Do cement resistors have specs resistance when cold?

[DreamV4]

Resistor says 2.2 Ohms, but I checked 1.5 Ohm. Is it normal for cold resistors? Maybe it is expected to have 2.2 ohm after it gets hot?

Well, it looks like I found an answer.
I bought 5 of them, checked one, it was 1.5. I installed 4 and just checked last one, it is 2.2 ohm!!! So one or more of them are defective.

 

[02GF74]

These resistors typically have 5-10% tolerance, so 1.5ohm is well outside the range. I would expect resistance to be specified at 20c (room temperature)

I looked up a data sheet of vishay brand, similar to the ones you have, and they have thermal coefficient of 300 ppm.. I calculate the resistance with a 100C rise to be 2.27 ohm.

 

[DreamV4]

thanks! I will check all 4 installed resistors and go from there.

 

[Screwloose]

Resistor says 2.2 Ohms, but I checked 1.5 Ohm. Is it normal for cold resistors? Maybe it is expected to have 2.2 ohm after it gets hot?

Well, it looks like I found an answer.
I bought 5 of them, checked one, it was 1.5. I installed 4 and just checked last one, it is 2.2 ohm!!! So one or more of them are defective.

I do not know if you have considered this, but you need to NUL out your test leads on the meter before measuring, as all test leads have a resistance in themselves. Especially if you are doing fine measurements.

Put meter on resistance, touch the leads, and any/if resistance is showing take that from your final reading when measuring.

 

[crynool]

Is 10W sufficient?
12V / 2Ohm is ~~72Watt?

Asking, because I have NO idea about it ...

 

[DreamV4]

Is 10W sufficient?
12V / 2Ohm is ~~72Watt?

Asking, because I have NO idea about it ...

you are my personal trainer, you know everything!!! OEM fuse is 10 Amps, it means current for each coils is not more than 2amps. Right now I have 7.5A fuse

 

[02GF74]

1.5 ohm is a fair way off 2.2 ohm. Ensure you are measuring the resistor as isolated as possible when measuring its resistance, by that I mean disconnect the lead the ignition module and if possible from the COP.

I'm sure you know, but don't hold the probe tips onto the resistors with your fingers.

 

[crynool]

you are my personal trainer, you know everything!!! OEM fuse is 10 Amps, it means current for each coils is not more than 2amps. Right now I have 7.5A fuse

I am? Well, I got promoted. Yeha

Btw, we have a Spinning Instructor who is an Ex-COP ... his lessons are REALLY challenging ...