11 replies to this topic

[Hegnirst]

should i be able to hold on to it after a long run? as i cant do that,  it gets a hot as a water pipe!

 

jonspeed did build this.

 

im thinking a couple of things, 

 

the wrong resistance, 

the wrong coil, 

to much load on the coil,

the metal bracket that holds the coil which is attached to the engine, which possibly is transfering the heat?

 

hmmm

 

thanks :)

 

i have a multimeter, so if i need to test anything tell me how :) i wouldnt know where to start on it

[jaydee]

using a low resistance coil with a 12V feed can cause this iirc

coils get hot anyway, thats why theyre oil (or even epoxy) filled, so it could be the coil loosing oil hence getting hotter

Use a multimeter to see what voltage you get at the LT terminals of the coil and whats the resistance of the coil itself, if the resistance is 3-3.5 ohm you need to feed it by 12V, 9V feed is for coils with about 1.5 ohm resitance

[KernowCooper]

First check the resistance of the coil, set your meter to measure ohms. Then put the red lead on the + terminal of the coil and the black on centre (where the ht lead goes). 3ohms and it's not ballasted. 1.something and it is........

 

 

Sorry but your mistaken your testing between the LT Circuit and the HT windings of the coil, the correct way of testing a coil is as said above by jaydee you test between the coils + terminal and the coils - terminal to see if its 1.5ohms ballasted or a 3.0ohms standard coil.

 

Have a look here at this little video by Moss which you can see it done correctly,  we all make mistakes just some of us say we do.

[KernowCooper]

No Probs mate I edit mine if I'm wrong so the members see the right information

 

And the bonus is like me reading some of your technical posts You've learnt something today, and thats the way it should be on a forum.

Edited by KernowCooper, 03 July 2013 - 03:42 PM.

[KernowCooper]

Its not errors which as you said you make them as well I edit out, I just edit out the blunt, and remarks which fire people up and it turns into a heated off topic thread - which is different and Martins no longer posting here of which he has his own reasons. end off

Edited by KernowCooper, 03 July 2013 - 04:02 PM.

[KernowCooper]

Well dont give it then

[carbon]

Back to the OP's question - how hot should a coil get?

 

Even when the right non-ballast coil is used I have found some coils do run very hot (ie too hot to hold your hand on), others no so bad (hot to touch but don't burn you).

 

Don't know if this is linked, but my mini with alternator has a coil which runs a lot hotter than the old one with dynamo? Voltage different?

 

Also I have found that what causes coils to get really hot is sitting at tick-over for extended periods. Recent MOT cooked one of the original dynamo-mounted coils very comprehensively after 10-15 minutes sat at tickover.

 

Running at higher engine speeds does not seem to be such an issue, but this may be down to better airflow through the engine bay.

[jaydee]

I kinda remember that when i was running a DLB105 it was very hot after few miles of driving

It depends on coil manifacturing (they're not all the same) and the position, obviousely you need a balance between airflow and keeping it safe from the rain, most important is to have the terminals pointing down and not up, and to have it somewhere where it doesnt get too much vibrations (in a mini-yeah..). A bracket from the cylinder head or even mouting on the inner wing (if you have space) are good options.

[KernowCooper]

Have a read of this I just put up may throw some light as to why http://www.theminifo...checks-answers/

[Captain Mainwaring]

Back to the OP's question - how hot should a coil get?

 

Even when the right non-ballast coil is used I have found some coils do run very hot (ie too hot to hold your hand on), others no so bad (hot to touch but don't burn you).

 

Don't know if this is linked, but my mini with alternator has a coil which runs a lot hotter than the old one with dynamo? Voltage different?

 

Also I have found that what causes coils to get really hot is sitting at tick-over for extended periods. Recent MOT cooked one of the original dynamo-mounted coils very comprehensively after 10-15 minutes sat at tickover.

 

Running at higher engine speeds does not seem to be such an issue, but this may be down to better airflow through the engine bay.

 

 

First, that shouldn't happen. Something is wrong.

 

Secondly - it's important to realise that coils are not a straightforward resistance - they are an inductance (yeh I know, you all know this already) - and as such you can't really compare one to the next in terms of "power" absorbed based on resistance.

 

 

 

First check the resistance of the coil, set your meter to measure ohms. Then put the red lead on the + terminal of the coil and the black on centre (where the ht lead goes). 3ohms and it's not ballasted. 1.something and it is........

 

 

Sorry but your mistaken your testing between the LT Circuit and the HT windings of the coil, the correct way of testing a coil is as said above by jaydee you test between the coils + terminal and the coils - terminal to see if its 1.5ohms ballasted or a 3.0ohms standard coil.

 

Have a look here at this little video by Moss which you can see it done correctly,  we all make mistakes just some of us say we do.

 

 

Ironic the waffle in the video isn't altogether factual....hehehehe

 

and sticky sweaty fingers touching the test prods......

 

Low impedance coils are also not limited to ballasted applications....they are used with CDI applications where the low coil impedance won't cause heating as it would with points (large dwell) - CDI coils are designed to run with pulses 20 time shorter than with kettering (sp?) ignition systems. Go sticking them on a points system and they will cook, not just because of the low impedance, but because of the field collapse characteristics of the coil.

[Earwax]

Sorry to OP , don't know exactly how hot the can run and still be normal

 

To Capt,..  so are there two types of low ohm coils (fast pulse aqnd normal?)

 

a) ballasted just to help get over lower voltage  but the pulse rate is the same

 

b) CDI  - super zappy , fast pulse 

[Captain Mainwaring]

First - the resistance you measure is actually pretty meaningless...uhm....how to explain? you might measure the filament of a light bulb or a coil and try to turn that into watts, but you can't. The light bulb filament changes it's resistance as soon as it's juices up - it self current limits.

Coils do the same, but with yet another factor - inductance. 

HT coils will spark, but not very well if they don't have a capacitor, what they need is inductance or "ring" - the idea being that when the points open, the coil field collapses (which on it's own would only create a back EMF and arcing at the points, but the capacitor which is already charged drops that charge which causes the coil to "ring" and dump is back EMF more effectively as HT......the points closing again and charging up the capacitor/coil actually cause the spark to be extinguished - it's why dwell angle is important, you need the points to actually have an open period to allow the spark to do it's job, at high speeds, if the duration of opening is too short then the spark will be clipped and may not properly ignite the charge.

 

Most coils only have a turns ratio of less than a 100, so how come they can hit 10kV from 12V? should only make 1200Volts 'kan? They utilize the fact that as the coil field collapses the capacitor causes this great big spike to form - and 10kV to appear at the HT take off.

 

CDI's work different - they hit the coil with a big bolt of juice to start with - CDI systems have their own inbuilt gubbins that fires 600 plus volts at the coil.

 

Yes you can swap coils between systems - don't however try to run a coil designed for CDI on point and condensor ignition unless you're prepared to play games with point gap that reduces the dwell angle significantly - on twin motor bikes the trick is to put the points in series, open them right out (twin points normally do a little "double tap" and then use a CDI coil with dual output as a lost spark setup. It works, but pity the pore sod who tries to set the points correctly later on - the thing will start but will cook the coil in short time.

 

You're much better to buy a coil specifically designed for high energy systems - a lot of these after market systems are trying to kid the user that they do something more than points, which they don't, they just replace them. 

I've got a Triumph T140 that damn near needed tow starting to get it to run - but it's currently on points (I got sent the wrong coils with the electronic kit) and you can start the old lady on sooty plugs wearing flip-flops, the OEM system works perfectly well if set up right and maintained. 

 

so to finally answer your question - a TRUE CDI coil will have a different design compared to a kettering system coil, notwithstanding one may be interchangeable, it just won't be ideal.