"Hold button until at speed" induction motors - why not more common?

[Dan Friedrichs]

My Hammer combo machine has induction motors which appear not to have centrifugal switches, but rather, the "start" button is supposed to be held until the machine is up to speed. I'm assuming the start button has an extra set of contacts which energize a start winding, and the "run" winding is maintained through a contactor after the start button is released.

This seems like a very elegant system - no centrifugal switch to worry about. It took me a bit to get used to, but now I find myself holding the start button on other machines (unnecessarily) by habit.

I wonder why this isn't more common?

[Andy D Jones]

My Hammer combo machine has induction motors which appear not to have centrifugal switches, but rather, the "start" button is supposed to be held until the machine is up to speed. I'm assuming the start button has an extra set of contacts which energize a start winding, and the "run" winding is maintained through a contactor after the start button is released.

This seems like a very elegant system - no centrifugal switch to worry about. It took me a bit to get used to, but now I find myself holding the start button on other machines (unnecessarily) by habit.

I wonder why this isn't more common?

I was wondering the same thing... I like it on mine too.

-- Andy - Arlington TX

[glenn bradley]

I know it seems insignificant but, seeing the many posts by many people on many forums . . . the extra effort of holding the button for a few seconds would be too much. We are talking about people who spend enough time arguing about why they don't change their cutters to match a task that they could have changed cutters for the rest of their life in less time. Woodworkers are often the most brilliant and nearly as often the most lazy people I encounter

[Tom Bain]

Not an expert on induction motors, but what happens if you don’t hold the start button until the motor is at full speed? Does that put extra strain on the motor or other parts of the start-up circuit?

[Mike Henderson]

Not an expert on induction motors, but what happens if you don’t hold the start button until the motor is at full speed? Does that put extra strain on the motor or other parts of the start-up circuit?

Single phase power can be represented mathematically as two counter rotating vectors. A single phase induction motor will follow one of those two counter rotating vectors. The problem is to get the rotor turning in one or the other direction. That's the purpose of the starting circuit.

For a motor with almost no load on it, such as starting a table saw, you only need to get the motor barely turning. Note that one test for a failed starting capacitor is to just spin the shaft of the motor and if the cap is bad, the motor will rapidly run up to speed.

But if the motor is loaded that won't work. HP is torque times RPM times a constant. At low RPM there just isn't enough power to drive the load. Under those conditions, you want the starting circuit to stay in the circuit until the motor is at an RPM that is generating enough HP to drive the load.

So the quick answer is: If the motor is very lightly loaded, it will start with a very short push on the button. If the motor is heavily loaded, you'll have to hold the button until the motor is almost fully up to speed.

Mike

[If you don't hold it long enough, the motor will stall - it will stop turning and buzz angrily:-)]

[Wes Grass]

I was under the impression the Felder's have some electronics to prevent an accidental start, requiring a sustained hold on the button to make sure you really serious about it.

I haven't screwed up in awhile, but I think a short push requires power cycling the machine to reset it?

[Zachary Hoyt]

I would prefer having to hold a button to having to replace capacitors and switches and things, it seems like a reasonable tradeoff.

[Bruce Wrenn]

I would prefer having to hold a button to having to replace capacitors and switches and things, it seems like a reasonable tradeoff.

Some motors use potential relays in place of start switches. The extra current at start up engages relay, which drops out of circuit when current draw drops. Three wire well pumps do this. I have a Skill bench grinder, and a Delta sanding center that uses this technology. If you get a single phase motor for which there isn't replacement start switch available, this is the easiest fix.

[Rod Sheridan]

I would prefer having to hold a button to having to replace capacitors and switches and things, it seems like a reasonable tradeoff.

Yes, my thoughts exactly, nothing worse than crawling under the machine to take the motor out to replace the centrifugal switch or the start or run capacitor........Rod.

[Erik Loza]

I was there when we got the first "new" Hammer machines back in 2004. The technician kept trying to start one and thought it was a lemon because nothing was happening. I think someone from the factory had to tell him, "You need to push and HOLD". We all had a pretty good laugh about that.

Erik

[Jim Becker]

I was there when we got the first "new" Hammer machines back in 2004. The technician kept trying to start one and thought it was a lemon because nothing was happening. I think someone from the factory had to tell him, "You need to push and HOLD". We all had a pretty good laugh about that.

Erik

In parallel, there are folks who have similar issues with the "open the back hatch" buttons in vehicles that require "push and hold" for safety reasons. 'Kinda a "Read The Fabulous Manual" moments, if you will...

[Frank Pratt]

Clothes dryers used to require that the start button be held until the motor came up to speed. I suppose that was because a centrifugal switch would quickly get fouled in the open frame motor.

[Steve Demuth]

I was there when we got the first "new" Hammer machines back in 2004. The technician kept trying to start one and thought it was a lemon because nothing was happening. I think someone from the factory had to tell him, "You need to push and HOLD". We all had a pretty good laugh about that.

Erik

I have sympathy for the guy.

Earlier this summer I discovered that a tractor I have owned for several years has a start interlock on the PTO lever. I left the tractor idling and by mistake did not disengage the PTO running the brush chopper. Spent the next 45 minutes working on the fence, then came back and tractor wouldn't start. I am embarrassed to say that I spent another 45 minutes checking battery connections, and every other starter switch-related thing I could think of, before I traced one wire back toward where the only place it could possibly be going was ... the PTO lever.

I'm sure a PTO interlock has been standard equipment on tractors for decades, but honestly, but I've only owned "legacy" machines, and when I've used other modern machines, never foolishly left the PTO engaged when turning off the tractor. At least I didn't get a service technician out to "fix" it, so it was a 45 minute, not a $150 mistake.

[Bruce Wrenn]

Clothes dryers used to require that the start button be held until the motor came up to speed. I suppose that was because a centrifugal switch would quickly get fouled in the open frame motor.

Dryer motors do have centrifugal switches. They control heating element or gas valve. Neither will engage till motor is up to operating speed, which means the fan is running.