OK to Trigger 4 Relay coils with one output?

[skyfox]

Most I have come across is two loads switched on simultaneously using a single output point. Typically, an indicator lamp and a relay coil combination. Is there a downside to triggering 4-relay coils at the same time with using just a single output? Each relay draws around 42mA's (coil current). All 4 relays have free-wheeling diode protection built in. PLC output is rated for 2 AMPS per point. So when combined, all four relays draws fraction of what the output is capable of providing. Contacts from the relays are used as interlocks for other circuits and carry very low currents. (i.e. not switching on/off heavy loads) In order for the interlocks to function properly, all four relays must be in an on state. Failed relays (fused contacts, etc.), are accounted for via a separate monitoring circuit. Wanted to know the pros and cons of switching multiple loads using a single output. Any feedback would be greatly appreciated.


Cheers.

 

[Bit_Bucket_07]

Most I have come across is two loads switched on simultaneously using a single output point. Typically, an indicator lamp and a relay coil combination. Is there a downside to triggering 4-relay coils at the same time with using just a single output? Each relay draws around 42mA's (coil current). All 4 relays have free-wheeling diode protection built in. PLC output is rated for 2 AMPS per point. So when combined, all four relays draws fraction of what the output is capable of providing. Contacts from the relays are used as interlocks for other circuits and carry very low currents. (i.e. not switching on/off heavy loads) In order for the interlocks to function properly, all four relays must be in an on state. Failed relays (fused contacts, etc.), are accounted for via a separate monitoring circuit. Wanted to know the pros and cons of switching multiple loads using a single output. Any feedback would be greatly appreciated.


Cheers.

I don't see a problem with it, so long as the total load is less than the output rating. I'd like to see separate fused circuits from the output for each of the relay coils.

 

[rpoet]

Most I have come across is two loads switched on simultaneously using a single output point. Typically, an indicator lamp and a relay coil combination. Is there a downside to triggering 4-relay coils at the same time with using just a single output? Each relay draws around 42mA's (coil current). All 4 relays have free-wheeling diode protection built in. PLC output is rated for 2 AMPS per point. So when combined, all four relays draws fraction of what the output is capable of providing. Contacts from the relays are used as interlocks for other circuits and carry very low currents. (i.e. not switching on/off heavy loads) In order for the interlocks to function properly, all four relays must be in an on state. Failed relays (fused contacts, etc.), are accounted for via a separate monitoring circuit. Wanted to know the pros and cons of switching multiple loads using a single output. Any feedback would be greatly appreciated.


Cheers.

How about using one relay with enough poles to switch all the needed circuits?




-rpoet

 

[skyfox]

Bit_Bucket & rpoet,

Thanks for the feedback. Unfortunately, I cannot use a single relay with multiple contacts. Circuit requires that polarity of the output and common be able to be reversed depending on the externally connected interface. For an example;

Device A1, A2, & A3 requires 24VDC to turn them on.

Device B1, B2, & B3 requires 0VDC to turn them on.

So I need to also switch the common leg from 0VDC to 24VDC when device type "B" is connected. This has to be done using the same PLC outputs which are at 24VDC. Hence the need for additional relays. A 4th PLC output is used to energize/de-energize interface relays to select between A & B devices as well as energize/de-energize interlock circuits depending on the device type being used.

Thanks again.

Cheers.

 

[Holmux]

If I had to go this route I would probably add a extra relay to pull the other four

 

[JesperMP]

Unfortunately, I cannot use a single relay with multiple contacts. Circuit requires that polarity of the output and common be able to be reversed depending on the externally connected interface. For an example;

Device A1, A2, & A3 requires 24VDC to turn them on.

Device B1, B2, & B3 requires 0VDC to turn them on.

So I need to also switch the common leg from 0VDC to 24VDC when device type "B" is connected. This has to be done using the same PLC outputs which are at 24VDC. Hence the need for additional relays.

You have 2 potentials that you want to switch at the same time. 24V and 0V. Why cant that be done with a single relay or contactor with multiple (2) contacts ?

 

[plvlce]

You have 2 potentials that you want to switch at the same time. 24V and 0V. Why cant that be done with a single relay or contactor with multiple (2) contacts ?

This.


All a relay does is connect (or disconnect) two points in the circuit for each set of contacts you use. It neither knows nor cares what you are connecting/disconnecting as long as you are not exceeding its contact ratings.


The only reason I can see you might want multiple relays is due to sheer number of things you are switching.

 

[GaryS]

If it were me i would use an output for each relay the cost of the output in minimal then if later you find you need to split them it's just programming.
I see some are saying you use a larger relay with multiple contacts, keep in mind the larger the relay the more power it takes to pull in and hold in and the harder they are to replace if they fail.

 

[ndzied1]

Is this what you are trying to do?