Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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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?
Thanks,
Eric
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Default Current transformer help please

On 4/3/2012 11:43 AM, wrote:
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?
Thanks,
Eric


I'm over my head, it seems your saying all three phases run through
the current sensing transformer. Didn't know that worked.
I think we need to know how many turns of the 14 Gauge stranded wire
are wound through the current sensing transformer? Per phase?
From that someone can decide how many turns to remove.
Mikek
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Default Current transformer help please

On Tue, 03 Apr 2012 12:47:48 -0500, amdx
wrote:

On 4/3/2012 11:43 AM, wrote:
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?
Thanks,
Eric


I'm over my head, it seems your saying all three phases run through
the current sensing transformer. Didn't know that worked.
I think we need to know how many turns of the 14 Gauge stranded wire
are wound through the current sensing transformer? Per phase?
From that someone can decide how many turns to remove.
Mikek

I was able to push the wires aside enough and using a mirror and
flashlight I was able to read on the device that it is an Omron SET-3A
current converter. Looking at the data sheet at omron.com I see that
the SET-3A device connects to another device and the two together
operate as a unit. The sheet also says that the setup won't work with
waveform distortion. I'm thinking now that maybe my rotary phase
converter must have too much waveform distortion and that's the real
reason for the problem. Anybody have any thoughts about a device that
I can use to replace the current converter? Maybe just a circuit
breaker? Afterall, the motor just runs the chip conveyor, which just
pulls all the metal shavings (chips, AKA swarf) out of the machine.
And the motor is exposed so I can feel it to see if it's too hot. I
can see if the magic smoke is coming out too, but I don't want to wait
that long.
Thanks,
Eric.
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Default Current transformer help please

On 4/3/2012 9:43 AM, wrote:
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?
Thanks,
Eric


The alarm is going off because the motor is drawing more current than
the system designer thought reasonable??? You should be able to
measure that and compare to the motor specs???

Changing the measurement
system won't fix that, it'll just make it easier for you to ignore
the fault condition.

Who knows how the system works...you haven't disclosed enough info
to tell...but...if it's a current transformer, the trip point
is related to the number of turns. If there are three turns on the
primary, and you remove one, you move the trip point up 50%...maybe...
depending on how they configured the secondary and sense circuit.

Have you considered the possibility that there really is a fault?
Maybe something got bent in transport and is causing extra load
on the motor?

You don't say how you're measuring the voltage and "balance".
If the harmonic content differs between phases, the current sense
mechanism may be affected by that?

Random modification of alarm trip points based on recommendations
you got from an anonymous "expert" here on the interweb is risky.

If you have employees, you might want to consult with your attorney
about the benefits of defeating safety alarms.
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Default Current transformer help please

wrote:

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?
Thanks,
Eric


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.

Jamie




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Default Current transformer help please

wrote:

On Tue, 03 Apr 2012 12:47:48 -0500, amdx
wrote:


On 4/3/2012 11:43 AM,
wrote:

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?
Thanks,
Eric


I'm over my head, it seems your saying all three phases run through
the current sensing transformer. Didn't know that worked.
I think we need to know how many turns of the 14 Gauge stranded wire
are wound through the current sensing transformer? Per phase?
From that someone can decide how many turns to remove.
Mikek


I was able to push the wires aside enough and using a mirror and
flashlight I was able to read on the device that it is an Omron SET-3A
current converter. Looking at the data sheet at omron.com I see that
the SET-3A device connects to another device and the two together
operate as a unit. The sheet also says that the setup won't work with
waveform distortion. I'm thinking now that maybe my rotary phase
converter must have too much waveform distortion and that's the real
reason for the problem. Anybody have any thoughts about a device that
I can use to replace the current converter? Maybe just a circuit
breaker? Afterall, the motor just runs the chip conveyor, which just
pulls all the metal shavings (chips, AKA swarf) out of the machine.
And the motor is exposed so I can feel it to see if it's too hot. I
can see if the magic smoke is coming out too, but I don't want to wait
that long.
Thanks,
Eric.

Get a 1:1 3 phase transformer for it. pass the power through that and
then supply the electronics with that. The transformer will correct that
issue, if that is really the problem.


Jamie


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Default Current transformer help please

On Tue, 03 Apr 2012 20:14:34 -0400, Jamie
t wrote:

wrote:

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?
Thanks,
Eric


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.

Jamie

Greetings Jamie,
The current converter does indeed connect to a device that controls
the contactors for the motor and I can adjust it. I identified the
device last night. I'm hoping that adjusting the thing for a higher
current will work. I did put am amp clamp on the leads to the motor
and it is drawing less than the nameplate current. If adjusting the
device doesn't work then I'm thinking that putting a circuit breaker
with heaters in it in line with the motor to protect it while
bypassing the existing wiring. This should protect the motor but will
not turn on the alarm lamp.
Eric
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Default Current transformer help please

On Tuesday, April 3, 2012 9:43:51 AM UTC-7, wrote:
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?
Thanks,
Eric


It might be good idea to get the supply voltage down to the rated nameplate voltage for the machine. That in turn should reduce the current into the chip conveyor motor and possibly clear up your problem. 3 simple 15V 'bucking' transformers on the input to the machine should do nicely to reduce the supply voltage to the rated value.
Neil S.
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