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6 volt coil getting warm
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Rick
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PostPosted: Sun Jun 10, 2012 6:30 pm    Post subject: 6 volt coil getting warm Reply with quote

I took the truck for a run down the road today, but again it expired. I'd had it running 10 mins or so in the drive before setting off.

After a few attempts to gee it into life, I was able to get it down a side road where I left it to cool down. The NOS 6v coil seemed very very warm to the touch when I checked it after parking up, so I'm thinking it might be packing up once there's a reasonable amount of underbonnet temp generated.

With the temp back down again, after 45 mins or so, I was able to fire it up and drive it the 1/2 mile back home again.

How warm should a coil get? I could understand it if I'd left it for, say, 5 minutes with the ignition on but not running, but I don't recall 6v coils on other vehicles I've had getting particularly hot when stopping after a spin out.

RJ
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ukdave2002



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PostPosted: Sun Jun 10, 2012 7:30 pm    Post subject: Reply with quote

Rick

The heat that the coil generates it's self is minimal, unless the engine is very high revving. There is not much to go wrong with a coil, but an intermittent diss could be triggered by heat. It's always difficult to speculate as many things can fail with heat, if you can get the beast on a engine scope it would take the guesswork out.

It would also be worth measuring the coil current draw with the engine static.

Dave
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Bitumen Boy



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PostPosted: Sun Jun 10, 2012 7:40 pm    Post subject: Reply with quote

A generic 6v coil isn't a ludicrous price (assuming you haven't got one knocking around), so I would try substituting another one and go from there. Just a thought, but is the coil mounted on or close to hot parts of the engine? I seem to recall owners of some Minis (I think) having repeated problems with coils mounted on a bracket off one of the head studs (or something similar), when they relocated new coils to mount on the inner wing the problem never recurred.
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Rick
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PostPosted: Sun Jun 10, 2012 8:58 pm    Post subject: Reply with quote

Bitumen Boy wrote:
A generic 6v coil isn't a ludicrous price (assuming you haven't got one knocking around), so I would try substituting another one and go from there. Just a thought, but is the coil mounted on or close to hot parts of the engine? I seem to recall owners of some Minis (I think) having repeated problems with coils mounted on a bracket off one of the head studs (or something similar), when they relocated new coils to mount on the inner wing the problem never recurred.


I've another NOS one (Autolite) so I'll give that a whirl, these originals are based mounted to the bulkhead, with the feed from the switch connecting into the base, behind the bulkhead, and the LT connection that goes to the dizzy positioned next to the HT lead. I'll swap it over sometime and see if that improves things. I also plan to alter the fuel feed arrangements as I'm not convinced that they're working 100% either.

I'm not keen on altering more than one thing at a time, but as taking it out for test runs is a bit of a logistical exercise in itself, each trip has to count! Smile

RJ
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PAUL BEAUMONT



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PostPosted: Mon Jun 11, 2012 1:10 pm    Post subject: Reply with quote

Rick, the Green Spark Plug Co are in your area and they do new 6v coils with acorns and screw twerminals etc if that is what you have fitted - I'm not familiar with (presumably) Delco components.
Paul
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Rick
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PostPosted: Mon Jun 11, 2012 2:45 pm    Post subject: Reply with quote

This is the base-mounted coil fitted on the truck's bulkhead, all Mopar/Autolite parts.



I've another spare so I'll give it a whirl and see how it goes, I think I do have a normal pattern 6v Lucas one somewhere so if push comes to shove, I can rig that up for testing purposes if necessary.

RJ
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stuchamp



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PostPosted: Tue Jun 12, 2012 5:14 am    Post subject: Reply with quote

Rick, does your system use a ballast resistor?
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Rick
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PostPosted: Tue Jun 12, 2012 6:52 am    Post subject: Reply with quote

stuchamp wrote:
Rick, does your system use a ballast resistor?


No just the standard 6v system for the ignition.

R
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Julian



Joined: 19 Apr 2010
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PostPosted: Tue Jun 12, 2012 9:23 am    Post subject: Reply with quote

Rick wrote:
stuchamp wrote:
Rick, does your system use a ballast resistor?


No just the standard 6v system for the ignition.

R


So the question would be: Is this coil designed for a ballasted system or not? A 6V coil (as I've seen before) would typically be used on a 12 volt vehicle with the series ballast dropping the voltage.

It is possible for the coil to fail when hot, (the same as magnetos) the high tension circuit goes open circuit when warm, this doesn't always cause a complete loss of sparks as the HT voltage still can jump the gap.

I'd also consider the condenser, these little bsuggers can also fail. Finally, as daft as it sounds the power to the coil can fail, due maybe to an intermittent ignition switch or break in a wire - always try a quick 'hot-wire' to eliminate.

Julian.
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Julian



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PostPosted: Tue Jun 12, 2012 9:34 am    Post subject: Reply with quote

ukdave2002 wrote:
Rick

The heat that the coil generates it's self is minimal, unless the engine is very high revving.


Dave, you have that the wrong way around.

There's more current flow, and thus heat produced in the coil during operation at low revs, (idle) this is because the coil has more time to saturate and for current to reach maximum. (less switching from the points)

For ballasted ignition operation: During low speed operation current is maintained in the ballast resistor for a longer period of time, causing it to heat up, and resistance to increase. This action reduces the voltage in the ignition primary circuit, thereby, protects the coil from high voltage during low speed operation. As engine speed is increased the amount of time in which current is maintained in the primary circuit is shortened, causing it to cool off and resistance to decrease. This action raised voltage in the ignition primary circuit, which is required for high speed operation. (From a Mopar serice manual)

Julian.
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ukdave2002



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PostPosted: Tue Jun 12, 2012 12:50 pm    Post subject: Reply with quote

Julian wrote:
ukdave2002 wrote:
Rick

The heat that the coil generates it's self is minimal, unless the engine is very high revving.


Dave, you have that the wrong way around.

There's more current flow, and thus heat produced in the coil during operation at low revs, (idle) this is because the coil has more time to saturate and for current to reach maximum. (less switching from the points)

For ballasted ignition operation: During low speed operation current is maintained in the ballast resistor for a longer period of time, causing it to heat up, and resistance to increase. This action reduces the voltage in the ignition primary circuit, thereby, protects the coil from high voltage during low speed operation. As engine speed is increased the amount of time in which current is maintained in the primary circuit is shortened, causing it to cool off and resistance to decrease. This action raised voltage in the ignition primary circuit, which is required for high speed operation. (From a Mopar serice manual)

Julian.


No I havn't Idea

2 things. Generate the heat, you need to appriciate the coil is an inductor , not just a resistance.
1) is from the current in the coil,
2) from saturation and collapse of the field.

The coil has current flowing in the primary for the same time, and is not engine speed dependent; it's fixed by the dwell. Saturation & collapse of the field is obviously dependent on speed.

Dave
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stuchamp



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PostPosted: Tue Jun 12, 2012 4:37 pm    Post subject: Reply with quote

Rick wrote:
stuchamp wrote:
Rick, does your system use a ballast resistor?

No just the standard 6v system for the ignition.R




I'd try another coil but also check your points and spark plug gap.
Also check the wire between ign switch and coil for a ballast resistor.
That type coil might have one built in???
Some of the old Chevy's also had a polarity reversing switch between the coil and distrib. I don't know if Dodge ever used one though.
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Julian



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PostPosted: Tue Jun 12, 2012 4:44 pm    Post subject: Reply with quote

ukdave2002 wrote:


No I haven't Idea

2 things. Generate the heat, you need to appriciate the coil is an inductor , not just a resistance.
1) is from the current in the coil,
2) from saturation and collapse of the field.

The coil has current flowing in the primary for the same time, and is not engine speed dependent; it's fixed by the dwell. Saturation & collapse of the field is obviously dependent on speed.

Dave


Backwards thinking there!

Let's say the coil has a resistance of about 3 ohms. So, if you put a 12v battery on it, it will allow a current flow of 4 amps. At 12v, that is 48 watts! So, over a period of time it will get hot (too hot to touch you leave it too long).

Now, when the engine is running, the coil is switched on and off at twice engine RPM. Due to the physics of a coil ie inductance, the effect of magnetism, this effectively gives the coil a much higher "apparent" resistance, so it doesn't get as hot - or consume as much power. The faster the engine runs the higher the apparent resistance and the less the current.

That's just school boy physics, I remember enough of it from my 'A' level days. Dave, no doubt you'll not agree with the actual physics here (you can lead a horse to water etc etc) All I can say is that have a little look at some simple electronics theory or ask on a relevant forum... The way forward here firstly is to appreciate that pulsed DC, (to the coil primary windings) has the same characteristics as AC. The coil is an inductance, and inductive reactance (resistance) is higher at higher frequencies.
Julian.
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ukdave2002



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PostPosted: Tue Jun 12, 2012 7:54 pm    Post subject: Reply with quote

Bugger!!.....I'll have to go back to school then and learn some of this electrikary stuff Wink some of it might even be useful to me!
Julian I'll pm you!
Dave
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MVPeters



Joined: 28 Aug 2008
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Location: Northern MA, USA

PostPosted: Wed Jun 13, 2012 12:00 am    Post subject: Reply with quote

Rick

You seem to have a really HOT engine there!

Just some ideas from a long way away:
Try a perfectly normal 12V coil, robbed from the nearest A35/Mini - the electrical genii will have a fit, but it will work on 6V & it will give you sparks & no confusion over whether or not it's ballasted - it isn't. Get the pluses & minuses the right way round.
You've checked the points & condensor (several times!), right? Have you checked the ignition timing? I'd use a vacuum gauge - advance it until the needle just kicks & then back off a tad.
Can you drive the truck with the bonnet/hood/side panels off?
Is it possible the valve timing is off by a tooth?
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