megger

[rldavis]

I am trying to test the rotor and stator on a Microlite 2.8. The service manual says to use a megger or the highest scale if not using a megger. Trying to test for a grounded rotor - manual says not less than 1 megohm. Has anyone had any experience using a common meter for these tests or do you suggest taking them to a shop? Shop wants 95.00 to test both - does this sound reasonable?
Thanks,
RobertDavis

[TEXAS]

Is that the same as holding the plug wire. With your finger. While the wife turns the engine over.

[MEXICOWANDERER]

Course you could connect 120 v in series with a light bulb to the stator leads then stick your tongue on the laminations. Or through the slip rings then do the same to the rotor shaft

N-O-T !!!

Just joking

Engineer Humor

[Matt_Colie]

Robert,

If you are in California or the upper east coast, that is a good price, anyplace else, it is outrageous.

We are talking about a HiPot test here. (High voltage insulation test)

I am a ship's engineer by trade and sailed as the electrician for many years before I got a license.

A megger is a valuable instrument, but with the new DVOM(DMM) that are available this is much less true. Meggers get their glory by using 500 or 1KV as the measuring source. With old electrics this was essential. My good meters will indicate a ground leak just as fast as most modern meggers will.

If you are doing this because you suspect that a part has a problem, start with a good meter. Don't bother with a CCV(Cheap Chinese Version) as they tend to be less than reliable at the edges of the envelope (where you will be). We are only talking about a 120V piece of equipment here. (Even if it is 240, it is still only 120 over ground.) If that good instrument says you have a leak, believe it. If it does not, then you have to decide if the fare is worth it. You might even go on EBay and buy a CCV megger for half what the shop wants.

Thinking is the cheapest thing to do...

Good Luck Guy

Matt

[TEXAS]

Not a big fan of the megger. I saw a Cat unit fail a megger test in 1975. As for as I know. That unit is still in operation. I know it was as of two years ago.

[C_Schomer]

I work on mostly 480+ stuff and 1 meg would mean curtains for certain. In fact, already smoked! I want to see 10 meg minimum but I usually see close to 1 gig. $95 for 5 minutes work is great for the guy with the megger. A common DMM only measure resistance but a megger puts a selected voltage thru the circuit and measure insulation strength/leakage to ground. I gave up on ohmmeters for stuff like that decades ago. They usually got me into trouble. I tripped a power plant once cuz I didn't have a megger with me and I trusted an ohmmeter. They are not reliable for that at all. The first meggers I used were the hand crack Biddles that put out 5kv+ but about 20-30 yrs ago, it was decided it's bad to megger at a voltage that's very much higher than operating voltage so the newer meggers are voltage selectable. Craig

[Johno02]

Yes, you need a megger, AND someone that knows how to use one!!

[MEXICOWANDERER]

Critical not the faintest trace of voltage finds its way to ground. I was mean and used to use a 5KV Hi-Pot.

[donn0128]

Yes. You need a megger.