Hi,

This may be a long shot, but I was wondering if I could get some assistance with a wiring problem I am having. I recently acquired a Macromatic THR-3816U to use as a single shot relay. It has an onboard potentiometer that can be set to a desired time delay. This relay is not replacing a preexisting relay, but part of a system that we are building in our lab. I’ve included a schematic of how I have wired this relay in relation to the power supply and the load. The power supply is 24VDC at 1 amp. The load is a piece of nichrome wire that will heat up depending on the amount time power is supplied. The tigger is non-energized. The red dots represent LED lights. One that signals that power is being sent to the relay and one that signals that power is being sent to the load. What I am trying to accomplish with this circuit is that on application of the trigger, power from post 1 will be sent to post 8 for a set period of time before switching back to post 9.

When the I bridge the gap between posts 5 and 4. Power is intermittently supplied to the entire unit, i.e. both LED lights flash, and the relay does not function correctly. It’s almost like there is something being repeatedly tripped inside the relay. If I remove the connection between posts 1 and 2, the relay functions correctly, however I no longer have power being supplied to the load.

I gather that my wiring is incorrect. I am a biologist that has a very basic understanding of electricity. Any assistance in helping me wire this circuit would be greatly appreciated. Thanks!

 

Hello,

You have drawn 3 ground symbols in your diagram.
This can not be correct.

Did you read the instruction sheet?

Bertus

 

You want Interval On, what is the mode you have it set to at present?
Max.

 

Bertus, the three grounds are connected.

Max, I have it set to "off delay". From my understanding, when I apply the trigger in this mode, the output power is sent for a specified amount of time. I included a schematic that came with the unit. When I remove the power from post 1, I can achieve the desired time delay from the relay, however, I'm no longer sending power to the load. If I use interval on, I would have to have a switch on the power supply, correct?

 

Hello,

When the 3 ground are connected as shown, the load and powersupply will be shorted.
Also the relays contacts are bridged and will not do anything.
You will have to remove the 2 grounds with the red dots to have the relays do something.

Bertus

 

Thanks Bertus!

Could you help me with wiring this correctly? I want to be able to have the two lights, one for power to the relay, one for power to the load.

Am I correct in assuming that post 3 is the negative and therefore also the ground?

What do you mean the relay contacts are bridged?

 

Hello,

The 2 grounds with the red dots will be like a wire accross the relays contacts.
There is always a connection, no matter wich position the relays contacts have.

Pin 2 is the power input to the relays.
Pin 3 is the only ground connection needed.

Bertus

 

Thanks Bertus!

I understand the bridging now. The red dots represent LEDs. These LEDS have two leads, one for power and one for ground. Would they just need to be grounded separately from this circuit?

 

Hello,

It was not clear the the red dots where leds.
Leds will need a resistor to limit the current.
They can be used as indicators on the posistions you have drawn.
The bottom led (pin 2) will go on as soon as the power is applied.
The top led (pin 8) go on as soon as the relays is activated.

Bertus

 

Thanks!

How should I wire the resistors in this circuit? Would I connect the resistor to the ground leads from the LEDs and then to the ground?

 

When I remove the power from post 1, I can achieve the desired time delay from the relay, however, I'm no longer sending power to the load. If I use interval on, I would have to have a switch on the power supply, correct?

Either way you will need to reset the timer.
Max.

 

Could I just wire the LED lights inline? For example, could the power supply go to the first LED connected to the power lead and then connect the other LED lead to post 2?

For clarification, the LEDs that I have are 24VDC with two quick disconnects.

Thanks!

 

Could I just wire the LED lights inline? For example, could the power supply go to the first LED connected to the power lead and then connect the other LED lead to post 2?

For clarification, the LEDs that I have are 24VDC with two quick disconnects.

Thanks!

No you cannot just wire the LED inline. That it is what Bertus is trying to tell you. Yes the LED might (assuming you don't over power it so much it burns out the first time it is used) light without the resistor but you will severely limit the life of the LED.

Read up on current limiting resistors
https://www.sparkfun.com/tutorials/219

Do you have a datasheet on those LEDs? They might already have their own current limiters.

 

And you can't but the LED in series with your load because more than likely the current requirements of the load will exceed the max rating of the LED. Bad practice anyway because if your indicator goes out the you lose the who function of the relay.

 

Thanks spinnaker!

The LEDs are rated for 24VDC, so I'm assuming they have a built in current limiter. I'm supplying 24VDC and 1amp with the power source. I bought the LEDS from McMaster Carr, model 2779K1.

The load in this circuit is a bare piece of nichrome wire. It's intended purpose is to give off heat when current is applied through it. I understand that if the LEDs are wired inline and they burnout, then there will be a disconnect in power.

Assuming they have a built in limiter, could I wire them in this fashion? Thanks!

 

Unless the power supply has in-built current limiting you will probably destroy it if the resistance of the nichrome wire is less than 24 Ohms. Current (Amps) = 24V divided by wire resistance in Ohms.

 

Thanks Alec_t!

This is the power supply that I am using:

http://www.mcmaster.com/#70235k99/=zwu6ob

Not sure if the power supply has an in-built current limiter. Are you suggesting that I would destroy the power supply or the LEDs?

I've redrawn my circuit. Assuming the LEDs have built-in limiters, can I wire them in parallel like I have drawn? The nichrome wire does not have enough resistance, should I place a resistor where I have it in this diagram?

 

Your LED on pin 2 will not light for sure. It is shorted out. The load LED might not light if the resistance of the wire is low enough.

 

No!

You can buy 24 VAC/DC LEDs. They are common in the industrial environment. Just not common here.
5V and 12 V LED can also be bought, but a LED one AAC is a naked one or one that needs a current limiting resistor.

If you want a load indication, they can be wired ACROSS the load. If you want a power indication, they can be wired across the power supply.

Unless you have designed you heaters to be 24V, you MAY want a laboratory supply that is metered. A lot of these supplies have a logic contact to ground that turns on the supply. You woud end up with a 24 V supply for your timer and a laboratory supply for your load. Check out www.circuitspecialists.com

There is a product called an electronic load. These can be programmed to provide a constant current, voltage, power or resistance within limits. I don't know if logic control is possible. They are expensive. Some are USB or serial controllable.

If your part of a school or you company has a site license for LabVIEW, that's a programming environment that allows you to control instrumentation. It's graphical and "data-flow" based and it takes a while to get used to. It's the defacto standard.

The wire has strong temperature resistance dependence, I think, that you may be better off with the constant power control mode.

I worked a fair bit with custom tantalum heating

 

Thanks spinnaker! That makes sense to me.

Kiss, these are 24VDC LEDs.

I guess you're calling my nichrome wire a "heater"? The nichrome wire is bare and 8mm long. It's a consumable fuse, that will heat up and ignite a sample in a high pressure environment.