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# Amperage/draw of hot water heater elements

#1
02-13-09, 06:49 AM
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Location: Trevor, WI
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Amperage/draw of hot water heater elements

I am building a biodiesel processor, which is very similar to a hot water heater. I plan to use (2) 240V/4500W heating elements wired to 110V to heat the oil. Can anyone provide the amperage/draw of these elements so that I can figure out what circuit to plug them into.

I also have a 1/2hp Northern Tool water pump that needs to run at the same time. I think that it's 2-6amp draw depending on the load. I have to determine if these can be plugged into the same circuit/outlet or they must be on different circuits.

Thanks for any direction/information/help.

Steve H.

#2
02-13-09, 07:32 AM
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I=V/R and I=W/V so amps (I) is 4500/240=18.7 amps therefore 18.75=240/X=12.8 ohms so at 120v I=120vX12.8=9.37amps or half the voltage half the amps half the heat.

Last edited by ray2047; 02-13-09 at 09:21 AM.
#3
02-13-09, 09:21 AM
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Originally Posted by srponies
I am building a biodiesel processor, which is very similar to a hot water heater.
...except that you're heating flammable material. What kind of "facility" is this set-up in?

I plan to use (2) 240V/4500W heating elements wired to 110V to heat the oil. Can anyone provide the amperage/draw of these elements so that I can figure out what circuit to plug them into.
When you use 240V heating elements on 120V, the power output is one-quarter. That means the 4500W heating element produces 1125W of heat when powered by 120V.

Watts = Amps * Volts
1125W = Amps * 120V
Amps = 1125W / 120V = 9.3A

I have to determine if these can be plugged into the same circuit/outlet or they must be on different circuits.
They definitely should be on separate circuits, but that is just the tip of the iceberg in terms of safety considerations.

#4
02-13-09, 11:41 AM
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Originally Posted by ibpooks
...

Watts = Amps * Volts
1125W = Amps * 120V
Amps = 1125W / 120V = 9.3A

They definitely should be on separate circuits, but that is just the tip of the iceberg in terms of safety considerations.
Thanks for the information and formulas.

So that would be 9.3A per heating element, 18.6A for the 2. That would be pushing it for a 20A garage 120V circuit. Or would I be better off just wiring the elements for 240V and plug them into the circuit for my air compressor? And I am running this thru a thermostat set at about 130deg. I also am planning to wire the elements so they cannot be turned on unless covered with fluid and the pump on circulating fluid.

All this done in a sealed container with "proper" ventilation.

Thanks again.
Steve H.

#5
02-13-09, 12:09 PM
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Originally Posted by srponies
So that would be 9.3A per heating element, 18.6A for the 2. That would be pushing it for a 20A garage 120V circuit.
Based on the electrical code, anything that is expected to run more than 3 hours must be sized as a continuous load. This means you would need to design the circuit for 125% of the load if you expect to exceed that time. That would require you to increase to a 25A or 30A circuit wired with #10 copper wire.

Or would I be better off just wiring the elements for 240V and plug them into the circuit for my air compressor?
Depends on the breaker and wire size for the air compressor circuit.

And I am running this thru a thermostat set at about 130deg.
Make sure the thermostat contacts are rated high enough to handle the amps of the elements. Many thermostats have an upper limit of either 12A or 16A so watch out for that.

I also am planning to wire the elements so they cannot be turned on unless covered with fluid and the pump on circulating fluid.
Are you using a float switch or something similar?

All this done in a sealed container with "proper" ventilation.
I do mention that as a serious concern because thermostats produce a spark with every cycle. Likewise a failure in the heating element or a short from the element to the tank could spark or overheat to the flashpoint of the fuel.

Usually when a flammable liquid must be heated in a commercial setting we would wire an external or indirect heater strapped to the outside of the barrel rather than a submerged element so that any sparks from a failed element are not exposed directly to the fluid.

#6
02-13-09, 12:56 PM
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Join Date: Nov 2002
Location: Trevor, WI
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Originally Posted by ibpooks
Based on the electrical code, anything that is expected to run more than 3 hours must be sized as a continuous load. This means you would need to design the circuit for 125% of the load if you expect to exceed that time. That would require you to increase to a 25A or 30A circuit wired with #10 copper wire..
The heating element has to be on long enough to heat the oil to 130 deg. I'm not sure that it would take that long. Probably depends on the heating element(s) I'm using and how they're wired.

Originally Posted by ibpooks
Depends on the breaker and wire size for the air compressor circuit..
My compressor circuit is (2) 30A breakers and 10-3 wiring.

Originally Posted by ibpooks
Make sure the thermostat contacts are rated high enough to handle the amps of the elements. Many thermostats have an upper limit of either 12A or 16A so watch out for that.
The thermostat is a "standard" lower water heater part. It doesn't list the ratings. I'm sure I can get the specs if I search the internet or contact the manuf.

Originally Posted by ibpooks
Are you using a float switch or something similar?.
No float switch. The level is going to be subject to human input - mine. I have a fluid level indicator that will show me when there's enough fluid. I wanted to wire the element(s) so that the pump (switch and timer) had to be on before the element can be turned on. Was hoping a double pole switch could be used here.

Originally Posted by ibpooks
I do mention that as a serious concern because thermostats produce a spark with every cycle. Likewise a failure in the heating element or a short from the element to the tank could spark or overheat to the flashpoint of the fuel.
I have pressure tested the barrel for any leaks. All venting and pressure relief is done to an outside location quite a distance from the processor. There shouldn't be fumes in the air to deal with. I might try a different (upper water heater) thermostat with a breaker in it.

Originally Posted by ibpooks
Usually when a flammable liquid must be heated in a commercial setting we would wire an external or indirect heater strapped to the outside of the barrel rather than a submerged element so that any sparks from a failed element are not exposed directly to the fluid.
I think that the barrel heater might work fine. I believe that it would take longer to heat the fluid. I realize that you can't put a price on safety - but a drum heater is about \$200. The elements are \$12. The heating elements are only used when heating the vegetable oil - not methanol.

Afterthought on the elements - I should just wire (1) as 120V and test how long it takes to heat the oil. If it's adequate, then I'm good. If not I can wire (1) for 240V, and so on. I think that I just added the second element because I thought it would be easier to do when building the processor. A bit harder to add it later when everything is assembled.

Thanks for the info/ideas.
Steve H.

Last edited by srponies; 02-13-09 at 01:55 PM.

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