Start/Stop switch keeps kicking out

I purchased a couple of DoAll vertical milling machines a couple of years back. I was really impressed with one of them as far as appearance goes, but after transporting them 300 miles found that the best looking one had been steam cleaned and put in storage. Spindle bearings locked up and bad motor bearings. I broke down and rebuilt the machine head and it sure sounds good.
Now for the problem. It was 460 Volt. I rewired it for 240 and hooked it to my RPC. It has an Allen Bradley Start/Stop switch mounted on the rear of the machine. I can press the start button before starting my RPC button before. It clicks and stays in. After starting the milling machine, it will run for about 3 minutes and the AB Start/Stop switch kicks out and has a moderately loud buzzing sound. It will not reset unless I turn off the RPC
The only thing I can think of is since the mill was 460 Volt, maybe the Start/Stop switch needs to be rewired, or perhaps it is for 460 Volt and can't be used? My other DoAll milling machine does not have a separate Start/Stop switch and works very well just by starting the RPC and turning the milling machine on. This is not to be confused with the Forward/Reverse switch on the head of the milling machines.
Any help would be most appreciated.

Ed

Does the switch have heaters in it? The magnetic switch has heaters that act as breakers, on 440 volts they are usually rated at 1/2 the amps needed to run on 220.

Some reading for you.

Thanks swatkins,

I know a motor running on 240 volts will pull more amps than one running on 460 Volts. I am not familiar enough with the magnetic starter to know if the starter was designed to use only on 460 V or if it will work with 240 and a RPC.

Ed

On all the machines I have converted, from 440 to 220, I have had to change out the heaters. My Do-All 26 band saw is awaiting new heaters right now. The machine will start and run for a few minutes then blow one of the heaters.. Heaters are cheap and very easy to replace.

Here is what a typical heater looks like...

Ed,

If you can push your Start/Stop button in and it stays in a latched position it sounds like a manual starter. These are usually protected on two legs with heaters, as Swatkins has noted. If this is true it and you swapped to the lower voltage then these heaters would be undersize...again as Swatkins noted. Pull the cover of the switch and take a look. Older manual starters usually protected only two legs while the newer versions addressed all three.

Stuart

The main issue is, however, that when you went from the machine being made for 460V, and you changed the motor to bein 230V, the current going to the motor doubled. So although the STARTER is designed for anything up to 600V, it is the HEATER ELEMENTS that must change, because they are the component that will turn off (trip) the starter if too much current is being drawn. So for example let's say this is a 1HP motor, 1.4A at 460V, 2.8A at 230V. If you left the heater elements from the 460V motor in there, as soon as the 230V motor current gets above 1.4A, the heater elements are starting their timed process of melting. 2-3 minutes later, the solder has liquified and the ratchet lets go, tripping the starter. It will not reset until there has been enough time for the motor to cool off. In this case the motor will not really be hot, but by you not changing the heater elements, the starter "thinks" it is.

Side note: this is predicated on this being a "manual motor starter". If it is a "magnetic motor starter", then there is an additional issue in that if the contactor coil is taken from the "manufactured" 3rd leg of an RPC, it could work OK at first, but as soon as you have a load on that 3rd leg the voltage will drop and the coil can chatter. If that's the case, do NOT continue using it, chatter can destroy that contactor in minutes! You will have to trace out the coil circuit and make sure it is tapped off of the "real" legs of power.

Also along those lines, many older machines used the line power as the coil power, so your contactor might have a 480 V coil. If you only feed it 240V it likely would not even pull in, but it might, it just would drop out really easily.

OK, The Allen Bradley switch is a push button with start and stop. I can push the start button without the RPC producing power but can't push the start button as long as the RPC is running. When the switch kicks out there is a fairly loud buzzing coming from it. I will remove the cover and see if it has two or three heaters.
swatkins, how do I know that the link to the heaters will be the right voltage for my needs and not for another 460 Volt unit? My Harrison M300 has a magnetic switch, I can hear it click as soon as I power up my RPC.

Ed

I pulled the cover. Inside is a push-button switch that is 1-3/4" wide and 3" tall with wiring at the top and bottom. I saw no heaters in the switch unless I have to take it out of the enclosure and get to them from behind. Below is the model:

PKZM 1-4-NA
4A VDE 0660 IEC 157 IEC 292
660V
AC 3
Thermal Magnetic

It has a small yellow rotary switch that can be turned with a small screw driver with the positions of 4, 32 and 24. It has short dark lines between each set of numbers and is currently set on the dark line between 4 and 32.

It has a very small schematic on top with what looks like voltages 330, 440, 500 and 660. There is no 240 voltage shown.

I am not at all familiar with magnetic switches. I am a Journeyman Machinist / Certified Welder by trade. I have done a fair amount of wiring for residential homes but I am like a lost ball in high weeds on magnetic switches.

My other DoAll vertical mill does not have any such switch. I would prefer to utilize the switch, but if I can't, what is to stop me from wiring around this switch like the other mill?

Ed

Ed here is a page I found for your switch..

I have NO experiance with these switches so please ask for more help... With that said I think your switch is a type that has adjustable " heaters" I'm not sure and I have no idea what the dial should be set for.

IF it were mine I'd be experimenting with adjusting the dial , to increase the amps for the bimetal trips, but I would do very cautiously and after I searched for more advice and information on that switch.

Jraef said:

as soon as the 230V motor current gets above 1.4A, the heater elements are starting their timed process of melting. 2-3 minutes later, the solder has liquified and the ratchet lets go, tripping the starter. It will not reset until there has been enough time for the motor to cool off. In this case the motor will not really be hot, but by you not changing the heater elements, the starter "thinks" it is.

Click to expand...

??????????
Solder liquified ????

Sorry, never seen such a device Must be unique to the US I think

PKZM 1-4 Thats a thermal protecting swith adjustable from 1 to 4 Amps
With these one no solder liquifies Just some bimetal contacts

peter from holland

OK, a bit more information. Looking up the specs for my starter switch, it is rated for 2 HP at 460V and 1 HP at 230V. My milling machine has a 2 HP motor which means this magnetic switch will not work with it on 230V. I will either have to find another magnetic switch or do away with it entirely.
I really appreciate all the input on helping me getting on this figured out.

Ed

Ed,

I think those little manual starters are very neat and compact. The most important thing is they provide motor overload protection for you mill (which you must have) as well as a convenient ON/OFF switch. It would be worth a eBay or similar search to find one that met your needs. Yours is a Allen Bradley but I think Klockner Moeller makes the same thing. This style is discontinued so you could probably find one very reasonably priced.

Small IEC starters are all over eBay if you could find one with the proper parameters for your load. These would require additional wiring and a START/STOP station...that's whats neat about the manual type you have, it's got all that in one unit.

Sort of like this.. http://www.ebay.com/itm/SQUARE-D-25...273?pt=LH_DefaultDomain_0&hash=item5197cb7c81

Stuart

peterve said:

??????????
Solder liquified ????

Sorry, never seen such a device Must be unique to the US I think

PKZM 1-4 Thats a thermal protecting swith adjustable from 1 to 4 Amps
With these one no solder liquifies Just some bimetal contacts

peter from holland

Click to expand...

Yes, it is somewhat unique to North America, it's called a Eutectic Melting Alloy Over Load Relay. Eutectic means it melts at a specific temperature all at once, it does not get progressively softer. The trip mechanism is spring charged, held in place by a ratchet pawl embedded in solder. When the current increases and heat up the solder to it's eutectic point it liquifies, the spring is allowed to pull on the ratchet pawl and opens the circuit. Bi-metal Over Load Relays work by having two dissimilar metals welded together in a strip and when they heat up at different rates, the strip bends, tripping the mechanism. The problem with bi-metal elements is that over time, they develop a thermal memory, meaning they do not go all the way back to their original shape when cool, so it begins to take less and less time to trip. That's not inherently unsafe, but it becomes a nuisance. Then human nature takes over and because the bi-metal OL relays have adjustment dials, annoyed people turn up the dial to make the problem go away, but they end up burning up their motors, then afterward the person turns the dial back down once they realize their mistake and everyone disclaims any knowledge of why the motor is destroyed. You can't do that with Melting Alloy OL relays. You can put in a larger heater element, but that leaves behind a tell-tale signature of what was done so at least you know why the motor burned up.

Jraef,

What company manufactured the overload relay with the melting alloy relays. I have worked on Furnas units which had a ratchet-pawl mechanism but I believe they used a bi-metal 'spring' arrangement that 'screwed' the overload open. Were the melting alloy deals a one shot thing?

Stuart

hurst01 said:

OK, a bit more information. Looking up the specs for my starter switch, it is rated for 2 HP at 460V and 1 HP at 230V. My milling machine has a 2 HP motor which means this magnetic switch will not work with it on 230V. I will either have to find another magnetic switch or do away with it entirely.
I really appreciate all the input on helping me getting on this figured out.

Ed

Click to expand...

Not exactly, it will wear out faster, that's all.... IF:

You can get a 240 volt coil OR feed it 480 with a backfed control transformer.
AND
You can install the proper rated heaters.

I would most likely go the route of using/abusing the starter until it failed, then debate the cost of a starter versus the cost of a VFD, which can easily replace the starter's function, and can offer variable speed facility, if desired.

While the raw components (contactor, overload relay, enclosures, etc.) are available as separate pieces on ebay at greatly reduced prices, a turnkey motor starter (with the required, exact components) may still have a price tag that will make a VFD an option to consider.

How these folks meet this price, I have no idea, but a few guesses.
Elimia Dol Start Stop LED Motor Starter 240V Coil 5 5 8 Amp 2 HP Pre Wired | eBay

Jraef said:

Yes, it is somewhat unique to North America, it's called a Eutectic Melting Alloy Over Load Relay. Eutectic means it melts at a specific temperature all at once, it does not get progressively softer. The trip mechanism is spring charged, held in place by a ratchet pawl embedded in solder. When the current increases and heat up the solder to it's eutectic point it liquifies, the spring is allowed to pull on the ratchet pawl and opens the circuit. Bi-metal Over Load Relays work by having two dissimilar metals welded together in a strip and when they heat up at different rates, the strip bends, tripping the mechanism. The problem with bi-metal elements is that over time, they develop a thermal memory, meaning they do not go all the way back to their original shape when cool, so it begins to take less and less time to trip. That's not inherently unsafe, but it becomes a nuisance. Then human nature takes over and because the bi-metal OL relays have adjustment dials, annoyed people turn up the dial to make the problem go away, but they end up burning up their motors, then afterward the person turns the dial back down once they realize their mistake and everyone disclaims any knowledge of why the motor is destroyed. You can't do that with Melting Alloy OL relays. You can put in a larger heater element, but that leaves behind a tell-tale signature of what was done so at least you know why the motor burned up.

Click to expand...

A bit overkill for a 2HP motor isn't it

how do you reset a device like that
you have to remelt the alloy ????
Solder all in place again
Just a one time thing then


peter from holland

The alloy is totally contained in a stamped housing; you wouldn't know it was there by looking at it. It goes solid as soon as it cools, and pushing the reset button compresses the spring and cocks the action for next time. These things last about forever, and rarely fault. Only downside, they are not adjustable; you need to purchase the correct size elements for the load, although as Jraef says, this can be a virtue. Square D is a big user, although I'm sure there are others.

See page four of this brochure:

http://static.schneider-electric.us/docs/Motor Control/Overload Relays-NEMA Style/9065CT9701.pdf

Dennis

SteveBausch,

That overload has no replaceable heaters. The unit is purchased in a range of adjustable current that meets the users needs. I believe HP rating of a relay or any electrical device with contacts is predicated on the physical size/area of the contact surfaces themselves. This means a device rated for ONLY 2 HP at 480 volts would have smaller contact surfaces than a device rated at say 2 HP at 240 volts..I could be wrong on this though. Contact surface area and rated ampacity go hand in hand.

Stuart