[GreenKeys] Machine speed and VFDs

[Ralph Mowery]

As long as the shaft is turning very close to the rated speed , that is all
that matters.  

I worked with VFDs among other things at work. You just have to be sure the
VFD will have enough power to turn the shaft at a reduced speed.  That is
the motor looses tork as the speed is reduced and may not be able to turn
the shaft.  Some drive and motor combinations work well and some do not at
low speeds.  Also the motor will have a fan on the back of it to cool the
motor.  We had to add external driven fans on some motors as the speed was
reduced very much.  

You may come out better if you gear up at 75 wpm and only have to go down a
small amount, but could go up ok.

I don't recall where I saw it, probably in a back issue of the RTTY Journal
but someone had made an optical interrupter for feedback and made something
similar to a VFD.  Supposed to have worked well.




-----Original Message-----
From: greenkeys-bounces at mailman.qth.net
[mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of Robert Goff
Sent: Sunday, September 02, 2018 9:49 PM
To: GreenKeys at mailman.qth.net
Subject: [GreenKeys] Machine speed and VFDs

This is probably a really stupid question,  BUT:

I was just looking at the gear chart in an old Atlantic Surplus
catalog comparing the gear ratios from 100 speed to 60 speed on a
model 28.  It looks to me like for 60 wpm the 3600 rpm of the motor is
being reduced to 525 rpm by the combination of the pinion and the main
gear.  For 100 wpm it is 857 rpm, approximately the ratio of 5:3.

If you had a machine geared only for 100 wpm and you used a freq drive
to reduce the motor speed to 2205 or so, so that the main gear was
spinning at 525 rpm, would the machine then operate at 60 wpm?

Has anyone tried this?  Is there something I'm missing?  Frequency
drives for fractional horsepower motors have really gotten pretty
cheap, and maybe easier to track down than 60/67/75/100 gear sets.

Thanks,
de Robert W7MKA