On 2017-04-12, wrote:
On 12 Apr 2017 04:01:56 GMT, "DoN. Nichols"
wrote:

On 2017-04-11, wrote:
I'm sue someone here can help. I need to get power to a solenoid
operated valve spinning at 5000 RPM. Low power, 24 volts at 5 watts.
The power will be on for about 4 seconds and off for 7 seconds. This
on/off cycle will be going on 10 hours a day.

Is this 24 VDC or 24 VAC? Can you *use* AC? If so, mount a
coil around the rotating shaft, and another one close to it to the
stationary surrounds. If you make it well balanced, there should be no
problems for transmitting AC.

I ahve looked at slip
rings online but the high speed through hole type are really spendy.
Then I got to thinking about the slip rings in alternator. They
certainly can carry enough current but I don't know how fast
alternators typically spin. I do have an old alternator that would
make a good slip ring donor. Anybody know or have a better idea? I
need about 1 inch through the slip rings.
Thanks,
Eric

I would skip the idea of slip rings, as the electro-magnetic
coupling will last pretty much forever.

Enjoy,
DoN.
Greetings DoN,
I thought about that but dismissed it because I really don't know how
I would go about doing it. So maybe you could help. Sticking out the
back of the lathe will be a steel tube.

Mild steel, or hardened? Mild would be better.

Inside this tube will be the
solenoid actuated valve and counterweights so that the tube is
balanced. And the plumbing that will bring the air from the valve to
the collet closer mounted in the spindle. Into the end of this tube
will be screwed a rotary union that passes air.

Hmm ... any reason why you can't put the valve on the outside
end of the union? That looks like it (the union) might wear faster than
the slip rings anyway.

If I have a coil
wrapped around the steel tube won't that be a problem? What if a
plastic sleeve were to be pressed over the O.D. of the tube and the
coil wrapped on it. Would that be better?

Hmm ... let's make the part which contains the coil fairly
short, and put a plastic spacer say 1/4" thick or a bit more between it
and the main tube. Let me sketch how I would make it for reasonable
magnetic coupling.. (I'm sure that there are many ways.)

BBBBBBBBBB
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXBBBBBBBBBB
XXX:::::::::::: :::::::::::XXXBB
XXX:::::::::::: :::::::::::XXXBB
XXX:::::::::::: :::::::::::XXXBB
XXX:::::::::::: :::::::::::XXXBB
XXX:::::::::::: :::::::::::XXXBB
XXX:::::::::::: :::::::::::XXXBB
XXXXXXXXXXXXXXX XXXXXXXXXXXXXXBB
PPPPPPPPPPPPPPP
PPPPPPPPPPPPPPP
PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP
PPPPPPPPPPPPPPPPPPPPPPPPPPPPPPP
SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS
SSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSSS

This image is only above the centerline of the tube.

If your newsreader is using a proportional space font, the image
will be distorted -- unless you can send it to a printer which has a
fixed-space font like Courier available. Proportional space fonts will
squeeze the ':'s closer together than the 'P', 'S' and 'X' characters.

The second and third row of Ps should end just below the
right-most '|'s

The parts made of ||| are mild steel cups. The one to the left
fits onto a plastic sleeve PPP over the steel sleeve SSS.

The ::: are the ends of wires in the coil wound and glued into
the cup. (With the wire ends brought out though a hole or two drilled in
the bottom wall of each cup.

BBB is a bracket -- steel, aluminum, or perhaps a strong plastic. The
two cups will concentrate the magnetic field fairly well from one coil
to the other. Whether it goes up, or down depends on where you have
something to bolt it to.

voltage to the stationary coil it seems tome that a 1:1 ratio between
the coils would be easiest to do. Does this mean that I can also get
away with just about any number of turns provided the wire can handle
the minute current?

Too few turns will make the inductance too low for the 60 Hz
voltage, even with the steel cups, and will draw too much current from
the supply. At a guess, I would go for perhaps 100-200 turns on each
coil.

The valve only needs .2 amps to operate so the
wire can be pretty fine.

Probably 24 to 30 ga magnet wire. Measure it and calculate how
much area would be taken up by 200 turns to decide how deep to make the
cups. You can use mild steel pipe and bore it out truly round (since
most pipes have an internal weld bead) and then turn a mild steel plate
to press into the pipe. Or -- machine the whole thing out of a mild
steel. If you want it to look nice, and have some, 12L14 machines
nicely. Pipe is usually ugly to machine. :-)

The valve operates on DC but a rectifier can
be stuffed into the tube along with everything else. Will the tube
coil need a snubber diode too? Any advice?

A snubber diode will short half of the AC voltage. Bad news
here. Maybe put one on the DC coil of a relay from whatever is
generating the pulses, and use that to switch the AC into the coil.

On the output coil (between it and the solenoid valve) you'll
want a small bridge rectifier. If you use a plain single diode, you
will only get power for half of each cycle (1/120 second on, 1/120th
second off) which will likely buzz, and you may need to boost the
voltage a bit (maybe 20-50% to get sufficient current into the solenoid
valve.


Thanks,
Eric

You have my thoughts above -- including putting the solenoid
valve outside the union so it does not need to rotate. :-)

Enjoy,
DoN.

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