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Relay Option Questions
Old 4th September 2011
  #1
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Relay Option Questions

Hey, I'm in need of a DPDT relay that can control 120VAC on one set of contacts and maybe 70-100VDC on the other.

Is the rating I'm looking for the switching voltage?


Thanks for the help, sorry for the remedial question
Old 4th September 2011
  #2

I'd use two separate relays - run the primaries in parallel and plan for the extra current in the control (usually isn't a problem).

Keeping voltages like that away from each other is probably a good idea.




-tINY

Old 5th September 2011
  #3
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Quote:
Originally Posted by tINY View Post

I'd use two separate relays - run the primaries in parallel and plan for the extra current in the control (usually isn't a problem).

Keeping voltages like that away from each other is probably a good idea.




-tINY



So how do I run them in parallel off the same switch? I've trenched through pages of relay help pages and all I can find is "if you wire the relay like this, you can do lots of stuff, like turn on a car. Let's talk about using relays to turn on cars..."
Old 5th September 2011
  #4


Wire it like the control circuit you want - then add the other primary by wiring the "+" to the "+" and the "-" to the "-".

If you are running what is known as a "current loop", you wire then in series (like multiple batteries + to - to + to -...). But you have to make sure you have enough voltage available.



-tINY

Old 5th September 2011
  #5
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Alright, I think I get it. Thanks for the help!
Old 5th September 2011
  #6
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djmukilteo's Avatar
Quote:
Originally Posted by Torea View Post
Hey, I'm in need of a DPDT relay that can control 120VAC on one set of contacts and maybe 70-100VDC on the other.

Is the rating I'm looking for the switching voltage?


Thanks for the help, sorry for the remedial question
Contact ratings for relays are rated in voltage and current carrying capability.
So for example....the contact rating might be [email protected] or maybe [email protected]
That's what the contacts can handle...just don't exceed that current or you'll burn the contacts.
What Tiny was getting at is mixing AC and DC on the same relay...bad idea.
Better to use two separate relays (SPST) each rated for the specific voltage and current, then run your control and parallel the coils, if you want them to operate at the same time.
There are solid state relays also available for all purposes if you don't want electro-mechanical, but they are pricey.
What voltage are you using for the control coil to operate the relay? That is the other criteria needed. 12VDC, 24VDC, 28VAc, 120VAC etc..?
Also diode suppression on the coil can be an important consideration as well....
Old 6th September 2011
  #7
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Quote:
Originally Posted by djmukilteo View Post
Contact ratings for relays are rated in voltage and current carrying capability.
So for example....the contact rating might be [email protected] or maybe [email protected]
That's what the contacts can handle...just don't exceed that current or you'll burn the contacts.
What Tiny was getting at is mixing AC and DC on the same relay...bad idea.
Better to use two separate relays (SPST) each rated for the specific voltage and current, then run your control and parallel the coils, if you want them to operate at the same time.
There are solid state relays also available for all purposes if you don't want electro-mechanical, but they are pricey.
What voltage are you using for the control coil to operate the relay? That is the other criteria needed. 12VDC, 24VDC, 28VAc, 120VAC etc..?
Also diode suppression on the coil can be an important consideration as well....

What's diode suppression? I would think 120VAC would be easiest to use, since I have a 120VAC power-in planned. But I'm still a bit fuzzy on what would be best. Would it be easier to do something like 12VDC and find a cheap power supply for some small appliance?

I'm fine with electromagnetic, that's kinda what I was planning on. I don't want to skimp here because this is more than a learning project, but I'm also on a bit of a tight budget.
Old 6th September 2011
  #8
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djmukilteo's Avatar
Relays are typically used to switch larger currents and voltages using a much lower voltage as a control signal and switch. That way things are more isolated and safe.
i.e. I push a button on a control panel using a safe low voltage 12VDC switch and start up and operate a 240VAC compressor pump...
A good example and a very common relay would be a 12VDC coil switching 120VAC contacts.
If you want to turn 120VAC off and on using 120VAC that's fine but maybe just use a switch to begin with!
If you describe what it is you're trying to do, it would be easier to figure out what you need..there are hundreds of options.
Hope I can help...there are no stupid questions....
Old 6th September 2011
  #9
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djmukilteo's Avatar
Oh...diode suppression is a relay with a diode across the control coil, usually an optional feature of the relay.
It can be important because when a relay coil is "opened" after being energized there is a collapsing magnetic field created which generates a current spike back into the control circuit which can cause noise EMI/EMF which can bleed into the rest of your system and cause problems.
The diode shunts that effect.
If it's just a simple single control circuit and relay not that important to have...
Old 6th September 2011
  #10
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Quote:
Originally Posted by djmukilteo View Post
If you want to turn 120VAC off and on using 120VAC that's fine but maybe just use a switch to begin with!

Forgot about that. But the key here isn't switching just 120VAC, it's switch both AC and DC. I'm creating a box to switch Leslie motors, 147 style relays use AC and 122 style relays use DC. To use both at the same time, I need to switch both at the same time. They do sell a halfmoon switch that will do this, but it uses a second set of contacts. I'd like to use a normal switch to switch the relay to switch the Leslie relays, that way I can move the box from organ to organ and use the same switches.


Trying to do this simply so as to not create too much bulk (like extra power supplies) but I guess if it's necessary...
Old 6th September 2011
  #11
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djmukilteo's Avatar
OK...use a 120VAC 20A switch DPST switch and one relay.
One pole of the switch for the 120VAC leslie motor and the other pole to operate a 120VAC coil relay SPST and run one of the DC motor hot leg thru the contacts of that relay to turn that on...how many amps are the two motors?
Just make sure you have the right current for the contacts
Old 6th September 2011
  #12
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Quote:
Originally Posted by djmukilteo View Post
OK...use a 120VAC 20A switch DPST switch and one relay.
One pole of the switch for the 120VAC leslie motor and the other pole to operate a 120VAC coil relay SPST and run one of the DC motor hot leg thru the contacts of that relay to turn that on...how many amps are the two motors?
Just make sure you have the right current for the contacts
If I'm getting a new switch I might as well get the one that can switch both currents anyway. I'd like to keep the original switch. That's why I want the relays.
Old 6th September 2011
  #13
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djmukilteo's Avatar
Quote:
Originally Posted by Torea View Post
If I'm getting a new switch I might as well get the one that can switch both currents anyway. I'd like to keep the original switch. That's why I want the relays.
Well if your original switch can act as the coil power for two relays then do it that way....just use the proper voltage coils and the proper contact current ratings for all the parts.
Old 6th September 2011
  #14
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Quote:
Originally Posted by djmukilteo View Post
Well if your original switch can act as the coil power for two relays then do it that way...

Coil power meaning being able to switch the power to both? Should be able to, it's made to switch one or the other.



Going back to my original question: What do these parameters mean? I got them from Digi-Keys relay search: Switching Voltage; Coil Current; Coil Voltage; Turn On Voltage Max; Turn Off Voltage Min.

Thanks for the help!
Old 6th September 2011
  #15
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djmukilteo's Avatar
Quote:
Originally Posted by Torea View Post
Coil power meaning being able to switch the power to both? Should be able to, it's made to switch one or the other.



Going back to my original question: What do these parameters mean? I got them from Digi-Keys relay search: Switching Voltage; Coil Current; Coil Voltage; Turn On Voltage Max; Turn Off Voltage Min.

Thanks for the help!
Switching voltage: would be the voltage across the contacts your switching on and off (there should be a current rating there as well)
Coil Current: current needed to turn the coil on (typically 100ma)
Coil Voltage: Nominal voltage needed to operate the coil (typical coil voltages are anywhere from 5-50VDC or 100-240VAC)
Turn On Voltage Max: highest voltage to operate the coil not to be exceeded
Turn Off Voltage Min: lowest voltage when the coil will drop out.
Old 6th September 2011
  #16
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Quote:
Originally Posted by djmukilteo View Post
Switching voltage: would be the voltage across the contacts your switching on and off (there should be a current rating there as well)
Coil Current: current needed to turn the coil on (typically 100ma)
Coil Voltage: Nominal voltage needed to operate the coil (typical coil voltages are anywhere from 5-50VDC or 100-240VAC)
Turn On Voltage Max: highest voltage to operate the coil not to be exceeded
Turn Off Voltage Min: lowest voltage when the coil will drop out.

Thank you! Digi-key doesn't have a current rating with the switching voltage, but I'll probably check the datasheets for it.
Old 6th September 2011
  #17
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djmukilteo's Avatar
Quote:
Originally Posted by Torea View Post
Thank you! Digi-key doesn't have a current rating with the switching voltage, but I'll probably check the datasheets for it.
Do you know the current and voltage of the two motors?
You said one was 120VAC and one was 70-100VDC
Then you just need some voltage thru your control switch...you could use either of those two supplies.
Old 6th September 2011
  #18
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Quote:
Originally Posted by djmukilteo View Post
Do you know the current and voltage of the two motors?
You said one was 120VAC and one was 70-100VDC
Then you just need some voltage thru your control switch...you could use either of those two supplies.

I was talking about the relays that switch the motors. Those relays are in the Leslie power amp and switch AC power for the motors. One relay is turned on by AC, the other by DC.

The relay I want to put in will control those two relays with one switch.
Old 6th September 2011
  #19
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djmukilteo's Avatar
Do you have a schematic?
I'm getting confused??
Old 7th September 2011
  #20
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Quote:
Originally Posted by djmukilteo View Post
Do you have a schematic?
I'm getting confused??

Sorry, I don't. This is a self-made thing. Basically, the relay I'm asking about (that I want to buy) will be used to switch other relays.


Think of it like this, where S is the switch (I think SPST), R1 is the relay I want to get, R2 switches with AC and R3 switches with DC (both control the motors), and Ms are motors.
.....S......
.....R1....
..../..\....
.R2....R3.
./.\..../.\.
M.M..M.M

So I want one switch to control a relay, that controls two relays that switch on different power sources. Normally R2 or R3 could be controlled with my switch, but I can't control both with my switch.

Seems a bit redundant when I explain it but it makes sense on this end.
Old 7th September 2011
  #21
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djmukilteo's Avatar
Quote:
Originally Posted by Torea View Post
Sorry, I don't. This is a self-made thing. Basically, the relay I'm asking about (that I want to buy) will be used to switch other relays.


Think of it like this, where S is the switch (I think SPST), R1 is the relay I want to get, R2 switches with AC and R3 switches with DC (both control the motors), and Ms are motors.
.....S......
.....R1....
..../..\....
.R2....R3.
./.\..../.\.
M.M..M.M

So I want one switch to control a relay, that controls two relays that switch on different power sources. Normally R2 or R3 could be controlled with my switch, but I can't control both with my switch.

Seems a bit redundant when I explain it but it makes sense on this end.
OK that seems pretty straight forward. I think that is the simplest way short of just using a different common switch (DPDT) to turn both R2 and R3 on at the same time.
But because you want to use the original switch to do this go with the R1 approach.
Good luck...
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