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. 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.
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 would skip the idea of slip rings, as the electro-magnetic
coupling will last pretty much forever.
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. 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. 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? Since I can supply any
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? The valve only needs .2 amps to operate so the
wire can be pretty fine. 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?
Mild steel, or hardened? Mild would be better.
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.
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.)
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
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.
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
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. :-)
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
You have my thoughts above -- including putting the solenoid
valve outside the union so it does not need to rotate. :-)
Thanks for the advice. The reason for the valve is that the rotary
union has only one air passage and I need two for the closer. The
rotary union I am using will last thousands of hours. I know this
because I have used this exact model for thousands of hours. I don't
know why it is but two passsage rotary unions that can handle the air
pressure and speed are about 10 times more expensive than single
passage ones. For liquids, like oil or coolant, two passage rotary
unions have much higher pressure and rpm limits. Anyway, the only cost
effective way to get the setup to work is to do the valving in the
spinning tube. I use DOM tubing for spindle liners and will be using
some for this project. I have another coil question. What if the coils
face each other rather than being concentric? Harder to wind maybe but
it might be easier to mount the stationary coil if it is facing the
I assume you need two air feeds because the closer has a double acting
cylinder. If we can also assume that the closer requires a higher
pressure for clamping than for releasing, then you may be able to use
a single passage union and a sequence valve circuit rotating with the
closer and a 2-pressure supply to the union. When the rotating circuit
sees low pressure it routes the pressure to the closer's release port;
high pressure switches the pressure to the clamp port. In other words,
the union is carrying both the working air pressure and the data
needed to route the pressure to the proper port.
If you're not familiar, there's some info on sequence valves here:
what kind of electric motor? I'm assuming a universal motor. What
advantage do you get using a brushed motor with a commutator in place
of the VERY much simpler slip rings?????? Also, with a rotating
transformer the pulse timing for the solenoid is likely going to get
pretty hairy due to the magnetic retention of the cores.
There is really nothing wrong with using slip rings, and it is the
most elegant solution due to it's sureme symplicity. NOTHING he is
trying to do contraindicates using slip-rings.
Well ... most of our electric motors are induction motors, where
the rotor is just iron and copper (or aluminum) -- no connections to it
other than magnetic coupling.
However -- a universal motor (wound rotor and commutator) could
perhaps act as a transformer -- with say AC fed into the field, and
power picked up from the commutator. But the commutator would be fixed
with relation to the field coil, so you still have the problem of
getting the power to the solenoid valve. Break out the commutator, and
pick one of the rotor windings and you have your AC (modulated by the
rotation of the rotor poles relative to the field poles), but running
those wires out to the solenoid valve would still be tricky. The wires
would interfere with mounting of the bearing at that end -- unless you
milled a couple of slots in the rotor shaft where the wires could be
passed under the bearing.
I really think that moving the solenoid valve to the outside of
the rotary coupling would make more sense as I suggested at the start of
my followup -- in spite of my having posted the design for machining
magnetic cups and coils for getting the power in through the rotating
[ ... ]
O.K. One to close it and one to open it? What happens with no
pressure -- does it default to an open or a closed position -- or
Can you mount two single unions on the tube? That would cost
less than a two-channel one.
I can't really picture what you are talking about. Perhaps you
mis-read my drawings (now snipped from above). There are two coils,
each in a cup, one rotating and one stationary facing each other. Think
of the cup as a coffee mug with a tube mounted in the bottom and
extending up to the level of the rim. The coil is wound on a form, and
then pushed into the cup and around the tube. That coil faces another
one just like it. Obviously, the coffee mugs need to be magnetically
conductive (e.g. mild steel) and with two small holes drilled in the
base of the cup -- one near the center tube, and one out near the outer
mug wall for bringing the wires through.
The center tubes in the mugs will have to be big enough to pass
your steel tube through -- and enough for perhaps 1/4" thickness of
plastic between the steel tube and the ID of the mug.
Indeed! Built a crude slip ring back about 1985 that had three
channels plus ground, two of which pulsed at different rates. One
for a LED and the other for a sonalert. Very low RPM obviously, but
it worked! Used copper coated PCB board and slot car brushes. Which
were kind of hard to find in the mid 80s. Slot cars had been out of
fashion for over a decade and no internet to just 'look things up'.