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Schaublin 135 - Help upgrading electrical system

I will measure the voltage across 50 and 53 and report back, the challenge with the control transformer is its behind the panel which the main fuses are mounted to and not sure if its an easy job to expose it without some serious juggling with wiring.

d2 failed because the case holding the wire coil broke and this damaged the coil wire at the fracture I would suspect, I'm guessing the 60 year old plastic/bakerlite decided to give up at this stress point, I might be wrong with my diagnosis and you might be right so lets see what the voltage result gives.
 
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What you say rings true: it is unlikely that the one contactor coil which burned out is also the one where the coil form failed. Nevertheless, it would be good to get the control transformer secondary down into the 220-230VAC range. The control components are clearly marked for 220V at 50Hz.

It would be surprising if there is no straightforward way to access the coil transformer primary windings. Perhaps the main fuses are on a removable plate, and if you pull that off you'll find the primary taps behind it. Or something similar. Be a detective, look for access panels and back door approaches.

PS: did you measure the coil resistance of the other contactors, just to confirm that it's in the 5-600 ohm range?
 
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I would connect the existing contactor *in series* with the soft starter, rather than replace it outright. You'll note that it doesn't break L1, only L2 & L3. I am unsure whether leaving L1 energised on a dual-speed motor when the other speed is engaged would be an issue - it would depend on whether the two sets of windings are completely independent.

This also ensures that the interlocking continues to be effective between slow and fast speed. Note that the soft-starter could ramp the voltage down after the run signal is removed - it's set to zero seconds currently, but 'zero' is potentially a bit open-to-interpretation. Physically disconnecting the phases with a contactor and using the NC contact prevents that, more or less.
 
I would connect the existing contactor *in series* with the soft starter, rather than replace it outright. You'll note that it doesn't break L1, only L2 & L3. I am unsure whether leaving L1 energised on a dual-speed motor when the other speed is engaged would be an issue - it would depend on whether the two sets of windings are completely independent.

It is a valid concern. But according to the documentation and several online threads of information, the two windings are completely independent. They are also illustrated that way in all of the electrical documentation.

Marc: if you are concerned about this, then do as I described in post #206, and put the soft starter in series with c4 rather than replacing c4. See diagram below.

This also ensures that the interlocking continues to be effective between slow and fast speed. Note that the soft-starter could ramp the voltage down after the run signal is removed - it's set to zero seconds currently, but 'zero' is potentially a bit open-to-interpretation. Physically disconnecting the phases with a contactor and using the NC contact prevents that, more or less.

It's a good point. My thought was that if the windings are independent and the ramp down time is small, even if both windings are being fed at the same time, they are turning the motor in the same direction, so it shouldn't be a problem, in fact it should in principle make the transition smoother.

Anyhow, these are both good arguments. Marc, if you are concerned about this and want to be conservative, put the soft starter in series with c4 rather than replacing it. Diagram below.

Screenshot 2023-08-13 at 12.12.51.png
 

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248VAC is the voltage across one of the coils.
I am pretty sure that your transformer primary has different taps, and that by using the correct one you can reduce that to the range 220-230VAC. That would be healthier for the control electronics, which are designed for 220/230VAC at 50Hz. So if it's possible to get to the transformer without undue suffering, that would be worthwhile.
 
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I am pretty sure that your transformer primary has different taps, and that by using the correct one you can reduce that to the range 220-230VAC. That would be healthier for the control electronics, which are designed for 220/230VAC at 50Hz. So if it's possible to get to the transformer without undue suffering, that would be worthwhile.
Is the higher than normal voltage an issue with the transformer degrading over time? Surely if it was originally set to this voltage (248VAC) that this was normal and within tolerance for the electronics fitted at the time.

I will have a look at the way the panel is secured, I do have an image of the whole board removed in one piece with all the terminal connections at the base still connected so maybe there is a way - will explore.
 
Transformers don't degrade with time. The voltage ratios are determined by the number of windings in the primary and secondary coils and by fundamental physics. Provided that the coils are unchanged, neither do the voltage ratios. (Typically transformers don't fail, they are extremely reliable. If they do fail, it is because the insulation inside degrades, and then the failure is catastrophic, meaning a spectacular blue flash and fireworks on the primary side, or nasty smoke and sizzling on the secondary side, followed by complete loss of secondary current. Insulation failure is typically a consequence of overheating. Transformers build in the 1970s or after and operated under design conditions should last centuries or millenia.)

But something that I should have asked you to check: what are the input voltages? In particular across the R/T terminals, which feed the control transformer? (But also across R/S and S/T, for the record?) Perhaps your 3-phase power source has a voltage which is higher than I expect (either 380VAC or 400VAC for the three different measurements).
 
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Grid voltages have crept up over the decades in some locations - I believe Germany has officially moved from 220/380 to 230/400, which is *close enough* that most equipment should remain in tolerance. This is a meet-in-the-middle approach against the UK's historic 240/415.

They're also pretty dependent on exactly where you are, local loading, the time of day etc. A previous workshop on a different distribution transformer could have had a fairly different voltage.

I would generally be tempted to bring it down to at most 230V. Slightly higher voltage for motors is OK - they draw less current. Heaters draw a bit more but the thermostat cycles them off faster.

However, if you're having issues with the contactors dropping out on undervoltage... the voltage will be proportionally even lower.

There's no other advantage to running a contactor on a higher voltage - they just get hotter.
 
Transformers don't degrade with time. The voltage ratios are determined by the number of windings in the primary and secondary coils and by fundamental physics. Provided that the coils are unchanged, neither do the voltage ratios.

But something that I should have asked you to check: what are the input voltages? In particular across the R/T terminals, which feed the control transformer? (But also across R/S and S/T, for the record?) Perhaps your 3-phase power source has a voltage which is higher than I expect (either 380VAC or 400VAC for the three different measurements).
Will check the input voltage as this could be a factor - I'm thinking its around 400VAC but will check the output and speak to the manufacturer.
 
Grid voltages have crept up over the decades in some locations - I believe Germany has officially moved from 220/380 to 230/400, which is *close enough* that most equipment should remain in tolerance. This is a meet-in-the-middle approach against the UK's historic 240/415.
Correct
They're also pretty dependent on exactly where you are, local loading, the time of day etc. A previous workshop on a different distribution transformer could have had a fairly different voltage.
I believe that Marc is running the system from a mechanical or solid-state RPC.
I would generally be tempted to bring it down to at most 230V. Slightly higher voltage for motors is OK - they draw less current. Heaters draw a bit more but the thermostat cycles them off faster.
Just to be confirm: the transformer in question is only powering control circuits. But I share your dislike of 250V on those controls, somewhere in the 220-230v range would be healthier in the long term. I suspect that the control transformer primary has a set of taps, perhaps 380/400/415 and Marc can just shift to a higher voltage input tap.
However, if you're having issues with the contactors dropping out on undervoltage... the voltage will be proportionally even lower.
There is only one contactor with a dropout problem: d1. However, that is the emergency power off contactor and so when it drops out, that shuts the lathe off. Hopefully the slow starter will fix that: the dropout problem is only when the motor high-speed windings are connected, presumably from the initial start-up surge current.
There's no other advantage to running a contactor on a higher voltage - they just get hotter.
Indeed. This is used lathe, made 50 years ago. Probably when it was first delivered, it was correctly configured for the input voltage. But as it has changed hands and moved around over the years (probably across national boundaries) who knows what has transpired. For example the main input fuses were 25A (they should be either 10A or 15A).

Anyway, it is good to get these things right. Electronics works better and lasts longer if it is operating under the design conditions and not beyond them.
 
However, if you're having issues with the contactors dropping out on undervoltage... the voltage will be proportionally even lower.
There is only one contactor with a dropout problem: d1. However, that is the emergency power off contactor and so when it drops out, that shuts the lathe off. Hopefully the slow starter will fix that: the dropout problem is only when the motor high-speed windings are connected, presumably from the initial start-up surge current.

The soft-starter should alleviate the drop-out problem when switching to high-speed, as the voltage should drop less. There will still be a voltage sag.

Suppose the contactor d1 drops out when the '230V' line drops to 180V, corresponding to an input voltage of 310VAC. If you retap the transformer to 400V, the contactor will instead drop out at an input voltage of around 330VAC.

I didn't spot that this was on a phase converter. OP may be able to bring external 230VAC power into the machine by connecting a neutral, and avoid the control transformer altogether - though the 30V tap would still be needed for the brake.
 
Transformers don't degrade with time. The voltage ratios are determined by the number of windings in the primary and secondary coils and by fundamental physics. Provided that the coils are unchanged, neither do the voltage ratios. (Typically transformers don't fail, they are extremely reliable. If they do fail, it is because the insulation inside degrades, and then the failure is catastrophic, meaning a spectacular blue flash and fireworks on the primary side, or nasty smoke and sizzling on the secondary side, followed by complete loss of secondary current. Insulation failure is typically a consequence of overheating. Transformers build in the 1970s or after and operated under design conditions should last centuries or millenia.)

But something that I should have asked you to check: what are the input voltages? In particular across the R/T terminals, which feed the control transformer? (But also across R/S and S/T, for the record?) Perhaps your 3-phase power source has a voltage which is higher than I expect (either 380VAC or 400VAC for the three different measurements).
OK here are the input voltages...
R/S is 396VAC
S/T is 420VAC

This is the reply from the 3P convertor designer and manufacturer:

The phase to neutral voltage varies depending on which phase you use, we recommend using L1 – N this is more stable, the voltage is dependent on the mains input and the size of the run/ bal capacitors

Reduce the capacitors and the L1 – N will be reduced also the phase to phase (420V) will be reduced it is a trade-off, by disconnecting the Balancing cap will reduce the L1 – N and the L2 – L3 phase.

The 230v SUPPLY tolerance in the UK is 230V +10% -6% (252V – 216V) most equipment should run within that tolerance.

Hope this helps.
 
The soft-starter should alleviate the drop-out problem when switching to high-speed, as the voltage should drop less. There will still be a voltage sag. Suppose the contactor d1 drops out when the '230V' line drops to 180V, corresponding to an input voltage of 310VAC. If you retap the transformer to 400V, the contactor will instead drop out at an input voltage of around 330VAC.
Since the d1 contactor does NOT drop out when the low-speed motor windings are turned on, I think the odds are good that a slow starter will fix the high-speed motor winding dropout issue.

But if it is possible to rewire the transformer to reduce the control voltage, then after that is done we should verify that there is still no drop out problems with the motor low speed windings.

I didn't spot that this was on a phase converter. OP may be able to bring external 230VAC power into the machine by connecting a neutral, and avoid the control transformer altogether - though the 30V tap would still be needed for the brake.
In principle we could rewire just the 230VAC part of the control circuitry to run direct from mains, leaving the 30V brake circuit still wired to the existing control transformer. But I don't very much like the idea that the 230VAC control circuit is not isolated from the motor currents that are being controlled. I'd want to put an isolation transformer in the path. Do you agree that this is a sensible precaution?

So, with this approach, we add a 1.4kW 230/230VAC isolation transformer, disconnect the 230VAC secondary of the existing control transformer, and replace that with the isolation transformer driven directly from the mains. Note that this would also require an additional cut-off switch and fuse set at the input side to the isolation transformer.
 
Hi Marc,
OK here are the input voltages...
R/S is 396VAC
S/T is 420VAC
You have left out the most important one: R to T, which is the input voltage for the control transformer.
This is the reply from the 3P convertor designer and manufacturer:

The phase to neutral voltage varies depending on which phase you use, we recommend using L1 – N this is more stable, the voltage is dependent on the mains input and the size of the run/ bal capacitors
But your lathe does not use L1 to neutral. It only uses L1, L2 and L3. Please pass this back to the
3P convertor designer and manufacturer.

Cheers,
Bruce
 
The soft-starter should alleviate the drop-out problem when switching to high-speed, as the voltage should drop less. There will still be a voltage sag.

Suppose the contactor d1 drops out when the '230V' line drops to 180V, corresponding to an input voltage of 310VAC. If you retap the transformer to 400V, the contactor will instead drop out at an input voltage of around 330VAC.

I didn't spot that this was on a phase converter. OP may be able to bring external 230VAC power into the machine by connecting a neutral, and avoid the control transformer altogether - though the 30V tap would still be needed for the brake
Hi Marc,

You have left out the most important one: R to T, which is the input voltage for the control transformer.

But your lathe does not use L1 to neutral. It only uses L1, L2 and L3. Please pass this back to the
3P convertor designer and manufacturer.

Cheers,
Bruce
R to T is reading at 420VAC
 
Reply from the convertor man re - L1/L2/L3 (I had a long conversation with him a year ago about this when wiring up the lathe, he must have forgotten as he deals mainly with expensive CNC equipment!)

take it from your electrician your m/c only requires 3 – phase i.e. 4 wire 3-phase and earth NO neutral. All m/c in the UK are tolerant to the 3 - phase supply i.e. 400V + 10% - 6% ( 380V – 440V) The converter is within this tolerance your m/c should be fine we run complicated CNC m/c computer controlled no problem.

I take that your m/c has a step down transformer from 400V to 240V if the input is a bit higher the output higher, 248V is ok and should present no issues with your m/c as this is within the mains electricity supply parameters.

As I have said converters run CNC, Robotic m/c’s etc our converter should run your m/c without any alterations to the converter, if you are having issues it is within your m/c and not the converter.

People will always blame the converter as they do not fully understand the artificiality your m/c should be fine with the voltages check your m/c fully for any issues.

Just for your information L1 – L2 is the function of the MAIN SUPPLY input i.e. 240V in 420V out (L1-L2)

230V in 400V out

220V Iin 380V out

These voltages are fixed by the input 240V supply

Hope this helps
 
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Hi Marc,

earlier, we tried to fix the dropout problem by making sure that the control transformer was powered by a certain pair of RPC outputs, but it made no difference. That pair R/T is 420V. The pair R/S is lower voltage, which would reduce the voltage into and out of the control transformer. So if you swap the lines feeding T and S, that will reduce the transformer primary voltage from 420V to 400V (but make the motors turn the wrong way). So then swap R and T to make the running direction correct again. This is only a 5% voltage reduction, but should get the control transformer voltage down to (say) 236V.

If you have gotten access to the control transformer primary, and there are multiple taps, that's a better solution.

Cheers,
Bruce
 
Hi Marc,

earlier, we tried to fix the dropout problem by making sure that the control transformer was powered by a certain pair of RPC outputs, but it made no difference. That pair R/T is 420V. The pair R/S is lower voltage, which would reduce the voltage into and out of the control transformer. So if you swap the lines feeding T and S, that will reduce the transformer primary voltage from 420V to 400V (but make the motors turn the wrong way). So then swap R and T to make the running direction correct again. This is only a 5% voltage reduction, but should get the control transformer voltage down to (say) 236V.

If you have gotten access to the control transformer primary, and there are multiple taps, that's a better solution.

Cheers,
Bruce
Will try that wiring option.
Not had time to try to get to the transformer, its a big job and not something I am looking forward to doing to be fair.
Is there a way simple or cost effective way to reduce the input voltage from the mains to the convertor down to say 210-220VAC as that would have the same result in reducing the step down transformers VAC output?
 
There is no good way to reduce the mains input voltage with the kind of currents that you require. If the control transformer is a big job to reach, I suggest that we just move on and finish the repairs, possibly swapping the input lines as described above to lower the control voltage somewhat. Lowering the control voltage more, if you think it's important, can be a longer-term project.

So.... have you tried the new coil with d2? Does it work? I suggest you test that, and then let's proceed to wire in and try out the soft starter.
 








 
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