Do I need a switch
6654 forum posts
Two things in Alan's post jumped out at me:
Not quite an assurance the 'Motor turns and runs smoothly'.
But quite right, I didn't mean Alan should dump the motor without trying a few things first. Worst comes to worst though, and the motor is a dud, then I think going 3-phase is the besr solution, money permitting.
I do suggest a half horse motor shouldn't ever trip a circuit breaker. Something ain't right. Earth leak would be my bet.
|Maurice Taylor||03/12/2020 23:39:52|
|162 forum posts|
Hi,A 1/2 hp Brook motor on an ML7 takes nearly 50A for 100mS on start ,this will sometimes trip a domestic mcb but probably wouldn’t trip an inductive load mcb ,as previously mentioned .An earth leakage fault would trip the elcb not the mcb.
PS If I’m writing rubbish , electrical experts please correct me.
Edited By Maurice Taylor on 03/12/2020 23:54:08
|113 forum posts|
Maurice, I'm interested in your scope setup. I'm familiar with the picoscope as I have one myself but never seen or used the automotive one. Are you using it with a clamp meter probe? I have a clamp meter but not for the scope. If I needed current logging I might use a current sense resistor and do it that way.
|not done it yet||04/12/2020 05:54:48|
|5352 forum posts|
Thanks for the ‘scope print-out. You seem in much agreement with me - where I also clearly pointed out that it was an overload trip and not the RCD. An RCD trip would have sounded alarm bells for me as any imbalance would likely indicate a leakage to earth.
All the evidence ( ‘I think because’ was a very speculative suggestion with no actual evidence supplied - I took that to likely mean it could have been the whole lathe that was stiff, not necessarily just the motor) indicates the motor is likely in fair fettle, but possibly needing maintenance.
A good earth connection (readily checked with a normal DMM) should protect the user in the event of leakage, but a resistance test for the motor is, of course, the far better option - as long as the motor windings are completely dry, of course.
|Maurice Taylor||04/12/2020 21:50:59|
|162 forum posts|
Hi, My setup consists of Picoscope 4225 and a current clamp Picoscope TA167 .The automotive scope will also run the ordinary Picoscope software.
When I got my clamp I wanted to measure starter motor current ,so I couldn’t consider a sense resistor ,it goes up to 2000A, There is a cheaper Pico clamp at £99 , this goes up to 600A, I would go for a clamp,no chance of damageing scope.
Hope this helps
|not done it yet||05/12/2020 07:16:00|
|5352 forum posts|
I blew a fuse yesterday. I left a 5A fuse in a plug on a lead for a 1 1/4 HP motor drive (via a VFD). It lasted for quite a lot of soft starts but gave up on a heavy load. Fitted the correct 13A fuse for the supply lead and all has been OK since.
|Michael Gilligan||05/12/2020 09:16:23|
16990 forum posts
It may be worth reading this old thread from 2012 :**LINK**
I took advice from MEW and did what appeared to be the right thing
... and was then chastised/ridiculed for it
... but life’s like that.
|old mart||05/12/2020 16:18:11|
|2465 forum posts|
Having looked at your link, Michael, I would also warn those people with old electric drills about the state of the insulation of the wiring. I bought a Black & Decker D720, (the two speed with the metal body and 3/8" chuck) in the late sixties. About 20 years later, I had reason to unscrew the plate on the side of the handle and found the wiring insulation all cracking up. It got binned straight away and replaced by a plastic bodied double insulated one. There are lots of cherished old mains operated tools out there still in use, hopefully their earth connections are still good and the RCD's in use today will save somebodies life.
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