Electrical slip ring questions

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. Thanks, Eric
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http://www.hotrod.com/articles/0206sr-understanding-your-alternator/ "Most alternators need to spin at about 2,400 rpm at idle, have their maximum output above 6,000 rpm, and should never exceed 18,000 rpm."
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On Tue, 11 Apr 2017 13:46:24 -0700, snipped-for-privacy@whidbey.com wrote:

Look at the pulley size ratio on your car. Minimum 2:1 - so if the engine cranks up to only 3000 RPM the alternator is spinning at 6000 RPM.. No problem at all handling 5000.
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On Tue, 11 Apr 2017 21:31:10 -0400, snipped-for-privacy@snyder.on.ca wrote:

That's what I was thinking Clare, but I though I was wrong because 6000 seems awfully fast. Thanks. Eric
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On Wed, 12 Apr 2017 08:54:19 -0700, snipped-for-privacy@whidbey.com wrote:

It's fast for a merry-go-round and slow for a jet turbine - - -
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wrote:

The question wasn't how to make the pulse Gunner - but how to trasnmit the power pulses to a spinning shaft.
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wrote:

How does he get the power to the spinning part???
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On Wed, 12 Apr 2017 20:29:20 -0400, snipped-for-privacy@snyder.on.ca wrote:

Via the not-encoder bits?
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wrote:

It was my understanding he has a solenoid valve in the shaft to contol the air. Energized it puts air to the cyl to close the collet chich, de-enrergised it puts air to the release cyl and vents the close cyl. He needs to get the electical signal to the spinning solenois - and the SIMPLEST way is to use a set of slip-rings to feed the electrical signal into the 5000 RPM spinning collet eaaembly.

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    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.
    Enjoy,         DoN.
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wrote:

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. 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? Thanks, Eric
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wrote:

Is there a reason why you can't control the air flow upstream of the rotary union? -jsw
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    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.)
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.

    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.

    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 valve.

    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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How well do you think an electric motor would work as a rotary transformer? They are already balanced and built to withstand the RPMs. -jsw
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On Thu, 13 Apr 2017 07:35:32 -0400, "Jim Wilkins"

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.
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On Thu, 13 Apr 2017 16:43:02 -0400, snipped-for-privacy@snyder.on.ca wrote:

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'.
http://alt-config.net/slipring.jpeg
Um, the LED was in the bats mouth;-)
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On Thu, 13 Apr 2017 20:50:14 -0400, William Bagwell

Hah! Well, that explains things, Mr. BSC. ;)
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    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 shaft.
    Enjoy,         DoN.
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wrote:

Of course the valve mounted outside would be better. But that won't work because the closer is basically a double acting cylinder. This means that it needs air pressure to clamp and remain clamped, and air pressure to unclamp. So the rotary union would need two passages.The way I use the closer now is with a solenoid operated valve the has one air inlet, two outlets, and two exhausts.So when one side of the piston is pressurized the other side is exhausted to the atmosphere. Since air needs to be sent to both sides of a piston there needs to be two passages in a rotary union if the valve is outside. Eric
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On Thu, 13 Apr 2017 18:15:09 -0700, snipped-for-privacy@whidbey.com wrote:

Slip rings with a set of alternator brushes, or heater motor brushes, or brushes from a power tool or vacuum cleaner motor that can handle 5000RPM + are extremely simple to set up and very reliable.
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