Jan, thanks for the input on this. Lee I really appreciate the lead on the GE
handbook, I downloaded it and indeed that circuit on pg 293 looks perfect for
this project; I am kind of helping / mentoring a friend of one of my sons with
his project and he doesn't have anything for money so its a fantastic find.
Looks like we can build it for under 10 bucks and it is simple and will do
everything he needs it to do so its an "Occamatic" solution. One question tho,
you said something about it needing a capacitor and looking at the schematic I
don't see one, in the notes below the drawing (fig. 10.5) it says "A capacitor
on the arm of R2 is not a cure because there will be no phase shift on the
reference due to full wave rectified charging." I wonder if an R/C drain to
ground between the SCR and C1 might accomplish turning off the SCR quickly?
Since this is a pm motor I will just leave out the field connection and diode
piece. BTW, would you just put the 15 amp fuse in the "hot" AC lead before the
bridge rectifier? Or is there a better place in the circuit? Thanks again, I
really appreciate you you taking the time to offer advice. Dach.
On Wednesday, January 24, 2018 8:17 PM, Lee Hart via EV <ev@lists.evdl.org>
wrote:
Jan Steinman via EV wrote:
> Is this permanent, or temporary/intermittent use?
That's important, because while most treadmill motors have high advertised
horsepower; in fact, they rarely deliver even a small fraction of that.
>
> I’d put a full-wave bridge rectifier as close to the motor as possible,
> and just call it a 120 VAC motor. Put a standard plug on it. Then you
> could plug it in to a wide variety of AC power control devices, as Lee
> suggests.
Good point! You do have to rectify the AC before it gets to the motor.
> Then, it sounds like a job for a good old-fashioned variac transformer.
That would work great if it can handle the current. Small variacs (rated at a
few amps) are pretty common and inexpensive used. But ones big enough to handle
15 amps continuously are quite a bit heavier and more expensive (like 20 lbs
and
$100).
> Lee’s ideas will still produce AC, and so would work fine for a universal
> (series-wound) motor, but probably not for a permanent magnet motor
Definitely not for a PM motor. For some reason, I was thinking he had a
universal motor, which doesn't care whether it's running on AC or DC.
Light dimmers typically use triacs, which are AC devices. But speed controls
for
electric drills more often use SCRs, which do have a DC output. The circuits I
mentioned from the GE SCR manual are all suitable for PM DC motors as well as
shunt and series motors, because they use SCRs for control. SCRs are better
suited to inductive loads.
> So, rectify that puppy, and lots more options become available!
Yes. :-)
--
It is vanity to do with more that which can be done with less.
-- William of Ockham
--
Lee Hart, 814 8th Ave N, Sartell MN 56377, www.sunrise-ev.com
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