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Old 01-05-2009, 01:02 PM   #1
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Simple electrical question (Amperage/voltage)


If have a hot water heater element that I'm going to be using in another application. The element draws 23 amps when wired at 240 volts and puts out 5500 watts. If I wire it at 115 volts I know that since I'm roughly halving the voltage that wattage will roughly quarter giving me 1375 watts, but how much amperage will I be drawing?

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Old 01-05-2009, 01:35 PM   #2
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Simple electrical question (Amperage/voltage)


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If have a hot water heater element that I'm going to be using in another application. The element draws 23 amps when wired at 240 volts and puts out 5500 watts. If I wire it at 115 volts I know that since I'm roughly halving the voltage that wattage will roughly quarter giving me 1375 watts, but how much amperage will I be drawing?
Half the amps. You are probably closer to 120 than 115. So about 11.5 A. Watts/volts

And for the love of God, don't blow yourself up with some crazy water heater based Mythbusters steam engine!

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Old 01-05-2009, 01:41 PM   #3
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Simple electrical question (Amperage/voltage)


I think those heaters are of the immersion type, and will blow out very quickly (and possibly violently) if they are not immersed in water.
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Old 01-05-2009, 01:45 PM   #4
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I submit that working with 1kw+ levels of power is probably not a project to start learning Ohm's law on. Just be careful with whatever you are doing.
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Old 01-05-2009, 01:48 PM   #5
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Simple electrical question (Amperage/voltage)


I think he is just going fishing......
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Old 01-05-2009, 02:48 PM   #6
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Simple electrical question (Amperage/voltage)


No worries-I'm just heating some vegetable oil so that it can be filtered and eventually used as fuel in my truck. The element will be immersed in the oil at all times as KE2KB is correct, they don't last long if not immersed in something. Nothing that dramatic happens-they simply burn out. The danger would be if they were immersed in oil and then taken out-this would cause the oil clinging to the element to overheat and catch fire. Anyway, I suspected that the amperage would halve-I just wanted to be sure. I'll be using two elements at the same time so I'll still have to plug them into receptacles on separate circuits because my house has 15 amp breakers.
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Old 01-05-2009, 03:29 PM   #7
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No worries-I'm just heating some vegetable oil so that it can be filtered and eventually used as fuel in my truck. The element will be immersed in the oil at all times as KE2KB is correct, they don't last long if not immersed in something. Nothing that dramatic happens-they simply burn out. The danger would be if they were immersed in oil and then taken out-this would cause the oil clinging to the element to overheat and catch fire. Anyway, I suspected that the amperage would halve-I just wanted to be sure. I'll be using two elements at the same time so I'll still have to plug them into receptacles on separate circuits because my house has 15 amp breakers.
Make sure your insurance is current and your beneficiaries are correct. This sounds like a Darwin Award in the making.
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Old 01-05-2009, 03:59 PM   #8
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Make sure your insurance is current and your beneficiaries are correct. This sounds like a Darwin Award in the making.
And your basis for this assumption is...? Heating vegetable oil in a 55 gallon drum outdoors with a class F extinguisher close at hand while wearing the proper protective gear could hardly be considered reckless. I've actually been running my F-350 on vegetable oil for quite a while, but filtering oil outdoors in New Jersey in 20 degree temperatures is not feasible anymore. In the past six months and nearly 20,000 miles I've only purchased about 150 gallons of diesel fuel. That works out to about 133 MPG

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Old 01-05-2009, 04:20 PM   #9
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Hey Badfish, are you just trying to keep it warm to stay viscous enough to flow through a filter? A quick calculation says 1000 watts can raise the temperature of 50 gallons of water 60 degrees over ambient, don't know about dirty oil or how long it would take.
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Old 01-05-2009, 04:30 PM   #10
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Hey Badfish, are you just trying to keep it warm to stay viscous enough to flow through a filter? A quick calculation says 1000 watts can raise the temperature of 50 gallons of water 60 degrees over ambient, don't know about dirty oil or how long it would take.
Thanks for the info-I know that oil will absorb heat slower than water, so we'll see. This method of oil heating is pretty well established by folks using vegetable oil to power their diesels, so I'm not that concerned about how well it works, I was more concerned about the load on my electrical system. In any event the oil will be held at about 120 degrees for a few hours as this will cause any water dissolved in it (very very bad for diesel injectors as you can imagine) to settle out to the bottom leaving dry, less viscous oil to pumped off for filtering.
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Old 01-05-2009, 04:39 PM   #11
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Another caveat I will add is that I see you will be bringing two separate circuits out to the heaters from outlets, just be aware there is a chance that you could have 240vac between the hot conductors if they come from different sides of the breaker box.
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Old 01-05-2009, 04:43 PM   #12
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Simple electrical question (Amperage/voltage)


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And your basis for this assumption is...? Heating vegetable oil in a 55 gallon drum outdoors with a class F extinguisher close at hand while wearing the proper protective gear could hardly be considered reckless. I've actually been running my F-350 on vegetable oil for quite a while, but filtering oil outdoors in New Jersey in 20 degree temperatures is not feasible anymore. In the past six months and nearly 20,000 miles I've only purchased about 150 gallons of diesel fuel. That works out to about 133 MPG
You sound very prepared. Just having a little fun. How long does it take to process a drum of oil? Did you have to modify anything on the truck? BTW, you may want to insulate the drum and make a lid for it with some 2" Styrofoam. You would probably lose a lot of heat through a bare drum.

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Old 01-05-2009, 05:04 PM   #13
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The current draw at 120 volts will likely be somewhat more than half that drawn at 240 volts; how much more is not easy to predict.

At all times the current drawn multiplied by the resistance of a portion of a circuit equals the voltage measured across that portion of the circuit. (definition of Ohm's Law)

If the resistance of the element remained constant, then the current draw at 120 volts would be half that drawn at 240 volts.

But the resistance varies with temperature. At 120 volts the element will run at a lower temperature and have a lower resistance. So the current will be greater than you first expected.
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Old 01-05-2009, 05:07 PM   #14
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You sound very prepared. Just having a little fun. How long does it take to process a drum of oil? Did you have to modify anything on the truck? BTW, you may want to insulate the drum and make a lid for it with some 2" Styrofoam. You would probably lose a lot of heat through a bare drum.
The truck was modified using a Dino Fuel Alternatives conversion kit ( www.dinofuelalternatives.com ) which set me back about $3000 between the tank, fuel lines, and fuel heating/filtering/pumping unit. In order to use straight vegetable oil in a diesel vehicle it must be hot or else the injectors cannot effectively atomize it. The heating is accomplished by teeing into the coolant lines and running them through the fuel heating module and a coil in the fuel tank. This raises the temperature of the oil to approximately 180 degrees before it hits the injectors. The truck starts on diesel fuel until the oil and engine are at operating temperature, then the computer automatically switches to vegetable oil. If at any time the vegetable oil system loses pressure due to a clogged filter, insufficient temperature, empty tank, or simply taking a sharp corner, the stock diesel pump automatically takes over making the transition seamless. When you arrive at your destination you simply take the key out and walk away. The computer will continue to run the truck for 90 seconds to purge any vegetable oil remaining in the system so that the truck is ready to start.

Of course, collecting and processing oil takes some time so it's not "free," but then I guess none of the "free" firewood I cut is really free either, but in either case it beats shelling out $150 a week for diesel fuel or $200-300 a month for heating oil. Plus I enjoy tinkering. In any event, I have tracked my fuel use and (Keep in mind that when I started this, diesel was 4.99 a gallon!) not counting the $3000 ROI I have saved about $2300 in fuel costs thus far. I am currently stockpiling oil for the summer as wifey and I plan to drive to Florida (from New Jersey) to stay with relatives and stop and see some folks in South Carolina on the way down. I anticipate using about 3 gallons of diesel for the entire trip.

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Another caveat I will add is that I see you will be bringing two separate circuits out to the heaters from outlets, just be aware there is a chance that you could have 240vac between the hot conductors if they come from different sides of the breaker box.
I'm not sure I understand. Are you saying that if I run the heaters at the same time that I could have an unsafe condition inside the panel itself? How can I be sure to avoid this?

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Old 01-05-2009, 11:45 PM   #15
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How do you pay the road tax on this?

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