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Author Topic: off grid today  (Read 4772 times)

mikern

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off grid today
« on: November 18, 2009, 05:08:12 PM »
We went off grid last wednesday, 1 week today, fieldmarshall 6/1 with st5kw. the only REAL problem is our water heater, it's new (6mo) and 240V. has anyone wired one of the to 120V successfully? any ideas would be appreciated. the FM is doing a great job, and its on filtered WVO. thanks in advance. MikeRN

compig

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Re: off grid today
« Reply #1 on: November 18, 2009, 05:55:57 PM »
Thing is , you will only get half the watts from it on 120V , so the water can't be heated as much. Whether it can be heated ENOUGH , is a different story.
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toydiesel01

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Re: off grid today
« Reply #2 on: November 18, 2009, 06:54:52 PM »
I don't know about the 120v, never tryed it before .  But if you have two hot water tanks take the heaters out of 1 of the tanks and connect a heat exchanger to where the heaters came from, now with the cooling of your engin connect into the heat exchanger and heat the heat exchanger with your engin. When the heat exchanger becomes hot it will automaticly circulate the water in the hot water tank.  Connect the in from the out on the hot water tank so 1 tank feeds the other one the second tank has the electric heaters.  This will help the electric tank becouse example before you are putting in 36 degree wate that needs to be heated to 120.  After heat exchanger change you would be putting in 90 degree water  and trying to heat to the 120.  You can see from example your 120 volt heater need to work a lot less.   

Tom

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Re: off grid today
« Reply #3 on: November 18, 2009, 09:16:47 PM »
We have a 240 volt water heater wired for 120. It is used to make use of our extra electricity from the PV panels during the summer. When wired this way you use 1/4 the wattage so a 4500 comes in at 1125. I have confirmed with my wattage calcs with a Watts up meter.
Tom
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ronmar

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Re: off grid today
« Reply #4 on: November 19, 2009, 01:45:53 AM »
Tom is exactly right.  A 240V 4500W(typical) heating element has about 12.8 ohms of resistance.  The math says that same 12.8 ohms will use about 9.3A at 120V and deliver about 1125W.  You will still get to full 120F or so tank temp, it will just take 4 times as long:)

You are off-grid and you are not harvesting engine coolant heat?  I can get 3/4 GPM of 120F(with about 70F inlet) water out of my heat exchanger at a 3KW electrical load on my generator.  2KW gives me about 1/2GPM and 1KW around 1/4GPM.  At 1/2GPM, it will take 100 minutes to replace all the water in a 50 gallon hot water tank with 120F water from the engine heatex...  Below is a diagram of just such a system(mine), and it can be done with about $250 or so worth of parts and some misc plumbing and hose components.  Depending on how you plumb in the radiator unit, you can either dump the excess heat, once the hot water tank is fully heated, into the home, or outside into the atmosphere if you don't need the heat inside.  You are going to all the effort to process the fuel for use in the engine.  you might as well get all the heat out of it that you can...  Here is a basic parts list.  The brazed flat plate heat exchangers will thermosiphon well, but it does require a little bit of vertical space to accomplish this.  Mine is about 30" above the engine to get adequate flow at all load ranges...

600SQ/IN brazed flat plate heatexchanger with 1" NPT ports(E-bay woodfired boiler vender)
18" X 18" pressure rated coil radiator(E-bay wood fired boiler vender)
Small Taco bronze circ pump(E-bay plumbing vendor)
120F Thermostat from a Mercurty Mariner 9-14HP outboard motor( marine parts wharehouse) 

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BruceM

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Re: off grid today
« Reply #5 on: November 19, 2009, 03:21:12 AM »
If you wire both your 220V elements in parallel, off of the main thermostat, that should hotten things up for 120V use.     Bradford White water heater thermostats are rated for two 4500 watt elements in parallel, don't know about the others.

There are also 120V replacement elements in a variety of wattages