Coil trips RCD/GFCI

Started by July 9, 2018
A 1946 mains vibrator electrically consists of a large coil with moving centrepiece.
240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but
often trips the 30mA RCD when switched off. 500v inuslation testing shows no
problem. I assume it has no built in snubber. I'm not working out why it trips the
RCD. Any ideas?


NT
On Monday, July 9, 2018 at 1:04:43 PM UTC+2, tabb...@gmail.com wrote:
> A 1946 mains vibrator electrically consists of a large coil with moving
centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v inuslation testing shows no problem. I assume it has no built in snubber. I'm not working out why it trips the RCD. Any ideas? Presumably the turn-off voltage spike is higher than 500V and something sparks over to earth. That could well trip the RCD. Back to back avalanche diodes to 0V rather than ground might be enough to cure the problem. http://www.farnell.com/datasheets/2046235.pdf?_ga=2.13928951.1986742322.1531137221-903798115.1499933451 -- Bill Sloman, Sydney
tabbypurr@gmail.com wrote in
news:bb5b0cf2-dccf-4110-b868-10f7809724db@googlegroups.com: 

> A 1946 mains vibrator electrically consists of a large coil with > moving centrepiece. 240v 240 ohms measured, 10w (according to rating > plate). It works flawlessly, but often trips the 30mA RCD when > switched off. 500v inuslation testing shows no problem. I assume it > has no built in snubber. I'm not working out why it trips the RCD. Any > ideas? > > > NT >
It is called "back EMF".
On Monday, 9 July 2018 12:55:23 UTC+1, bill....@ieee.org  wrote:
> On Monday, July 9, 2018 at 1:04:43 PM UTC+2, tabby wrote:
> > A 1946 mains vibrator electrically consists of a large coil with moving
centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v inuslation testing shows no problem. I assume it has no built in snubber. I'm not working out why it trips the RCD. Any ideas?
> > Presumably the turn-off voltage spike is higher than 500V and something sparks
over to earth. That could well trip the RCD.
> > Back to back avalanche diodes to 0V rather than ground might be enough to cure the
problem.
> >
http://www.farnell.com/datasheets/2046235.pdf?_ga=2.13928951.1986742322.1531137221-903798115.1499933451 obviously being a 1946 appliance there is no earth connection, and no user shocks occur, and the insulation is sound. If it were arcing it would have degraded. NT
On Monday, 9 July 2018 13:09:40 UTC+1, DecadentLinux...@decadence.org  wrote:
> tabbypurr wrote in > news:bb5b0cf2-dccf-4110-b868-10f7809724db@googlegroups.com: > > > A 1946 mains vibrator electrically consists of a large coil with > > moving centrepiece. 240v 240 ohms measured, 10w (according to rating > > plate). It works flawlessly, but often trips the 30mA RCD when > > switched off. 500v inuslation testing shows no problem. I assume it > > has no built in snubber. I'm not working out why it trips the RCD. Any > > ideas? > > > > > > NT > > > > It is called "back EMF".
Back emf is certainly called back emf. Would you like to explain how that trips an RCD? NT
On Mon, 9 Jul 2018 04:04:39 -0700 (PDT), tabbypurr@gmail.com wrote:

>A 1946 mains vibrator electrically consists of a large coil with moving
centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v inuslation testing shows no problem. I assume it has no built in snubber. I'm not working out why it trips the RCD. Any ideas?
> > >NT
The switchoff transient could pump a current spike through the winding-to-ground capacitance. Try adding a MOV somewhere. Or reversing the coil connections. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On Mon, 09 Jul 2018 07:16:33 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

>On Mon, 9 Jul 2018 04:04:39 -0700 (PDT), tabbypurr@gmail.com wrote: > >>A 1946 mains vibrator electrically consists of a large coil with moving
centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v inuslation testing shows no problem. I assume it has no built in snubber. I'm not working out why it trips the RCD. Any ideas?
>> >> >>NT > >The switchoff transient could pump a current spike through the >winding-to-ground capacitance. Try adding a MOV somewhere. Or >reversing the coil connections.
Some GFDs have arc detectors. An MOV could help that too. -- John Larkin Highland Technology, Inc lunatic fringe electronics
On 09/07/2018 12:04, tabbypurr@gmail.com wrote:
> A 1946 mains vibrator electrically consists of a large coil with > moving centrepiece. 240v 240 ohms measured, 10w (according to rating > plate). It works flawlessly, but often trips the 30mA RCD when > switched off. 500v inuslation testing shows no problem.
With respect to what? How was the 'insulation' being tested. Is there an earth?
> I assume it has no built in snubber. I'm not working out why it trips > the RCD. Any ideas?
I might run in through a filtered trailing socket. -- Mike Perkins Video Solutions Ltd www.videosolutions.ltd.uk
On 09/07/2018 12:04, tabbypurr@gmail.com wrote:
> A 1946 mains vibrator electrically consists of a large coil with moving
centrepiece. 240v 240 ohms measured, 10w (according to rating plate). It works flawlessly, but often trips the 30mA RCD when switched off. 500v inuslation testing shows no problem. I assume it has no built in snubber. I'm not working out why it trips the RCD. Any ideas?
> > > NT >
I had a set of hair clippers that did that. An RC snubber across the coil fixed it. I think 100R 100nF. MOV should be good option also. My guess is the residual current detector HF response is wrong, somewhere I once saw reference to response should fall off above 2.5kHz - RCD/GCFI should not trip on a high energy burst of RF. piglet
bill.sloman@ieee.org wrote...
> > On Monday, July 9, 2018, tabb...@gmail.com wrote: >> >> A 1946 mains vibrator ... works flawlessly, but often trips >> the 30mA RCD when switched off. > > Presumably the turn-off voltage spike is higher than 500V > and something sparks over to earth. That could well trip the RCD. > > Back to back avalanche diodes to 0V rather than ground > might be enough to cure the problem.
Those diodes have an avalanche voltage between a bit above the rated value and 1600V. He needs one that's guaranteed to be below 350V, etc. That would be a TVS type. Like a 1.5KE200A for 190 to 210V peak, or a 1.5KE440A for 418 to 462V, etc. -- Thanks, - Win