Max Voltage To Resistor

[egleaves]

Hey all, here's a question I haven't found the answer to anywhere else.

I'm wanting to use my old ballast resistor for a home-brew project completely unrelated to bikes. It has the resistance I want, but the circuit I'm thinking of putting it in is 24VAC.

How much voltage can these things handle before they fry?

Does it care if the current is AC or DC?

[clcorbin]

Generally, the voltage rating of a resistor is based on the break down voltage of the insulation (plus a safety factor). For a big resistor like a ballast resistor, I would be STUNNED if it had any issues at all on 24V.

Just make sure that you don't exceed it's power dissipation ratings. Unless you have resistance equal to the ballast resistance in series with it, you will pull more current through it than it is designed for and it will get hot. How hot depends on on how much extra current and how good the cooling is on that resistor.

[tw1980]

24 volts is fine and no it doesn't matter if it's ac or dc to a resister.But that doesn't mean it will work in the circuit you're planing on using it for.What do you want to use it for and how did you come to the conclusion that a 3 ohm resister is what you need?

Terry

[egleaves]

I'm trying to use the resistor as a stand-in for a broken hot surface ignitor until I can get a replacement part on Monday.

The ignitor is supposed to have 2-3ohms resistance normally, and up to 10ohms before it has to be replaced.

The resistor off of my XS has the right resistance, but I'm trying to learn of any other factors to consider. I'm beginning to think heat is going to be a problem, although the HSI is supposed to get hot I'm not confident that the resistor will stand up to the same kind of heat.

I appreciate the input from you guys, I think I'm just going to wait until I can get the replacement part.

[tw1980]

No it won't work a hot ignitor has to turn red hot to ignite the burner.By the time your resister gets that hot the place will be filled with smoke!Unless I'm misunderstanding your intentions.

Terry

[egleaves]

The intention isn't to use the resistor as an ignitor, but rather to fool the gas valve into thinking the ignitor is there. I would have to manually light the burner.

If the resistor gets that hot it would go up in smoke for sure!

[tw1980]

In that case 24 volts and 3ohms = 8amps.P=EI witch is 196 watts.So no don't try it.The ignitor may only measure 3 ohms when it's cold but when it starts to warm up the resistance increases.

Terry