Practically of using a Megohmeter for testing transformers and motor windings

What are you going to do with the results?   A megger will tell you the insulation condition of the motor or transformer windings.   If the results are low then what.   These items are run to failure.  

The short answer is I have Heartland Vintage Train repair in Oklahoma and I repair a lot of Transformers and Lionel engines. If the Megohmeter will give me an indication off a field winding or a transformer winding is questionable it would be helpful to know. I hope Gunrunner John will add his opinion on this , besides, the old Lionel test centers had a insulation tester on them.

Agree with Steims, what’s the purpose? …..If a coil ain’t shorted or open, you’re gonna roll with it, if an armature ain’t shorted, or open, you’re gonna roll with it……..if you invest in a piece of equipment, the idea is that tool is there to make you money,……no??…….what’s the plan? You gonna charge for an insulation condition report?  Sadly, this business ain’t like automotive repair, or appliance repair, where folks gotta fix it, ….these are toys, you go getting into charges on top of charges, the first thing folks are gonna ask is if there’s a dumpster near by and could you please insert the trains in it……..invest that money in quality hand tools that can help you beat the clock,…..that’s the name of the game, ……😉

Pat

The purpose of a Megohm meter is to increase the voltage used to test resistance high enough so the meter can read the very small current flow found in very high resistances.  With the low voltage used in toy trains very high resistance leaks do not mean anything, as there is almost no current flow. If there were applications where the measuring of very high resistance was useful, maybe between the plug prongs and the case screws, what resistance value is not acceptable?  Without a condemning limit standard the results are useless.  Also, there need to be guidelines on how high the Megohm meter voltage should be set without damaging the transformer you are testing.   I believe you would better served with a Lionel 5D tester. It does have many transformer tests built in to it and the Lionel manual for the 5D tester gives guidelines for the acceptable levels.

@MNeafus posted:

Would it worthwhile to use a Megohmeter on Lionel transformers and pullmor motors?

This is used for mission critical applications, toys do not full under that.

I'm going to have to sing with the chorus.  Obviously, it can't hurt to test the insulation resistance, but in practical terms, I doubt it's going to be a major difference maker.  If you have the megohmmeter, that's one thing, but I wouldn't go out and buy one for this use only.

Thanks John , a short answer is all I wanted.

Gunrunner John, the old Lionel test centers had an insulation test port . If I’m correct, it was to test for leakage in the transformers. Is there a way to perform a test like this or would it be possible to build a test unit that would do this when evaluating a transformer. This was the information I was looking for with the post about using a megohmeter to check for leakage.

A little off-topic, but I think Dennis Waldron (RIP) had a "growler" used by the Lionel factory to test armatures.  I think Trainz (of Georgia) bought Dennis' stuff after he passed away.  It would be great if the TCA could somehow obtain the growler and offer armature testing for a modest fee.

@MNeafus posted:

Gunrunner John, the old Lionel test centers had an insulation test port . If I’m correct, it was to test for leakage in the transformers. Is there a way to perform a test like this or would it be possible to build a test unit that would do this when evaluating a transformer. This was the information I was looking for with the post about using a megohmeter to check for leakage.

I'm not sure how they did that, basically they probably had all the elements of a megohmmeter, it's just a very low current high voltage power supply.

If you really want to do this test, I'd consider one of the inexpensive insulation testers that are available, they perform the function of the megohmmeter and more.

Here's one of many low cost insulation resistance testers available on Amazon.  This will be far easier than trying to roll-your-own.

Thank you everyone for the constructive answers and information