My resistor is no longer resisting...

wad4ever

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Joined
May 14, 2013
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3
I have a Volvo Penta AQ120B. (I looked for a serial number and a year, but I couldn't find it... if anyone needs it, let me know and I'll look harder, but please give me a hint where to look.)

The alternator (might not be original, the boat is a 1980) has three electrical terminals. One of them goes to a purple wire, on its way to the coil (I think, I didn't carve open the wrapped portion of those wires), but it has a segment marked "resistor". I checked it with my multimeter, and it's not resisting anything at all. I'm pretty sure this piece is toast.

Problem: I've got the book for the engine, and it doesn't seem to mention this resistor anywhere. How many ohms? I need to replace it, but I can't figure out what with!

Any help is appreciated.

--- wad4ever
 

wad4ever

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Joined
May 14, 2013
Messages
3
Re: My resistor is no longer resisting...

I'd be happy to take a photo of it, if that helps. It's very old, a whitish ceramic-looking rectangular prism shape.

Also, I tried to figure out how to be alerted by email from this forum, but I don't see a way... my email is:
EDIT
Thanks!
 
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Mullin

Petty Officer 1st Class
Joined
May 12, 2011
Messages
256
Re: My resistor is no longer resisting...

Here's one, 1.4ohm rating Heavy-Duty External Ballast Resistor for Ignition Coils, Points and Electronic Ignition Systems

You can also replace the coil with one that is internally resisted. I got one at carquest for like ten bucks. Just grabbed any old chevy oil filled coil, first one off the shelf actually said "do not use with external resistor" right on the side of it. I measured all the specs with an ohm meter and its been running great since last year.

I'd also read up on the section "Measuring Coil Resistance". Compatible Ignition Coils, Ballast Resistors, Hot-Spark Electronic Ignition

What is the voltage at the battery and what is the voltage at the coil? I think the resistor is supposed to drop the voltage from 12v at the battery to no lower than 9v at the coil. IIRC.
 

gm280

Supreme Mariner
Joined
Jun 26, 2011
Messages
14,605
Re: My resistor is no longer resisting...

Maybe your OHMs meter IS reading the resistance but it is so low in value that it seems like it is shorted. Resistant values in the single number values sometimes are looked at like a short, especially if it is a percentage of a resistance (i.e. .1, .4, .6 ohm values). Most OHM meters are not setup to read mili-ohm values... So maybe there is nothing wrong with that resistive wire or package... Sometimes you can make those mili-ohm values show up a little better with using a know resister in series with the reading. You can then see the meter read just a little higher and maybe not know the exact value, but know there is some resistance there. Really depends on the actual meter. And when those resister values are that low, it is usually used as a current limiting part... JMHO! :D
 

wad4ever

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Joined
May 14, 2013
Messages
3
Re: My resistor is no longer resisting...

Thanks for the help, guys! I'll give it a shot!
 
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