Contactor Overload Relay not working - need help
#21
OK, I had another look at it this AM, and it looks like it is wired like the schematic you posted, Mike. The OL relay won't reset even with no output (motor) wires connected to it.  I removed it from the contactor and ran the motor wires  to the output terminals of the contactor, so there's no overload protection now but the motor runs and Ken is in business until I can figure out how to replace it. 

I brought the OL relay home and opened the cover.  Two of the legs that connect to the contactor were broken or fried off where they were welded to the internal connections.  Of course, other parts started popping out and I have a hand full of tiny parts now.  At least one of the world's tiniest springs left for parts unknown, too.  But without a spot welder I won't be able to repair the busted lugs anyway so it doesn't really matter.  I didn't see anything broken or fried besides the power legs so I don't know why the relay wouldn't reset unless it needs power on at least two of the legs to do so. 

I was looking for a "universal" type OL relay but didn't find any in 30 or 40 minutes of searching, which seems rather strange.  Anyone have any ideas how to add on an OL relay (in the 10 - 12 amp range)?  I haven't checked to see if an AB, Schneider, or similar unit would actually fit but that's my first look see if I can't find a separate, universal relay. 

Thanks.

John
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#22
OK, I'm somewhat better informed now.  I found a cross reference chart for Telemecanique and found a new version of the OL relay that fits the contactor we have.  Nice.  But I was bothered by why the relay only has 5.5 - 8 amp rating for a motor drawing 11.4 FLA so I wanted to understand how that could be correct before ordering a new relay.  There's a lot more to it, as I'm sure TDKPE could explain, but if you divide FLA by the sq. root of 3 it will put you in the right range, so that's 6.58 amps. 

I found the new version of the contactor on Amazon w/o a problem, so we'll have full motor protection soon and a happy ending to this story.  Maybe Ken will post a picture of the jointer now that it's all together and running.  It is a 16" wide, 99" long, 1600 lb smooth running monster.  

John
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#23
Could the old overloads have been for a 480v 3 phase motor ?  That would be about half the current for a 230v motor of the same hp.   As far as the fl amps, that is the current per leg, you don't divide by  √3.
 If you have a chance take current readings and voltage readings on each leg while running.   I am not sure how even they are when single phase is converted to 3 phase.   Maybe Tom will see this and comment.   Roly
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#24
The jointer was and is wired for 220V 3 phase operation, though it is capable of running on 440 V as well.  The old (original) motor was run on 3 phase power, the new one runs off 1-phase input into a static phase converter to get it's 3 phase input.  As I reported above, the new motor draws around 9 - 10 amps per leg when it's running under no load other than turning the cutterhead.  This motor is rated at about 11.2 FLA, the old one was rated slightly higher.  The old OL relay had a rating of 5.5 - 8 amps and was a Class 10 type.  

Yes, you are right.  I misspoke on how to size the OL relay.  Let's see if this is about right.  FLA/1.732 = Phase current, so 11.2/1.732 = 6.5 amps. Minimum OL relay setting = phase current x 70%, so 4.6 amps.  Maximum OL relay setting = phase current x 120%, so 7.8 amps. 

If that is correct, or close, it looks like the old relay was sized correctly, and should be OK with the new motor as well.  If anything, it seems if it should be even smaller as the motor is now down to 2/3's of its rated 5 HP by running off the static phase converter.    


John
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#25
You don't divide the fla by 1.73. The nameplate current is correct, the motor will draw the 11.2 amps on each leg. You need an overload relay sized to the motor fla as printed on the motor.

The motor is making less power because it is essentially running on only two of the three windings, but at the full rated current on those two.
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#26
How was it the old motor ran on that overload relay?  Must be it never pulled more than 75% or so of FLA?

John

This was the reference I used for the calculations:  Link
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#27
Did you or Ken see it running before?  Did the pulley size change with the new motor?  Grasping here because if all else was the same, it should have tripped before. If it didn't, it was loading that OL to the max and that would explain why it cooked.
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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#28
Sounds like the old motor was running on 480V utility power.

sqrt(3) is used to convert line current to total volt-amps via VA = I x sqrt(3) x V, or motor hp to line current via I = HP x 746 / V x pf x eff x sqrt(3), where the square root of 3 is only used for three-phase loads. If it's a resistive load, like heating coils, you get watts. Reactive loads, like motors and transformers and lights with ballasts, will have higher volt-amp values than wattage, but that's another topic.
Tom

“This place smells like that odd combination of flop sweat, hopelessness, aaaand feet"
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#29
Thinking back on it I'll bet it was originally run on 440, 3 phase power.   The last owner said he ran it on 220V, 3 phase, and that is how the motor was wired, but Ken and I question if he ever indeed ran it.  On the other hand, the OL relay was set at the max of 8 amps (and would not have been at 440 V) and two of the legs were broken/fried off, so who knows.  

So, all said and done, I need an OL relay in the range of 8 - 13 amps for a motor pulling 11. 2 amps at 220 V, correct?  There is a Telemechanique rated at 9 - 13 amps.  Will that be OK?  

John
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#30
Run some material through taking a heavy cut and see what the motor is drawing under load. What does the phase converter have for overload protection or will it be tasked to different machines at times?
Blackhat

Bad experiences come from poor decisions. So do good stories. 


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