RE: [TCML] SRSG Rotor Mods difficulty

["Phil Tuck (hvtesla)" <phil@xxxxxxxxxxx>]

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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