Contactor question

I'm building a dust control system in my shops attic.
The blower is an old General No4, with a motor salvaged off my lathe (7.5 h, 3 ph, 220v)

To trigger this remotely, I purchased this contactor:
Packard C340A 3 Pole 40 Amp Contactor 24 Volt Coil
Details here: https://www.johnstonesupply.com/storefront/product-view.ep?pID=L45-052

I wired it in this weekend and tried to start it.

It basically cycled on/off rapidly, a bit of arcing, then I quickly cut the trigger circuit.
(from my reading, arcing is not unusual)
The motor was spinning when I checked it. So 3 phase power did get to the motor.

Note: the blower was not connected to the motor at the time, so there was no load.
And I have run this motor off this RPC for a while. Also, no breakers blew. So I doubt its overload.
I was just trying the circuit, to see if I'd wired it correctly.

Not sure what I did wrong, I have a couple of theories

1 - does the 24v trigger need to be AC or DC? Oddly the spec's don't say. And my general research didn't yield any answers
2 - would the trigger circuit need a certain amount of current to keep the relay closed?

Sorry, these may be basic - I've just never used a contactor before

Thanks

Assuming push button station somewhere to activate coil?

What is MISSING is aux contacts that close with mains so you can take your finger OFF the start button

These are commonly present on the usual magnetic starter such as on a lathe

shandit66 said:

I'm building a dust control system in my shops attic.
.....

Sorry, these may be basic - I've just never used a contactor before

Thanks

Click to expand...

You have answered the most basic question that I have namely 'you don't know what you are doing'.

Either buy a book on basic motor controls or hire a real (qualified in your area) electrician.

What ever you do update your will and buy extra life and liability insurance.

johnoder said:

Assuming push button station somewhere to activate coil?

What is MISSING is aux contacts that close with mains so you can take your finger OFF the start button

These are commonly present on the usual magnetic starter such as on a lathe

Click to expand...

I basically followed this:
http://library.automationdirect.com/wp-content/uploads/2013/09/Full-voltage-non-reversing-3-phase-motors.jpg

So it seems I need:
- 24v DC and
- a momentary switch, not an On/off.

is that correct?
thanks

So it seems I need:
- 24v DC and
- a momentary switch, not an On/off

Click to expand...

Yes. Besides a postive uniform method of actuating the power contacts, the point of a magnetic contactor is that with a power interuption, it will not restart when power is restored, possibly (with a power tool) creating a dangerous situation. So a momentary switch is required.

I'm not a great electrician, I tend to study and figure out a control or circuit when forced to, and forget details in between. I did not research your specific motor contactor/motor controller. That said:

You can either install a small 24v transformer to run the contactor; or most modern contact sets can have the coils swapped for various other voltages. So you could get a 120v coil (from the options page of the manufacturer's catalog on that specific control), and replace the 24v unit that is in the main contactor. (or even a 240v coil) 24v has a certain safety benefit, especially if your shop is subject to OSHA. But there is no particular safety hazard in using 120v for the magnetic control circuit, either, assuming common sense and normal wiring practice. You can split that off one side of your mains input to the power contactors.

smt

PS- don't wire to the generated leg of your shop made 3ph to run the magnetic contactor. That can lead to buzzing and dropping in & out.

The contactor specs do not specify whether the coil is AC or DC. Without a DC specification I would suspect the coil would be 24V AC.

Bob
WB8NQW

The link in your last post is correct and presented very nicely. The biggest problem you have is that your initial purchase was for a 'definite purpose contactor' and not a motor starter. This means there is no accommodations for motor overload protection or for a auxiliary contact to act as a latching relay for your START/STOP circuit.

You can purchase stand-alone overload blocks and can rig up a circuit to act as a latching relay but this will require more electrical control knowledge, something you admit you are a bit shy on.

A motor starter for a 7.5hp setup isn't cheap..maybe that's why you went with the definite purpose contactor. A motor starter is the proper way to go...get one that has a coil for line voltage, don't goof around with a transformer.

Stuart

atomarc said:

The link in your last post is correct and presented very nicely. The biggest problem you have is that your initial purchase was for a 'definite purpose contactor' and not a motor starter. This means there is no accommodations for motor overload protection or for a auxiliary contact to act as a latching relay for your START/STOP circuit.

You can purchase stand-alone overload blocks and can rig up a circuit to act as a latching relay but this will require more electrical control knowledge, something you admit you are a bit shy on.

A motor starter for a 7.5hp setup isn't cheap..maybe that's why you went with the definite purpose contactor. A motor starter is the proper way to go...get one that has a coil for line voltage, don't goof around with a transformer.

Stuart

Click to expand...

Thanks, its a bit clearer now.
My circuit currently doesn't have the overload, as you say.

I found 3ph, 7.5 - 10 hp units on eBay from $100 upwards.
Including and Allen Bradley with remote push button capability, for just a bit more.

The downside is that, if this is really hard starting, I might be tripping the overload.

The other option is to take the 10 hp VFD off my lathe, swap in a 5hp which is the motor size. Then I could have soft start, speed adjust (not sure I need that) and remote trigger.
It just means moving a bunch of stuff around. Time and labour.

Utilizing your frequency drive would be the absolute ideal scenario for sure. Before taking this route make sure your drive will handle the load if you are not feeding it with 3 phase power. What I'm trying to say is these drives are rated for much less HP if only fed with single phase 'IN'.

If your incoming power is 3 phase and your drive is rated for 10hp and your load is only 7.5hp then you are all set. Feeding the drive from a RPC may have other issues...I've never done that, but it's certainly something to research.

Stuart

Well I have a 10hp RPC, providing 3ph power to a 10 hp VFD.
Thats currently on my lathe. And that 7.5 hp motor came off that same lathe.

The current draw for the blower might be higher, but its really tough for me to tell.
Its a wood lathe, so won't draw much unless I;m actually cutting. At that point its tough to put down the chisel and measure the amperage. And the number would be highly variable. All I know is that I've never tripped and overload on that setup.

Olaf

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Olaf,

If the combination of RPC and VFD worked on the lathe then it should work on the dust collection fan provided you don't load the RPC up with a draw exceeding its capacity.

That seems like a very large motor/fan combo for a wood turning lathe which equates to expensive to operate. My brother-in-law is a avid wood turner and his Delta cyclone system uses a 1.5hp motor...and I believe that's considered pretty husky.

Stuart

atomarc said:

Olaf,

If the combination of RPC and VFD worked on the lathe then it should work on the dust collection fan provided you don't load the RPC up with a draw exceeding its capacity.

Stuart

Click to expand...

Looks like I'll bite the bullet and go that route.
At least I can wire it up and get it running for next weekend.

atomarc said:

That seems like a very large motor/fan combo for a wood turning lathe which equates to expensive to operate. My brother-in-law is a avid wood turner and his Delta cyclone system uses a 1.5hp motor...and I believe that's considered pretty husky.

Stuart

Click to expand...

Yes, true. However I do a lot of power sanding and that generate a TON of dust.
These are large end grain bowls platters.
Large Platters - THE ART OF DESIGNING IN WOOD
Those are older pictures, before any DC was in place. All rough cutting at that time, no sanding. Now I have a stack of rough cut, dry pieces...waiting to be sanded.

Normally, you can just spin them again and hopefully get a fairly decently smooth final cut, then sand a little. But at this size, the pieces have warped a lot while drying. So finish cutting them is not an option. Hence brute force dust removal.

Currently I run a 3 hp King Canada DC system and it can't do it.
A dust shroud will also go around the lathe

A big disk sander, say 24", can be used as an extra 3phase supply idler when needed. Turn it on when you need more 3 phase juice for a different motor.
Bill D..

On a used contactor/starter pay a little extra for a newer model with adjustable overloads so you do not have to buy new overloads for your motor size and so it can be switched over to a different machine at some time in the future.