stop/start switch

[George Sanders]

I am in need of a stop/start switch for a 2 HP Leeson motor. It's going on my Parks planer. I am having no luck finding online retailers. I know G.E. makes them for table saws and other woodworking machines. The A.B. Dick brand runs about $50 and this is prohibitive to me. Any help would be greatly appreciated. thank you.

[Chuck Lenz]

Hello George. Would this work for you ? http://www.woodworker.com/cgi-bin/FULLPRES.exe?PARTNUM=140-066 Today is the last day on free shipping I believe. I just bought one this week for my table saw.

[Jim Heffner]

George, you might want to check Busy Bee's website, they have been advertising a nice looking paddle switch really cheap ....about $12.00 I think until Jan '08.

[M Toupin]

George,
I know you said that the cost of a magnetic starter with overload protection is prohibitive, but let me suggest you can't afford not to... A proper starter does two things, first, it protects that very expensive motor and second it protects that nice Parks planner. A planner is not something you want to automatically restart in the event of a momentary power failure. Real bad things can happen.

While I'm not a fan of putting modern looking plastic boxes on a vintage machine, you can get them from Grizzly, factorymation or a host of other sources in the $50 range. Another option is to ask on OWWM.org. There's a trove of information available and many of those guys have a ton of old parts, starters included, that they sell very reasonably.

It sure would be a shame to see that beautiful old machine or that expensive motor damaged when a proper starter could have avoided it.

Mike

[Tom Veatch]

I am in need of a stop/start switch for a 2 HP Leeson motor. It's going on my Parks planer. I am having no luck finding online retailers. I know G.E. makes them for table saws and other woodworking machines. The A.B. Dick brand runs about $50 and this is prohibitive to me. Any help would be greatly appreciated. thank you.

Does the motor not have overload protection built in? My Leeson 5HP has a manual reset incorporated in the motor connection box. A quick check of the Leeson web site and all the motors I checked showed either a manual or auto overload protection included. Check the data plate on your motor. If yours does, all you need is the mag switch and they are simple enough to build with a relay rated for 2HP and a couple of low amperage momentary contact switches. You could get there for much less than $50 by investing a little "sweat equity".

[Erik Christensen]

From what I remember in EE class decades ago - an induction motor draws max current at startup - even more than when fully loaded. The difference in rotational speed of the magnetic field and the rotor is what induces current and this is maximized when starting as the rotor is stopped. A magnetic starter limits this current draw to keep from overheating the motor and either burning it up or prematurely aging it. If the motor is one that is infrequently started - say only once an hour (like on a DC system) then a relay is fine. If it is run for short durations (TS, planer, compressor, etc) a mag starter is the only way to go.

Don't depend on a safety reset switch to provide this function, that is only for emergencies. Frequent high current draws can severely heat your motor even though the reset limit is never reached and results in degradation of the insulation of your windings drastically shorting its life. Depending on your motor reset switch is like saying you don't need brakes in your car because your have airbags :D :D

[Tom Veatch]

.... A magnetic starter limits this current draw to keep from overheating the motor and either burning it up or prematurely aging it. If the motor is one that is infrequently started - say only once an hour (like on a DC system) then a relay is fine. If it is run for short durations (TS, planer, compressor, etc) a mag starter is the only way to go.

Don't depend on a safety reset switch to provide this function, that is only for emergencies. Frequent high current draws can severely heat your motor even though the reset limit is never reached and results in degradation of the insulation of your windings drastically shorting its life. Depending on your motor reset switch is like saying you don't need brakes in your car because your have airbags :D :D

Erik, perhaps you can advise me in the situation I find myself. I just finished verifying what I remembered about the induction motor powered tools in my shop. They range in power from 6.5HP down to 1/2HP. One and only one of them (a 3HP table saw) has a magnetic switch which includes an overload relay. None of the others, not one, has a motor control that is more sophisticated electrically than an on-off toggle switch. So I suppose that I've been relying on the air-bags for many years.

One of my "get-to-its" is to replace the on-off switches with a relay and switches to prevent auto restarts after power failures. My quandry now - based on your post - is whether I need to go beyond what the tool manufacturer provided and incorporate overload/overtemp sensing into those replacements. Since the tool designers/manufacturers did not see the need, and since the motor has no way of knowing whether its power is switched by a toggle switch or an electromechanical relay, I seriously question the need.

Incidentally, since my DC is controlled by the tools and runs automatically when one of the tools is running, it sees more on/off cycles than any other machine in my shop. And, if I interpret your post correctly, it is the frequency of power on events, not run duration, that would cause the effects you warn about.

[M Toupin]

Tom,

As a general rule, motors above 1 1/2 to 2 hp generally have starters with properly sized heaters to protect them. The little "overload" buttons on motors are really not effective. Generally they kick out after the motor gets way too hot. They are just a little strip of expansion metal like the thermostat in your car. Keep in mind that inrush can be 10X. that's a lot of juice and heat to put through a light duty switch.

Motor starters on the other hand with heater overloads matched to the motor serve two purposes, first The relay contacts are heavy duty and are rated for the motor starting current. Delicate contacts, will fail much sooner than normal if used directly to start a large motor. Light duty switches are used to operate the motor starter relay rather than the motor. Second, circuit breakers are designed to protect building wiring, not your motors. f your circuit breaker trips before your motor burns up, great, but it's not the purpose and can't be counted on to perform that function. Motor starters are designed to trip on heater overload before the motor they start burns up.

I have no idea what type of equipment you have, but I will say that a 6.5hp motor is a fairly odd size, I assume it's an older motor. If that motor is running on a regular switch without a relay/contactor it must be quite the switch. That's a whole lot of current to run directly through a regular switch. If it is an older machine and you got it used, then it's entirely possible it was modified prior to you acquiring it. I would definitely put a proper starter on it. If you burn up that motor it'll cost you a small fortune to replace it:(

I kinda like the airbag analogy, but I would use the emergency brakes. You can stop your car with the emergency brakes, but it's much harder hard on everything. A properly functioning set of service brakes will last a lot longer and is easier on the drive train:D

Mike


Erik, perhaps you can advise me in the situation I find myself. I just finished verifying what I remembered about the induction motor powered tools in my shop. They range in power from 6.5HP down to 1/2HP. One and only one of them (a 3HP table saw) has a magnetic switch which includes an overload relay. None of the others, not one, has a motor control that is more sophisticated electrically than an on-off toggle switch. So I suppose that I've been relying on the air-bags for many years.

One of my "get-to-its" is to replace the on-off switches with a relay and switches to prevent auto restarts after power failures. My quandry now - based on your post - is whether I need to go beyond what the tool manufacturer provided and incorporate overload/overtemp sensing into those replacements. Since the tool designers/manufacturers did not see the need, and since the motor has no way of knowing whether its power is switched by a toggle switch or an electromechanical relay, I seriously question the need.

Incidentally, since my DC is controlled by the tools and runs automatically when one of the tools is running, it sees more on/off cycles than any other machine in my shop. And, if I interpret your post correctly, it is the frequency of power on events, not run duration, that would cause the effects you warn about.

[Rick Christopherson]

....A magnetic starter limits this current draw to keep from overheating the motor and either burning it up or prematurely aging it. If the motor is one that is infrequently started - say only once an hour (like on a DC system) then a relay is fine. If it is run for short durations (TS, planer, compressor, etc) a mag starter is the only way to go. Erik, While you are correct about the high inrush currents, a magnetic starter does not limit the inrush current, and more importantly, you don't want it to. Doing so would cause the motor to start slower, and this will prolong the time that the inrush current is high.

A magnetic starter is nothing more than a high-power relay with integral overload protection. This overload protection is frequently referred to as "Heaters" because they are intended to simulate the heating within the windings of the motor. In most cases, these are simply bi-metal elements similar to the pop-up circuit breakers that Mike Taupin incorrectly suggested people shy away from. The purpose and function is the same--they break the circuit when enough cumulative heat is built up in the heating element to simulate a damaging heat build up in the motor. A motor contactor is either On or Off, but it does not limit the current.

[Rick Christopherson]

Incidentally, since my DC is controlled by the tools and runs automatically when one of the tools is running, it sees more on/off cycles than any other machine in my shop. And, if I interpret your post correctly, it is the frequency of power on events, not run duration, that would cause the effects you warn about.Tom,
Yes, the high start-cycle frequency of a motor can have detrimental effects on the motor due to the cumulative heating caused by the start-ups. This can be very significant for dust collection systems that are wired to start automatically when one of several tools are started. I generally steer people away from these especially when the dust collector serves multiple tools that can each have short duty cycles.

For example, say you were alternating between the tablesaw and the jointer for a series of operations. Even though the duty cycle on each tool was low, the dust collector would be cycling at the combined rate of both tools. More importantly, the dust collector is starting under a higher load that the other tools. As a result, the motor on the dust collector is going to experience a greater cumulative heat build up higher that the tools that are controlling it.

This isn't necessarily true for all tools, of course. For example, a wide belt sander requires the dust collection system to be running, and it also typically runs for a longer time than other tools. The problem may arise with other tools that have short duty cycles, especially when they are frequently used in conjunction with other tools.

[Tom Veatch]

Tom,

As a general rule, motors above 1 1/2 to 2 hp generally have starters with properly sized heaters to protect them. The little "overload" buttons on motors are really not effective. Generally they kick out after the motor gets way too hot. They are just a little strip of expansion metal like the thermostat in your car. Keep in mind that inrush can be 10X. that's a lot of juice and heat to put through a light duty switch.

...

I have no idea what type of equipment you have, but I will say that a 6.5hp motor is a fairly odd size, ...:(

...
Mike

Mike, thank you for your reply. Also, Rick Christopherson, if you are reading this, I'd appreciate your inputs as I particularly value your opinions.

To address the 6.5 HP motor first, I crawled around it and finally, with a mirror, was able to find the data plate. The motor output is shown as 2.98KW which equates to 4HP. I really don't know where I got the 6.5HP figure. The machine is clearly marked in large letters, "3.5 Running HP". The motor has a manual reset circuit breaker enclosed within the motor casing. The switch, although the electrical equivalent of an on-off toggle switch is actually a pneumatically actuated contactor. It's a stationary air compressor.

Now, your post distinguishes motors (I'm assuming single voltage induction type motors) that are below the 1 1/2 to 2HP output level from those that are above. My question is, "Why the distinction?"

Is there some technical reason the larger motors generally use "magnetic starters" while the smaller motors do not? I'm semantically differentiating between "Magnetic Switch" and "Magnetic Starter" by assuming the "Starter" includes overload protection while the "Switch" does not. Are there differences in design or implementation that would make the larger motor susceptible to electrical overload damage while the smaller motor is not. Or is it simply an economic decision that the the larger, more expensive motor warrants the "insurance" expense of a circuit breaker while the smaller, cheaper motor does not?

Apparently, the stated opinions seem to weigh in on side of the auto/manual reset functions included on many motors being essentially worthless for their intended function. Does anyone have an explanation for why the motor manufacturer would go to, what could be, significant additional manufacturing operations and expense to include those circuit breakers on their motors when they are effectively worthless for the purpose?

From the Leeson (http://www.leeson.com/products/techref/electrical.htm) site:
Thermal Protection (Overload) A thermal protector, automatic or manual, mounted in the end frame or on a winding, is designed to prevent a motor from getting too hot, causing possible fire or damage to the motor. Protectors are generally current and temperature sensitive. Some motors have no inherent protector, but they should have protection provided in the overall system's design for safety. (emphasis added)

My interpretation of that is motors with "inherent protectors" are protected by those circuit breakers from current as well as temperature overloads and thus need only magnetic switches (see above for the semantic definition) while those motors without "inherent protectors" should have protection provided by the "overall system's design". I read thas as meaning a "magnetic starter" is required when the motor has no "inherent protector" and is the basis for my response to the OP.

What am I missing?

[Tom Veatch]

Tom,
Yes, the high start-cycle frequency of a motor can have detrimental effects on the motor due to the cumulative heating caused by the start-ups. This can be very significant for dust collection systems that are wired to start automatically when one of several tools are started. I generally steer people away from these especially when the dust collector serves multiple tools that can each have short duty cycles. ....

That's why I used a delay-on-break relay with a delay which can be set via a potentiometer from 2 sec to 1000 seconds (16+ minutes). When the tool is turned off, the DC continues running until the delay time expires. This prevents closely spaced start events.

[Rick Christopherson]

Knowing that constant restarts may cause a problem is the most important aspect. How to handle the situation is dependent on each person's needs. The off-delay relay is a good method. When I get around to rebuilding the workshop this winter (hopefully) I will install low-voltage controls at the primary tools so I can decide when (or if) to turn the collector on for quick operations. Using this setup, I can also turn on the collector at one workstation, but turn it off at another workstation. This is my preference because I frequently will jump from several machines in succession, but don't need the collector running any longer than necessary (I hate the noise).