Fixing the electrics in my old German mill Ruhla 250/710

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Bill Shields
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by Bill Shields »

Well that is good.
Too many things going on to bother listing them.
John Hasler
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by John Hasler »

Your relays will be fine. A transient protector in parallel with each coil could lengthen contact life.
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tornitore45
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by tornitore45 »

Your relays will be fine. A transient protector in parallel with each coil could lengthen contact life.
...lengthen contact life of the driving relay.

AC snubber you can start with R=1/2 x Rcoil and C = 0.47uF or less X Rated Capacitors are NOT rated as Movies

Values have wide latitude when one has not much data on coil
Mauro Gaetano
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liveaboard
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by liveaboard »

tornitore45 wrote: Thu May 27, 2021 12:31 pm
AC snubber you can start with R=1/2 x Rcoil and C = 0.47uF or less X Rated Capacitors are NOT rated as Movies
All I understand from that is capacitors.


I intend to add reversed diodes to the clutch + brake coils to drain reverse emf when disconnecting.
We know that when this machine was built, silicone diodes weren't available...
John Hasler
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by John Hasler »

Measure the resistance of one of the relay coils. That's Rcoil. Connect a resistor equal to Rcoil/2 in series with a .47 uF capacitor. Connect that series combination in parallel with the relay coil. Do that for each relay. Use 1/4 watt resistors and 100 volt or higher ceramic capacitors.

Or connect a 50 volt transient protector (MOV or TVS) across each coil.
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liveaboard
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by liveaboard »

got it, thanks for the clarification.

But with 230v coil voltage, don't I need capacitors rated at 230+ ?
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Bill Shields
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by Bill Shields »

Unless you like fireworks...yes on higher voltage
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liveaboard
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Re: Fixing the electrics in my old German mill Ruhla 250/710

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I love fireworks.

Maybe not in the workshop though.
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tornitore45
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by tornitore45 »

The diode is good for any coil that is DC driven.
For coils AC driven a MOV rated Higher than the line voltage or a RC snubber as John described. R + C in series rated for line voltage.
TVS are like 2 Zener diodes back to back they are a Semiconductor "equivalent" of the MOV
Mauro Gaetano
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John Hasler
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by John Hasler »

liveaboard wrote: Fri May 28, 2021 2:10 am got it, thanks for the clarification.

But with 230v coil voltage, don't I need capacitors rated at 230+ ?
I somehow got the impression that you had a 24 V control transformer. Yes, the snubber network components must be rated for the coil voltage plus a comfortable margin.
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liveaboard
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by liveaboard »

230v control transformer; input voltage is 380.

Some other models by this company did use 24V control.
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Re: Fixing the electrics in my old German mill Ruhla 250/710

Post by liveaboard »

I'll connect the power tomorrow.

I'm only slightly terrified.
Ruhla 250 710 new relay bank.jpg
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