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Old May 26th, 2009, 03:57 PM   #1
jimmycooker
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Contactors and PLC 24VDC

Hi,

Just wondering if anyone can tell me what kind of signal I need for this contactor.

http://www.tlc-direct.co.uk/Products/HGES220.html

It's 24VDC, just wondering about the mAmp rating, the 24VDC PWR OUT and VAC NEUT don't energise it when connected up (is the VAC NEUT ok to complete the circuit?)

Total newbie, just trying to get my head wiring up some AB input / output cards and bought this contactor to make things a bit more interesting!

Thanks,
James.
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Old May 26th, 2009, 04:09 PM   #2
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You have a 230VAC coil 2 pole contactor (as stated - typically used in consumer units).

Not sure if i should advise at all based on the little knowledge you sseem to have! (No offence - i know we all have to start somewhere!!).

You need to give us more info on the PLC hardware you are trying to configure...manufacturer, type, part no. etc.

The terminals you describe sound a little like an SLC power supply terminals but can't be sure. If you had a RELAY output module/card you could then switch 230VAC to the coil of your new contactor - but like i said above, it would help us to help you if we had more info!

Hope this helps (a little)!

Rob
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Old May 26th, 2009, 04:21 PM   #3
jimmycooker
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Ha ha, a little bit of info can be very dangerous!

I have an 1746-P2 PSU, SLC 5/03 CPU, DC Sink Input & Output Cards (and a fe few others0 in front of me which i bought to mess around with, i'm a process engineer but want to get into automation as I find it interesting.

I'm basically trying to write a simple program and wire up a switch to an input & a contactor to an output. If I can get this far i'll be able to focus a bit more on the ladder logic side of things and maybe use the PLC for zoning my heating system at home or something.

I bough a contactor so i could wire up a lamp or something, it's encouraging to see things turning on and off!

I'm trying to get the contactor to energise directly from the PSU by connecting two of it's poles to the 24VDC & VAC NEUT terminals on the PSU. From looking at this,

http://www.eod.gvsu.edu/~jackh/books...plc_wiring.pdf

it appears to me that the input card is acting as a switch? Therefore I just wanted to energise the contactor to make sure it was suitable / possible running from the PLC PSU without anything in between....
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Old May 26th, 2009, 04:32 PM   #4
Mickey
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STOP. If you are trying to use 24VDC with a VAC neut to pull in a 240V contactor coil. Then you have no idea what you are doing and are going to kill yourself or worse someone else. GET SOME HELP.
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Old May 26th, 2009, 04:37 PM   #5
mellis
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The problem is that unless you gave a link to the wrong part, your contactor requires 230vac (240v coil) to pull in the coil! Hooking it up to 24vdc isn't going to work.

You can use a small interposing relay with a 24vdc coil to pull in the contactor with 230vac. See figure 18 in the Jacks book.

Or there may be a different model contactor available with a 24vdc coil. However, the extra 24vdc output on the SLC power supply is VERY limited and probably couldn't drive it. You probably need a separate 24vdc power supply.

Oh, if you want to use the extra 24vdc output from the SLC power supply for something else (like the input card), the proper terminals are: 24VDC PWR OUT and 24VDC PWR COM. As others have pointed out, using the VAC NEUT is bad. Lucky you didn't let the smoke out or worse.

And for the record, I agree with them... You're sounding like an accident statistic about to happen. Hope things don't get TOO interesting.

Last edited by mellis; May 26th, 2009 at 04:47 PM. Reason: 2nd thoughts
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Old May 26th, 2009, 04:39 PM   #6
bernie_carlton
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Look again at the contactor whose link you posted. Its coil voltage is not 24 volts DC (as available from the PSU) its 240 volts and that's probably AC.

If you are set on using this unit you will have to have a source of 240 VAC.

And the 'VAC neutral' is not the common side of the 24 volt DC supply. The 'PWR OUT COM' is the common side.
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Old May 26th, 2009, 04:46 PM   #7
jimmycooker
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Mellis / Bernie,

Thanks for your response, that explains that...it's just that this datasheet mentioned 24VDC on page 4.30

http://download.hager.com/hagergroup...larDevices.pdf

Didn'c click that there would be a contactor using the same voltage on the coil as the load, that might seem silly as i'm sure there are other factors to consider.

Thanks for telling me the PWR OUT COM is the common side too, I thought I had it wired as instructed.

Thanks again lads, this really is an excellent forum.
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Old May 26th, 2009, 04:48 PM   #8
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Could either of you give me an example of a relay / contactor i could use directly from the output to switch a small domestic central heating pump, does this exsit? Or do i need to use a relay and contactor?
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Old May 26th, 2009, 05:02 PM   #9
mellis
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In the catalog you linked, I couldn't find what you wanted. All the units on page 4.30 that say 24V control were 24vac when I checked the spec sheet for that model. I didn't spend a lot of time at it, just checked those models.

The heat pump in my house is on two 30A breakers. One for the pump and one for the fan. I suggest you avoid taking on such a heavy load to experiment with. A wiring error in that ciruit is not going to be forgiving. I think a 24vdc light would be a LOT safer.
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Old May 26th, 2009, 09:34 PM   #10
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Jimmy - from having been in your position I can safely say you are clearly in over your head.
I am an electrician so I tried to learn PLC at home - I decided that I was clear over my head and had a total ignoramous for an instructor.

You need to get a qualified instructor - just like I did. So I went to a night school to learn about PLC. I recommend it highly. Otherwise unless you got lots of money and are willing to blow stuff up and zap or kill yourself or burn the house down you can try learning this at home.

Also get yourself a good class on basic electricity, basic motor control. If you keep fooling around with this stuff you are gonna tear up expensive equipment like a heat pump

Oh yes welcome aboard and have fun learning. PLCs are actually a lot of fun AFTER you pretty much know what you are doing.
Dan Bentler

Last edited by leitmotif; May 26th, 2009 at 10:16 PM.
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Old May 26th, 2009, 09:58 PM   #11
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I agree with Dan's suggestion.You must have heard that electricity is dangerous and especially when you dont have enough knowledge of it. The point is,if you do it wrong,things will go wrong unpredicted. It safe to learn the basics first so you are at least able to predict what is going to happen to the load when the circuit is energized. Different components have different voltage and current rating/types. Its better to view a product datasheet/catalogue before you purchase anything so you can select the product which suits your application. Something like this should be helpfull. http://static.schneider-electric.us/digest/17418.pdf

Look at pages 2 & 23 for the various types of contactors and relays.

Good luck,
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Old May 27th, 2009, 11:28 AM   #12
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Jimmy I'm going to have to agree with what everyone else here has said.
But i will tell you this much when it comes to motor contactors you have to know the following info to size it properly

What is the voltage for the contactor COIL?: usally 24VDC or 120-240VAC or 12VDC are 3 of the most common ones. This is NOT the voltage thats going to turn on ur pump its just the voltage to pull in the plunger coil of the contactor.

What is the current load of the contactor coil?: this is how many amps you need your power supply to provide to the coil. this depends on the size of the contactor itself - but typicaly for contactors that are rated for 1-5HP motors your looking at about 200mA (0.2A)

What are the HP, voltage and current rating for the motor your trying to start?: These can be anything from 240VAC single phase to 460-575VAC 3 phase, heck theres even DC motors but you don't see them to often.

Your contactor has to be matched with those 3 items, which are usally found on the motor nameplate

Fuseing and overloads?: to size your overloads for your contactor you have to look at the FLA (full load amps) rating on the motor.

small motors in the 1-5 HP range typicaly all use the same size contactor the only items that would change would be the size of your fusing and your overloads which would be based on the FLA rating of that particular motor.

But again as the other guys have said - i think all of thise falls into the "don't try this at home catagory" for newbies - - - powering up a LED pilot light is alot more forgiving then powering up a 575V 5 HP motor :-p
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Old May 27th, 2009, 11:43 AM   #13
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I would suggest buying a small 12 volt DC PLC (try Ebay)and then play around with that to your heart's content to get familiar with PLCs and programming, etc. Can't cause too much damage with 12 volts!
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Old May 27th, 2009, 11:47 AM   #14
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Quote:
Originally Posted by rwy34ils View Post
I would suggest buying a small 12 volt DC PLC (try Ebay)and then play around with that to your heart's content to get familiar with PLCs and programming, etc. Can't cause too much damage with 12 volts!
My car battery will put out over 500 amps !! Damage??
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Old May 27th, 2009, 12:14 PM   #15
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lol hummmm mickey i dono - how bout you stick your tongue on the terminals like people do with a 9V battery lol if anything else ti should be entertaining for anyone else near by ;-)
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