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Post by csulaguy on Aug 6, 2019 0:43:26 GMT
While putting some things in my DR2, I happened to have my hand on my hallway door AND the cabinet, and I shocked myself. After doing some testing with my multimeter, I found that the cabinet is putting out about 84-85VAC when I connect my multimeter to the door screw on the cabinet and to the same on my hallway door. When I connect to a screw on the top that holds the badge/heater cover in place, I get a full 124V. When I reverse polarity on my plug and put neutral on the common wire for the motor, those values change to 44VAC for the cabinet and 62VAC for the top.
I'm concerned there could be an internal short to ground or something. The fridge otherwise runs great. Nearly as quiet as a CK, and cabinet temps are in the 36-40 degree range.
I measured from start to common - 3.4
run to common 4.6
start to run 7.8
common to chassis 124k
heater to chassis - no connection
I just checked things again and confirmed what I wrote above.
Any suggestions are much appreciated. I'm not wild about the possible prospect of a motor rewiring if it comes down to that, though if it did, I might not be opposed to it in the future, as I have plans to finish restoring the cabinet (when I have a break from work).
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Post by csulaguy on Aug 6, 2019 3:28:39 GMT
UPDATE - I tried an isolation transformer, per Travis' recommendation. With neutral connected to motor common, I got the ground/chassis voltage down, to 40-ish on the top and about 24VAC on the cabinet door handle. It doesn't isolate it completely, and my other concern is that the isolation transformer I have is only 1000VA, so the start relay was energized about a good 5 seconds. Connected to the wall outlet by itself, we're looking at maybe a second before the run winding takes over.
Now I'm concerned I might be looking at a motor rewinding... Any thoughts?
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Post by coldspaces on Aug 6, 2019 4:36:18 GMT
It does sound like the cotton insulation is going. 124k to ground is not normal.
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Post by csulaguy on Aug 6, 2019 7:24:22 GMT
It does sound like the cotton insulation is going. 124k to ground is not normal. Ugh. With that said, is it still possible mine could potentially be a viable candidate for restoration, at least without actually looking at it after opening? It runs as quiet or quieter than my CK and the pig evap frosts up really good. I feel like I've checked a short to ground before, when I had my defective bellows tube (and the motor was seized), but there wasn't a short to ground then. |
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Post by turbokinetic on Aug 6, 2019 9:22:23 GMT
Hi Paul, the 124K to ground is low but not unheard of. Using Ohm's Law, that's about 1 milliamp of current when the full 125V us present. That's enough to cause a shock, but it should not be a strong shock.
I would investigate the insulation beneath the compressor for moisture, as well as the wiring going to the compressor.
Ultimately, a grounded cord would bleed off the leakage current and prevent future shocks.
Sincerely,
David
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Post by csulaguy on Aug 6, 2019 15:18:14 GMT
Thanks David. I never put insulation between the compressor and cabinet, because its operation was intended to be a test (this is the DR-2 we worked on before). It clearly passed its test on working without a hangup.
And you're correct - the shock was enough that I pulled away quickly, but it didn't throw me back against a wall (a capacitor in a camera flash is great at doing that).
Where would you connect the ground point at? I've currently been using the original cord, so I'm trying to think of how I'd implement ground, unless I were to connect a ground wire elsewhere and just use a separate cord (for simplicity's sake and to ensure it works).
Also, a grounded cord wouldn't construe a ground fault at this point, because the current draw is low?
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Post by turbokinetic on Aug 6, 2019 16:17:14 GMT
Thanks David. I never put insulation between the compressor and cabinet, because its operation was intended to be a test (this is the DR-2 we worked on before). It clearly passed its test on working without a hangup. And you're correct - the shock was enough that I pulled away quickly, but it didn't throw me back against a wall (a capacitor in a camera flash is great at doing that). Where would you connect the ground point at? I've currently been using the original cord, so I'm trying to think of how I'd implement ground, unless I were to connect a ground wire elsewhere and just use a separate cord (for simplicity's sake and to ensure it works). Also, a grounded cord wouldn't construe a ground fault at this point, because the current draw is low?
Well, it's all down to terminology. The way we use "fault" in the power generation field is an excess current that causes a protection device to operate. In the sense of a GFCI protected outlet, those trip at 4 to 6 mA whereas your measurements indicate a likely leakage current of 1 mA. In the sense of a trip occurring, it would not be a fault.
The compressor may (and likely will) continue to operate for a long time with this level of leakage current.
The cord conundrum could be solved in a few ways; some more aesthetically pleasing than others. When I restored the CA Form-A for my parents, I kept the original round two-wire plug, which fits the start-relay pins. I drilled a new hole in the center of the plug insulating piece, and fed the ground wire out through that hole, and then attached it to a grounding screw underneath the start relay. The cord is no longer detachable, but it looks 100% original and it is solidly grounded now.
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Post by csulaguy on Aug 6, 2019 18:14:39 GMT
Out of curiosity, did you have a similar leakage problem with your parents' CA? Ideally, if this solves my issue, I'd much prefer this over a motor rebuild, and I think others will agree, especially given how quiet this thing operates.
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Post by turbokinetic on Aug 6, 2019 18:37:32 GMT
Out of curiosity, did you have a similar leakage problem with your parents' CA? Ideally, if this solves my issue, I'd much prefer this over a motor rebuild, and I think others will agree, especially given how quiet this thing operates. To be honest, I never ran it without a 3-wire grounded cord! |
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Post by cablehack on Aug 7, 2019 13:25:45 GMT
UPDATE - I tried an isolation transformer, per Travis' recommendation. With neutral connected to motor common, I got the ground/chassis voltage down, to 40-ish on the top and about 24VAC on the cabinet door handle. It doesn't isolate it completely, and my other concern is that the isolation transformer I have is only 1000VA, so the start relay was energized about a good 5 seconds. Connected to the wall outlet by itself, we're looking at maybe a second before the run winding takes over. Now I'm concerned I might be looking at a motor rewinding... Any thoughts? 1000VA is more than enough. I use a 500VA stepdown transformer for my CA-2. The one used for my CA-1 is overkill at 750VA, but it came with the fridge. The intermittent rating of a transformer is much more than its continuous rating. I should also point out that if a digital multimeter is being used to determine leakage, by measuring voltage to earth, the results will be erroneous, because of the capacitance between windings and the core of the motor or transformer. A digital meter has an input resistance of around 10M ohms, so it doesn't take much capacitive reactance to show a voltage. Professional appliance testing instruments therefore use DC for leakage tests, because this will show actual insulation weakness, rather than just capacitive leakage. |
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Post by Travis on Aug 7, 2019 13:40:03 GMT
It’s not normal to have that kind of leakage. It’s also impossible to inspect the motor leads on a DR this old. All three wires are bound together and are fed through a 1” hole inside the neck area. The D models changed this are are easier to deal with.
Cablehack was the one that suggested the isolation transformer some years back. I’m suspicious of your weighted start coil as the unit was designed to run at 110 volts and not the 124 volts you have. This is why I suggested you make a test cord to try the transformer. I suggested a good grounding point was the rear screw holding the control.
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Post by cablehack on Aug 9, 2019 3:15:34 GMT
Just out of curiosity I tested my CA's for insulation. Rather surprised to see it was over 100 megohms at 500V DC for both. I don't think I need to worry about insulation breakdown - MF is obviously a very good insulator. Measuring the capacitance of the motor windings to the casing revealed about 0.0015uF. At 50Hz, the reactance is about 2.2 megohms, which means the maximum current that can flow is about 540uA. No surprise when connecting a digital meter with about 10 megohm input resistance between the cabinet and earth, it showed 85V.
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