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DC motor AOC alarm

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Titanium
Joined
Feb 7, 2013
Location
midlands,UK
This is on my Beaver CNC mill ,10hp Bull DC motor ,Control Techniques Mentor II drive.

For some reason I am getting an AOC (armature over current) alarm ,almost always when the motor is slowing down (M5) from a relatively high speed ,the strange thing is that the program I am using has two opps using the same spindle speed but the problem almost always occurs on only one of the ops ,I have tried slowing it down a bit on that op which has improved things but still fine on the other op.

The top speed is 2600 rpm and the problem is 1800 to 2000 ,haven't yet tried faster but much slower is fine ,incuding tapping 200 holes at 800 rpm.

From memory full voltage is at 1000rpm then field weakening is used the rest of the way.

Is this the motor on its' way out or something else?
 
I'm wondering if it is brush /com. related ,I haven't used this machine for a while and I think I have previously thought that tapping (ie reversal of the motor) might be an issue ,perhaps chewing up the brushes, although I can't see any real evidence of that.

The drive is much newer(2005) than the rest of the machine(1987)but I guess that means nothing!
 
Armature over current when the motors slowing down points to something in the breaking circuitry side, if it has regenerative breaking?. A dc motor will become a generator on rapid slow downs, That will try and increase the armature voltage - current. Do it hard enough (think fast and with a high mass spindle tool)- too fast yeah you would be capable of tripping over voltage - over current alarms. If its a large tool causing it, you just probaly have to increase the slow down ramp.

PS i have no detailed knowledge of that drive, but have delt with too many DC drives showing similar faults over the years.
 
Yes it is regenerative braking ,the tool is only a 6mm endmill holder so not big mass. This is a recent issue ,I will be doing another job which I intend to use max RPM so we will see what happens then ,if the problem remains a slowing down issue it is not so bad ,what I don't want is a trip when a tap is at the bottom of a hole.
 








 
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