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Static Testing Of A Coil And Condenser .

cub cadet 72 104 124 coil condenser

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#1 mike912e OFFLINE  

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Posted March 24, 2014 - 10:04 AM

This question applies to most all garden tractors, but since all mine are Cubs and this issue applies to my 124 , I thought it best to ask here on this forum . How can I use my digital ohm/voltage meter to test the engine's coil and condenser statically ,  in other words, they are not wired into the tractor's electrical system . 

I just learned a valuable lesson on my almost completed 124 restoration : make sure the key switch is in the full " off " position before walking away from the tractor . I left the key in the " on " position and blew the top off of the coil, spraying oil all over my 124 and the floor underneath . I was fortunate in that there was only a lot of smoke generated, filling the garage but luckily no fire . It would have been disastrous since I had just filled the gas tank located just above the coil ! As I understand , the situation was caused by a combination of the key switch in the " on " position and the engine's point set was closed causing the coil the draw more current than usual, overheating to the point of exploding . The coil was a used one that had been painted, the condenser and point set were both brand new .  Here are pics of the resulting damage , as well as two " before " pics :

 

Attached Thumbnails

  • Coil exploded on the 124 001.JPG
  • Coil exploded on the 124 002.JPG
  • 124 almost done 3-14-14 003.JPG
  • 124 almost done 3-14-14 004.JPG

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#2 JDBrian OFFLINE  

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Posted March 24, 2014 - 10:52 AM

You must have a good strong battery. I've left the key on and had the battery go flat but I've never seen a coil blowup like that. It must have heated the oil in it and caused the pressure to build up to the point that it popped. It's easy to forget to turn it off and it could probably be prevented if there was some sort of seat interlock on the coil circuit.  

  To test the coil I think there is a procedure in the Kohler service manual. Check that for a detailed description. From what I remember you measure the resistance between the 2 low voltage terminals and it should be somewhere in the 3-4 ohm range. You then measure the high voltage winding resistance which is much higher. I don't remember off hand but I am going ot guess it will read 10,000 ohms between the spark plug wire and the low voltage terminals. To test a condenser you can use a digital volt meter with a capacitance scale or if that is not available you can do a basic test with an ohm meter. It should read as an open circuit. If you have an analog meter you may be able to see a small kick to the meter needle when you connect the leads to the condnenser. That is an indication that it has some capacitance. This is an old rough  method of testing a capacitor and any meter deflection will depend on the meter used and the size of the capacitor. Condenser is simply another name for capacitor.

  Very nice Cub by the way!!


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#3 New.Canadian.DB.Owner OFFLINE  

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Posted March 24, 2014 - 10:54 AM

Condensers are hard to test with a standard digital multimeter, unless you have one with a capacitor setting.  With an analog meter, you can test them by doing a resistance test & watching the meter slowing climb in resistance until it shows infinite ohms.  The other, more fun, way to test them is to put it across a battery & toss it to a friend.  If he screams & chases you around trying to hurt you, it held the charge. Yes, the stuff we learn in high school.  

 

The coil should, and I do say should, have a low resistance between input & ground, and a higher resistance from output to ground.  Higher is somewhere around 100 to 200 ohms.  Low is 5 to 10 ohms.  I may be off on my numbers depending on the specific coil & internal winding setup.  As they say, you mileage may vary.


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#4 New.Canadian.DB.Owner OFFLINE  

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Posted March 24, 2014 - 10:55 AM

JDBrian beat me to it.


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#5 propane1 ONLINE  

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Posted March 24, 2014 - 03:40 PM

Never heard of coil blowing up, I too have left the key by accident and never had that happen, just lucky. If it was wired backwards, would that cause it ? Nice cub. Noel


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#6 JDBrian OFFLINE  

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Posted March 24, 2014 - 04:29 PM

Never heard of coil blowing up, I too have left the key by accident and never had that happen, just lucky. If it was wired backwards, would that cause it ? Nice cub. Noel

No, it shouldn't make the coil blow up if it's simply wired backwards. When the points are closed continuously you get a continuous DC current flowing through the coil. If you have a DC resistance of 3 ohms and a 12volt battery you end up with 4 amps flowing. That is 48 watts being dissipated in the coil. It will heat up and apparently it can blow it's top. This reminds me of my first motorcycle. A 1974 Honda XL175 with points and a tiny 6volt battery. I flattened the battery on it many times and would push it in gear to turn the engine over (It helped if it was down hill) and it would eventually produce enough spark to start. 


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#7 propane1 ONLINE  

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Posted March 24, 2014 - 04:51 PM

Thanks for the info. I have seen the coil get hot, never thought it would blow up. Down hill is better for sure. Back in the days of working as a mechanic if you took the coil wire out of the coil and looked in the top and saw oil it was considered the coil was bad and you replaced it. 35 years ago. Noel   


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