Anyone know how to test a coil and a condensor???

RTR · Nov 18, 2010

Hey guys, does any of you experts out there know how to test an ignition coil (6 or 12 volt)? I would also like to know how to test the condensor that goes inside the distributor as well. I have several Farmall tractors as well as a Cub Cadet Lawn Mower that I am working on.

If there are any special testers/tools required please let me know. If the testing equipment can be home made, I can do that as well. Thanks for all your responses!!!

Wayne in MN · Nov 18, 2010

Find an old timer in the marine or motorcycle business and ask if they have a Merc-O-Tronic tester. They can test coils and condensers.
I have one here in MN.

John T · Nov 18, 2010

You can use a simple ohm meter to see if a coil is BAD buttttttttttt it will not tell you if its GOOD. Theres typically say 1.25 to 3.5 ohms (depedns if a 6 or 12 volt coil) in a coils LV primary between its lil + and - terminals and maybe 5,000 to under 10,000 ohms in its HV Secondary. If either is open (no continuity) the coil is baddddddddddddd but even if it passes both those checks, it can still fail once its warmed up especially a HV breakdown failure which youre not gonna see with that LV ohm meter test.

Likewise an ohm meter will show if a condensor is baddddddd but it cant tell you how good it is or its MFD rating or if its leaky, it takes a real capacitor tester to do that. Using a DC ohm meter it should show an open circuit once its charged but if its a short its baddddddddd. If you have an old analog ohm meter like my Simpson 260 a kickback/charge test can tell a bit more about how well and if shes charging up or not.

Good way to test a coil is wire it up and allow curent to flow then interrupt the current (simulates points closed then opened) flow n see if theres a spark by using a coil wire out the top tower to ground.

My Ignition troubleshooting shows other coil checks

http://www.ytmag.com/cgi-bin/viewit.cgi?bd=farmall&th=5745

John T
John Ts Ignition Troubleshooting

mike paulson · Nov 18, 2010

Check the ignition coil primary coil resistance by connecting an ohmmeter between the small terminals on the coil. The resistance should be around .5 ohms.
Check the ignition coil secondary coil resistance by connecting an ohmmeter between the coil output terminal and the ignition coil negative terminal. The resistance should be 5000 to 8000 ohms.
these are round about numbers, but if your coil is shot you will get an open reading on either side of the coil or a reallly high reading for ex 100k ohms.

RTR · Nov 18, 2010

(quoted from post at 07:50:32 11/19/10) Check the ignition coil primary coil resistance by connecting an ohmmeter between the small terminals on the coil. The resistance should be around .5 ohms.
Check the ignition coil secondary coil resistance by connecting an ohmmeter between the coil output terminal and the ignition coil negative terminal. The resistance should be 5000 to 8000 ohms.
these are round about numbers, but if your coil is shot you will get an open reading on either side of the coil or a reallly high reading for ex 100k ohms.

THANKS GUYS!!! Any ideas on how to test the condensors? (besides the Merc-0-Tronic tester.)

RTR · Nov 18, 2010

Also, here is a picture of my multimeter. What setting do I use for all of the above tests (found on the posted link)? The different settings on the multimeter look like Greek to me, and there are so many different ones I have no idea where to turn the knob to. THANks for putting up with my electrical ignorance. HAHA

RTR · Nov 18, 2010

Picture...

Bob · Nov 19, 2010

.
Testing a coil with a little help from the Army...

WSJ · Nov 19, 2010

Almost all automotive distributor coils use a 0.25-0.29 microfarad capacitor. I measured one at 0.22 uF.

Harbor Freight sells a multimeter that measures capacitance as well as all the following standard functions. I have used this model for several years.

DC voltage: 2-20-200-1000V
AC voltage: 2-20-200-700V
DC current: 2mA-20mA-200mA-20A
AC current: 20-200mA
Hz range: 20K
Resistance: 200 Ohms-200 Meg. Ohms
Capacitance range: 2nF,20nF,200nF,2uF,20uF
Temperature probe: 20° Celsius to 1000° Celsius

http://www.harborfreight.com/ac-dc-digital-multimeter-37772.html

mike paulson · Nov 19, 2010

as far as condensors, i just buy a new one, they are cheap enough...and readily available.

Brownie 450 · Nov 19, 2010

To check coils, I have put together an old set of points & condenser with jumper wires for + &- to the battery and jumper to the coil. Connect the wiring the same as in a regular distributor & coil arrangement, & open/ close the points by hand. A plug wire out the coil nose & anchored 1/4 inch from the coil case will give a good indication of coil quality.

Anonymous-0 · Nov 19, 2010

You really need a good coil tester like a Merco-Tronic or Graham-Lee tester. Those will tell you how much of your secondary windings are shorted and will test for insulation breakdown on the outside of the coil. These testers also apply a higher voltage to the coil and condensor during testing. The standard voltmeters can't do that and mislead some people into thinking that their coil or condensor is good.

AL Farmall Boy · Nov 19, 2010

anyone out there used a multimeter to test coils?? I am trying to do the same thing and don't know which setting to use as RTR explains.

John T · Nov 19, 2010

A typical old tractor coil would have in the range of 1.25 to 4 ohms (use ohm meter on Rx1 scale) primary winding resistance as measured between its little + and -terminals, while something like 5K to 10K ohms (use meter on Rx100 or Rx1000 scales) in its HV Secondary IF EITHER SHOWS AN OPEN CIRCUIT THE COIL IS BADDDDDDDDDDDDD

HOWEVER even if it passes BOTH those ohm meter tests (which it MUST or its bad) that dont tell you if its GOOD cuz she can break down once warmed up and especially at high voltages (HV insulation breakdown) which the low voltage ohm meter test simply cant show you.

A realllllllllll coil tester, however, can test for higher voltage breakdown and thats often where a coil fails anyway especialy after its warmed up

John T

Bob · Nov 19, 2010

You CANNOT prove that a coil is good by using a multimeter with any degree of certainty.

You CAN, however prove that one is BAD (completely OPEN or badly shorted).

You CANNOT tell if there's a shorted "turn" or two which is what commonly happens, GREATLY reducing coil output and instead dissipating potential spark energy as HEAT.

The ONLY reliable test equipment is some type of coil tester that "rings" the coil, which detects shorted "turns".

bc · Nov 19, 2010

I guess if you were rummaging around the junk yard or had a pile of coils over in the corner, testing for an open or dead shorted coil with a multi-meter would be a start.

Regarding the output: Is there any size resistor that one end could be stuck in the output of the the coil to test voltage or amperage with a multimeter? The same would apply for testing the output of any of the spark plug wires from the distributor.

WSJ · Nov 19, 2010

A functional ignition coil tester can be built for about $30.
Part numbers are available if anyone is interested in building this coil tester.

Owen Aaland · Nov 20, 2010

I guess I just take the easy route. I hook the coil to my Sun diagnostic center, set it for coil test, and watch the pattern on the scope. The built in capacitor tester was also great for charging up capacitors and leaving them lay for some unsuspecting soul.

WSJ · Nov 22, 2010

Testing Electrical Systems with a Digital Multimeter
http://assets.fluke.com/appnotes/automotive/beatbook.pdf

36 Coupe · Nov 23, 2010

A spark plug wire will eat your meter.

JJHein · Dec 22, 2010

(quoted from post at 18:38:32 11/18/10) Hey guys, does any of you experts out there know how to test an ignition coil (6 or 12 volt)? I would also like to know how to test the condensor that goes inside the distributor as well. I have several Farmall tractors as well as a Cub Cadet Lawn Mower that I am working on.

If there are any special testers/tools required please let me know. If the testing equipment can be home made, I can do that as well. Thanks for all your responses!!!

Hey RTR I have a very old MercoTronic dual tester model number 57-15-0-15 amp.-voltmeter that may be what you are looking for. It belonged to my Grandfather who ofter worked on boats and various other engines. It may or may not be what you are looking for just thought I would offer it just in case.
After reading many posts about these testers you would need a manual for it which are available according to other posters that are willing to copy them. Let me know if you are interested, I can take a picture of it if that will help.
JHein

mkirsch · Dec 23, 2010

If you don't even have a decent multimeter, you'd be best off simply buying a new coil and a new condenser, and replacing the suspect parts.

Anyone know how to test a coil and a condensor???

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Well-known Member

Member

Member

Member

Well-known Member

Member

Well-known Member

Well-known Member

Well-known Member

Member

Well-known Member

Member

Well-known Member

New User

Well-known Member

Similar threads