. It just seemed like a good idea at the time.

We go in the water Thursday. Masts go up on Saturday.

Rik
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Old 05-20-2013
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Re: Inverter for hot water tank

Another way to look at it:

A typical deep cycle battery can store about 1.800 kw-hr of energy or about 6100 BTUs. However, only 40% of this safely useable, so about 2440 BTUs.
Warming 10 gallons from 65-105F takes about 3300 BTUs.

Thus, each shower would flatten about 1 1/2 batteries. Different showers and different batteries change the calculation.

Batteries just don't store that much energy, not like liquid fuels (130,000 btus/gallon for diesel). Only a fraction of an ounce of fuel per charge cycle, the challenge of electric drive.
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Old 05-26-2013
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Re: Inverter for hot water tank

Another option would be to convert the water heater to 12 volt operation by changing the element. Here's an example 6 Inch 12 Volt DC Submersible Water Heater Element 6 Inch 12 Volt DC Submersible Water Heater Element [430] - $49.98 : Missouri Wind and Solar, DIY Wind and Solar Energy
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Old 05-28-2013
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Re: Inverter for hot water tank

Quote:
Originally Posted by tibtib View Post
Another option would be to convert the water heater to 12 volt operation by changing the element. Here's an example 6 Inch 12 Volt DC Submersible Water Heater Element 6 Inch 12 Volt DC Submersible Water Heater Element [430] - $49.98 : Missouri Wind and Solar, DIY Wind and Solar Energy
Unfortunately, this doesn't change the amount of energy that a battery can store and how much water it could heat. Those low wattage elements will only increase (signficantly) the time it takes to make hot water.
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Old 05-28-2013
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Re: Inverter for hot water tank

You could always use a lower wattage heater element.

Now that I'm use my extra solar power to get the freezer extra cold... (Goal is no battery usage for the freezer at night.) I'm thinking about running my extra solar to an inverter, driving a lower wattage 120v heater element. It's extra energy anyway, so efficiency matters less.

Regards,
Brad
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