3 ohm Dyna coils testing at 3.5 ohms

[grizilla]

Hi all,
I've just had some used Dyna coils delivered and when tested they read 3.5 ohms primary resistanceSecondary resistance is good.*I understand higher primary resistance will result in a cooler running TCI box but is it likely to suffer any damage from the higher than spec resistance?Mine's a 5K7 btw.

Thanks for any advice,
Gareth

[TopCatGr58]

Hey there Gareth,

Well, I'm no electrical guru, but like you said, the TCI likes to see ~3.0 ohms on that circuit going to the coils. The problem that fries the TCI is when folks use too low ohm coils, either the 1.5 style or even the 0.7 type that is for CDI type ignition systems, these draw way too much current thru the TCI's triggering system, and causes it to heat up and eventually burn up. The higher resistance should not cause a problem because it will not put as much of a load on that circuit, so I can't see it causing any problems.

With that said, hopefully Crazy Steve, Caption Zap, or some other more knowledgeable electronics guru will chime in.

Another thing, have you checked the calibration of your ohmmeter?? 3.5 ohms isn't very much, are you getting a true 0.0 ohms when the test leads are touched together? JAT.

T.C.

[BA80]

The slightly higher resistance shouldn't be an issue. As TC said, it's lower resistance in the primary ignition circuit that can cause trouble with the TCI.

They should work just fine.

[grizilla]

Thanks for your replies.
My multi meter reads 0.3 ohms with probes touched together.
I've been told by a car electrical tech that double the recommended resistance would be OK on a car, but lower resistance is bad.
Some say they've ridden for years with 1.5 ohm coils without ballast resistors.
Seems the TCI box is pretty robust.

[HalfCentury]

Thanks for your replies.
My multi meter reads 0.3 ohms with probes touched together.
I've been told by a car electrical tech that double the recommended resistance would be OK on a car, but lower resistance is bad.
Some say they've ridden for years with 1.5 ohm coils without ballast resistors.
Seems the TCI box is pretty robust.

Subtract the 0.3 from 3.5 to give you 3.2. Chances are that your DMM is not calibrated nor guaranteed to be accurate enough to care about a 0.3 ohm uncertainty. Your coil primary is probably spot-on.

Precision DC measurements are my day job.

[grizilla]

Yeah I reckon so.
Now I just need to find time to fit and balance carbs.