20 Amp Safety Switch for C Series Headstocks

[JPG]

The specs do detail the cutout requirements and they provide the electrical characteristics.

But what do I need to look at in the electrical requirements other than the amperage rating? It is a 20 amp breaker. Need I know more?

Both the amperage and the voltage rating 'matter'. Also the HP rating is informative.

The voltage typically includes 125vac and sometimes ranges up to 277vac.

The HP rating is an indication of the 'robustness' of the contacts due to the inductive nature of a 'motor' load which will cause erosion of the contact material when arcing.

As such, the HP rating is more meaningful than the current rating.

In any event, 20A is indeed better that anything less.

[everettdavis]

I have been looking for someone who has modified the switching circuit with a varistor working in concert with the capacitor start circuit on a Shopsmith, but haven't found anyone.

Quite a bit of office equipment that had heavy inductive loads present used them to help protect power switch contacts on gear I used to service.

Very common to burn up a power switch on some gear in a year or two if the varistor circuitry was faulty. We had some terribly difficult quick disconnects that often dropped back a pin from repeated disconnections required for preventative maintenance cycles. Most often, it was part of the varistor circuitry.

Never have seen it done in woodworking tools, though one might be present in the PowerPro headstock circuitry. I would love to dig into those schematics some day.

Is that something any of you are familiar with?

[dusty]

Everett
You may want to try here in the future.

http://www.grizzly.com/products/Toggle- ... itch/D4163
Bill V

That is a good price for this switch and it meets the electrical specifications.

How many terminals does it have? In the image, it appears to have only two (a single section switch) which might explain the price difference from what I have been paying.

[everettdavis]

Everett
You may want to try here in the future.

http://www.grizzly.com/products/Toggle- ... itch/D4163
Bill V

That is a good price for this switch and it meets the electrical specifications.

How many terminals does it have? In the image, it appears to have only two (a single section switch) which might explain the price difference from what I have been paying.

Mine, an EATON 20A was a double pole, single throw switch DPST. Powered to terminals when switched one direction and not the other (no poles to connect to) This appears like you say to have only two, that are bridged side to side when switched.

For those not familiar with those terms DPST means 4 poles. The Center are considered 2 common poles. The other, the switched or load poles.

This is opposed to DPDT Double Pole Double Throw switches which would have 6 terminals. Center are again the common, and power can be applied to separate load circuits at either end. These are traditionally three position switches with center position Off (not connected circuits at either end) You may hear folks call them DPTT Double Pole Triple Throw, but it is more common in my neck of the woods to hear DPDT-CPO which would be double pole double through center position off. Same thing whether rocker or toggle switches which just describes the lever being moved.

As some here have correctly noted, the newer Shopsmith circuits switch only the black (hot) side and have the white wires connected all the time, which allows this DPST switch to function with just one pair of the contacts connected and in use.

That means if you have yours connected in this manner, you automatically have an unused pair of contacts you could switch the wires over to should your contacts in use actually fail. That presumes the rest of the rocker or toggling mechanism in the switch is still internally mechanically functional.

That would certainly get you operational while you ordered another switch. If you buy a used machine, it would be prudent to check both sets of contacts to insure the last owner hasn't already used that procedure and find yourself without an option when those in use fail. You can presume quite accurately how I know this.

It is indeed why I recently went shopping for a switch before encountering the last one, with embedded pigtails last week.

I think you will also find the professional headstock rebuilders here and those who are more experienced than I, already plan to replace the power switch on headstocks they acquire or bring in for service.

Sage advice to do that, or at least be prepared.... seems like I heard that growing up.... I guess I earned a part of my Shopsmith Wood Badge if you will....

Everett

[dusty]

While it is true that a DPST switch will have four terminals, I reiterate that in the image linked to in this thread the switch does not appear to have four terminals and the component description does not indicate DPST. I suspect it to be a SPST switch thus the lower price. This is not necessarily bad. It simply means that there is no "spare set of contacts".

[JPG]

An attempt to clarify some 'terminology'.

Most of what has been posted is correct, but contain a 'few' misuses of terminology.


A DPST switch has 4 TERMINALS

A DPDT switch has 6 TERMINALS.

A DT 'toggle/lever' switch can have two or three positions. on-on or on-off-on

A ST switch has two positions. on-off

One or both of the throw on positions may be spring return if a 'center off'.

There are other possible combinations seldom encountered.

S = single

D = double

P = pole

T = throw

The center terminal is the common for switching to the on terminals for each pole.

Different poles may have different throw configurations.




A varister is not suitable for a load which is switched with short duration between on cycles. Thermal cycle(cool down) is too long.

[JPG]

While it is true that a DPST switch will have four terminals, I reiterate that in the image linked to in this thread the switch does not appear to have four terminals and the component description does not indicate DPST. I suspect it to be a SPST switch thus the lower price. This is not necessarily bad. It simply means that there is no "spare set of contacts".

[everettdavis]

While it is true that a DPST switch will have four terminals, I reiterate that in the image linked to in this thread the switch does not appear to have four terminals and the component description does not indicate DPST. I suspect it to be a SPST switch thus the lower price. This is not necessarily bad. It simply means that there is no "spare set of contacts".

I did state " This appears like you say to have only two, that are bridged side to side when switched."

It would indeed have been helpful to have a view of the back of that switch.

[JPG]

. . .
Never have seen it done in woodworking tools, though one might be present in the PowerPro headstock circuitry. I would love to dig into those schematics some day.

. . .

You would likely find a full wave diode bridge with the dc output connected to filter capacitors, then control circuitry that controls pulses to the DVR motor. That includes slow speed startup ramping and power down braking. So a varister would be redundant.

[everettdavis]

I am trying to mitigate the damage caused by contact arcs present when inductive load of the motor starts and stops. Some sort of Arc Suppression similar to that used in relay circuits which often switch rapidly, is very similar to a power switch in that the relay manually engages and disengages contacts by action of a magnetic field pulling on a spring loaded actuator, while switch contacts are manually moved by a lever mechanism which manually engages and disengages contacts.

Below I have placed an illustration that shows the result of switching loads with and without suppression. My point is only that if we can determine an affordable option for similarly arc suppressing Mark V Shopsmith power switches, we can significantly prolong their life.

Arc Suppression.jpg (197.43 KiB) Viewed 5633 times