Trying to Figure Out if a Relay is What I'm Looking For?

See contact ratings of your relay. It might have been melted and disconnected.

Your power comes in at terminal 2 and 7, this runs the timer....8 and 5 are normally closed...and 8 makes to 6 on activation....the same on the reverse.... so your neg can run directly to the motor and the pos can be jumped to 3 which will make on activation to 1....which can power the motor on...or if you are using a variable voltage control that would be fed through the 1 to 3 connection and no jumper would be used....

http://www.macromatic.com/blog/cat/relays/time-delay-relays

You should have a relay or some control feeding the 24v to the timer...If you want the fan to come on immediately with the control, then you would wire your + leg through the normally closed contact 1 and 4 or 8 and 5...The first wiring above would delay the start....

I understand now how I was wiring it wrong, thank you. Now I just have to figure out how to power the relay separately... Is there anything wrong with getting a new relay that runs from 120V AC but using it to switch 24V DC ? Should AC powered relays only be used for AC and DC for DC or does it not matter?

It doesn't matter what the control voltage is, although it can be confusing for somebody troubleshooting this system that the control voltage is different from component to component and that you have both 24v ac and 24v dc....For simplicity the control voltage is usually uniform throughout the system....usually 24v dc is preferred because it's not lethal...Where are you getting the control voltage for the timer? ...is the motor 24v dc or 24v ac? Why don't you list the components you have, exactly what you want them to do, and the voltage sources you have available and we can provide you with a wiring scheme......if you like....

This is the DC control I'm using- http://www.kbelectronics.com/manuals/kbmd_240d_manual.pdf

The DC control is set to plug into 120VAC and output 24VDC that is variable by means of a potentiometer. It's powering a 24VDC variable speed 1A motor.

I'm using a DPDT switch to reverse direction of the DC motor as needed along with a SPDT momentary switch (normally open) to start/stop the motor.

I want to be able to push a switch (ideally the NO SPDT momentary switch that's already being used) and have the 24VDC motor shut off after a set time, variable from half a second up to at least 10 seconds.

My original idea was to use the 24VDC from the DC control to power the relay but that won't work because the voltage is variable and once it gets below 18V the 24V relay no longer works. So my new idea is to tap into the 120VAC lug on the DC control to power the relay but then I would loose my momentary switch... So I'm lost again.

Let me know if you need more info and thanks for your help already, I really appreciate it.

OK so you need a small transformer 120v ~40va to 24vdc for the control voltage on the timer and reversing relay....then you need a DPDT relay to reverse the voltage when desired....and you need an on/off switch to activate the reversing switch...

If I only used the timer in one direction, I could omit the switching relay, correct?

You said to look for ~40va transformer. It seems like most of the 120VAC to 24VDC power supplies I can find are rated 1A. I don't know how 40VA would compare to 1A?The coil rating of the timer relay I have is 2VA if that matters?

Yes if you only needed the fan to turn in one direction you wouldn't need the switching relay....40va = ~.33 amps....

Also, I don't see where the momentary switch that's already being used to start/stop the motor would be wired?

If I wanted to bypass the timer relay for normal function, I guess it would be adding another DPDT switch?

Is the momentary switch feeding power to variable voltage supply? Yes to bypass the timer another DPDT relay....

No, the momentary switch is between the variable voltage supply and motor.

You can eliminate it or use it to feed the bypass relay for manual control...

It's a foot operated switch that is needed to start/stop the motor... Is there anyway it could be incorporated into your schematic in post #7?

I would use it to feed power to the entire circuit...

I wouldn't think power cycling the DC controller every time you start/stop the motor would be a good thing?

You indicated a momentary contact switch to start the motor. I assume this is the footswitch, yet you say the footswitch is used to start and stop the motor.

Do you want to press and release the foot pedal once to start it, and press and release it a second time to stop it, or press and hold to start, then release to stop?

Since you are asking about a timer, I would assume that you actually want the timer to do the stop action. If you want to press and release the footswitch to start the motor, then there must be some form of latching, which can be done with one set of the relay's contacts, while the other set actually turns on the motor for the duration set by the timer.

On the other hand, what I just described has no provision for stopping the motor before timeout. If you simply use the footswitch to supply power to the relay, holding it down will make the motor run for the time set by the relay, but releasing it will stop it at any time before timeout.

If SE does not provide a diagram, I can...

Yes, the momentary switch is a foot switch. I want the press and hold the foot pedal to start and release to stop. I would like the timer to do the stop action but would also like the motor to stop early and reset if the pedal is released. As it's wired now, it's working as I would like but now I want to add the timer function. A diagram would definitely help. Thank you

It's a good thing you included a link to your speed controller manual, and that I looked at it! It specifically warns NOT to connect a switch or relay between the DC output and the motor, as that would destroy the controller.

That means you have no choice but to control the 120VAC input, for this particular speed controller.

Here's a circuit that will use that controller and your selected relay to do the job:

I've shown the speed controller as if it were a variable transformer, while of course yours is an electronic circuit. Just consider the dashed rectangle to be the controller. Since you say the unit is already in use, you presumably don't have the option to change it. I see that a Fwd-Brake-Rev switch is an option on that controller. Since you have said that you have a DPDT switch for Fwd/Rev, I assume that you do NOT have that option. NOTE: You should NEVER change the position of that Fwd/Rev switch while the motor is running. It may not blow the controller the first time you do, but that is a real possibility

Virtually any 24VAC transformer you can find will be able to power the coil on that relay. 2VA/24V=0.08A to activate the coil. If you haven't yet purchased the relay, you could get one with a 120V coil, and then you wouldn't need the 24V transformer. Here's the circuit for that:

NOTE: This circuit connects 120V to the foot pedal. That means the footswitch must be rated for 120V, and the wiring must be appropriate for safety.

I've shown two power plugs. It should be obvious that you could instead get the 120V for the footswitch and relay from inside the motor controller box.

Also, since you say the unit is already in use, I assume that you realize that this is a 90 Volt controller, with plenty of power to destroy your motor if you turn it up too far!

I misspoke when I said the foot switch was on the DC output. It's wired between P3 of the potentiometer and is currently working perfectly. The foot switch I'm using is 15A 125/250VAC 1 NEMA, connected by 10' of grounded 18AWG SVT cord.

I have a DPDT switch wired that serves the same function as KB's Fwd-Brake-Rev switch, minus the braking ability which isn't needed with such a small motor.

I like the idea of using a 120V relay but it may be easier to just plug in a wall wart to power the 24VDC relay I already have... Thank you for the option though. In your 120VAC foot switch diagram, what does S1 Power and F1 stand for?

Where would a second relay fit into this if I wanted to bypass the timer relay? I'm starting to run out of room in the control box... Are there small relays (1" square?) with solder terminals maybe that would work for this?

What are you guys using to draw these nice wire diagrams?

Thank you

"I misspoke when I said the foot switch was on the DC output. It's wired between P3 of the potentiometer..."

It's wired between P3 of the potentiometer and what?

I suspect this means that the footswitch is connected between the slider of the speed control potentiometer and the input to the speed control circuitry. That's an excellent idea, and avoids high voltage going to the foot pedal. There should be a resistor, perhaps a 47kΩ, between the input to the speed control circuitry and the bottom of the potentiometer (quite possibly ground), to guarantee zero voltage when the foot pedal switch is open.

I assume this was done as a modification to the speed control unit. Although it undoubtedly nullifies the warranty, congratulations to whoever thought of it!

Here's the circuit for that method, with a VASTLY simplified form of the speed control circuitry:

In this circuit, R1 drops the supply voltage down to a reasonable level for the control potentiometer (VR1), the output of VR1 goes through the relay contacts (when they are closed) to the input of the control circuit (shown here as an NPN transistor). When the relay contacts are open, R2 guarantees that no voltage will go to the control input, so the motor will be off. There may well be something in the circuitry that provides the function of R2; If it is working reliably now, don't worry about it.

The two wires that currently go to the footswitch would now go to the relay contacts, and the footswitch would now be connected between one side of the relay power source and the relay.

F1 and F2 are fuses. The size of F2 was determined by whoever set up the speed control originally; F1 could be a 1 Amp or even a 1/2 Amp value. S1 is a power switch that guarantees no accidental movement of the motor when in the Off position.

I presume you can use this diagram, together with the previous one using the wall wart, if you decide to use the 24V relay on hand. That would indeed be safer than using the 120V relay.

These drawings were done in CAD (Computer Aided Drafting). I happen to use a CAD program called Vectorworks, which is sort of a middle of the road program: much cheaper than the high end CAD programs, yet powerful enough to do most of what I want to do. I've been using it for 30 years, so I'm very accustomed to it...

Sorry, I forgot about the question about a second relay. What would be the function of that second relay? If you simply want to bypass the timer, just put a simple SPST toggle switch connected across the relay output terminals. If that switch is in the ON position, the motor will run regardless of the contacts in the footswitch or the timer.

Sure, there are small relays. Generally speaking, physically smaller relays will likely have lower current ratings or fewer contacts, but there are exceptions to both of those statements. Some of our older machines contain dozens of "Ice Cube" relays that are 3/4x1 1/16x 1 1/4", and have four sets of double throw contacts @3Amps. (https://www.amazon.com/Potter-Brumfield-KHP17D11-Relay-24VDC/dp).

If all you want is a SPST contact, then there are reed relays that are only 1/4" square by an inch or so long, or even smaller. I don't have any personal experience with smaller timing relays, but I suspect they can be found for a price...

I should also point out that some similar speed controllers, like the Minarik Units we use at our plant, contain Inhibit terminals and/or a Run/Stop Switch, You can connect a footswitch directly to either of those.[/p] If I understand correctly, opening the connection between the Inhibit terminals allows the motor to coast to a stop, while the Start/Stop switch applies braking action when moved to the Stop position. I presume a foot pedal could be connected either in parallel with the Run/Stop switch, or instead of it, although I don't have one handy at the moment to check...

I haven't read all of this thread, so it may have already been mentioned, but while an AC relay will generally work fine on DC, a DC relay will often chatter when used on AC as it does not have the shading coil fitted.

I have it working correctly thanks to all your help. I very much appreciate it and will stick around to try to help others if I can.

Thanks for telling us it is working. Can you show/tell us what you ended up doing?