Band saw tripping overload

jaddy · Jan 7, 2018

I recently purchased a Kalamazoo h9wa, 2 hp 3 phase. It runs good but after a few minutes it trips overload on contractors. I am running with a phase converter which is plenty large enough. Voltage is 120 on 2 legs and 230 to ground on the stinger leg. Amps while running is 8amps on the two 120 legs. And 2amps on the stinger. Is this too much? Could the overloads be weak? I did check resistance between l1,l2,l3 it was 2.5 and none to ground. I don’t know what else to check any help would be appreciated!

toolnut · Jan 7, 2018

3 phase VOLTAGE measurements should be made Phase to Phase. Phase to ground tells very little
The low amps on your generated leg is not normal.
State the amp rating of your starter heaters also. They may be undersise.
Bruce

jaddy · Jan 7, 2018

L1-L3 275v
L2-L3 257v
L1-L2 240v
Max 20 amp on overload. Dial has 4-6
The low amp was not on stinger leg as previous stated

ewlsey · Jan 7, 2018

My chart says full load amps on a 2hp motor is 5.6A. So, your heater is properly sized, depending on the service factor.

If it's pulling 8 amps on any leg then something is wrong.

Ziggy2 · Jan 7, 2018

Is this a static phase converter?

Your currents sort of make me think that the motor is two phasing under load which might mean that it is the phase converter.

jaddy · Jan 7, 2018

Ziggy2 said:
Is this a static phase converter?

Your currents sort of make me think that the motor is two phasing under load which might mean that it is the phase converter.

No, it’s a American Rotophase 25hp

Jraef · Jan 8, 2018

Something's still wrong. 8A on two legs is why your OL relay is tripping. DON'T BLAME THE OL RELAY, it's doing its job of preventing a fire in the motor!

SAF · Jan 9, 2018

My thoughts are you have 2 issues going on here, contributing to the problem.

First is the RPC size. Most converters have a minimum size load motor you can run without overheating it. This is due to the amount of capacitance provided in the unit, being sized for the maximum converter load. With too much capacitance for a small motor, the voltage being produced will be high, driving the load motor magnetics into saturation. Saturation and high voltage, causes excessive currents.

Your highest voltage was stated at 275V. This should be around 260V maximum with the small load connected. The phases with the highest voltages will be the ones with the highest currents. The converter needs to be re-tuned for a smaller motor if you want to get the output voltages in line.

Second is the overload relay. As stated earlier, the motor is pulling over its rating, causing a trip. Helping to facilitate that trip quicker is the overload type. IEC type adjustable overloads normally have built in differential protection, to guard against single phasing. This means that when the current between lines is unequal, it causes the relay to trip faster than it would with a balanced overload.

Bottom line is you need to balance the output of the large RPC, in order to be able to run a small motor successfully, without killing it and the overload relay.

SAF Ω

jaddy · Jan 9, 2018

SAF said:
My thoughts are you have 2 issues going on here, contributing to the problem.

First is the RPC size. Most converters have a minimum size load motor you can run without overheating it. This is due to the amount of capacitance provided in the unit, being sized for the maximum converter load. With too much capacitance for a small motor, the voltage being produced will be high, driving the load motor magnetics into saturation. Saturation and high voltage, causes excessive currents.

Your highest voltage was stated at 275V. This should be around 260V maximum with the small load connected. The phases with the highest voltages will be the ones with the highest currents. The converter needs to be re-tuned for a smaller motor if you want to get the output voltages in line.

Second is the overload relay. As stated earlier, the motor is pulling over its rating, causing a trip. Helping to facilitate that trip quicker is the overload type. IEC type adjustable overloads normally have built in differential protection, to guard against single phasing. This means that when the current between lines is unequal, it causes the relay to trip faster than it would with a balanced overload.

Bottom line is you need to balance the output of the large RPC, in order to be able to run a small motor successfully, without killing it and the overload relay.

SAF Ω

Thanks for all help. This is the first small motor I have ran with overload protection. (which found my problem maybe) I did notice when I was running multiple machines it dropped the amps a little bit and ran longer before tripping. I have a 5hp on my lathe with reversing contactors, the motor was rated at 200v so I put a buck/boost transformer to take care of the voltage.

Could balancing the voltage of the RCP be as easy as unhooking some of the run capacitors, until I get desired voltage?

Guest · Jan 9, 2018

jaddy said:
Could balancing the voltage of the RCP be as easy as unhooking some of the run capacitors, until I get desired voltage?

Yes and no. Problem is what it takes to balance a simple rotary will vary depending on what loads it is running. I would not balance a 25hp rotary using 2hp as a test load. It does seem odd that your bandsaw is being feed with high voltage and pulling high amps, high voltage should lower the amperage. Have you tested the motor for issues?

jaddy · Jan 9, 2018

I did an ohms test to each leg which read 2.5 and to ground from each leg which was OL

atomarc · Jan 9, 2018

This may have been covered and I missed it. Have you pulled the blade and looked for or considered a mechanical issues? The motor may be working hard because you have a worn out gearbox or a binding band-wheel or guide block.

Stuart

Guest · Jan 9, 2018

Was your voltage from inside the motor cover or taken at the converter or incoming breaker or switch on the saw? If that voltage is what is inside the motor cover look for an excessive load due to mechanical problem as stated above. It seems the motor is probably okay.

SAF · Jan 9, 2018

A test that you can do is to connect the saw to the output of your buck transformer. If the overcurrent is due to the high voltage, it should be somewhat reduced on the lower voltage feed. Maybe still not perfectly balanced but better.

Have a read on this document for balancing procedure of a RPC.

http://www.practicalmachinist.com/FitchWConverter.pdf

SAF Ω

jaddy · Jan 9, 2018

I tested another motor in shop. A 5hp 2 of the legs has 15 amps and one has 0. So the phase converter must be a fault.

jaddy · Jan 9, 2018

I inspected Rpc cabinet there is 12 100ul run capacitors. They have been leaking, it’s hard to tell which one. Think my next step will be taking each out and testing them.

Guest · Jan 10, 2018

jaddy said:
I inspected Rpc cabinet there is 12 100ul run capacitors. They have been leaking, it’s hard to tell which one. Think my next step will be taking each out and testing them.

I have found leaking capacitors that were working just fine. Didn't you say the output on the RPC was good? Maybe I misunderstood. Honestly a basic AC 3 phase motor on a manual machine should me able to run on an unbalanced RPC. I have a rotary RPC that sends out all kinds of high unbalanced votages running all my manual equipment and have not had an issue in over 20 years. I would just remove the run caps, measure the voltages and try the bandsaw again. My guess is you have a bad connection somewhere. Please let us know what finally fixes the problem.

Lanso · Jan 10, 2018

atomarc said:
This may have been covered and I missed it. Have you pulled the blade and looked for or considered a mechanical issues? The motor may be working hard because you have a worn out gearbox or a binding band-wheel or guide block.

Stuart

I agree with Stuart, I’m not saying it’s mechanical but it deserves a check. I had a similar issue and checked everything electrical before I discovered it was a simple mechanical problem

jaddy · Jan 10, 2018

Lanso said:
I agree with Stuart, I’m not saying it’s mechanical but it deserves a check. I had a similar issue and checked everything electrical before I discovered it was a simple mechanical problem

I have check that, it turns free by hand. I would think that was an issue.

jaddy · Jan 10, 2018

Dualkit said:
I have found leaking capacitors that were working just fine. Didn't you say the output on the RPC was good? Maybe I misunderstood. Honestly a basic AC 3 phase motor on a manual machine should me able to run on an unbalanced RPC. I have a rotary RPC that sends out all kinds of high unbalanced votages running all my manual equipment and have not had an issue in over 20 years. I would just remove the run caps, measure the voltages and try the bandsaw again. My guess is you have a bad connection somewhere. Please let us know what finally fixes the problem.

In process of checking. One thing I did try something that was cut all equipment on at same time which was 2(5HP) 1(1hp) 1(1.5hp) 1(2hp). I checked my voltage output for RPC and it was pretty close to the same. And the saw didnt trip the overload. So i'm studying on how to balance the voltage (i think its my problem) its not common to run all at once.

The reason for large RPC is i paid $300 for it, replace the switch that kicks start up caps out, has been working pretty good.

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