motor advice

[wallace]

Hi all, I am in the process of makeing my old sagar saw bench look all pretty. I have got a 3 phase motor which I bench tested before installing and it worked well. Now I have put it in the bench and wired everything up the same way as when I bench tested it and it is not working properly. It is not running upto full speed and the boost on my static converter is not going out as it should. What have I done wrong?
thanks Mark

 

[CHJ]

Are we talking the bare motor or with it fitted with drive belts ?

 

[gardenshed]

Is the motor dual voltage? . is it wired Star or Delta ?.

 

[wallace]

At first I tried it belted up and it was really slow I then tried it bare with no belts and it went faster but not full speed. The motor is a really old thing. It has six terminals A1,B2,B1,C2,C1,A2. I have it wired A1,B1,C1.
There are linking wires from A1 to B2 B1 to C2 and C1 to A2. Heres the beast in question

Its the one on the left.
thanks Mark

 

[9fingers]

That sounds like the straps are set for Delta assuming it is 240/415 dual voltage (which at that power it might not be??)
Star would be a2,b2,c2 connected together and phase inputs a1,b1 and c1

Make sure what the correct voltages required by the motor are first of all.

Bob

 

[wallace]

Funny thing happened this morning. I tried the motor again and it worked but then I put the belts on and it wouldn't run up. I haven't got a clue when the last time this motor has been used so I thought I would run it with no load for a little while to blow out the cobwebs. I then put the belts on and it ran ok. The motor is not dual voltage just 400V. After leaving the motor for a couple of hours I tried it again and it took quite a while to build upto speed. Heres a little vid of it running


http://youtu.be/UMxRWqCLVDU

Mark

 

[9fingers]

OK I suspect your motor is wound as delta 400v for use with a start delta starter for some applications. You don't need this mode for the saw.
I would not be concerned with that start up rate in the video when running from a converter but i wonder if the are bad connections inside that have now settled down and it works as intended.
The big problem with stripping down old motors like this is that the internal insulation becomes brittle with age and there is a high risk of breaking it during the investigation. Best left alone until you really have to dive in I reckon.

Do you have the DOL starter connected or are you directly connected to the converter?

hth
Bob

 

[wallace]

Hi Bob, thanks for the reply. I have tried the motor again with load ie belts and it really does struggle to get upto speed. Also the switch starter terminals got very hot. Presumably because of the initial start up current. I am useing the original starter untill I get a DOL one
Mark

 

[9fingers]

Mark, I think the problem is that you don't have enough starting power from the converter. You could try adding a pilot motor to the converter and get that running first- effectively making a rotary converter.

Have any of your capacitors in the converter failed or maybe it is a new/nearly new one

If the starter terminals are hot the the contacts must be even hotter unless you have loose connections.

Is your converter rated greater than the motor (sorry you possibly said elsewhere but i can't recall)

Converters usually have a single motor rating less than the maximum rating - see data sheets on the transwave website.

Bob

 

[wallace]

Hi again, How would I tell if capacitors are not working. The converter was bought second hand. The maximum single motor is 5.75hp. I think I have a little gryphon motor off my jubilee lathe kicking around some where, would that suffice. The cable I used was 2.5mm would that have a bearing on things. I think I will check all the connections on everything. Is contact cleaner any use. Thanks for all your help.
Heres another clip.

http://youtu.be/XPypEvf5p10

 

[9fingers]

Capacitors would need measuring under load - not easy without the right equipment.
This is a 5hp motor? so you are close to the maximum but should be Ok if the converter is working properly
The pilot motor ought to be near or close to the maximum output - 3hp or above will possibly make a difference.
2.5mm cable should be fine and (hopefully) should not get warm.
Contact cleaner is not likely to help - that is more for electronic applications.
As a test wire, the motor direct to the converter.

That start up was far too slow and much slower than the earlier video - what was the difference in set up?

Bob

 

[wallace]

The differance was with the converter not on the maximum setting and the belts on, starting after being left for a few hours.
mark

 

[9fingers]

OK well you certainly need max boost (and some!) to get it going.

Bob

 

[wallace]

Hi Bob just a little update, just out of interest I sent an e-mail to the people at transwave asking for their thoughts. One of their suggestions was that I might be suffering from a voltage drop feeding the converter? I have the converter wired direct to consumer unit in workshop which is fed from the house with its own fuse box via very heavy duty cable. Another suggestion was like you mentioned dodgy capacitors. He also thought it might be usefull to add more starting capacitors to my unit. Apparently my converter was made in 1989.
Mark

 

[9fingers]

Hi Mark,
Transwave are very helpful people.
I nearly suggested adding capacitors but had second thoughts as I wondered if you would be comfortable with that approach.

One way to check if low voltage might be a problem is to see if your workshop lights dim significantly during the protracted start up period.

Bob

 

[gardenshed]

Just to add, the capacitors wear out over time, in fact to keep some of the converters in warranty some of the suppliers want you to change them every year.

 

[wallace]

Just out of interest, is it a specialist thing to replace capacitors or is it relatively simple.
Mark

 

[9fingers]

Very easy. Most have simple spade connector to pull on and off and an m8 threaded stud to hold them in place.

Buy them as motor run capacitors making sure the voltage rating on the new ones is at least the same or greater than the old ones.
I would expect Transwave to supply them as they must buy shed loads for their production.

MAKE SURE THE OLD ONES HAVE BEEN DISCHARGED FULLY BEFORE YOU TOUCH ANYTHING INSIDE.

Bob