Re: Magneto

Posted by John T on August 17, 2005 at 13:30:06 from (66.244.90.73):

In Reply to: Magneto posted by June on August 17, 2005 at 10:23:16:

June, YES you can "sort of partly" test a coil and condensor using an ohm meter to see if they are definitley BAD, but just cuz they test good with these crude checks dont necessarily mean they are really okay under actual and high voltage operating conditions.

CONDENSOR: To a cheap low voltage (1.5 or 3 volts) battery powered DC test lamp type continuity checker, a condensor MUST SHOW AN OPEN CIRCUIT i.e. no continuity n light dont light up. If it shows continuity through it to DC and the light works ITS BAD/SHORTED OUT. But even if it checks good this way, thats no guarantee its totally good which a true condensor tester may find. Similar, place an ohm meter on the R x 1 scale and it should show an open circuit (infinity ohms) but if it shows low resistane, its bad/shorted.

CONDENSOR KICKBACK/CHARGING TEST: If you first discharge a condensor, then place an ohm meter on the R x 10,000 scale and connect it to the condensor, it should initially swing over to low resistance (cuz condensor conducts ONLY till its charged up) but then kick back over to an open circuit near infinity ohms.

COIL: Again, an ohm meter will tell you if a coil is open/bad, but just cuz it passes a continuity and ohms test dont it it may not be breaking down at high voltage and warm temperatures. The Coils low voltage primary, the circuit from a ground lead to the points, should typicall be very low ohms maybe in the 0.5 to a few ohms, but it must obviously be continuos or its bad/open. The high voltage secondary winding, from ground to the high voltage terminal, should be very high ohms, maybe in the thousands of ohms, however, it must also be continuous.

Of course, at slow cranking speeds, the mag needs a good strong n working spring wind n trip assembly to SNAP loud n sharp to fire.

Im only familiar with the JD type mags, but most mag problems are from burned or corroded or pitted or carboned up or gray oxide coated points or they are mis gapped. If only gray oxide coated but good otherwise, try to non abrasivley clean/buff/polish the surfaces n try her, but replace if burned or pitted or carboned up badly. A point file may be fine to get you back to the shed, but once you cut off the silver coating they dont last long. CHECK THE POINTS FIRST............

With such low energy levels typical in Magnetos, the size/rating and quality of the condensor is VERY important, so make sure its the correct one for your mag.

John T Nordhoff in Indiana, retired electrical engineer

Follow Ups:

Post a Followup Name: E-Mail: Subject: Comments: Optional Link URL: Link Title: Optional Image URL: Email Notification: If you check this box, email will be sent to you whenever someone replies to this message. Your email address must be entered above to receive notification. This notification will be cancelled automatically after 2 weeks.

TRACTOR PARTS	TRACTOR MANUALS

We sell tractor parts!  We have the parts you need to repair your tractor - the right parts. Our low prices and years of research make us your best choice when you need parts. Shop Online Today. [ About Us ]