What's with my graph?

[wptski]

A HVAC tech in another forum was wanting to purchase a megger to use on sealed compressor motors in residential work. He was considering a Fluke 1507 to run PI/DAR tests. Since I have one and have stated several times here that they will generate out of range errors almost every time even if 1000V is used because they don't have a high enough range. I also have a old dehumidifier that either out or low on freon, I agreed to try the 1507 on it.

As I suspected the 1507 errored out but I used a AEMC 1060 also. The AEMC will generate the same error at 100V but doesn't at 250V or 500V.

Anyway, I saved a 10 minute test at 500V and here's the strange graph. I've seen this before on some old grey/black Romex that's used in my home.

Anybody have any ideas as to why it looks as it does? I guess this one goes out to zog really. I may retest just to see if I get the same results again.

 

[ptonsparky]

What do you mean by errored out?

 

[hurk27]

A HVAC tech in another forum was wanting to purchase a megger to use on sealed compressor motors in residential work. He was considering a Fluke 1507 to run PI/DAR tests. Since I have one and have stated several times here that they will generate out of range errors almost every time even if 1000V is used because they don't have a high enough range. I also have a old dehumidifier that either out or low on freon, I agreed to try the 1507 on it.

As I suspected the 1507 errored out but I used a AEMC 1060 also. The AEMC will generate the same error at 100V but doesn't at 250V or 500V.

Anyway, I saved a 10 minute test at 500V and here's the strange graph. I've seen this before on some old grey/black Romex that's used in my home.

Anybody have any ideas as to why it looks as it does? I guess this one goes out to zog really. I may retest just to see if I get the same results again.

That spike looks like a switch opened after an event, maybe the low pressure switch opened after the compressor equalized? but then it closed? naw that just doesn't make sense

How long did you have the dehumidifier off before you tested it?

 

[wptski]

What do you mean by errored out?

Out of range error, test incomplete.

 

[wptski]

That spike looks like a switch opened after an event, maybe the low pressure switch opened after the compressor equalized? but then it closed? naw that just doesn't make sense

How long did you have the dehumidifier off before you tested it?

Since about the first week in June! The compressor did run, it was blowing ambient air when it should be warmer than ambient.

 

[wptski]

One of the aligator clips must have lost contact. I retested without touching the ground clip and the average readings were much lower.

The following are the Sart, Run and Common terminals. Still odd though, I think!

 

[zog]

What do you find odd about these? The 1st minute or the fluctuations towards the end of the tests?

 

[wptski]

What do you find odd about these? The 1st minute or the fluctuations towards the end of the tests?

The first minute is the same in all three. Yes, the fluctuations in the last two.

You have two windings in series, R terminal at one end, S terminal at the other and C terminal in the middle. Your basically testing at the same electrical point, shouldn't they all look the same? The average reading of C and R were eaxctly the same.

I was wondering of back to back testing caused stress? I tried a thirty minute test on the S terminal but the software chokes on the file for some reason! I email AEMC Tech Support about the issue.

If one were checking this motor, you'd ohm out the windings to check for a open and do a one minute test which results in the hundreds of Gigs. For all general purposes, this motor would look good.

 

[zog]

The first minute is the same in all three. Yes, the fluctuations in the last two.

That is from your capacitive charging current and polarization current decaying like you expect to see.

You have two windings in series, R terminal at one end, S terminal at the other and C terminal in the middle. Your basically testing at the same electrical point, shouldn't they all look the same? The average reading of C and R were eaxctly the same.

I was wondering of back to back testing caused stress? I tried a thirty minute test on the S terminal but the software chokes on the file for some reason! I email AEMC Tech Support about the issue.

Exactly, try the test again but fully charge your batteries, then leave it on charge for your test.

If one were checking this motor, you'd ohm out the windings to check for a open and do a one minute test which results in the hundreds of Gigs. For all general purposes, this motor would look good.

You want to compare phases of each winding, they should be within 5% of each other. Motors should have a 10 minute test done, calulating DAR and PI. Results should be tempature corrected to 40 degrees C.

 

[wptski]

You want to compare phases of each winding, they should be within 5% of each other. Motors should have a 10 minute test done, calulating DAR and PI. Results should be tempature corrected to 40 degrees C.

Aren't you refering to a 3-phase motor about the 5%? This is a single phase PCS motor. I've read that a PCS motor's two windings are exactly the same so it's easy to reverse rotation. This isn't true with the PCS motors used in these hermetically sealed compressor units. HVAC guys that have worked on hundreds of them vouch for that.

 

[hurk27]

just about any capacitive start motor is kind of a three phase motor, the capacitor just shifts the phase angle over to give rotation, the size of this start winding and capacitor is just dependent upon the required torque.

can you run a 3-phase motor using capacitors to the third phase, yes, Wascomatt washers have done so for years, all thier machines have three phase motors in them, but when installed in a location where three phase is not availble then you get this big bank of capacitors in the bottom to do just that.

 

[zog]

Aren't you refering to a 3-phase motor about the 5%? This is a single phase PCS motor. I've read that a PCS motor's two windings are exactly the same so it's easy to reverse rotation. This isn't true with the PCS motors used in these hermetically sealed compressor units. HVAC guys that have worked on hundreds of them vouch for that.

I was refering to a 3 phase motor, my bad.