|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
07-01-2019, 02:51 PM | #1 |
Junior Member
Join Date: Feb 2019
Posts: 2
|
Cause of hot ignition coil?
Hi,
I have a model A that the coil seems to be getting hot on. The car runs fine, but after driving for about 30 minutes the coil is pretty hot. Hot enough to only keep your hand on it for a short time. The car is 12v negative ground. I have tried 3 different 12v coils running both internally resited and a coil with a external resister. The first 2 coils showed a resistance of 1.4-1.5 on the ohm meter. The coil that is currently on the car is a Bosch 12 volt blue coil. This coil shows a resistance of 3 .0 on the ohm meter. Currently the amp meter shows a charge of about 10amps while driving. Any ideas what might be causing the coil to heat up? |
07-01-2019, 03:27 PM | #2 |
Senior Member
Join Date: Aug 2018
Posts: 2,332
|
Re: Cause of hot ignition coil?
I assume the 1st 2 that measure 1.5 ohms were specifically for Model As. You could also ohm each of the 1.5 ohm coils terminals to the high voltage output. Should measure 7k-15k ohms. Not sure what teh reading would be for a 12 v coil
I am unclear on your email. The coils that measure 1.5 ohms require the 1.5 ohm external resistor when used on 12 volts. Otherwise they are running twice their desired current and will heat up. The 12 v coil should measure about 3 ohms and does not need the resistor. Then, do not ask why, can not supply a reasonable answer - but would try a different condenser. |
Sponsored Links (Register now to hide all advertisements) |
|
07-01-2019, 05:38 PM | #3 |
Senior Member
Join Date: Jun 2010
Location: San Antonio, Texas
Posts: 16,425
|
Re: Cause of hot ignition coil?
The 3-Ohm coil should be able to take the heat. Later types like that are usually insulated with an epoxy resin that is designed to work at the higher temperatures. As was mentioned previously, the 1.5 would need the ballast of 1.3 to 1-5-Ohm. This splits the heat between the resistor and the coil. It makes the older type coils a lot more reliable otherwise they will burn up in a short time. The 1.5-Ohm coils will work on a 6-volt system with no ballast at all.
|
07-01-2019, 05:52 PM | #4 | |
Senior Member
Join Date: Jun 2014
Location: Melbourne, Australia
Posts: 7,496
|
Re: Cause of hot ignition coil?
Quote:
I suspect the coils that overheated will be labelled 6 v (if they're labeled at all) and the 3 ohm one labelled 12 v.
__________________
I'm part of the only ever generation with an analogue childhood and a digital adulthood. |
|
07-01-2019, 10:14 PM | #5 |
Senior Member
Join Date: May 2010
Location: Windy City
Posts: 2,919
|
Re: Cause of hot ignition coil?
Heat in a coil is also a function of 'dwell'. The less your point gap the more time the coil dwells in saturation mode, heating up from primary coil resistance. If you have a "B" dizzy cam it has a profile that will give more dwell for the same point gap, resulting in more coil heat. Checked your point gap lately? Have a dwell meter?
|
07-02-2019, 03:27 AM | #6 |
Senior Member
Join Date: Nov 2011
Location: Sonoma, CA.
Posts: 1,496
|
Re: Cause of hot ignition coil?
Sponsored Links (Register now to hide all advertisements)
|
07-02-2019, 03:32 AM | #7 |
Senior Member
Join Date: Jul 2010
Location: United Kingdom
Posts: 1,441
|
Re: Cause of hot ignition coil?
as well as all above .... poor condenser (or condenser not earthing correctly) can also cause overheating of coil.)
Last edited by johnbuckley; 07-02-2019 at 07:17 AM. |
07-02-2019, 05:48 AM | #8 |
BANNED
Join Date: Jan 2016
Location: newfoundland,canada
Posts: 128
|
Re: Cause of hot ignition coil?
I just had to sort out this issue. johnbuckley is correct ,but Dodge is more probably ..most guys when switching to 12V just mount a coil upside down and it overheats from oil not covering wiring internally. how do I know? because original coil wire to 6V is to short when 12V is mount correct side up......
|
07-02-2019, 09:25 AM | #9 |
Senior Member
Join Date: Jul 2010
Location: Pennsylvania
Posts: 1,101
|
Re: Cause of hot ignition coil?
I'd also check the little carbon button in the center of the distributor cap that makes contact with the rotor. A friend burned out 3 coils, and finally found that the carbon button was cracked. This caused resistance in the secondary circuit, and caused the coils to overheat.
|
07-02-2019, 09:35 AM | #10 |
Senior Member
Join Date: May 2010
Location: Long Island, NY
Posts: 3,464
|
Re: Cause of hot ignition coil?
Heat produced by the natural function of the ignition coil should transfer out to case, so the case will get hot to the touch. Coils with an internal resistor will run hotter.
Check this out: https://youtu.be/UEmSFDn8Rlw
__________________
Bob Bidonde |
07-02-2019, 09:58 AM | #11 | |
Senior Member
Join Date: Apr 2016
Location: Bellingham, WA
Posts: 1,163
|
Re: Cause of hot ignition coil?
Quote:
I know (20,000,000) VW Bugs and (500,000) MGBs also mounted the coils with the connectors pointed down (and there are probably others. Seems like a preferred, more weather proof mounting system). I hang out on forums with the Bug and MGB groups. No discussion of coils failing when mounted in the factory orientation. Is there any science or manufacturer instructions that anyone can point to that backs up the "upside down" oil filled coil claim? Not just anecdotal data, but actual science or manufacturer instructions?
__________________
All steel from pedal to wheel |
|
07-02-2019, 10:10 AM | #12 |
Senior Member
Join Date: Aug 2018
Posts: 2,332
|
Re: Cause of hot ignition coil?
Richard - any update?
|
07-02-2019, 10:16 AM | #13 |
Senior Member
Join Date: May 2010
Location: Long Island, NY
Posts: 3,464
|
Re: Cause of hot ignition coil?
Incorrect timing and or a points gap that has decreased causes the coil to energize longer than normal resulting in its overheating.
A high resistance in the high voltage circuit will cause the coil to overheat and fail. High resistance may be due to a worn-out distributor cap carbon contact, excessive rotor to distributor body electrode gaps, a faulty high voltage coil wire, etc.
__________________
Bob Bidonde |
07-02-2019, 10:20 AM | #14 | |
Senior Member
Join Date: May 2016
Location: Glide, Oregon
Posts: 1,336
|
Re: Cause of hot ignition coil?
Quote:
|
|
07-02-2019, 01:32 PM | #15 | |
Senior Member
Join Date: Apr 2016
Location: Bellingham, WA
Posts: 1,163
|
Re: Cause of hot ignition coil?
Quote:
Decrease in point gap = an increase in coil saturation time. I can see that. I can't see how changing the timing one way or another changes the coil saturation time, however.
__________________
All steel from pedal to wheel |
|
07-02-2019, 01:37 PM | #16 |
Senior Member
Join Date: Nov 2011
Location: Sonoma, CA.
Posts: 1,496
|
Re: Cause of hot ignition coil?
Old coils were filled with pcb’s lilke a PG&E transformer not oil, shake one and see,
When they banned the use of pcb’s they went to oil. The oil filled are meant to go straight up not down and not on their side. I’m just saying to try it and see if it works better. There are instructions with the MSD coil that say stand it straight up or use one of their epoxy filled coils. Had the problem on my truck and went to they epoxy coil. No more problems. |
07-02-2019, 02:33 PM | #17 |
Senior Member
Join Date: Jul 2010
Location: United Kingdom
Posts: 1,441
|
Re: Cause of hot ignition coil?
What's pcb?
|
07-02-2019, 02:53 PM | #18 |
Senior Member
Join Date: Aug 2018
Posts: 2,332
|
Re: Cause of hot ignition coil?
Here is a Wikipedia link.. It was heavily used in cooling concoctions used in oil filled transformers, coils, and other uses. Was found to be nasty stuff and the U.S. EPA (Environmental Protection Agency) clamped down on its use.
https://en.wikipedia.org/wiki/Polychlorinated_biphenyl |
07-02-2019, 05:00 PM | #19 | |
Senior Member
Join Date: Apr 2016
Location: Bellingham, WA
Posts: 1,163
|
Re: Cause of hot ignition coil?
Quote:
I'm still going to wonder why for other makes the inverted coil isn't a problem. Maybe they are running old PCB filled ones, or installed epoxy replacements?
__________________
All steel from pedal to wheel |
|
07-02-2019, 06:10 PM | #20 | |
Senior Member
Join Date: Jun 2015
Posts: 1,414
|
Re: Cause of hot ignition coil?
Quote:
|
|
|
|
Sponsored Links (Register now to hide all advertisements) |
|