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1st Apr 2020, 07:54 PM #76
That diode is there to catch the spike and suppress it. Diodes usually go short circuit ! It obvious that it hasn't in this case, but that doesn’t stop them from going open and not doing the job they are supposed to do. Check forwards and backwards with an ohmmeter. Or simply replace it fast diodes are as cheap as chips.
EDIT: I also checked the current draw on the clutch. Only 1.2A so much lower than what I expected.
That suggests that the inductance is quite high (24V / 1.2 = 20ohms).
I was originally thinking I'd need to fix this timer, but seeing as it looks like I might be OK to just relocate the one from the spindle circuit, then maybe I don't have to repair it. I'm fitting a VFD for the spindle motor, so pretty sure I won't need that timer - but I need to do a bit more digging to confirm it doesn't serve a secondary purpose.
On the issue of sourcing a replacement oil pump belt, there's good news and bad news, and more good news...
Good was that I'd found the correct part number - bad is that there's none in stock even with the manufacturer in the US. They can make to order with a MOQ of 48!!
The saving grace is that PIES Australia have the next length belt - albeit 50mm longer. I've had a look and have enough room to space the motor out from its original mount to consume the extra length. Otherwise I was looking at changing to a modern eg T5 belt style but would have meant new pulleys etc.
SteveBest Regards:
Baron J.
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1st Apr 2020, 09:30 PM #77Most Valued Member
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Had to work this evening so only had 5 mins for a quick look to see if I could spot the diode.
Found diodes V1-V8, but no V9 and V10 for the feed clutches.
I can however see there are 2 wires on the terminal block that feeds the clutch. One will be the power, hopefully the second goes back to a diode. Looks like I'll have to remove the back off the cabinet to trace it though...
Steve
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1st Apr 2020, 09:52 PM #78
Hi Steve,
The catch diode will be directly across the coil, there may also be a resistor/capacitor combination across it as well. The idea is the diode chops off the inductive spike and the R/C combination slows it down. Modern fast diodes don't often need the snubber (R/C).
If there isn't one there you need to add one. I'll have a look in my data book for something suitable.
1N5008 near bottom of the page
https://www.switchelectronics.co.uk/...ctifier-diodes
These people also do the relays.Best Regards:
Baron J.
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1st Apr 2020, 11:09 PM #79Most Valued Member
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The joy of having a TOS.... ( FNGJ32 mill )
Thanks John.
Yes, the diode is across the coil - but only electrically. Physically its about 2m away in wire length!!
Finally found the rest of the diodes in the next layer of the electrical cabinet.
For context, the timer is in the middle of this one, and terminal block 255 that connects the timer to the clutch is in the very bottom row of terminal blocks.
The diodes are physically located in the next swing-away section of the cabinet to the left.
Here they are - nicely labelled with the sticker next to them:
I've had a quick look around at what is available locally in the way of 24v relays.
There are some NOS ones of this Omron G5LA N.O. version: https://au.mouser.com/datasheet/2/30...la-1189866.pdf
Package fits in the available space, I only need the one set of contacts, and thinking I'd just glue it to the PCB and run hookup wire to connect it.
Interested in your thoughts on that.
Steve
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2nd Apr 2020, 12:16 AM #80
Hi Steve,
Yes those are the relays that I mentioned with 10 amp contacts. I've a few kicking about. I assume that they are not the same physical pin layout as the original one. But as long as it works, fits in the space and is secure, why not.
Those diodes are easy to get at, but the long length of wiring connecting them across the coil windings won't help with the voltage spike ! They really should be wired directly to the coil, certainly within a couple of inches. The voltage spike will ring for a good number of cycles before it dies. Also that style of diode is notorious for going open circuit and then measuring good. Something to do with the way the bond to the chip inside is made.
One way to test those is to have them actually rectify a voltage into a load with about 100 uf across the load, whilst looking at the output on a scope.Best Regards:
Baron J.
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2nd Apr 2020, 09:49 PM #81Most Valued Member
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2nd Apr 2020, 10:33 PM #82
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3rd Apr 2020, 06:36 PM #83Most Valued Member
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It looks like the designer for the electricals on this mill was on an acid trip.
I'm not saying to do this but you could probably throw most of that stuff in the bin and simplify
the wiring and switches....
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3rd Apr 2020, 07:36 PM #84Most Valued Member
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The joy of having a TOS.... ( FNGJ32 mill )
Agreed. It’s very old school. What could easily be done these days with something as small as an arduino and a few miniature relays is made up by stringing a bunch of full size contactors and wiring together.
Good thing is that although there is lots of it, it’s quite simple and mechanical.
My next task is to get the VFD integrated so I can control it from the main control panel.
Steve
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3rd Apr 2020, 08:05 PM #85Most Valued Member
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The joy of having a TOS.... ( FNGJ32 mill )
Here's the drawing of the control panel again for reference:
Console.JPG
I want to use the following switches/buttons to control the VFD for the spindle:
S3 - Stop
S2 - FWD
S4 - REV
S5 - Jog
Complexity is that FWD/REV buttons also control turning on the main gearbox lube pump, and the spindle stop also stops any power feed that is running.
Time to open up the control panel and take a look:
Hadn't counted on the stacked switches behind each button, but on further thought its probably better than I could have hoped for.
Just need to work out which ones currently control the spindle contactors and use them for the VFD instead.
Back to the wiring diagram to see if that's possible...
Steve
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3rd Apr 2020, 08:46 PM #86Most Valued Member
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Steve I recently fitted a VFD to my lathe, I removed the 3 phase motor wiring from the forward and reverse contactors, all other switches and wiring remained so that all switches operated as normal.
I used the inputs/outputs on the front of the VFD, ran wires from these to the (now vacant) 3 phase motor contactors to switch them.
So then you would need to program the VFD inputs/outputs for the function required, eg forward and reverse, brake ect
eg. You can do this because your motor power now comes from the VFD outputLast edited by shedhappens; 3rd Apr 2020 at 09:13 PM. Reason: more
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3rd Apr 2020, 09:18 PM #87Most Valued Member
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3rd Apr 2020, 10:05 PM #88Most Valued Member
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Pondering complete. I'm going to follow that approach.
If I've thought it through properly I think I only need to:
- Disconnect the 3ph supply/output from the spindle contactors
- Connect the motor to the VFD output
- Provide 3ph supply for the VFD
- Provide 2 pairs of signal wires for the VFD - one switched closed by the FWD contactor, the other switched closed by the REV contactor.
- Run 1 pair of signal wires from the VFD to a new pot on the main console to control frequency.
- Sort out the programming on the VFD so it only runs while either the FWD or REV input remains closed
Plan is to also install a tacho on the spindle, but for starters if the VFD is mounted on top of the ram just in front of the motor where I can see it and set to display FREQ then I should be good to go.
Steve
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4th Apr 2020, 05:28 PM #89Most Valued Member
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Steve on the VFDs that I have fitted I use twisted pair cable to connect those inputs, this is to reduce the chance of
interference and the possibility of an unwanted start or stop. This has never happened to me but I did read about this somewhere,
maybe others can shed some light on that.
The other thing is to also try to keep these wires away from power wires for the same reason.
I have some twisted pair cable (4 pairs in there i think) if you want some of this i will post some to you.
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4th Apr 2020, 06:58 PM #90Most Valued Member
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Thanks for the info Shed, and appreciate the cable offer.
Pretty sure I've got some suitable wire around, probably alarm cable offcuts that I intercepted on the way to the bin at work.
Will give you a shout if I can't find anything though.
I hooked the motor up to the VFD today - had to use some 2.5mm orange circular as I was out of flex. Will replace it once I've got everything running OK.
Ran fine from the front panel on the VFD when powered from my phase converter which is good as I was concerned the VFD might be upset by the non-perfect power. I've run it previously on mains 3 phase at work so already had the VFD basically configured.
Mounting it on the side of the spindle housing wasn't practical, so I put it behind the electrical cabinet. Its pretty well protected, but I'll put a shroud over the fan outlet on the top to stop anything dropping in.
Next step is to sort out the programming so its controlled by the terminal block. I'll test that with an external switch first before I go messing around inside the cabinet hooking it up to the contactors.
Steve
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