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Ballast Coil fitted ??


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Slightly off topic - working on my 1984 Mini 25 which has a ballast wire system - The PO was a bit of a "maverick"  Brake callipers fitted upside down (bleed nipples pointing down!) 2 brake compensators fitted etc, etc - because of this and as I'm working through the ignition system, can someone confirm that using a multimeter set to 20k OHMS, testing the Positive terminal and the HT lead terminal of the coil, if I get a reading above 1.5 (1500) that the COIL is a NON ballast type coil ??  The reading I get is 6.35  so I suspect that this is a standard coil (I cannot see any markings or labels on the coil)

 

Thanks 

 

Matt

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A non-ballasted coil should be around 3 Ohms Matt when measured across the two spade terminals. You are being a bit optimistic if expecting to measure it on a 20kOhm meter scale.  How many display digits does the meter have (assuming it is digital)?  Can you not use a 2kOhm scale or even lower if there is one?

Edited by RobH
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Thanks for the reply Rob - its a fairly basic Draper digital meter - with it set below 20k, I'm struggling to get any meaningful readings - also testing the terminals is for the primary coil and the positive HT lead is for the secondary ? 

 

cheers

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7 minutes ago, mattyb said:

Thanks for the reply Rob - its a fairly basic Draper digital meter - with it set below 20k, I'm struggling to get any meaningful readings - also testing the terminals is for the primary coil and the positive HT lead is for the secondary ? 

 

cheers

Hi Matt!

Beware some BL cars use a resistive wire in the harness to drop the voltage to the coil to 6v. What is the voltage at the coil after having started the engine?

Bruce.

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Hi Bruce - yes pretty sure that this has a resistive wire fitted - what I'm doing at the moment is pre checks prior to trying to start the Mini ! 

I've just found something on SimonBBC electronic ignition  website - will have a read 

 

 

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33 minutes ago, mattyb said:

Thanks for the reply Rob - its a fairly basic Draper digital meter - with it set below 20k, I'm struggling to get any meaningful readings - also testing the terminals is for the primary coil and the positive HT lead is for the secondary ? 

 

The low resistance primary winding is between the two spade terminals. The high resistance secondary winding is between the HT terminal and either of the spades but measuring that doesn't tell you much. 

You probably won't get meaningful readings on the primary as it will only be the very last digit that changes - i.e. if it is a 3 Ohm coil a  3-digit meter should read '003' on a 200 Ohm range but the meter can only display within ±1 digit accuracy so it could show 002 or 004.   You need to short the meter leads together and ensure it reads zero before you start though.  

Edited by RobH
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Rob that's very helpful and informative - thank you - I set the meter to 200 (the lowest setting it has) and tried to zero the display, however the lowest it would "reset" to was 01.6   - I did then try placing the leads on the primary (with wires and HT detached ?? ) and got a reading of 04.7 ?  

 

I did the same with the meter set to 2000 - it rest to 001 and on the primary got the result of 004 - can any conclusion be reached from these readings ? other than I should invest in a better meter !

 

Thanks again

 

Matt

Edited by mattyb
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If you subtract that 1.6 from the reading of 4.7 it looks as though the real reading might be 3.1 Ohms give-or-take the meter inaccuracy, so the coil may not be a ballasted one.  

 

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Thank you Rob - yes that's very much a possibility - appreciate your input 

 

All the best

 

Matt 

IMG_2902.JPG

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Cheers Roger - yes I bought a very nice set of metric ratchet spanners from Lidl !

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Things are pretty easy:

If you do not have the tools use some tricks.

I would buy the recommended coil from simonbbc with 3 ohms.

Connect it to the wiring as it should be, make a connection from the point side of coil to minus.

Measure voltage at the plus side of the coil against minus.

Put ignition on and read:

If you have 12volts you have non resistor, if it is reading six than the voltage is split between

the coil and the ballast wire, so you have a resistor in the wire somewhere.

All coil switching on and of produces a spark, so be carefull.

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