Bad DC Motor Brushes?

If the brushes on my CNC Lathe DC motor are bad, would that cause problems with my spindle not coming up to speed, or drawing excess voltage from my RPC when trying to come up to speed? I had a problem with my RPC a couple weeks ago, and had to send back the panel with the capacitors in it to the manufacturer so they could replace what they figured were some bad ones. The unit was still under warranty so other than being down for a few days it wasn't too big a deal. They replaced all the capacitors in the panel and added a couple extra of the oblong ones to help with my low incoming voltage problem (226 coming in from the pole)at least that is what they told me it would help alleviate. So the panel comes back, get it all hooked up and everything runs fine, except my 15HP CNC Ikegai lathe still will not come up to speed, and as soon as I hit the spindle start button, I get a "Phase Loss" error on one of the VFD's I have hooked up to another gear head CNC lathe. I mentioned this problem in another thread "Spindle Not Getting Up To Speed" and it was mentioned that perhaps the brushes may be bad, and I just figured before I go and remoeve all the guards around the motor and try to get access for checking them, I would ask this question again. Could it be brushes? Is there some other reason why the spindle won't come up to speed? If I enter in S2500 RPM it will take about 15 seconds to get up to speed, and that is about the max it will go, even though I should be able to get 3150 RPM's. I don't use this lathe all that much but I know it will go that fast because I've had it running that fast before, I just thought this was tied in to my RPC problems, but now that the RPC is not the problem I must look else where. Anyone have any thoughts on where to start?

IKEGAI CNC LATHE 15HP
A-B-NO LOAD-224 AMPS-12 LOADED-224 AMPS-25
B-C-NO LOAD-232 AMPS-13 LOADED-230 AMPS-15
C-A-NO LOAD-224 AMPS-6 LOADED-214 AMPS-18


Best Regards,
Russ

Post information on the spindle drive and the motor. Without that (even a photo) we would all be guessing.

If it is a DC drive, it has ONE voltage, i.e from + to - on the motor...... if you have the DC motor voltage for the no load and loaded conditions, that would help.

Brushes? anything is possible, what makes you think they are bad...aside from the "no workie right"?

The three phases with such different currents does not look right.

If the unit has a power supply with SCR control, one phase may have a bad SCR, or bad trigger circuit.

Here is the info off of the drive and the motor.

Fuji DSR Compact
Type FSD 15SNBZ
Input AC200/220V 50/60HZ
Output DC 220V 92.5 AMP
Serial #664973-17H
MFD Jan. 1980

Fuji DC Motor
Type - GGN 3168A
Output - 11KW
Volt - 220
Rule - JEM 1170
Amp - 61
Insul - F
RPM - 1150/3500
Excit - SEP.150V
4.9A/1.3A
Rating - Cont.

Not sure if I missed anything, but hopefully this will give you some of the info you were asking for. Thanking you in advance for any and all help.

Best Regards,
Russ

Sounds like the drive has a bad SCR and cannot maintain a steady current into the drive.

Looks like the base speed of the motor is 1150 rpm - that means that the drive must field weaken the motor in order to over speed to as high as 3500 which is probably the mechanical speed limit.

Given the problems with the front end of the drive (SCRs as JST has mentioned) it is likely that the drive has gone unstable and could well have flashed the commutators (arcing between commutator bars on the motor). This usually requires cleaning the commutators and in some cases dressing the brushes if they are really pitted.

Look up how to maintain DC brushes / commutator on the internet. . . lots of information out there with good photos.

Your drive is likely the culprit - have it checked out by someone who knows Fuji drives or just replace it. DC drives are the cheapest available - just make sure you replace it with a regenerative drive if that is what it is to begin with or you will be dissatisfied with a non-regen drive as far as braking performance is concerned.