Help with making a heating element with a 3 phase power supply

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  • Thread starter k0kster
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  • #1

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hi everyone.

my uncle currently has a big "cylindrical rolling cooking pot" (imagine a cement mixer with burners at the bottom) that he uses to cook his stuff, ie sesame seeds.

this cooking pot currently runs on gas.

as he has been facing some issues with the gas supplier, he intends to replace the gas with a heating element.

can anyone tell me whether it is economically feasible to make the switch?

from my understanding, the amount of power consumed by the heating element is affected by many variables.

he wants the heating element to be a meter in length and generate about 300 degree Celsius to cook the sesame seeds.​
we are situated in Singapore, where the weather is a steady 30 degrees Celsius daily.​
i am unsure of the gas usage of our current setup, but i can check.

thanks in advance


Answers and Replies

  • #2
Science Advisor
There are many others here that can help with the details, but here are a couple of comments to get things started.

1) Electricity usually costs more than gas. That's because the electric company buys the fuel, burns it to turn water to steam, uses the steam to generate electricity, then has to string wires to get the electricity to you. If it's hydroelectric power, someone still had to pay for the dam and the generators.

2) The amount of heat you will need depends largely on the surface area of the container, whether it is indoors, outdoors, insulated, and if there is any ventilation that allows the internal heated air to escape.

Once those pieces of information are known and addressed, the minimum energy requirements and costs can be evaluated. Once the minimum energy is found, any excess energy capacity can be used to more rapidly raise the temperature from a cold start.

A photo and dimensions would be a great help in answering number 2) above.

For addressing number 1), the current gas usage and price, and electricity price are needed.

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  • #3
thanks for your reply Tom.

1) What you said makes sense. Unlikely for electricity to cost less than gas itself. But, knowing my uncle, he would want to know the difference in cost and see if the problems justify the additional costs.

2) I am unable to provide a picture right now. Will get one up asap.

I got an update from my uncle. He has found a contractor to put together the heating element. He tasked me with calculating the amount of power required to run the pot.

I found some guides online to how to calculate the power consumption.

kWh = watts x hours x days
Watts = 0.05 x Lbs of Steel x ΔT (in °F) / Heat-Up Time (in hrs)

From what I understand from the website, if i have the weight of steel, ΔT and plug in a heat-up time(eg 15mins), I am able to calculate how many watts the heating element will consume?

Also, can i use the same formulas for a 3 phase power supply?
  • #4
kWh = watts x hours x days
This formula isn't right. kWh = kilowatts x hours.

For example, a 100W light bulb operated for one hour would use 0.100 kW of energy (0.1 kWh, or 100 watt-hours). If it were operated for 3 hours it would use 0.3 kWh (300 watt-hours), and so on.

1 kWh is equal to 3.6 megajoule, and approximately 3412 BTU.

In what units is the gas supply metered (cubic meters? cubic feet?).
What you might do is determine how much gas is used per hour by the cooker, convert it to kWh, then compare the cost of a kWh of natural gas to a kWh of electricity.

You'll need to determine the energy content of your natural gas supply, which depends on the constituent gases (methane, ethane, propane, butane, etc). An approximate number that I've seen used is 1030 BTU per cubic foot, or 0.30 kWh per cubic foot.

A resource to help frame an answer is this paper by the Oklahoma State University.

For three phase power, P=sqrt(3)*volts*amperes*cosΦ.
In resistive heater loads, power factor (cosΦ) is very nearly unity (1.0), and the formula simplifies to
P=1.732 * volts * amperes.
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  • #5
Science Advisor
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If it's any help.. here in the UK electricity is about three times the price of mains gas on a like for like basis (eg for 1 kWh of each). It will vary in other countries and you would need to consult your energy providers.

One problem I see is that the temperature depends on two things 1) How fast energy is put into the machine, which depends on the power of the heating element and 2) the rate at which heat is lost from the machine, which depends on a bunch of other factors that are likely to be unknown.

Best bet might be to find out how much gas the machine consumes then estimate the input power from that. This would give you a rough idea for sizing an electric heating element. You could then build and test it - but be prepared to have to resize the elements depending on the results. This is essentially what Asymptotic is proposing.
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