Author Topic: Got stuck today, t'was a burned-out ballast resistor  (Read 796 times)

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 862
  • Total likes: 25
  • Karma: 0
    • Copenhagen, Denmark
Got stuck today, t'was a burned-out ballast resistor
« on: April 20, 2018, 05:44:43 PM »
As the weather sort of skipped Spring and is finally Summerish, I finally took the mini out of the garage today - yeah - and headed for a semi-local magic-wand car wash.  Everything was going great; a fresh oil change, new fuel hoses in the engine bay (decided to turn on the fuel pump after winter storage and discovered fuel pouring out of the hoses) and fresh water bottles in the cup holders.

Arriving at the car wash, I switched everything off, went inside to buy an overpriced token ($7 for 4 minutes) and the mini wouldn't start.  Ok, I figured that it might just be an empty fuel tank or bit o'vapor lock, so I pushed it to a pump and put a bit o'gas in it.  Still wouldn't start, but I could hear the pump running, so I pushed it into a parking space, popped the bonnet and waited a bit.  Still not starting, but it would fire up while the starter was turning and promptly die when the key was brought back to 'run'. 

Perplexing...  Ok, what to do - of course, my test lamp and ohm-meter is in the garage.

Not wanting to be stuck at a car wash all night, I took a bit o'wire and ran 12V from the accessory fuse box directly to the coil and it started right up and limped home.  Fortunately, I had an extra ballast resistor, so out came the ohm-meter and I measured the resistance - 1.6Ω, just like it should be.  So I then measured the resistor that I've been using, and it was 'open'.  Huh...  Took it out and it has a nice brown stain on the back and a wobbly post.  Put the new one in and she fired right up.

I just hope I didn't fry the coil by running a full 12V through it.  I also wonder why the old resister burned out.

No car wash today.
« Last Edit: April 20, 2018, 05:49:51 PM by John Gervais »
- Pave the Bay -

Offline jeff10049

Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #1 on: April 21, 2018, 12:25:08 AM »
coil will be fine the points are what the ballast protects. should be fine also a short time shouldn't fry em.

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 862
  • Total likes: 25
  • Karma: 0
    • Copenhagen, Denmark
Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #2 on: April 21, 2018, 03:59:34 PM »
Cool - thanks Jeff -

I'm not using points; I have an infra-red optical trigger Luminition system.  I will, however, keep an extra ballast resistor in the boot.
- Pave the Bay -

Offline MiniDave

Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #3 on: April 21, 2018, 08:50:04 PM »
Why are you using a ballast resistor with points free ignition? I thought those required full 12V power? I can't imagine the need for it with that system.......

I have a similar system on my old Jag, it does not use the ballast resistor......
1989 Cooper Racing Green
2009 Clubman S
1969 Jaguar XK-E FHC
2004 Audi Allroad 2.7 TT

Offline jeff10049

Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #4 on: April 21, 2018, 10:38:47 PM »
I was thinking the same as you, Dave.
 
But I looked up what I think John has and it actually calls for a ballast resistor with certain coils not what I'm used to with conversions but I guess if that's what they want.

Maybe they did it for ease of use on cars with a resistor wire to the coil like chevy.

You can run non-ballast with a 3-ohm coil I think I would do that and lose the ballast resistor one less thing.

http://autocar-electrical.co.uk/lumenition

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 862
  • Total likes: 25
  • Karma: 0
    • Copenhagen, Denmark
Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #5 on: April 21, 2018, 11:03:02 PM »
Yep, I thought about re-installing my other coil and running it without the ballast resistor.  Hmm, I might just do that... 
- Pave the Bay -

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 862
  • Total likes: 25
  • Karma: 0
    • Copenhagen, Denmark
Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #6 on: April 23, 2018, 05:33:57 PM »
I converted back to the old, normal non-ballasted DLB105 Lucas sports coil and I'll probably reduce my spark plug gap to 0.040".  In a laps of focus with wrench in hand, I did over-tighten the coil bracket, though.  I hope it'll be ok - the coil definitely won't move or slip, that's for sure.

http://forum.triumphdolomite.co.uk/viewtopic.php?f=4&t=16235

This is probably the best message thread discussion/article regarding 'why' a ballast resistor is a good idea, and why some minis use the 'pink' resistor wire on the coil +.
- Pave the Bay -

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 862
  • Total likes: 25
  • Karma: 0
    • Copenhagen, Denmark
Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #7 on: April 23, 2018, 06:04:29 PM »
Why are you using a ballast resistor with points free ignition? I thought those required full 12V power? I can't imagine the need for it with that system.......

I have a similar system on my old Jag, it does not use the ballast resistor......

Dave, the power module receives a full 12V from the ignition switch (I extended the original 12V wire from the switch that was connected to the old coil + and connected this to the ballast resistor.).

Here's the original diagram using the ballast resistor and a diagram I found in their downloadable leaflet for installation without the ballast resistor:
- Pave the Bay -

Offline jeff10049

Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #8 on: April 25, 2018, 12:47:05 AM »
Good thread on resistors but not relevant for the electronic systems that I have seen most don't use a bypass wire anyway like the old points systems did. I don't see one used on yours either.

Offline John Gervais

  • A Really Swell Guy
  • 1380cc
  • *****
  • Posts: 862
  • Total likes: 25
  • Karma: 0
    • Copenhagen, Denmark
Re: Got stuck today, t'was a burned-out ballast resistor
« Reply #9 on: April 28, 2018, 05:06:08 PM »
It all depends which coil one uses.

This is the kit I had installed:
http://autocar-electrical.co.uk/products/optronic-ignitions/standard-optronic-ignition/pmc-50

The power module and optical eye can be used without a ballast resistor, simply use a 'normal' 2.5 - 3Ω coil instead of the Lumenition MS4 (1.5Ω) coil.

I originally opted for the complete kit including ballast resistor in order to get that little bit extra starting power on cold mornings. 

I've now got the old 3Ω Lucas sport coil installed and it seems to be working fine.
- Pave the Bay -