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Jamie Jamie is offline
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Default Current transformer help please


I have a CNC lathe, a Miyano, that I just bought. The machine was made
in the early 90s. I ran it in a different shop for the last year and
it worked fine. The shop had only single phase power available, like
my shop. But in the old location the machine ran on solid state phase
converter and in my shop it runs on a rotary converter. The line
voltage at the old location was 235 volts. In my shop it is 245 volts.
The machine is made to run on 230 volts. My phase converter is well
balanced and the manufactured leg measures 245 volts. The problem is
one three phase fractional hp motor that powers a chip conveyor. The
power supply wires for this motor are wound through some sort of
current sensing transformer. Thes are regular 14 gauge stranded
insulated wires that appear to be hand wound through the current
sensing transformer. So I'm thinking that with the higher voltage
running through the wires the voltage output from the transformer is a
little high and it causes the machine to alarm out on the chip
conveyor. I disconnected the output from the current xmfr and the
machine now does not throw an alarm, but this also removes the
protection. I'm thinking that if I take a couple turns out of the xmfr
then the voltage output would be lower and I can then still use the
xmfr to protect the motor. Will that work?

So, what you're saying is, it has a current sensing system to detect
jam ups ? In which case, there should be some point of calibration you
can set.

Are you sure you don't have a Max Current pot some where on the drive
board? If it even has a real drive! Maybe It don't ?

Also, I guess this could of been some make shift sensing system, too.

I guessing that maybe there is a 3 phase rectifier in there somewhere
converting this to DC for a reference. In that area, there should be a
way to calibrate this. Maybe adding a R across this rectified circuit to
load it down.