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Post by keith1500 on Jan 29, 2022 22:33:02 GMT
I was a few minutes into using the Centec mill when there was a Big Bang and the lights went out! I knew it was a short circuit as it dropped several MCBs and RCDs. So much for discrimination. As suspected it was the mill which had a short circuit. The fault was found in the Dewhurst switch where the neutral had come into contact with the live copper part of the switch. Centec2 mill by GL5Keith1500, on Flickr The under laying cause seems to be due to the copper contact getting hot which in turn was caused by worn/ pitted contacts in the rotary part of the switch. Centec2 mill by GL5Keith1500, on Flickr
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Post by springcrocus on Jan 30, 2022 0:06:03 GMT
I'm suprised that the RCD tripped for a L-N fault. You might have some leakage elsewhere that's pushing your 30mA threshold.
Regards, Steve
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Post by keith1500 on Jan 30, 2022 7:27:01 GMT
Yes, looking at the cpc ( earth ) it’s slightly damaged. Probably from the arc etc. it tripped the workshop/garden RCD which is there for additional protection and is a 30mA device. The one on the main supply is 100mA was fine. The poor ole Dewhurst Switch has seen some wear. Having removed the rotating drum you can see one of the copper contacts has worn a bit thin with noticeable dent in it The lower right one. Noticeable from giving them all a quick rub with some fine emery cloth. Centec2 mill by GL5Keith1500, on Flickr The rotating drum is quite clever. It’s basically a stack of round metal contacts. Some are long and link through to the adjacent stack. This facilitates reversing etc. some of the round contacts are badly pitted and worn. Probably the cause of the heat that melted the blue insulation. I tried cleaning them up but it wasn’t really good enough. Luckily I found an off cut of M12 stainless thread in the scrap box and machined some replacements. Centec2 mill by GL5Keith1500, on Flickr The worn copper contact has been repaired by letting in some silver solder and dressing back. I hope that works okay. Centec2 mill by GL5Keith1500, on Flickr
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Post by norfolkandgood on Jan 30, 2022 9:37:16 GMT
Worth keeping 'on the road' Keith they are quiet robust switches compared to the modern equivalent. Guy
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Post by Roger on Jan 30, 2022 9:47:23 GMT
Yes, looking at the cpc ( earth ) it’s slightly damaged. Probably from the arc etc. it tripped the workshop/garden RCD which is there for additional protection and is a 30mA device. The one on the main supply is 100mA was fine. The poor ole Dewhurst Switch has seen some wear. Having removed the rotating drum you can see one of the copper contacts has worn a bit thin with noticeable dent in it The lower right one. Noticeable from giving them all a quick rub with some fine emery cloth. Centec2 mill by GL5Keith1500, on Flickr The rotating drum is quite clever. It’s basically a stack of round metal contacts. Some are long and link through to the adjacent stack. This facilitates reversing etc. some of the round contacts are badly pitted and worn. Probably the cause of the heat that melted the blue insulation. I tried cleaning them up but it wasn’t really good enough. Luckily I found an off cut of M12 stainless thread in the scrap box and machined some replacements. Centec2 mill by GL5Keith1500, on Flickr The worn copper contact has been repaired by letting in some silver solder and dressing back. I hope that works okay. Centec2 mill by GL5Keith1500, on Flickr It would be worth putting an MOV across the Live and Neutral to suppress the arc you're going to get every time the switch opens. I don't suppose those even existed when this switch was made, but it's the reason it's ultimately failed. Out of interest, exactly the same design flaws are being perpetrated today. My friend has Electric Gates that kept burning out the relays because the designer failed to protect the contacts from the motor back EMF. I added some protection and it hasn't happened since.
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Post by ettingtonliam on Jan 30, 2022 10:10:10 GMT
I think you can avoid creating an arc when the switch opens by not using the Dewhurst as an on-off switch. I've got a separate on off switch, and only use the Dewhurst as a forward reverse when the machine is stationary. That way it only gets used every few days, rather than every time the motor is switched on. I like Dewhurst switches a lot, pity you can't buy them anymore, or spare contacts.
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Post by Roger on Jan 30, 2022 10:42:41 GMT
I think you can avoid creating an arc when the switch opens by not using the Dewhurst as an on-off switch. I've got a separate on off switch, and only use the Dewhurst as a forward reverse when the machine is stationary. That way it only gets used every few days, rather than every time the motor is switched on. I like Dewhurst switches a lot, pity you can't buy them anymore, or spare contacts. Fair enough, but the motor is switched on and off somewhere, and that needs suppression. It's best to protect the contacts that are as close to the motor as possible. You can put the MOVs there, or on the motor terminals itself. All of the variable speed drives have this protection internally. They wouldn't last a minute without providing a path to dissipate the back EMF from the motor.
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JonL
Elder Statesman
WWSME (Wiltshire)
Posts: 2,912
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Post by JonL on Jan 30, 2022 11:20:36 GMT
My toolmakers chest was made by my Grandfather for my Mother, when she started work at the aircraft factory at Filton (Bristol) in WWII. It too, had lost its key, but that wasn't too difficult to conjure up. My great grandparents and my grandmother worked there too! Small world.
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stevep
Elder Statesman
Posts: 1,070
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Post by stevep on Jan 30, 2022 15:18:24 GMT
My toolmakers chest was made by my Grandfather for my Mother, when she started work at the aircraft factory at Filton (Bristol) in WWII. It too, had lost its key, but that wasn't too difficult to conjure up. My great grandparents and my grandmother worked there too! Small world. That probably says much about our respective ages!!!
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Post by keith1500 on Jan 31, 2022 12:27:10 GMT
I think you can avoid creating an arc when the switch opens by not using the Dewhurst as an on-off switch. I've got a separate on off switch, and only use the Dewhurst as a forward reverse when the machine is stationary. That way it only gets used every few days, rather than every time the motor is switched on. I like Dewhurst switches a lot, pity you can't buy them anymore, or spare contacts. Given there is nothing much to the contacts the Dewhurst switch is easily repairable. I made new stainless steel round bits. The copper contacts are a simple shape. I think the tricky bit with the copper is making it hard again so it acts like a spring. I think this can be done by gently tapping the copper with a nice flat hammer? I might be wrong as never tried it…yet. The copper contact I did repair just needed a bit of tweak with pliers to make sure it lined up nicely with the stainless steel and was touching the same time as the others. I tried it a few time with the cover off ( lots of exposed live parts! ) to see if there any sparking issues. I was quite amazed how clean the disconnections were. Well happy I like Rogers suggestion of putting a suppressor / MOV ( metal oxide Varistor) across the motor terminals. I’ll look into doing that. …and the lesson learnt here. I should have given the electrics a once over when I brought the machine, including checking the fuse size in the plug!
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Post by andyhigham on Jan 31, 2022 14:49:32 GMT
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Post by vulcanbomber on Jan 31, 2022 23:35:12 GMT
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Post by davewoo on Feb 2, 2022 16:11:08 GMT
Interesting little job finished today, I've been puzzling over the injector feed for my Aspinall, the drawings show no filters fitted which I wouldn't be happy with. Came up with all sorts of complicated ideas and finally settled on the filters pictured below and home made ball valves as described in the injector book. Small block solders into bottom of tender tank and filter fits with four M3 stainless cap heads and is sealed with an o ring, filter is 1/2" dia so hopefully no problems with water flow. Space is a bit tight under the tender tank so the square body fits in tighter to the frame stays, would have been a bit more awkward to have screw in fittings. seem to be making some progress at last.
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kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 566
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Post by kipford on Feb 2, 2022 18:19:36 GMT
Dave Interesting. How do they link in with the tender water valves? Dave
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Post by davewoo on Feb 2, 2022 23:03:02 GMT
Hi Dave I've departed from the water valve in the tender tank arrangement as drawn, it will be externally piped to home made miniature ball valves under the tender, I've used the arrangement before and it worked well. The valves are described in the miniature injectors book,They will be operated by the water valve handles in the scale position, I've got a thing about having everything accessible. I don't think the pipework and valves will be too noticeable when on the track, coat of satin black coming up!
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kipford
Statesman
Building a Don Young 5" Gauge Aspinall Class 27
Posts: 566
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Post by kipford on Feb 3, 2022 17:05:33 GMT
Dave Be interested to see your finished set up. Dave
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Post by andyhigham on Feb 3, 2022 20:53:39 GMT
I made the new "steam end" fitting for the drain cock valve. I made it adjustable so I can set the number of turns full open to full vent. I set it to 1/2 a turn and it passes the gob blow test.
Got to be easier than 7 1/2 turns to open the cocks then 7 1/2 turns to close them again
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smallbrother
Elder Statesman
Errors aplenty, progress slow, but progress nonetheless!
Posts: 2,269
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Post by smallbrother on Feb 3, 2022 22:04:18 GMT
My 17 year old pupil (my son) passed his driving test today. I started teaching him last July because there were no professional instructors available. As far as I can tell there still are very few able to take anyone on.
I am obviously pleased both for him and for myself. We used a lot of YouTube videos as there are some excellent ones showing things in a logical and simple way.
The only downside is I am mentally and physically exhausted by it all. With lockdowns, knee problems as well I have been out of the steam engine game for nearly 2 years. My only contribution to the club is money. My bones ache too much to contemplate mixing and laying concrete etc.
I wonder if it's time to call it a day as far as running big engines is concerned, just do a bit of building in 3.5" gauge as and when I feel like it.
My principle love in life has always been the great outdoors and doing some sort of sporting type activity. Model engineering was always a side show, something quiet to do as a contrast.
On top of all this I am considering trying to move to Spain, for several months a year initially with a view to making it permanent. The outdoor life would be far more accessible there of course.
Sorry to ramble on but I've been in this game since 2009 and it's not easy to think of packing it in.
Pete.
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Post by andyhigham on Feb 3, 2022 22:10:41 GMT
3 1/2" can be big engines
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dscott
Elder Statesman
Posts: 2,438
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Post by dscott on Feb 3, 2022 23:42:38 GMT
My 17 year old pupil (my son) passed his driving test today. I started teaching him last July because there were no professional instructors available. As far as I can tell there still are very few able to take anyone on. I am obviously pleased both for him and for myself. We used a lot of YouTube videos as there are some excellent ones showing things in a logical and simple way. The only downside is I am mentally and physically exhausted by it all. With lockdowns, knee problems as well I have been out of the steam engine game for nearly 2 years. My only contribution to the club is money. My bones ache too much to contemplate mixing and laying concrete etc. I wonder if it's time to call it a day as far as running big engines is concerned, just do a bit of building in 3.5" gauge as and when I feel like it. My principle love in life has always been the great outdoors and doing some sort of sporting type activity. Model engineering was always a side show, something quiet to do as a contrast. On top of all this I am considering trying to move to Spain, for several months a year initially with a view to making it permanent. The outdoor life would be far more accessible there of course. Sorry to ramble on but I've been in this game since 2009 and it's not easy to think of packing it in. Pete. We went on Holiday many years ago to Spain and found many hiding from the English winters... Including us!! Many years earlier met up with several in Tropical Philippines having ditched all the aches and pains! And another on crutches counting down the days to getting to a WARM place. Now we know why they literally almost COOK the old people in their homes. Tomorrow I start on the inner wall build and pack in the insulation behind. Sunday is Public Running in a Cold Feb of course. Well done on passing your test. Good thing it was a very Clean Car!! David and Lily. Steaming since 1976.
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