Where to get inexpensive: terminal relay for direct connect on DIN Rail

[trend]

Hello

Where can I get inexpensive Relays that directly mount on a DIN rail like:
http://www.plctalk.net/qanda/attachment.php?attachmentid=3048&stc=1
that is mentioned here:
http://www.plctalk.net/qanda/showthread.php?t=10653

I need to run ~120vAC 2amp motors (one at a time).. and I need to run maybe 70 of them.. maybe 60.

any ideas?.. i was hoping to get something for under 6bucks each..

thanks!
Lee

 

[Lancie1]

Trend,

Cutler-Hammer, Square-D, Allen-Bradley, Omron, and practically any other electrical distributor all have DIN-mounted relays rated for 10 amps or more. For example, the Square-D class 8501, catalog number RS41-S is rated for 1/6 horsepower at 120 volts, but the price is about $18. What about the Idec #RH1B-UAC120V, contacts rated for 10 amps, available from Allied Electronics (www.alliedelec.com) in quantities > 50 for $7.47 US not including the socket which is #SH1B-05 for $4.46.

Here is a cheaper one: Allied stock # 850-0190, SPDT 15 Amp contact, for $4.69, with DIN-rail socket # 850-781D-1 for $2.53, for a total of $7.22!

Allied offers a discount on relays when you buy more than one, so if you don't like this one, search the Allied site for a better one.

If you are talking about Terminal-Block relays, that is a different type, and more rare and harder to find.

If you only need to run the 60 motors ONE AT A TIME, then you really only need one PLC and some GOOD PLC relay output modules rated for 6 or 8 amps (whatever your motor starting current is). An alternative would be to use ONE good relay rated for your motor starting current (probably 6 amps or better), then use some cheaper PLC relay output modules to switch the relay between the 60 motor leads. This will work if you do the PLC switching BEFORE you energize the relay.

Another option is to use a cheaper relay, but use both of the relay contacts of a double-pole relay in parallel, instead of one, to get a higher current rating.

 

[trend]

thanks for the info!

Man.. it really looks like I should be trying to use 24vDC motors instead of AC motors

 

[rsdoran]

If you only need to run the 60 motors ONE AT A TIME, then you really only need one PLC and some GOOD PLC relay output modules rated for 6 or 8 amps (whatever your motor starting current is). An alternative would be to use ONE good relay rated for your motor starting current (probably 6 amps or better), then use some cheaper PLC relay output modules to switch the relay between the 60 motor leads. This will work if you do the PLC switching BEFORE you energize the relay.

I am not sure I understand the second method, what would the plc switch to the relay?

One PLC with 60-70 outputs would cost more than $6 per output, at least from the pricing I have looked at it seems that way.

The cheapest method may be to use a bank of selector switches or something along that line....ie Main/Motor power switch off, use switch to select motor then turn on main/motor switch.

I keep thinking of options then deciding they wont work.

I beleive a 16 output plc could be used with 16 4 pole relays and use a 4 position selector switch to change the feed...switch in position 1 would send power to first contact on relay 1 for motor 1 so output 1 would turn on motor 1. Put switch in position 2 it would feed second pole/contact and goto motor 16.... Using an AD DL06, 16 relays, 16 relay bases and pushbuttons would run around $500-$600. You would also have to buy the software and cable which is $180. This puts cost around $9 per output not counting software and cable. Depends on what you are doing but expansion output module could control 4 more relays to do the switching and an HMI could allow you to auto set the "banks" just by choosing the motor number...ie motor 1 is selected then "bank 1" relay is turned on to feed relay 1 pole 1 then output turns on relay 1.

What are you making if I may ask.

 

[Lancie1]

I am not sure I understand the second method, what would the plc switch to the relay?

The PLC could switch each of the 60 motors to the relay, 1 at a time as he said he wanted to run them. After switching a motor to connect to the relay, then the PLC program could use another single output to energize the relay. My thought was that if the switching is done BEFORE the motor is started, then the PLC outputs could be a lower current rating, only needing to be rated for maybe twice the 2A. running current, as there would be no arcing current through the PLC contacts at startup. One of the Automation Direct relay output modules can handle 4 Amps (if my memory is correct). That would probaly be enough to run the motor if the initial arcing switch is done with a relay rated for motor starting.

 

[JohnW]

These are what I use, will switch up to 6 amps.



From Phoenix contact PLC-RSC-24DC/21 The 24Vdc is the coil voltage.

They have a commoning bar and a feeder section as well.

they won't be under 6 bucks each though. the work out at about £7.00 GB list.

Here under interface relays PLC

 

[bernie_carlton]

If you really are only running one at a time then 16 RELAY outputs on a PLC could select one of 64 lower current steering relays (of the type Lancie1 suggested) in a matrix arrangement. Then use one other output to energize an external, higher current relay to so the actual motor turn on/off. Just make sure to allow for a proper time interval (at least 1/10 second) after selecting the steering relay before energizing the power relay and again after de-energizing the power relay before de-energizing the steering relay and selecting a different one.

 

[Unregistered]

If you really are only running one at a time then 16 RELAY outputs on a PLC could select one of 64 lower current steering relays (of the type Lancie1 suggested) in a matrix arrangement. Then use one other output to energize an external, higher current relay to so the actual motor turn on/off. Just make sure to allow for a proper time interval (at least 1/10 second) after selecting the steering relay before energizing the power relay and again after de-energizing the power relay before de-energizing the steering relay and selecting a different one.

Yeah, that is actually what I was thinking of.. then someone pointed out:

Look at the following picture:

http://nikita.argia.net/kmaxon/motors_307.gif

In the image the hot side of the AC source is connected through relay R2 to
motor M4. Relay R4 connects the return side to the AC source thus
completing the circuit. This is probably what you are thinking of...

Where the problem comes in, is that all of the motors hooked up to relay R2
have one side hot. Take M5 for example, it conducts to the wire attached to
R5, which conducts through the motor M8 which conducts through the motor M7
and completes the circuit through R4... See the following image...

http://nikita.argia.net/kmaxon/motors_308.gif

As you can see, through all of the multiple paths, every motor will become
energized...

-Kenneth

I am kinda swayed towards just designing and cutting my own PCB board now.. I could get a cheaper solution and easier to wire...

I am still up for suggestions. please prove me wrong!

thanks-Lee

 

[bernie_carlton]

I was implying that up to 64 RELAYS would be selected, each one selecting both leads for its own motor. But of course the problem still exists with the coils of the relays unless you use DC relays each with its own diode on one side. This prevents the rverse current flow for the other relays.

 

[Lancie1]

Bernie,

You have a great solution. If Lee will select relays with DC coils, then he will only need 16 PLC outputs (or even 16 selector switches - he has never said he is using a PLC), and 64 relays with 6 Amp AC contacts and 24 vdc coils, and 64 diodes. Unless he has an in-house Printed Circuit Board manufacturing facility, this will still be less expensive.