3-phase 2-speed question

Ken,

I can't help with a diagram but my advice is to check the motor thoroughly when disocnnected from the control box. When you are sure the motor is good on both speeds, then trouble shoot the control box.

Bob Swinney

Check Wiki-answers:

Paul

Another possibility - there's a wire swapped, or most likely the shorting contacts aren't shorting.

Tear down all the contactors (again) and inspect the contact points first. That's often where the trouble lies, one of the contacts has burned to the point it is going open. And unless it's one of the European DIN-rail miniature units that you just toss and replace, almost all motor starters and power contactors have field replaceable contact kits.

Sometimes you can repair a bad contactor TEMPORARILY by filing off the contacts flat and smooth, then swapping one half of the contacts during reassembly - the filed-off bad base contacts now mate with a good moving shoe, and a bad moving shoe with good base contacts.

The contact swap will only buy you a few days before the trouble reappears, but it proves where the fault is and gets the gear running. And that's usually enough time to find and ship the needed parts.

And always check your phasing carefully when you are done, jog it in each speed before allowing automatic operation - if there's a wire swapped and the motor tries reversing as it shifts from Low to High while it is running, this is not good at ALL.

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Thanks for the reply Bruce. I tore down the contactor which was preventing any operation at all.... it was pretty bad inside (the machine uses Siemens Minicont contactors) not necessarily fun to get apart, but do-able. Pretty poor shape inside, but I got it dressed up and back together good enough to get the machine to fire up. I have ordered a replacement contactor to get that particular one out of the pile that's in there, and the machine will run on low without problems. When the new contactor comes in, I will swap it into the stack and then try to figure out which one(s) are causing the high-speed problem. The problem with the Siemens contactors that were use in this machine is that the only way you can see if they are pulled in is by looking at a little tiny red tip inside the contactor face to see if it moves. I'm thinking I may rig up several 120v small bulbs on leads to connect across the coil terminals to see which contactors are energized when switching into high gear. There are probably 7 or 8 contactors in this mess, and no paperwork to help. Thanks again for the link - I'll check it out, but I'm unfamiliar with the terminology of U,V,W (1 & 2) as I'm used to working with T1,2,3. Ken.

This is a European convention that's become common in the US. U,V,W denote the conductors or conections supplying a load; R,S,T are supply conductors. The connection thru a 3-phase contactor would look like this:

Line Load R--||--U

S--||--V

T--||--W

Thanks, all, for the great information. I'm learning...... One of the main problems with working on this unit is that there is VERY LITTLE room in the control cabinet - it's nice and neat, but very tight and hard to see where everything goes. When the new contactor comes in, I'll just have to take a little time to "figger it out". Worse to worse - it'll still run on low speed..... which is way better than mixing a bunch of pizza dough by hand . (At least according to the boys in the shop that have been building up their muscles lately) Thanks again to all..... Ken.