My first YouTube video! Glow plug test TEST VIDEO

[argve]

that was pretty impressive it held together you had her burning for quite some time... the single coil ones I have tested were hitting at around 30 ohms or so when hot and 2 ohms and under when cold. You were flowing 7 amps at 12 volts so that means that it was around 1.73 ohms when fully heated. What was the amp draw when it was cold (first applied power)?

 

[Fishin76]

Dual coils don't work like that. At full-on heated up, it was reading >140 ohms. That how it keeps the heat down, and doesn't burn out. I could watch the ohms come down as it air cooled. Thats why the single coils burned out, they only provided 30 ohms resistance, and at twice the voltage. ( 6 volt plug was OEM). At that resistance, the voltage can overcome the resistance, passing more current, and over heat the plug.

I don't know what the amp draw from cold was, I think I'm going to get a amp meter and wire it in between the positive terminal and the glow plug to get a rough estimate of the draw. I could watch the chargers meter peg out, then start to come down about 6 seconds later.

The plugs output is 90W 12 volts X 7.5 amp (fully hot) = 90W

 

[argve]

but your readings for amperage don't work for Ohms Law... You said in the video that you were flowing 7 amps and at 12 volts that means 1.7 ohms...

Ohms law is R=E/I
Watts Law is P=I*E

Replace E with V because Energy is Voltage.

By the calculation Resistance is much lower than 140 ohms. Not saying that it didn't work - heck the video proves they are good plugs and in my opinion something someone should look at but the numbers just don't jive. Why I don't know because it's a purely resistive circuit so you don't have to worry about phase shift.

You mention that they were Wellman brand and I used them in the E (7.3) and I was always happy with them - I only had one plug that was a constant bother and it was on the number 2 cylinder - I always suspected that there was a problem there with timing or something but never really worried about it - that hole would kill a plug while the others kept them alive and we all know that advanced timing is ******* glow plugs.

if ya want to play with numbers go here...

http://www.the12volt.com/ohm/ohmslaw.asp#pie

or here

http://www.the12volt.com/ohm/page2.asp

but either way the plugs are keepers and if I had an IDI I would be looking at installing them in it. they heated up pretty quick - a little slower than I remember the ones I used for testing back about 8 years ago - but memory is foggy after that long so that that with a grain of salt....

 

[Fishin76]

Ohm's law really doesn't apply except when they are cold, I've found out. There are other formulas that apply here. These plugs are variable resistance, so there are more factors at play. such as voltage drop, length of the wires, amperage at given voltage.

Also, your giving up energy as heat. A purely resistive circuit does not necessarily give up heat.

There are more factors here than I have the knowledge to test.

I don't know how the charger measures the amperage either. it could very well be all screwwed up.