Dc drive

Do you loose the enable signal intermittend?

roxusa said:

My DC motor has 4 field wires marked f1-f2-f3-f4 and the wire diagram shows f2 &f3 wired together with my leads on f1 & f4.
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This is what I have, Thanks

Click to expand...

Yep. Makes sense.

Your connection descripton is correct for 300v, which is the norm for 480v input (1/2 wave, 3ph rectifier).

The motor should run 1800rpm at the high field current rating (1.35a) and 2300rpm at the low (.81a)

At room temp, the field should measure about 158 ohms. With a fixed 300v supply, it will start at 1.9a, and drop as the temperature comes up until settling around the 1.35 as specified. The winding resistance will increase considerably as it heats up, thus the drop in field current on a fixed supply.

If the field has a partial short:
- On a fixed or voltage regulatd field supply, the voltage will likely be about right, but the current will be high, and the resistance will be low.
- On a current regulated supply, the current will likely be right, but the voltage will be low.

If you measure the resistance F1-F2 and F3-F4, they should be the same. Each should be around 79 ohms at room temp.

My motor shop just got back to me and said "We found an issue with the fields which we are going to correct" They did not elaborate, They had just serviced this motor before we installed it.

It wouldn't be the first time i have seen the motor shop screw up a repair on a DC machine. The tough part is getting them to recognize it and fix it. they probably crossed up the field connections reversing the polarity and canceling the magnetic fields.
Fee fortunate that they caught it without a lot of fuss.

Found the problem (NOT IN SCHEMATIC) Looking at a drive book on the BBC Dive they
show the field economy wires typically wired to aux contacts on the armature contractor.
I opened my drive up and physically traced the 2 wires to a cube relay in the machine that had a bad coil. Once replaced I had the 300 vdc to field and all was fine with it out I only has 100 vdc which let it run fine with no balls.
Appreciate everyone's input