Electric Heating Element

[nuckythompson]

Hi there, I am looking at two heating elements, one is 12V, 300W and the other is 12V, 600W. The only physical difference is the size.

If I supply each heater with the same amount of current will I get the same amount of heat?

Ex. they are both 12V and if I supply 25A I should get 300W. Would the 600W element produce the same amount of heat and just have capacity for more? Will the 600W just heat slower?

Thank you!!

 

[LarryFine]

You supply each heater with a given voltage, and the resistance will affect the resultant current.

The 600w heater will have half the resistance of the 300w heater, and will flow twice the current.

 

[Tulsa Electrician]

If you supply 12 volts to each the amount of heat and current draw will be based on the difference wattage of the elements since there both rated at 12 volts.

 

[Sea Nile]

What is the maximum wattage rating of the heater? For example, light fixtures may have a maximum bulb allowance of 60 watt bulb because the fixture will get too hot with a 100w bulb. Ceiling fans usually have a thermal switch to cut power.

There may be a thermal switch in the heater and it may constantly cycle the power to the heater on and off if you put a higher wattage element in it.

 

[nuckythompson]

You supply each heater with a given voltage, and the resistance will affect the resultant current.

The 600w heater will have half the resistance of the 300w heater, and will flow twice the current.

Thank you. So the heat produced is based on current flow. If i supply the same amount of current and voltage to both elements, the 600W heater will output more heat because it has less resistance?

 

[Sahib]

Thank you. So the heat produced is based on current flow. If i supply the same amount of current and voltage to both elements, the 600W heater will output more heat because it has less resistance?

How can you apply same voltage and current to different resistances?
Use Ohm law.

 

[nuckythompson]

How can you apply same voltage and current to different resistances?
Use Ohm law.

Sorry meant just same voltage.

 

[JoeStillman]

Can you see where this is going?

 

[kwired]

Do a little research on Ohm's and Watt's laws

 

[nuckythompson]

Okay I get it. Thanks everyone.

 

[Sea Nile]

Simple answer is the 600w element will get hotter and draw more current. Just be mindful that the conductors may not be large enough to safely handle the increased current and the insulation may melt, the breaker may trip, the fuse may blow, and if any of these protective devices are disabled, you may cause a fire.

 

[nuckythompson]

Simple answer is the 600w element will get hotter and draw more current. Just be mindful that the conductors may not be large enough to safely handle the increased current and the insulation may melt, the breaker may trip, the fuse may blow, and if any of these protective devices are disabled, you may cause a fire.

Yes, thank you. And if I use more than one heater it gets a little more complicated.. Please correct me if I am wrong but if I wire two in parallel I get a lower resistance but the higher current may be too much for the circuit, and if I wire them in series then I may not get enough current flow..

 

[wwhitney]

Simple answer is the 600w element will get hotter and draw more current.

For the question in the OP, the 600W element will generate half the heat of the 300W element (half the rate).

The ratings are based on a fixed voltage supply, so the higher wattage rating has a lower resistance due to P = V²/R. If you instead apply a fixed current supply, where the voltage drop over each element will be different, now power is proportional to R from P = I² * R. So the higher wattage, lower resistance element will generate less heat.

Cheers, Wayne

 

[Tulsa Electrician]

Try to use ohms law and then if have an issue just ask and post your math. We all will glad to help walk you through it.

 

[Sea Nile]

the question in the OP, the 600W element will generate half the heat of the 300W element (half the rate).

Ahh I see, I misunderstood what the OP was asking.

When he said "the only physical difference is the size", made me think that he was talking about the physical size.

For some reason I assumed he was at a hardware store looking at elements to replace a bad heater element and comparing two different ones on the shelf.

 

[Jraef]

Yes, thank you. And if I use more than one heater it gets a little more complicated.. Please correct me if I am wrong but if I wire two in parallel I get a lower resistance but the higher current may be too much for the circuit, and if I wire them in series then I may not get enough current flow..

No. If you wire them in parallel, you get 900W of heat produced, because each heater will draw their respective current from the source (assuming the source has the capacity).

In series, you are INCREASING the resistance. Resistances in series add together. So if one is 10 ohms and the other is 20 ohms, in series the total circuit becomes 30 ohms and that changes the power (watts) through the circuit to be LESS. But you should not connect heating elements in series if they are not the same rating anyway, because they will split the voltage unevenly and the smaller one will get such low voltage that it might not even get hot.

You also need to divorce yourself from the concept of “giving” current to anything. You can “give” voltage to a device, but it “takes” the current it needs (assuming the source can deliver it). If the source can’t deliver it, something usually goes wrong.

 

[LarryFine]

So the heat produced is based on current flow.

Heat, which is power, is the product (mathematically and physically) of current and voltage. A higher voltage across a larger resistance can cause the same current, yet produce more heat (power).

For a given voltage, which is what we mean when we correct you for saying for a given current, the current is inversely proportionate to the resistance. We normally control the voltage.

Your 600w heater, if designed for the same voltage, will have an element with half the resistance of the 300w heater. So, twice the current at the same voltage will produce twice the power.

If i supply the same amount of current and voltage to both elements, the 600W heater will output more heat because it has less resistance?

As we've been saying (I know you get it now), how would you directly control the current? You can vary the voltage, which will vary the current, which will in turn vary the power.

If i supply the same amount of current and voltage to both elements, the 600W heater will output more heat because it has less resistance?

Yes, this exactly.

Remember the difference between varying the voltage supplied to a given piece of equipment (same resistance) and designing a piece of equipment (different resistance) to produce the same output on a different voltage.

 

[nuckythompson]

No. If you wire them in parallel, you get 900W of heat produced, because each heater will draw their respective current from the source (assuming the source has the capacity).

In series, you are INCREASING the resistance. Resistances in series add together. So if one is 10 ohms and the other is 20 ohms, in series the total circuit becomes 30 ohms and that changes the power (watts) through the circuit to be LESS. But you should not connect heating elements in series if they are not the same rating anyway, because they will split the voltage unevenly and the smaller one will get such low voltage that it might not even get hot.

You also need to divorce yourself from the concept of “giving” current to anything. You can “give” voltage to a device, but it “takes” the current it needs (assuming the source can deliver it). If the source can’t deliver it, something usually goes wrong.

OK, thank you. I think I get it.

Ex.
V = 12V
R = V^2/P, R = 0.48Ω for a single 300W heater.

If you wire 2 x 300W elements in parallel:
Rtotal = 0.24Ω
I = 12V/0.24Ω = 50A
P = I^2*R = 600W

If you wired 2 x 300W elements in series:

Rtotal = 0.96Ω
I = 12V/0.96Ω = 12.5A
P = I^2*R = 150W

And thank you for the note about voltage split and device taking the current it needs.

Please let me know if I have something incorrect. I know my questions were confusing because I did not understand, but I much appreciate all of the help.

 

[LarryFine]

Simple answer is the 600w element will get hotter and draw more current. Just be mindful that the conductors may not be large enough to safely handle the increased current and the insulation may melt, the breaker may trip, the fuse may blow, and if any of these protective devices are disabled, you may cause a fire.

Of course, all of this is taken into account when designing a supply for a given known load.

 

[LarryFine]

Yes, thank you. And if I use more than one heater it gets a little more complicated.. Please correct me if I am wrong but if I wire two in parallel I get a lower resistance but the higher current may be too much for the circuit, and if I wire them in series then I may not get enough current flow..

Wiring different loads in parallel is how almost every electrical system and circuit are wired. Your home, your car, everything. intentionally wiring two loads in series is very rare in comparison.

In parallel, each load passes the current the resistance requires (allows to pass, actually) to operate, and it's up to us to make sure as much of that voltage drops across the load as possible.

Dissimilar loads in series causes dissimilar voltages across each load, inversely proportionate to each load's resistance. The larger heater will cause the small one to see the most voltage.