Coils 101 (Or Coils For Dummies)

[Anonymous]

OK, I need a bit of a primer on coils. I understand HOW they operate (the primary winding inducing a field in the secondary and so on), but I am short on experience of the nuts and bolts of them. I have measured the primary side resistances on my existing coils (they are not OEM, however, as they do not fit the mounting tabs properly... :? ). They come out to 4.7 and 4.9 Ohms. Within spec as the manual says 3.0-5.0 is acceptable. I have a set of GSXR coils I bought as replacements and they measure 3.0 Ohms on the primary side.

1) Does the lower resistance on the GSXR coils mean they will charge faster/higher voltage and produce a stronger/hotter spark than my old coils? Do coils start with low resistance when new and slowly go up with age?

2) I have tried to measure the secondary resistance (plug cap to plug cap) and get no continuity there at all. I tried on both my existing coils and the GSXR ones. I have tried touching the probes to everywhere inside the plug caps and even directly to the wire cores on the GSXR coils after I unscrewed the plug caps. What gives? I am useless on electrical matters, but even a brain dead mechanical engineer can manage to hold the multimeter probes on a piece of metal properly (surely? )

Any help/info very appreciated. Earlfor and Keith Krause are you out there?

BTW, the GSXR coils (from a 93 600, I believe it was) will bolt perfectly onto the GS mounting tabs. Nice of Suzuki to not change that spacing over the decade.


Mark

 

[Anonymous]

Hi Mark:

First of all - how did your muffler system turn out?

Anyhow..

Generally coil resistance affects charge rate and maximum current the coil will draw. I think lower R will charge faster. They will also draw more current putting more stress on the v regulator.

Also the spark may or may not be hotter due to resistance parameter only - why - spark is also dependant on the turns ratio between the primary and secondary - which affects the spark volts.

lastly you should have continuity between the plug caps....I guess. Unless each secondary is it's own winding to ground. But if that were the case, the windings would look like a Y circuit for two of the legs with the center ground connected. Maybe your VOM doesn't measure high enough resistance. Anyhow, try coil to ground.

A coil needs to create sufficient voltage for the spark gap to fire reliably. Larger gap, higher firing voltage needed. Also, the coil needs to achieve "breakover" voltage quickly enough to allow a spark to occur when the cylinder needs.

I would type in "automotive coil theory" or "spark transformer theory" into a browser. It's just a stinkin transformer right? Well the theory can be quite intense. - Dieter

 

[stiksave]

Mark,

I did the same swap on my 1100. My bike is verrrry happy!

Chris

 

[Anonymous]

Hey Tony,

How are things at your end?

First of all - how did your muffler system turn out?

Nothing yet. I've been busy working and getting everything else sorted. I can run with the Kerker for now and ride while I build the new tail pipe, so I have been concentrating on getting it running right first. My wife finds the Kerker too loud for her tastes, though, so I should have no problem getting time for the new tail pipe if it will be quieter...

I think lower R will charge faster.

That was my thought, but I know nothing beyond basics regarding the electrical/ignition system.

lastly you should have continuity between the plug caps....I guess. Unless each secondary is it's own winding to ground. But if that were the case, the windings would look like a Y circuit for two of the legs with the center ground connected. Maybe your VOM doesn't measure high enough resistance. Anyhow, try coil to ground.

The manual gives a resistance value of ~30 Ohms for plug cap to plug cap. I was reading on a 0-200 scale, so it should have been OK for that. I think I am just missing something obvious here... Maybe I will try it with a spark plug in each cap and go electrode to electrode for my reading.

I did the same swap on my 1100. My bike is verrrry happy!

That's what I like to hear.


Mark

 

[lecroy]

I am useless on electrical matters, but even a brain dead mechanical engineer can manage to hold the multimeter probes on a piece of metal properly (surely? Smile )

Not always the case. The meter may not be very accruate in the lower range. Even if you zero out the error caused by the probes, a better way would be to use a 4 wire system. A constant current is passed threw the device you are trying to measure, then a voltage reading is taken across it.

 

[Griffin]

The manual gives a resistance value of ~30 Ohms for plug cap to plug cap. I was reading on a 0-200 scale, so it should have been OK for that. I think I am just missing something obvious here... Maybe I will try it with a spark plug in each cap and go electrode to electrode for my reading.

Mark

Look a little more closely. The resistance is listed at 30-50 k ohms (kilo ohms).

I'd be rather surprised if you got any readings set at 0-200 ohms on your meter.

Put it on the 200k ohm setting.

 

[Anonymous]

Look a little more closely. The resistance is listed at 30-50 k ohms (kilo ohms).

Look at that. You're supposed to READ the directions...

Thanks for pointing out the obvious here, Griffin. I knew I was missing something stupid. I guess being out by 3 orders of magnitude would qualify. :roll:

Mark

 

[Anonymous]

Ahh that's right Mark / Griffin

If you read plug wire to plug wire (the secondary winding of the "transformer" or coil"

Then if the plug caps are resistor type - it will not be the secondary but the secondary plus the resistor in each plug cap times 2...

So - unscrew the plug caps off the ignition wires and read center conductor to center conductor for the actual secondary winding resistance.

- Tony

 

[earlfor]

The resistance between the plug caps is normally (in stock configuation) betweem 20,000 and 40,000 ohms, or 20-40k. The scale to use on the meter is 200K, not 200. You will not get any reading if using a scale that doesnt include the highest range you are trying to test for.
My manual specs 10K ohms as the lowest acceptable resistance. I'm using accel and dyna coils on my two bikes with graphite wires and no resistors.
I have about 14K resistance on the secondaries on both bikes.

Earl

The manual gives a resistance value of ~30 Ohms for plug cap to plug cap. I was reading on a 0-200 scale, so it should have been OK for that. I think I am just missing something obvious here... Maybe I will try it with a spark plug in each cap and go electrode to electrode for my reading.

 

[Anonymous]

The resistance between the plug caps is normally (in stock configuation) betweem 20,000 and 40,000 ohms, or 20-40k.

I have now got that sorted. Seems being off a few orders of magnitude doesn't work really well with the multimeter...

I have about 14K resistance on the secondaries on both bikes.

I measured one of my GSXR coils from wire to wire with no caps and got 14.1K, so they are very similar. I have not got back to measure the GS coils yet, I have been wiped out sick for the last week and this weekend the new GSXR coils will be going on, so it is a bit of a moot point now.


Mark