MACHINE SWITCH

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whateg0
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MACHINE SWITCH

Post by whateg0 »

I'm working on getting my 10ee up and running and I want to use a specific type of switch for the VFD. I can't for the life of me think of what the switch is called. It's magnetic, so you push ON to make contact and it stays on until you push off or power goes out. If power goes out, you have to press ON again so it doesn't just start back up again. I can make this from relays and a couple momentary switches, but it would be easier to buy them. HELP! Thanks!

Dave
whateg0
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Re: MACHINE SWITCH

Post by whateg0 »

Never mind. I was overthinking it. I just searched for magnetic switch and found it. FYI, if you search for magnetic safety switch, you get something else. SMH!
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BadDog
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Re: MACHINE SWITCH

Post by BadDog »

I've built those with salvaged AB push-pull switches combined with a simple magnetic contactor (also salvaged).

Basically wire the NO pull side to the control circuit of the contactor coil, and tie the secondary relay (if equiped, or output if suitable voltage, or adjusted) of the contactor to hold the coil energized when you release the AB NO. So pulling the button closes the contactor, which stays on until it looses power or is told otherwise. The NC push side is wired into that contactor control circuit so that pushing the button de-energizes the coil and the contactor opens. You can get a lot more complicated than that, and depending on control circuit and contactor details you may have to tweak it a bit, but it makes a nice compact controller with 1 button that pulls on and pushes to turn off, but automatically turns off when it looses power.

I used this mechanism to manage the idler circuits on my staged RPC. Whatever idler(s) I wanted running, just push that button. If I didn't want or need one, just push it in (push for stop is safer). The mushroom buttons also light up when power is on, so at a glance you can see what is running or not. The whole thing is behind one master contactor (and fuses) that control the entire mess on/off. Turned out real nice.
Russ
Master Floor Sweeper
whateg0
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Re: MACHINE SWITCH

Post by whateg0 »

Yup. That's what I had in mind if I wire up my own. I was looking online today and I can get one for the price of the parts if I had to buy the parts. But, one goal here is to make this all fit in the original package. That means using the original switches if I can, or something that looks like them. I'm replacing the dual rheostats with a 5k pot to feed the VFD. The fwd/rev of the VFD is wired into the original circuit as well. Space isn't a bit of a concern. Removing the original DC motor and motor/generator left me with a cavern in which the 2 HP AC motor is barely noticed. I'm going to replace the matched V-belts with a multi-rib belt for ease and smoother operation, though I doubt I'll ever be able to tell. But that'll be hidden inside so I'm not worried about it's appearance. I don't know why I challenge myself with stuff like this. I could just as easily wire up a control panel with all of the controls and stick it on an arm hanging off the top of the machine, but that's just not how I do things, for better or for worse.

Thanks!
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BadDog
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Re: MACHINE SWITCH

Post by BadDog »

I like making it neat, and often times that means trying hard to make it fit invisibly within the original enclosure. When I got my VFD, I got a 2HP Automation Direct GS2 so that I could mount the pendant in a handy place, and mount the drive in a safe well ventilated place. But for a while I had become somewhat addicted to building salvage controls for my own builds, or replacing hinky implementations found on some machines (like the insane joke of a main control on a Robland X31).

About the time I got interested and also had a need for the first of those, I was fortunate enough to go by an open minded scrapper here who knew me and let me wander around. They had just gotten a HUGE (like several 40' dump) of large commercial AC and process control randomness. Lost of stuff busted and wasted, but a LOT of stuff as good as new. I got boxes of like new AB switches in a wide variety of styles, lights, premium contactors, fuse blocks, heaters, buss bars, wire loom, some case mount gauges, plug and pig-tails, cap and battery packs, 110V-24V and 220V-24V transformers for control circuits, and some sort of control boxes I never did figure out what to do with. There were even a few medium to large air tight NEMA control boxes that had only a sew small holes (just enough for cable in and out) but otherwise looked new. Boxes of stuff that I bought for scrap weight. I think I paid $0.30 a pound for 4 largish boxes (roughly 4 gallon volume I would say) full of stuff, and I think it came to $20 or so.

That stash has built a number of things, including my staged RPC that ran my old shop. It was very neat and compact, having 2 idlers (a 5HP Baldor and a 10HP Baldor) mounted vertically down near the floor for low CoG. Then the NEMA cabinet above and about the same horizontal dimensions as formed by the 2 idlers standing up. Built a frame to hold it all in position, add some casters that make it act sort of like a standard 2 wheel dock dolly, with all controls completely self contained in the door to the control box with a 20' industrial flex (used for extension cords, and loose machine cords) power whip. Very quiet, easy and intuitive to run, simple construction, and took up only about 24" long by 18" wide floor space with the top of the box about 36" off the ground.

And I had a plan in the works for a portable RPC built in an Army Amo can (smaller 50Cal preferred size, or 20mm if necessary), but never went through with it. The idea was that it had a 3PH female plug on one side, and a standard NEMA 50A "welder" plug on a whip to plug into the standard 50A 220V socket very often found for welders (or make adapters). A second pig tail would come off with various options for wiring to an arbitrary 3 ph idler motor within the starting spec as designed (would be anything from about 0.5 HP up to 3, maybe even 5 HP). This connection might be on a bus to make arbitrary connection easy, or maybe just wire nut. Plug in 3PH motor to be driven, wire up the idler, and finally plug into 220V outlet. Pull button to start idler, push button to stop idler. No run caps (not possible anyway without load and idler details beforehand), and imminently portable, as long as you can source some suitable idler at your destination. Seemed like a good idea, but never followed through.
Russ
Master Floor Sweeper
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tornitore45
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Re: MACHINE SWITCH

Post by tornitore45 »

Aren't VFD already designed to provide the fail safe feature described? Mine is.
Unless you do not trust the electronic and want safer fails safe.
Mauro Gaetano
in Austin TX
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BadDog
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Re: MACHINE SWITCH

Post by BadDog »

Good point, I had completely lost the VFD angle in the discussion.
Russ
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SteveHGraham
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Re: MACHINE SWITCH

Post by SteveHGraham »

Why would you need a magnetic switch with a VFD? Mine work off little pushbuttons built into the pad.
Every hard-fried egg began life sunny-side up.
whateg0
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Re: MACHINE SWITCH

Post by whateg0 »

Mine does turn on in the stopped state. However, it also retains power for a few seconds if the motor isn't running. I guess if the motor was running, it wouldn't, so maybe that's not a good enough reason. But, that combined with the fact that there is no On/Off for it bugs me. And yeah, I don't trust it 100%. :shrug:

I just have a DPST switch on it now and that's serving me fine. I think the original power buttons are momentary, though, too, so if I incorporate them, like I want to, that'll require something that latches.
TomB
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Re: MACHINE SWITCH

Post by TomB »

I had to hook up a large VFD (350 hp) for a snowmaking pump that was needed immediately. On the control terminal strip there was a low voltage out and on-off low voltage in. I put in a short piece of conduit, a normal house type wall switch and box, stuffed a pair of wires through it and hooked up. I told the operations guy to go find a magnetic switch and replace the wall switch sometime in the next few days or weeks. Well the wall switch worked per the operations guy and the local electrical supply did not know what a magnetic switch was so the wall switch was not replaced.

All was fine until municipal power went out while snowmaking was in progress. When that happens in a snowmaking operation there is a rush to open valves and drain all the mountain pipes before they freeze (within 10 or 20 minutes if its not below zero) and the crew did it successfully. They then went home but did not turn the wall switch off. When the morning crew came in several hours latter there was water running out of the pumphouse front door. Seems the power had come back on, the pump started (a 350 hp unit fed and feeding 8" pipes) and with the open drain valves all the water went into the 6' diameter by 8' deep sump. But the sump could not gravity drain back to the pond as fast as the pump could empty the pond into it. The overflow filled the floor of the pumphouse and ran out the front door, across the parking area and into a stream that flowed back to the pond.

Nothing was damaged. Some snowmaking hoses on the floor had to be unrolled and hung up to re-dry and I had to call in the sand and salt truck to make the parking area passable. But after they had to clean it up the operations guy knew what a magnetic switch was and why it was necessary.
whateg0
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Re: MACHINE SWITCH

Post by whateg0 »

I just thought of something. On my VFD, if I'm controlling it from the front panel, it comes up in the stop state. But, I'm not controlling it that way. I'm feeding the fwd/stop and rev/stop lines. So, if one of those is grounded when the power comes on, I'm not sure what happens. Guess I'll have to try that tonight and see. That would be the deciding factor, I think.
John Hasler
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Re: MACHINE SWITCH

Post by John Hasler »

whateg0 writes:
> Removing the original DC motor and motor/generator...

Wince. But it's your machine and I have no say in what you do to it.

What became of the Ward-Leonard system you took out?
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