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Thread: Vfd new or repair.
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29th Aug 2019, 08:32 AM #1Member
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Vfd new or repair.
Hi all I have a teco vfd fm50 and it's got a failed thermister I think but I can't find one in the Jaycar type shops to replace and try. To have a shop look at it it's 60 bucks up front and more if needed to fix. I know it's a better brand but I can't go past the eBay stuff for price. This is my first drive with a 3 phase motor i want to fit to a small mill machine i have restored , the motor is only .5hp and it's a small mill. I have been reading the comments so far but still unsure of which are worth buying, what has come from all your testing. Thank you Brett.
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29th Aug 2019, 08:38 AM #2Philomath in training
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I bought a Delta S1 the other day, which is now the 3rd one in my workshop. It did cost $65 secondhand but works, has all the usual features and the manual is fine.
Michael
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29th Aug 2019, 09:16 AM #3Member: Blue and white apron brigade
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You can get them at Element14 or RS and cost around $5-6.
However, (as I found out on one of Anorak Bob's VFD which had the same problem) the chances of the problem just being the thermistors is slim. Usually this means something else has gone wrong further back in the system. When I replaced the thermistors there was a nice loud bang that destroyed the thermistors and blew the breakers. With decent new ones available for ~$100 I'd be looking for a replacement.
I like the Powtrans. Purchasing is direct from the factory and a bit of a PITA as there's no website. Some info here. https://metalworkforums.com/f309/t20...ounced-powtran
If you want to buy from an Aussie supplier then Conon motors seem to have reasonably good stuff.
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29th Aug 2019, 09:21 AM #4Member
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Yes that's what I'm afraid of, having all the smoke coming out of the good bits left and then paying to fix it and costing more than a new one. So a delta s1, I'll have to chase one down micheal .
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29th Aug 2019, 09:27 AM #5Member
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29th Aug 2019, 03:45 PM #6Most Valued Member
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Here is a cheap VFD, new and in Aust for $76.00 https://www.ebay.com.au/itm/1-5KW-22...AAAOSws6ldTTTw
I don't mind the cheapies and have not had a problem with them yet, I have 5 of the cheap chinese VFD's.
Just a word about your 1/2 hp motor, I had a 1/2 hp single phase on my little Centec mill and it was gutless,
I put a 1 hp 4 pole 3 phase motor on it with a VFD, nup sorry, still I was not happy, it was ok but the cutter would slow down
when buried into the cut.
I then put a 6 pole 1 1/2 hp 3 phase motor on it with the same VFD and now I am happy, so what I am saying is that when you buy a VFD make sure that it will cater for a bigger motor should you decide to upgrade that.
cheers, shed
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29th Aug 2019, 07:30 PM #7
Hi Brett, Guys,
I agree its not worth attempting to repair unless you are sufficiently skilled to do it yourself.
The thermistor is a temperature sensing device and is usually there to monitor the power devices and shut the system down if the components gets too hot. The fact that it has catastrophically failed means that it hasn't reacted quickly enough and other components have failed.
Their not expensive devices nowadays ! Just get a new one heeding Sheds advice about the Centec mill.Best Regards:
Baron J.
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29th Aug 2019, 08:11 PM #8
One of the things I learnt fairly early in a reasonably long electronics and comms career is that if the protection devices have died, it's a 99.9% chance that it is the devices that they protect that let go first and then took the protectives out.
The high power devices exist by being in one of two states, either high voltage across them and no current flowing through them (low power disipation) or very low voltage across them and high current flowing (again low power disipation). Things get very interesting if/when something that is intended to operate in switching mode, but manages to go linear, medium/high voltage across the devices and medium/high current through them as well (extreme power disipation).
I recall that my first electronics employer (45 years ago) was working on a large, then experimental switch mode battery charger for the railways, intended to recharge flat loco batteries, or at a pinch start the huge diesel engine in booster mode. This monster had 100 TO3 metal switching transistors mounted on huge heatsinks for the output stage and another 20 similarly mounted to drive them. In the proccess of getting the prototype setup and stable one of the adjustment pots in the control system developed a fault sending the thing linear. Of the 120 metal can driver and output transistors, 4 kept their metal caps, the others went through the building, through the ceiling and through some of the roofing sheets. The protection circuits also were fried, but survived the mayhem longer than the gear they were supposed to be protection. The battery bank that was connected for testing was internally welded and shorted out by the current spike that hit it.
Hence in your situation, it is extremely unlikely that there are good bits left to smoke, at least in the power circuits and probably the driver circuits as well. I think replacement might be a good idea. If the failure experienced occurred while attempting to drive your motor, I would be having the motor fully insulation tested before connecting another VFD to it as well, as either it caused the vfd failure, or most likely will have suffered because of it.I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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30th Aug 2019, 08:17 AM #9Member
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Sorry I haven't replied yet, for some reason I couldn't sign in and the layout is now all different. I believe the motor could be a problem in size but I will not know until I put it together as it's not yet been used and I believe the mill has been hidden away for over 40 yrs untouched. I have no info on it so it's all guessing now. I can't afford a motor and vfd now but it's looking that way from the hard earned experience you have all given.
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30th Aug 2019, 09:01 AM #10Member: Blue and white apron brigade
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I don't know the Centec but my experience with the little Hercus Mill has been the opposite. It too had a 3P 4P 1/2HP motor and I was worried it would be too small when I fitted a VFD and I made plans to upgrade the motor. In the end I decided at least in the first instance to try the motor as is. One year+ on and provided I am not too greedy I have not come across any problems with power. The VFD is a Powtran vector drive so it retains reasonable power even at low RPM.
The same could not be said about the Hercus lathe which had the same motor and a Vector drive VFD. IN I swapped that to a 3P 4 pole 1HP with Vector drive VFD and all is now good.
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30th Aug 2019, 05:44 PM #11Most Valued Member
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Hi Bob, it is horses for courses I suppose, I like to be able to get stuck into it without a spindle or chuck slowing down as that is one thing that can stuff your tooling and job and blow out the hours.
I have a C model Hercus with a 3/4 hp and the oil soaked flat belt slips easily so I only use it very lightly, on the other hand the lathe that I use most of the time has a 7.5 hp motor and I often take 6mm cuts when roughing something down, I guess people are happy with what they have and can work around something like low HP but once spoilt you can't go back
cheers, shed
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30th Aug 2019, 06:17 PM #12Member: Blue and white apron brigade
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I agree that it's easy to get spoiled. I mainly do small stuff in my shed and don't expect much from my small mill so I don't push it. I had more in mind more the chance of seriously stuffing my mill up as one of the main gears is a fibre gear. I've seen what a big lathe can do to a bit of metal etc when something goes pear shaped and that reminds me to stop and think before just going bigger and bigger. On my lathe I keep the belts on the the loose side so that if something does grab there's a chance they will slip but that's not an option on an all geared system.
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30th Aug 2019, 06:30 PM #13
Hi Guys,
The headstock belt on my Myford from new got oil soaked very quickly ! But that does have the advantage that it will slip if anything jammed. I've had it start to slip when I used a hole saw to cut a 32 mm hole in a 1" inch thick block of steel using the four jaw. I've since used the slug that I cut out, but I've since bought a 1" diameter blacksmiths drill and that is much quicker and easier than the hole saw. But you basically swap drilling speed for the longer time it takes to bore out to size.Best Regards:
Baron J.
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31st Aug 2019, 10:33 AM #14Member
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This is my little mill, what motor size would you choose ?
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31st Aug 2019, 11:37 AM #15Member: Blue and white apron brigade
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