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RE: [TCML] SRSG Rotor Mods difficulty
Hello John.
I fly-cut the two flats 1.077 inches wide, based on measuring the poles, and
coincidently this width is also 50% of the 2.140 inch rotor. All works ok,
I checked for sync' with a photo-electric cell and oscilloscope just to make
sure! . Speed on an electronic tacho was 3002 rpm.
Phil
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On Behalf
Of futuret@xxxxxxx
Sent: 09 August 2009 22:21
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] SRSG Rotor Mods difficulty
Phil,
Yes, it makes sense that the poles would be half as wide for a 1500 rpm
motor vs. an 3000 rpm motor, since there are twice as many poles in
the 1500 rpm motor. I was thinking the same thing. Probably the
0.25 for a 4 pole motor, and the 0.50 for a 2 pole motor is a good
general way to modify these motors.
I'm sure your mod will work out well. Let us know.
Cheers,
John
-----Original Message-----
From: Phil Tuck (hvtesla) <phil@xxxxxxxxxxx>
To: 'Tesla Coil Mailing List' <tesla@xxxxxxxxxx>
Sent: Sun, Aug 9, 2009 4:48 pm
Subject: RE: [TCML] SRSG Rotor Mods difficulty
John.
Thanks for that. That works out around 56%. The motor I was going to
modify is
better than my own bench grinder so I have swopped them around. The
latest motor
(my old bench grinder) is a 'PSC' type - permanent split capacitor -
and it has
its start coils clearly discernable - they also happen to be very badly
burnt /
overheated as well!
Using the pole measurement approach, gives a flat width of 1.077 inches
needed
on a rotor diameter of 2.14 inches which is 50%.
The two starting coils (located @ 12 & 6 o' clock ) each use 4 of the
stator
poles, whereas a lot of the 1500 rpm's I've seen only use two stator
poles each,
but of course there are four 'groups' of them (located @ 12, 3, 6, & 9
o'clock).
Because the faster 3000 / 3600 rpm motors only ever have two 'groups'
of stator
poles occupied by the starting coils, maybe each 'group' of the faster
motor
occupies double the number of stator poles to make up for this. Hence
the need
for a wider flat (50% odd) ?
(Will grind the flats tomorrow)
Phil
-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of
futuret@xxxxxxx
Sent: 09 August 2009 20:56
To: tesla@xxxxxxxxxx
Subject: Re: [TCML] SRSG Rotor Mods difficulty
Phil,
I'm following up on my last posting here. I looked up the
specifications for my synch motor modification. It turns out
that the rotor was 1.875" dia. and I cut the 2 flats 1.062" wide.
I modified that motor on January 28, 1995.
My guess is that the flats could have been a little narrower,
and the motor probably would have worked just as well.
So yes, I made the flats much wider for a 3000/3600rpm motor
than I would for an 1500/1800 rpmm motor.
Cheers,
John
-----Original Message-----
From: futuret@xxxxxxx
To: tesla@xxxxxxxxxx
Sent: Sat, Aug 8, 2009 9:24 pm
Subject: Re: [TCML] SRSG Rotor Mods difficulty
Phil,
I never use the dead pole concept when I modify my motors for
synch operation. I use the proportion method. For 1500 rpm
motors I use 4 flats at 0.25 as you mentioned. For example a
2"dia rotor would receive 1/2" wide flats.
For 3000 rpm motors I use 2 wider flats. If I remember
correctly, I made my flats 7/8" wide on a 2.1" diameter rotor
(possibly the rotor was 1.85" diameter). My memory is a little
foggy here. I think I have it written down somewhere.
I don't know if this width is optimal, but the motor gave
very good torque after it was modified and locked into synch
very nicely. It was a 1/10HP motor.
Cheers,
John
-----Original Message-----
From
: Phil Tuck (hvtesla) <phil@xxxxxxxxxxx>
To: tesla@xxxxxxxxxx
Sent: Sat, Aug 8, 2009 2:47 pm
Subject: [TCML] SRSG Rotor Mods difficulty
Hello.
Having successfully machined a 1500rpm motor in the past, I now wish to
do
a (UK 50Hz 240v) 3000rpm one for my SRSG.
Previously, with the 1500rpm and based on advice from this group, I
measured
the rotor diameter and used one quarter of the measurement as the width
of
the machined flat. Like this:
http://www.hvtesla.com/images/tesla%20coil%20modding_motor.jpg
Yesterday I machined a 3000rpm bench grinder using the 0.25 formula and
the
motor just hunted afterwards without reaching a constant speed.
Increasing
the input to 270v did not help either. This motor was poor quality
anyway so
has now been discarded for other uses.
I have since been advised however that the 3000rpm motors do not
respond so
well to machining as the 1500rpm, and may need more material removed.
Unfortunately I am never able to correctly identify the 'dead' pole as
illustrated at http://evolve000.4hv.org/tesla/tc2srsg.html My motors
always
seem to differ to this.
I have now acquired a second 3000rpm motor (bench grinder) which is my
last
attempt for a while. This rotor is 2.128 inches diameter, the motor
itself
being rated at
250Watts (1/5 HP maybe??)
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