I was wondering how the professionals test things like coils, condensers

What happened to all of the old school electrical testers

Kiwiinwgtn

You've picked a couple of objects which won't fail gradually, or can't be fixed if they do. Symptoms of both are missing under load over time, cutting out completely, or (for condensor) pitted and damaged points. Diagnosis is by failure, and repair is by replacement.

A coil will either short to ground, or go open circuit internally. The end result is the same in that the engine will stop.

Condensors will also either short to ground or go open circuit. Short circuit will ground the coil permanently and not create any spark. Open circuit will lead to sparks across the points leading to the silvered points degrading and burning out. Same end result, but it takes a little time.

This is different to items like generators, alternators and starters. They will fail over time, and items can be pointed to directly for repair or replacement. Its cheaper however to replace than it is to repair (for good or for bad to the tradeskills we have available) for many items.

A ripple from an alternator output may point to the 3 output windings or one of the six diodes producing producing and converting 3 phase 60 volts AC into 13.8 volts DC.

A low or high output will point to the voltage regulator or rotor field.

These are better examples of items which degrade slowly, and can be tracked and repaired.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Check out a book entitled "Classic British Car Electrical Systems" by Rick Astley (No not the 80's singer ).
I'm a complete novice when it comes to car electrics but have learnt a lot from this book as it explains how the systems and components work and how to check and diagnose problems in simple and easy to understand terms.

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Your imagination is only limited by the size of your wallet
"61 850 original and crusty (Mavis)
"64 Smooth Roof Van (Colin)
"67 Deluxe resto project (Monty)

Agree with the good old swap it out policy.

The problem is I have used all of my new stuff in cars over the years.

I have just brought a spare set off points, condenser, cap leads, rotor and need to find a good spare coil to put in my test box.

I actually have that book.

The coil will be (depending on its specific type, and presuming its from a mini) around 3 Ohms across the terminals. You could Megger the insulation, but it will not really tell you anything as the output is at least ten times larger (>10000 volts) than a Megger provides at 1000 volts. So it won't really tell you much.

The condensor can be tested for capacitance, but along the same lines a large voltage spike will punch a hole right through it's internals when it does, and there's little you can do to prepare for it.

Best prep if you are unsure of the coil (perhaps you condenor as well if so inclined) is to fit it for a few days and be comfortable that it works. Then put it in your spares box. Easy to do the coil, harder to do the condensor.

Regular replacement was the go until recently. I used to change it out with a complete set of leads, plugs, cap and points about once every whenever-I-got-around-to-it..

Fifty dollar ignition modules remove all that. I don't look inside my dizzy from one end of the year to the next

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Despite the previous comments I have had several coils that have died a hard and extended death. The usual give-away is that they start to break down under load.

I once had a Volvo that suffered from a high rev miss. My Father in law ran an autoelecs for years and the guys tested the coil and pronounced it healthy. We replaced the computer (@ $600, many years ago) and went through all sorts of stuff. After a near head on - basically the engine died at about 5k revs just as I was getting past an 18 wheeler - we replaced the coil (no alternatives left) and all was sweetness and light.

I have had Mini coils that idled fine and would even allow gentle driving but would die as soon as you added load.

So, IMHO, if you have an engine that stutters under load - or is difficult to, try replacing the coil, and see what happens.

Testing may show certain failure modes, however....

Cheers, Ian

Cheers Ian, I did say above that they will at times miss under load. But that doesn't make it still somewhat serviceable in my mind. Just lucky to stutter home. So its still an immediate replacement item like a condensor.

Voltage supplied by the coil needs to be higher to jump a spark plug gap as air density rises. Air density rises inside a cylinder as you open the throttle butterfly and the relative vacuum is relieved in the manifold, drawing more air into the cylinder as the intake valve opens. This leads to more air being compressed, so a higher air density. Hence a higher resistive gap for the spark to jump across. It won't break over (spark) until a particular voltage is reached to do this.

The coil must charge for a long enough period to store enough energy to produce the higher voltage needed to jump the gap (dwell period). If the coil functions at a lower level of load (idle) it may break down higher up because the insulation has broken down internally, or it has shorted a number of turns within. A dirty or cracked cap, lead or plug will also fail as the spark finds a new and easier path to ground at the higher voltage, instead of the way the user intended over the spark plug gap. Having a dwell period adjusted poorly, so the coil does not have enough time to charge up will also create an identical situation at higher revs and load.

To bench test a coil at the conditions it suffers on the engine, you need to be able to reproduce the same voltage across an equivalent resistive gap. Its not an easy thing to do on a bench top, so will readily give false readings.

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SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

Not so useful on mini's, but for cars that typically run a large spark plug gap, if you suspect the coil is causing a miss under load you can close the plug gap down. If that makes it run nicely then either the plug gap was too big because it's worn or set wrong or its the coil.

Thanks for the comments, please keep them coming.

I did play the swap it out game with spares I had lying around. I tried three condensers all duds and a couple of coils.

All these parts are potentially 30 years old. The only reason I found the fault it was dark enough to see the coil arcing and i did not have the coil boot on. I did piss the neighbors off making too much noise so a quieter option is potentially needed.

I did some electrical training back in the 80s when IC's just came in. We used to do hot and cold testing where you heated up the IC with a hairdryer and then sprayed it with a can of freeze. That certainly brought on any issues / intermittent faults. I was hoping some one had a similar trick they could share.

I did a quick search on Ebay and you can get a coil tester (old School type) i will see if i can find one.

Thanks

Kiwiinwgtn