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Relay Assistance

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frosty101288

New Member
Hi All,

I'm really sorry to ask what I'm sure is a really stupid question however I'm really struggling to work it out. I have a basic working knowledge of electronics however relays are something that i have always struggled with.

I have a 24v dc supply that is powering my project but i want to power a 12v dc led that when the power supply is active. i have a step down transformer to convert the 24v to 12v.

So the question i have is what relay do i need. Am i correct in thinking that i need a 24v dc relay so the 24v input goes into the relay and activates the relay which then turns the 12v light on. Secondly with the actual does the output just switch say the positive like you would with a normal switch?

I look forward to hearing from you.

Thanks in advanced

Luke
 

Frozenguy

Member
Hi Luke.

Do you have a schematic/drawing of what you're doing? I'm not sure you need or want that relay.

What LED are you using? You don't need the transformer if you can get your hands on a ~2k resistor. 1/8 W or higher (1/4 W would be better). If your LED can take 6mA (I bet it can, but check.)
 

frosty101288

New Member
Hi Frozen Guy.

I'm sorry I don't have a schematic/drawing of what I am trying to do. Basically I am doing a control box for a CNC Plasma Cutter. Basically three of the stepper boards need a 24v supply and one of them needs a 12v supply hence having the step down transformer as they are all different boards not one single board. I didn't think to use a resistor on the input into the board. The reason for thinking that I needed a relay was purly because I didn't think of using a resistor and I'm not 100% sure on what size etc I would need to achieve it.

I have an emergency stop button that is detachable, as the machine will be portable, which is cutting the power feed to the stepper boards however I want a 12v panel led to be lit when the emergency stop button is connected and off so that there is a visual indication that the system is ready to use. I thought I could use the relay to activate because of the voltage difference and not being able to wire it in parallel.

Luke
 

ronsimpson

Well-Known Member
Most Helpful Member
I have a 24v dc supply
i have a step down transformer to convert the 24v to 12v.
We might not be using the same dictionary.
Transformer is used with AC voltage. It will not function with DC voltage.
You might have a "power supply" that inputs 24V DC and output 12V DC. (not a transformer)
Can you send pictures?
--------------------
I understand you have 24V but one device needs 12V. Do you know how much power or current (amps) this 12V device needs?
 

frosty101288

New Member
Sorry like I said I have a basic knowledge but not that extensive. what I have is apparently called a buck converter to take a 24v DC input and output a 12V DC.

I can upload some pictures of the project so far but its cables going everywhere so i will try and explain and hopefully that will help.

Basically I have the following:
1 x 24VDC Supply
1 x 12VCD Supply (Buck converter) feed from the 24VDC Supply
3 x Stepper Controllers (24VDC)
1 x Main Board (12VDC)
1 x Case Fan (12VDC)
3 x Panel LED's (12VDC)

I have an emergency stop button that is cutting the 24V power to the stepper controllers. One of the LEDS lights up and is wired in series with the fan so when you turn the fan on the LED comes on.

The other LEDS one comes on when the main power is turned on. The other one is then required to come on when the emergency stop button it plugged in and off. However obviously as I want to cut the 24VDC supply I cant wire the 12V LED in series like with the fan. As I have two supplies that's why I was thinking of the relay. Am I correct in thinking a SPDT Relay would would however I'm not sure on the type required as from looking at the types there are many different types. I was wondering if something like https://www.maplin.co.uk/p/15a240vac-spdt-miniature-relay-n07aw would work.
 

Frozenguy

Member
What model # led do you have?

The 12V fan and 12V LED in series with each other, is that powered by the 24V supply?
 

ronsimpson

Well-Known Member
Most Helpful Member
I think you want to use a relay because your switch is not what you want.
I am using a SPDT switch. "lamps" are 24 volt. We can probably make the 12V LEDs work on 24V by adding a resistor.
I bothers me that you are using a 12V LED and a 12V fan in series on 24V. That probably should not work.
Can you power the fan from 12V?
Is the diagram below right?
upload_2018-4-6_18-31-22.png
 

Mickster

Well-Known Member
Most Helpful Member
Hi Luke,
do you have a link to the E-stop switch you are using?
The inexpensive ones I have, use 2 separate circuits. One is NC and the other is NO when the switch is not pushed in.
When the switch is pushed in and locks, the NC side becomes open-circuit and the NO side becomes connected.

Also, can you tell us how the E-stop signal is handled by the controller?
i.e. "The controller requires a X Volt signal to be present/not present, on a particular pin, in order for an E-stop condition to be recognized."

As Frozenguy has hinted at, the "12V" LED that you already have will be able to work at 24V, but only reliably with an additional current-limiting resistor.

EDIT:
Cross-posted with ronsimpson - can you confirm whether ron's take on your set-up is correct, because the details from your posts so far are unclear.
 
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