[TR] TR3 coil question

Anthony Rhodes spamiam at comcast.net
Sat Sep 19 16:07:36 MDT 2015

1.5 ohm coils are typically used with a ballast resistor to make the overall resistance about 3 ohms except when starting the engine.  A total resistance of less than 3 ohms may damage an electronic distributor switching unit unless it is specifically designed for low resistance coils.  

I think that some racing applications, particularly 8 cylinder engines may use a lower resistance ballast, or none at all.  But at low revs like 2500 on a 4-cly, the peak current is too high for points and the usual electronic distributor.  


Sent from my iPhone

> On Sep 19, 2015, at 2:45 PM, Jason Sukey <jsukey at gmail.com> wrote:
> I don't have all the specs on me at the moment, but from memory, the "hotter" red coil has a primary resistance of about 1.5 ohm, and the "colder" coil had a primary resistance of 3 or 3.5 ohm.  My understanding is this is the typical situation where the lesser coil can't develop enough voltage at high rpm when the charge time is the shortest, thus needing the increased voltage of the lower resistance coil.
> Jason
>> On Sep 19, 2015 2:35 PM, "Anthony Rhodes" <spamiam at comcast.net> wrote:
>> That is can interesting question of why one coil was failing at high RPM while the other didn't.
>> Assuming both are in proper operating condition, then I would expect that the one that can't sustain high RPM has a lot more inductance than the one that worked ok
>> As a matter of fact, the "high voltage" coils probably get that extra oomph by having higher inductance.  The price you pay for high inductance is that it takes longer to "charge" the magnetic field of the coil.  So, there is a steeper drop off of output voltage vs RPM.
>> Do you have the specs on the two coils?  Btw the resistance of the secondary windings also has an influence.  So does the resistance of the primary windings though I am assuming both are 3 ohm.
>> -Tony
>> Sent from my iPhone
>> > On Sep 19, 2015, at 1:00 PM, triumphs-request at autox.team.net wrote:
>> >
>> > Message: 1
>> > Date: Fri, 18 Sep 2015 14:26:04 -0400
>> > From: Jason Sukey <jsukey at gmail.com>
>> > To: auprichard at uprichard.net, triumphs at autox.team.net
>> > Subject: Re: [TR] TR3 coil question
>> > Message-ID:
>> >    <CAMmo4o-UUO+VMFaKgUCjZiOEQHs1zfsV6fArUq9C+eKQ8s-Mzw at mail.gmail.com>
>> > Content-Type: text/plain; charset="utf-8"
>> >
>> > Andrew,
>> >    Not TR3 related, but I've had to play around with coils on my modified
>> > GT6 using the 123 distributor (USB tune model).  After a lot of fiddling, I
>> > found that with the recommended Bosch "blue" coil, it would "go flat" at
>> > high rpms when I was accelerating hard.  (this is compared to points dizzy
>> > with a hot coil).
>> > I ended up with the Bosch "red" coil (made in Brazil model, I'm told the
>> > made in Mexico version is of lesser quality).  This solved my problems and
>> > it once again is happy to pull strong up to 7,000 RPM's.
>> >
>> > My theory is that the lower voltage "Blue" coil is fine for stock
>> > applications, but isn't enough for higher performance use.
>> >
>> > Jason
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