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
Reply to
etpm
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"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."
Reply to
Jim Wilkins
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.
Reply to
clare
The question wasn't how to make the pulse Gunner - but how to trasnmit the power pulses to a spinning shaft.
Reply to
clare
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.
Reply to
DoN. Nichols
That's what I was thinking Clare, but I though I was wrong because 6000 seems awfully fast. Thanks. Eric
Reply to
etpm
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
Reply to
etpm
Is there a reason why you can't control the air flow upstream of the rotary union? -jsw
Reply to
Jim Wilkins
How does he get the power to the spinning part???
Reply to
clare
It's fast for a merry-go-round and slow for a jet turbine - - -
Reply to
clare
Via the not-encoder bits?
Reply to
Larry Jaques
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.
Reply to
DoN. Nichols
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
Reply to
Jim Wilkins
Greetings DoN, 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 moving coil. Eric
Reply to
etpm
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:
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Reply to
Ned Simmons
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.
Reply to
clare
I LOVE how you "engineers" complicate a simple solution. You need to get Colin Chapman on board!!!!
Reply to
clare
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.
Reply to
DoN. Nichols
[ ... ]
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 indeterminate?
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.
Enjoy, DoN.
Reply to
DoN. Nichols
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'.
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Um, the LED was in the bats mouth;-)
Reply to
William Bagwell

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