DC motor drive boards.

My tom senior mill has a dc motor with reduction gearbox at one end of the table to provide power feed in the x-axis. Ever since i bought the mill a few years ago, when using the power feed, especially with a heavy cut, there was a strong smell of something electrical burning and copious smoke from the electrical box on the base of the machine.

I know its nothing to do with the main motor drive as i removed the drive pcb to make room for a vfd to power the main motor. All i left was the pcb that powers the dc motor. I have examined the board and cannot see anything burnt, and i do not have access to a thermal imaging camera to see whats getting hot. The best thing i can do at this stage is buy a new dc board so i can once again use the power feed, getting tired cranking the handle.

Does anyone know of a company that makes or supplies drive boards for this type of application ?

Edited By ronan walsh on 24/03/2015 01:16:36

Hi Ronan,
More information is requred to make suggestions. First what type of motor is it ? (Permenant magnet, shunt wound. or series wound (Universal) ?) Second what is the voltage rating of the motor and the power rating ? (HP, amps, or watts) Third Is the board powered directly from the mains (230 or 415 volts) or via a transformer. Other useful information would be is it a standard tom senior fitting ? Is it one of the the propietry add on power feeds or is it a home made feed unit ?

Les.

Hi Ronan,
I have found this by Googling "Lenze 432"
At the price on that web page I would think I would think anout repairing the existing one.

Les.

If, as you say, there's 'copious smoke' when operating, could you not just run the motor with the cover removed from the control board to see where the smoke is coming from?

Despite that board having clearly come from the Ark, there's nothing on it that looks as if it's even got warm, so I doubt the smoke is actually coming from the board. Have you checked the connections and wiring? As Gordon says, see where it's coming from. "Let it develop".

The only date code visible is on the TO-66 metal can device (1981 week 45). I see a manual still available from Lenze dated 1979, so that sounds about right.

Hi Murray,
I agree with you that if the fault was bad enough to produce smoke then I would expect the board to be marked. I suspect that the photo may have been taken some time ago before the fault occured as Ronan has a number of pictures of the mill in his album. It would have been wise for him to investigate the cause of the smoke when it occured.  I found a site that claims to have a schematic but they want an email address and I do not trust sites like that.

Les.

Edited By Les Jones 1 on 24/03/2015 16:09:22

Hi

Two things that may be worthwhile checking, has oil/coolant got into the electrical box and if so is there a component getting hot enough to vaporise it and cause the smoke and secondly adjacent to the circuit board there is a transformer, albeit only 12V at 12VA but is this getting hot for some reason.

Cheers

Martin

Hi

There is a little more information here but may not be too helpful, mainly setting up etc of this family of controllers.

Cheers

Martin

Thanks for the replies everyone. I have contacted lenze via email and requested a manual, hopefully they will have one on pdf. The fact there is nothing obviously charred is confusing to me too, but as someone said the machine is from 1981/82 so something is getting tired. With the brief bit of research i have done on this board, it appears to have been around for a long time and been used widely, so it must be reasonably reliable. The motor is a swiss kemo unit, but there is no voltage info on it, just amperages.

Ronan,

if you read the label again.......the field winding is 210v dc and is rated to draw 0.18 A, the armature is depicted below.......

HTH.......

Yes John, i just copped that.

Hi Ronan,
Before replacing the board I suggest that you check that the motor is OK first. Check that the field winding resistance is about 1200 ohms (210/0.18 = 1167) Check that the brushes look OK Check the resistance between the armature connections and turn the shaft a few degrees at a time. The resistance should be about the same in all positions of the shaft and much less than the field resistance. (I would guess is should be less than 50 ohms) If these readings are as expected and you have a DC power supply of between about 50 and 150 volts try the motor on this. (Connect the field and armature in parallel to the supply.) If the motor runs OK like this then the fault must be the board. If you cannot obtain (Or repair) the original board then a KBIC-240 board would probably work, There is one of these on ebay in the UK on sale at the moment and several on sale in the US.

Les.

Thanks les. I hope a manual will shed a bit more light on this problem. Something was suggested to me before, and that is one of the old electrolytic capacitors might be breaking down. I'll do what you suggest and then i might replace these caps. The option of running the motor until something smoulders or burns worries me, as i don't want to do even more damage.

Hi Ronan,
Electrolytic capacitors are prone to fail with high internal resistance particularly if they are handling high ripple currents. If you have access to an ESR meter (Effective series resistance) it is worth using it to test the capacitors in circuit. I was under the impression that the table drive was no longer working which is why I suggested testing the motor, If it is still working then the motor is probably OK and you should be able to see the source of the smoke as Gordon suggests.

Les.

I suspect this is a wound field dc motor. Suitable drives are available from KB Electronics and also some quite nice ones from China on eBay.  The eBay one is item no. 181473818094

Edited By John Haine on 24/03/2015 22:46:57

Sorry Les , yes the motor is still working and responding to the controls, eg. on/off, working in both directions, speed contol and the jog. Its definately the lenze control board, there is nothing else in the panel anymore apart from the brand new vfd. Any of the old electronics and wiring concerning the main spindle drive motor i removed. There is a transformer between the mains supply and the lenze board, the usual iron core wound tranny. This is something else to inspect i suppose.

In cases like this, where the cause is not immediately apparent, I usually try the old trick of following my nose. If something has been overheating or smoking, it will have that distinctive smell for a long time after the event. Try to have a sniff round all the components and wiring to see if anything smells. For areas that are difficult to access with your nose, just use a suitably-sized piece of tubing.