Electrical/contactor problem on 9hp motor.

[stoneaxe]

Help please.

Quick overview- 9 hp wood shaper being refurbished in the garage. Power from a 30 hp RPC about 60 ft away, through a 10AGW cord. This machine has a electromagnetic disk brake.
Controls are main power, forward/reverse, brake on / off and a momentary start -stop.
The machine is designed to not start with the brake off- when the start button is pushed the brake releases.

When I got it, the shaper had problems with the magnetic motor brake only disengaging in one direction of rotation- switching leads changed the "good" direction but resulted in the other not working, or both not working. When I say not working,, the brake was not disengaging when the motor turns on. I was using an under powered converter at this time, although it did start the unit as long as the brake disengaged. The RPC folks told me I needed a bigger converter hence the 30 hp. No one could explain why it started OK in one direction if the converter was too small.

The meat of the question

After a examination today, and a minor rewire-( one of the transformer legs was coming off L3 RPC generated leg, so I changed it to L2) I ran some tests.

I disconnected the motor leads at the motor. Powered up the controls.

All seems normal- the power switch powers up the controls, the brake switch turns the brake off and on with the FWD and Reverse in either position, the start and stop switches close and open the main contactor and simultaneously take the brake off or on.

Fulling expecting the thing to run, I hooked up the motor leads and pressed the start button- the main contactor just chatters in and out like a machine gun.

I don't really know a lot about this sort of thing- any advice on how to proceed or what to check would be much appreciated.

Thanks, stoneaxe.

 

[stoneaxe]

Help please.

Quick overview- 9 hp wood shaper being refurbished in the garage. Power from a 30 hp RPC about 60 ft away, through a 10AGW cord. This machine has a electromagnetic disk brake.
Controls are main power, forward/reverse, brake on / off and a momentary start -stop.
The machine is designed to not start with the brake off- when the start button is pushed the brake releases.

When I got it, the shaper had problems with the magnetic motor brake only disengaging in one direction of rotation- switching leads changed the "good" direction but resulted in the other not working, or both not working. When I say not working,, the brake was not disengaging when the motor turns on. I was using an under powered converter at this time, although it did start the unit as long as the brake disengaged. The RPC folks told me I needed a bigger converter hence the 30 hp. No one could explain why it started OK in one direction if the converter was too small.

The meat of the question



After a examination today, and a minor rewire-( one of the transformer legs was coming off L3 RPC generated leg, so I changed it to L2) I ran some tests.

I disconnected the motor leads at the motor. Powered up the controls.

All seems normal- the power switch powers up the controls, the brake switch turns the brake off and on with the FWD and Reverse in either position, the start and stop switches close and open the main contactor and simultaneously take the brake off or on.

Fulling expecting the thing to run, I hooked up the motor leads and pressed the start button- the main contactor just chatters in and out like a machine gun.

I don't really know a lot about this sort of thing- any advice on how to proceed or what to check would be much appreciated.

Thanks, stoneaxe.

Been thinking and reading- this sounds like a voltage drop issue- because of the long cord and the fact all the control circuitry and contactor works OK with out a motor load on it.
I will put a vom across the coil and see what it says when the switch is thrown.

 

[JST]

You may have trouble due to the cord. The 10AWG is just about equally matched for full load current, and for 60 feet, I'd want the wire oversized. Plus, the 60 feet may not include the wiring to the RPC.

When the motor starts, it draws 5 to 8 times the normal current, which can develop a pretty good voltage drop.

If the drop is enough to drop out the contactor, there you are, you will get what you describe. AC coil contactors can be more fussy about voltage than DC coil contactors, so that may add to the problem.

Try moving a lot closer to the power.

 

[rons]

If you use a volt meter on the coil while it is chattering the reading will be an average and probably mislead you.

When you change the L3 wire back to the way it was and the motor starts, you have a repeatable condition. If the condition repeats when you swap
your wire then the problem is easy to identify. It's already fixed but delayed in time.

You should wire it back and run the idler and shaper motor. Now read the voltages between T1, T2, & T3.

Read voltages T1, T2, T3 on the RPC end.
Read voltages T1, T2, & T3 on the 9Hp motor side.
What is the voltage drop from the 60 foot cable?

 

[stoneaxe]

If you use a volt meter on the coil while it is chattering the reading will be an average and probably mislead you.

When you change the L3 wire back to the way it was and the motor starts, you have a repeatable condition. If the condition repeats when you swap
your wire then the problem is easy to identify. It's already fixed but delayed in time.

You should wire it back and run the idler and shaper motor. Now read the voltages between T1, T2, & T3.

Read voltages T1, T2, T3 on the RPC end.
Read voltages T1, T2, & T3 on the 9Hp motor side.
What is the voltage drop from the 60 foot cable?

I will check this out tomorrow- I did clean up a few control wires that had sketchy terminations.
The extension line is 50' of #10, with a plug in to the RPC, and a plug connection to another 20' of #10 coming out of the shaper- I will shorten it 20 ft by running it direct to the machine , and get rid of a plug connection also.

I have a analog vom, apparently they will show a rapid voltage drop as they do not average out the signal.- will see.

 

[JST]

The analog VOM you have to average by eye... the mark at half the needle swing.

 

[rons]

The RPC folks told me I needed a bigger converter hence the 30 hp. No one could explain why it started OK in one direction if the converter was too small.

A 20 hp converter was not suggested? Those nice RPC folks...

The meat of the question

After a examination today, and a minor rewire-( one of the transformer legs was coming off L3 RPC generated leg, so I changed it to L2) I ran some tests.

I disconnected the motor leads at the motor. Powered up the controls.

All seems normal- the power switch powers up the controls, the brake switch turns the brake off and on with the FWD and Reverse in either position, the start and stop switches close and open the main contactor and simultaneously take the brake off or on.

Fulling expecting the thing to run, I hooked up the motor leads and pressed the start button- the main contactor just chatters in and out like a machine gun.

You might want to check internal wiring to your contactor coil. On the outside of the problem you moved a generated/eratic leg.
But on the inside the L3 is not the same as the L3 on the outside. Otherwise it was fun writing this out. What else is there to do ...

BTW: You need to have some pretty fast moving eyeballs to track a VOM needle moving at 60 Hz.

 

[JST]

.........................

BTW: You need to have some pretty fast moving eyeballs to tracka VOM needle moving at 60 Hz.

Silly boy........ You do NOT "track" the needle. You look at the blur, and estimate where the middle of it is.

Obviously you have never had to do this......

 

[rons]

Silly boy........ You do NOT "track" the needle. You look at the blur, and estimate where the middle of it is.

Obviously you have never had to do this......

My RPC's get tuned to within 1-2 Vac leg-to-leg. Never had to do this.......

 

[stoneaxe]

Shortened the main power cord to 50', cleaned up a few connections, voltage at machine same as at the convertor.
Getting 233 245 255 between the legs.

Holding the contactor manually for a half second latches it and the motor runs fine.
My guess is low control circuit current or voltage. Or maybe bad contacts or dirty internally in the contactor.

This machine has a reverse switch, wired to a brake switch and a spindle lock switch and a transformer and fuse block and a momentary start-stop switch- a lot of wire- not like a standard on-off to the contactor relay. For a novice like me, it is hard to figure out where the sea of spaghetti is going.

There are a bunch of auxiliary connections at the contactor, and one coming from the overload relay-
I need to study some more- this thing has been messed with in the past, as there are masking tape labels on the wiring. At least I know it will run!

BTW, the 30 hp convertor is so a 15 hp planer or wide belt sander can be used in the future.

 

[JST]

Yes, low control voltage. You may have a choice of taps to adjust it, or whoever messed with it did some goofy thing.

Check it with no load, it should be a bit high.

There is also a chance that the transformer got replaced, and the new one does not have the "oomph" needed for AC coils.... Control transformers are a bit special if done right. They are rated by VA and voltage, the VA has to be at least the same as the coils it has to close at once. Preferably a a bit more.

 

[stoneaxe]

Yes, low control voltage. You may have a choice of taps to adjust it, or whoever messed with it did some goofy thing.

Check it with no load, it should be a bit high.

There is also a chance that the transformer got replaced, and the new one does not have the "oomph" needed for AC coils.... Control transformers are a bit special if done right. They are rated by VA and voltage, the VA has to be at least the same as the coils it has to close at once. Preferably a a bit more.

Played around a bit with it tonight- the spindle lockout switch had some intermittent resistance in the on condition- that might be the problem- took it out and cleaned it with contact cleaner and re- adjusted it. - I will put some power to it tomorrow.

 

[rons]

For a novice like me, it is hard to figure out where the sea of spaghetti is going.

Trace the wires and make a neat drawing. Otherwise your venture into novice land will always be your home with no path of escape ...

 

[stoneaxe]

Trace the wires and make a neat drawing. Otherwise your venture into novice land will always be your home with no path of escape ...

Good advice. I am thinking of doing just that- curiously the user and parts manual have no wiring diagram. Plus all the wires are the same color! (Standard complaint with Italian cars too)

 

[stoneaxe]

You might want to check internal wiring to your contactor coil. On the outside of the problem you moved a generated/eratic leg.
But on the inside the L3 is not the same as the L3 on the outside. Otherwise it was fun writing this out.

^^^^ This was good advice, and I totally missed comprehending it.

OK- I got it running. The spindle switch was NOT the problem.

As you stated above, there is something wonky in the switching- somewhere the legs are exchanged- unless I mixed up which line is the generated leg.

Measured voltage between the lines 257, 244, 233.

The interesting part- L1 to ground is 122, L2 to ground is 214, L3 to ground is 122.

I was powering from L1 and L2, under the belief L3 was the generated leg.

So I returned it to how it was originally wired, , L1 and L3- now the contactor latches.

YAY! Now I can get to work on the mechanical stuff.

Is it normal for the generated leg to have a high voltage to ground? Am I going to destroy something?