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Old 08-30-2010, 11:12 AM   #1
rtwdoug OP
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what causes a coil to get hot & boil?

Howdy
so Im in Turkey on my Harley
(but coils are about the same on all bikes)

Coil crapped out a few days ago, so I got a new one from the HD shop in Istanbul.

its for electronic ignition, & Im running points, but I've done the swap before with no ill effects.
(you can run an elecronic coil with points, but not a points coil with elec ign)

anyhow, new coil lasted about 4 hours, then died. the guts were spewing out of it, it got so hot.
I found a couple car coils to wire up & get down the road, but Im afraid they will die also.

Ive never had a problem of boiling coils like this before,
any ideas what it could be?

Thanks, Doug
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Old 08-30-2010, 11:32 AM   #2
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Some electronic igintions can run hot. Their output can be of a higher wattage (volts x amps). This shouldn't be a poblem with modern electronic ignitions though ... It was the earlier one's that had beefier outputs ... i

See if your elecronic ignition should have a resistor in line to your coil ... Was your bike points prior to going electronic? Probably?

Wierd problem ...

Just thinkin' out loud ...
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Old 08-30-2010, 12:23 PM   #3
rtwdoug OP
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Im running points ignition, it always has used points
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Old 08-30-2010, 12:50 PM   #4
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Really grsping at straws here, so forgive me - thinking out loud. Maybe you suffered with the low odds of having two bad coils, you need to add a balast resistor, or there is some gremlin in your wiring that leaves current to the points even when the switch if off?
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Old 08-30-2010, 12:59 PM   #5
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Modern electronic ignitions are for low currents ... they employ transitors and such ... therefore the 'output' is also very low wattage. Coils can be 'made for this super tiny current'.

Points (generally) have a higher output ... and coils can be made to take the higher output.

I *think* you have some coils designed to take a tiny ouput, and putting a big output (from your points) into them.

Like Mista Vern, I am guessing here ... and correct me if I'm wrong ... but If this is a new coil (for a newer bike) ... and from the Harley supplier ... then it's probably made for electronic ignition ... and not for points.
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Old 08-30-2010, 01:01 PM   #6
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I was riding when it boiled out & died, had been ridin about 90 minutes straight.

I'm clueless, the odds of a new HD oem coil being bad are slim.
specially to work fine for 4 hours of riding
the 1st coil lasted about 10k miles
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Old 08-30-2010, 01:03 PM   #7
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Ive run elec coils with points before & been fine.

in fact, Ive seen this coil listed as a direct replacement for the earlier coils in catalogs.
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Old 08-30-2010, 01:03 PM   #8
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Too bad there aren't any junk yards with Chevy in-line sixes running 12 volts there - be a snap to get a coil that would be bullet proof!
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Old 08-30-2010, 01:06 PM   #9
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Coils are rate by OHMS - eg: Big 70's Kawasaki fours like 3.0 ohms. This is the critical figure to match.

Check all connections - could be dodgy earth ?
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Old 08-30-2010, 01:06 PM   #10
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I have a couple car coils on it now, wired in paralell. they are working ok, but seem to get too damn hot. but then I dont know how hot they can get under usual use
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Old 08-30-2010, 01:18 PM   #11
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Sounds like a bad positive wire to me.
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Old 08-30-2010, 03:45 PM   #12
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I don't know my arse from my elbow about Harleys but so far you have cooked a couple of coils and the car coils are running hot? Coils have never been more than warm to the touch in my experience (shade tree mechanic here) so something electrical is making them hot, too much resistance in the circuit / poor connection. Find someone that knows auto electrics & owns a multi meter (or common sense), where you are they are good at making things live forever, failing that inspect all your connections and clean and tighten everything associated with the ignition. A random thought here, check your alternator output in case voltage is too high?

Good luck.
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Old 08-30-2010, 05:11 PM   #13
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Any 12 volt points type coil should be fine. The only thing you have to watch for, is some have an internal resister and some require an external resister. No resister means hot coil and burned points.
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Old 08-30-2010, 05:28 PM   #14
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Is the bike electric start? Does it have a ballast resistor? If the ignition system is designed such that the coil(s) see full battery voltage whist cranking (9-10 vdc) and then voltage after the resistor (also 9-10 vdc) and the coil(s) get the full 12-14 vdc of a running engine they can overheat and fail.

Did you change anything else on the bike before it started eating coils?

Try swapping the 12 vdc ignition input from one coil to the other and see if the symptom transfers.

Have you checked alternator diodes? A failed diode will still charge but can introduce A/C into the system. The coil may not like this.

My bet it that something has changed on the bike. The coil didn't just fail on its own.

R
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Old 08-30-2010, 05:36 PM   #15
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just like in real estate, sometimes failure or success of electronics is "location location location."

Is it shielded from engine heat? Does it get cooling air? Got tinfoil?

If those 3 answers = yes (at least the first 2) then you know it's really electrical.




I've only had things melt for 2 reasons. bad/inconsistent ground or incorrect wiring.


You know what you're doing so I think you'll just need to tinker and test and inspect and you'll figure it out.

Good luck. Bring me a good souvenir or t-shirt.
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