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Robert View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Robert Quote  Post ReplyReply Direct Link To This Post Topic: Hot coils
    Posted: 05 Jun 2020 at 18:02
The coils on my 82 sp get extremely hot if I have the ignition on for even 5 minutes.
I’m running a Dyna ignition with standard coils I do know they recommend 5 ohm coils with this system as they say the standard coil will run hot - but should they get so hot when the bike is not even running.
Robert
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Richard Hyatt View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Richard Hyatt Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jun 2020 at 19:35
Any ht coil will be using/consuming around 5 to 8 amps,  so this is why they get warm.
The internal resistance dictates the current used using ohms law , which I can't draw here sorry.
Amps , volts,resistance relationship
V= AxR
And any configuration of these 3 
12v= A? X 1.5 ohms

As Dacia says  you do the maths

If the bike is sitting with the key on , that's why they're getting warm , riding along in the wind and rain takes the heat away.
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Brian UK View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Brian UK Quote  Post ReplyReply Direct Link To This Post Posted: 05 Jun 2020 at 21:13
A "standard 12v coil would probably be 3.5 ohms. At a nominal 12v, it will consune about 3.5 Amps. At a running voltage of 14v, it will consume 4 Amps.

The 5 ohm coil @ 12v will pass 2.4 Amps, and at 14v - 2.8 Amps.

So the 5 ohm coils would run cooler. The heat produced will be directly proportional to the current consumption.
Brian.

Better 5 minutes late in this world than years early in the next.
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Dave P. View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave P. Quote  Post ReplyReply Direct Link To This Post Posted: 06 Jun 2020 at 10:13
This is interesting. So what factors determine the ideal coil resistance requirement for a given vehicle?
TO LIVE OUTSIDE THE LAW YOU MUST BE HONEST.

1971 V7 Special. 1972 850GT.
1970 T120 Bonnie. 2009 500 Bullet.
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