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Re: [TCML] How To Turn A Vacuum Cleaner Motor Into A Synchronous Motor
Stefan
What you are seeing is classic "pole slipping" of a synchronous motor.
You have to apply voltage to motor fairly abruptly (notice current dependence)
to get armature to lock in synchronism with utility. Also notice when
surging the abnormally high voltage seen on the armature brushes. When the
motor is slipping poles, it becomes to some degree a "rotating transformer"
and can generate higher then Vapplied across the brushes.
Also warning, do not isolate field connection from armature, very high voltages
from transformer action can occur and damage the windings, or present
a HV shock hazard (up to 8X Vapplied).
I have a detonated (literally) field terminal block from a 2300V,
350HP synchronous
motor, from the field circuit opening under load while the motor was
accelerating
as an induction motor. The field discharge resistor circuit opened and
a load BBUUUZZZAAAPP! Fortunately a GE SPM motor protector relay
saw the field loss OV event and shunt down the MV vacuum contactor to
the motor before damage was done to motor or controls.
Regards
On Thu, Dec 16, 2010 at 3:38 PM, Teslalabor <teslalabor@xxxxxxxxxxx> wrote:
> Hello,
>
> today I modified a 400W universal motor from a washing machine. I used 2
> diodes each 1kV/6A. I did a scope test which shows that the motor runs
> perfectly sync:
>
> http://www.youtube.com/watch?v=yOlfzxzucy8
>
> But there are 2 problems: The motor is not self-starting AND the motor
> sometimes runs in "crazy mode", as I call this strange behaviour.
> "normal-mode" and "crazy-mode" - both can be seen in the video.
>
> Best Regards
> Stefan
>
>
> ----- Original Message ----- From: "Clive Penfold"
> <clivepenfold@xxxxxxxxxxxxxx>
> To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
> Sent: Tuesday, December 07, 2010 6:46 PM
> Subject: Re: [TCML] How To Turn A Vacuum Cleaner Motor Into A Synchronous
> Motor
>
>
> Phil,
>
> Yes, that is correct. Brief explanation along with some photos here:
>
> http://4hv.org/e107_plugins/forum/forum_viewtopic.php?102515.last
>
> Regards,
>
> Clive
>
>
>
>
> ________________________________
> From: Phil Tuck <phil@xxxxxxxxxxx>
> To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
> Sent: Tuesday, 7 December, 2010 15:10:17
> Subject: RE: [TCML] How To Turn A Vacuum Cleaner Motor Into A Synchronous
> Motor
>
> DWP,
> I think there is some misunderstanding here. I don't think the sensor and
> magnet
> were triggering the strobe as you do (I think that is what you're thinking?)
> The presumption is that the magnet was attached to the motor shaft such that
> it
> passed and induced a voltage into a fixed coil once per rev.
> If so, the output will always coincide with the electrode passing that point
> in
> space.
>
> If the scope is setup to show both channels overlaid, and the output from
> the
> sensor coil is fed into one channel, with the mains fed in on the other
> channel,
> and the output from the sensor subsequently always coincides with the same
> point
> on the mains sine wave, then the motor is synchronous.
>
>
> I use an infra-red sensor being tripped by the electrodes and it work fine.
>
> Regards
> Phil
>
> www.hvtesla.com
>
> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
> Of
> dave pierson
> Sent: 07 December 2010 12:34
> To: Tesla Coil Mailing List
> Subject: Re: [TCML] How To Turn A Vacuum Cleaner Motor Into A Synchronous
> Motor
>
>> The poster mentions that he had "the mains on the other" [ channel] So
>> I assume a mains reference sine wave on the other channel.
>
> Good point. However:
>
>>> In usual engineering use of the term synchronous motor, the speed is
>>> set by the line frequency. Strobe Testing with a magnet spun by the
>>> same motor as a sync source demonstrates that one end of the motor
>>> (where the magnet is) is 'synchronous' with the other end.
>
>>> If a scope is to hand: most have a 'line sync' position, which syncs
>>> the scope to the _line_ freq. With line sync selected, a reading
>>> from the flying magnet to a sense coil would be interesting.
>
>>> A motor which (happens?) to be running at 3000 (ish) will appear
>>> synchronous to 50 (or 60, or 30 or 100). A proper synchronous motor
>>> will hold synch Under Varying Load.
>
> The key is just above. a 'truly synchronous' motor will
> hold speed, and phase, under varying load and input
> voltage, (within reason...).
>
> best
> dwp
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--
Dave Sharpe, TCBOR/HEAS
Chesterfield, VA USA
Sharpe's Axiom of Murphy's Law
"Physics trumps opinion!"
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