SPDT Relay NC switching but NO not

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Mageek
 
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SPDT Relay NC switching but NO not

Post by Mageek »

Hello, I am taking my first shot at using a relay, and have been following the following arduino relay schematic:
http://www.arduino.cc/playground/upload ... relays.pdf
With the following relay from Sparkfun:
http://www.sparkfun.com/products/100

I hooked everything up with a test led on the relay end, powered by a 6 V battery pack. When I use the arduino to switch the relay, I hear the mechanical clicking, and the normally closed (NC) contact opens as expected. The normally open (NO), however, remains open.

I tried building a new circuit by replacing the arduino with another 6V battery pack to powering the relay switch, and I can still hear the relay clicking when I apply power. However, verification with a multimeter confirms that NC is closed before applying power, but is open afterwards, while NO is open both before and after. I tried another relay of the same kind and got the same results, and tried powering the relay with 12 V instead of 6 V. No luck.

I suppose I could build a device which switches something on and off using the NC pin, but the NO would be greatly preferred, due to power consumption of holding the switch open.

Thank you in advance for any help.

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Franklin97355
 
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Re: SPDT Relay NC switching but NO not

Post by Franklin97355 »

Which pins are measuring across?

Mageek
 
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Re: SPDT Relay NC switching but NO not

Post by Mageek »

There are 5 pins for the SPDT relay. Two are for the inductor, which trigger the switching. The remaining three I will define as:
A: input pin of switch
B: output pin of switch, which is closed when inductor is not receiving the necessary 5V
C: output pin of switch, which is open when the inductor is not receiving the necessary 5V

I am measuring over A - B to get the NC continuity, and over A - C to get the NO continuity.

I have verified that the two inductor pins have continuity, and it does not matter whether I switch the poles, the relay does not function as I expect (with regards to NO).

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Franklin97355
 
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Re: SPDT Relay NC switching but NO not

Post by Franklin97355 »

Sounds like you got a bad one.

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zener
 
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Re: SPDT Relay NC switching but NO not

Post by zener »

1) Verify at the relay that it is getting the voltage at the coil that you think it is. What is the voltage rating of the relay (coil voltage) and what voltage do you measure at the coil pins at the relay?

2) Relay contacts have minimum voltage and current specs. I do not know what relay you have and what the specs are. However, it is possible a multimeter might not meet the specs, depending on what the specs are. Assuming you have enough coil voltage, you might try switching an actual load.

ericgu
 
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Re: SPDT Relay NC switching but NO not

Post by ericgu »

Mageek wrote:Hello, I am taking my first shot at using a relay, and have been following the following arduino relay schematic:
http://www.arduino.cc/playground/upload ... relays.pdf
With the following relay from Sparkfun:
http://www.sparkfun.com/products/100

I hooked everything up with a test led on the relay end, powered by a 6 V battery pack. When I use the arduino to switch the relay, I hear the mechanical clicking, and the normally closed (NC) contact opens as expected. The normally open (NO), however, remains open.

I tried building a new circuit by replacing the arduino with another 6V battery pack to powering the relay switch, and I can still hear the relay clicking when I apply power. However, verification with a multimeter confirms that NC is closed before applying power, but is open afterwards, while NO is open both before and after. I tried another relay of the same kind and got the same results, and tried powering the relay with 12 V instead of 6 V. No luck.

I suppose I could build a device which switches something on and off using the NC pin, but the NO would be greatly preferred, due to power consumption of holding the switch open.

Thank you in advance for any help.
Sounds like you aren't pulling enough current throught the relay to fully engage the relay. If I recall my transistor basics (and it's entirely possible that I don't), that happens if you don't have enought base current and/or the beta of the transistor you're using is too low.

You can try reducing the value of the base resistor but you may find that the arduino can't provide enough current to fully engage the relay.

Another option would be to use a FET instead of a bipolar transistor.

eventhorizon
 
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Re: SPDT Relay NC switching but NO not

Post by eventhorizon »

Have you tried using the relay without the arduino? If under current/voltage is the problem, try using the relay and directly connect the coil to it's voltage rating (i.e. 5v, 6v, or 12v). If it still doesn't work, the relay might be broken. Also, some relay have 6 pins, but only use 5, the 6th pin has no connection and is only used to steady the relay when soldered onto a board. If you have it's datasheet that would help you a lot.

ericgu
 
Posts: 58
Joined: Mon Oct 18, 2010 11:24 pm

Re: SPDT Relay NC switching but NO not

Post by ericgu »

To expand a bit on what I said:

Another option is to use a darlington transistor. This is two transistors in a single case, and it has a higher beta and therefore takes less base current.

To proceed, I'd try building the relay part separate from the microcontroller. Try various values of resistors and see if you can find one that switches the relay the way that you expect. If you have a good multimeter I'd try measuring the current through the relay to see if you are getting what the relay specifies. Then I'd measure the base current to see if the arduino can supply that.

Mageek
 
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Re: SPDT Relay NC switching but NO not

Post by Mageek »

Thank you for your replies.

I have isolated the relay from the arduino circuit, and tested it with a 6 V DC source as the switching voltage.

According to the data sheet, minimum switching load for the relay should be 10ma 5V DC. The "coil rated voltage" is 12 VDC. To be safe, I hooked up 12 V to the inductor to see if it would work, but I only got the same result, and the relay got really hot.

I tried switching an actual load by attaching a large resistor and an led, which worked when it was connected in series with a 6 V source, but did not when connected with the relay and the same source.

I assumed that "minimum switching load" means that I require 5 V to switch it. Is this incorrect? Does "coil rated voltage" define how much voltage I need to trigger the relay switching? According to the Sparkfun page: "This relay's coil is rated up to 12V, with a minimum switching voltage of 5V", which leads me to believe that the coil can take up to 12 V before it overheats or breaks otherwise. It is possible that "minumum switching voltage" refers to the voltage on the load end.

eventhorizon
 
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Re: SPDT Relay NC switching but NO not

Post by eventhorizon »

I don't understand how a relay won't work even if you are using the correct voltage ratings. The way I understand relays is that, NC's are open when the coil is activated, and the NO's are closed when the coil is activated. I tried under powering my 6 volt relay here with 4 volts, amazingly it works, it's just not as "snappy" as when you use 6 volts on it. But it works still. I also tested it with my mega8 directly connecting the coil to a port, again it works. All the relay needs to do is attract a small contact inside with like 1mm spacing, so in my case under powering isn't really the issue here. I suggest you open one up, and look manually if the contacts are doing what they're supposed to do. As your title states NC works, but NO doesn't (which is weird). Also, try using smaller relays, the 5 volt ones are not that bad for motors.

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zener
 
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Re: SPDT Relay NC switching but NO not

Post by zener »

If you hook 12V to the coil of a 12V relay it should not get "really hot". It should not get even warm. I think you are possibly hooking it up wrong. Can you provide the PN of this relay?

Mageek
 
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Joined: Thu Jul 15, 2010 3:13 pm

Re: SPDT Relay NC switching but NO not

Post by Mageek »

Problem Solved!

I followed your suggestion and broke open the top. Its neat to see the insides.

With the top off I could see the switching mechanism, and verified it was making contact every time I applied power. I verified that the leads were coming together, then checked the pins. No contact. I double checked continuity to the central contact, and found that I had foolishly mistaken the NC pin for the load input pin, and vice versa. Problem solved.

The image in the data sheet (http://www.sparkfun.com/datasheets/Comp ... Z%20EN.pdf) is incorrect, and leads one to believe that the pin on its own side is the input pin (top right of schematic image), which is not true. That pin on its own side is the NC pin.

Thank you too all who took the time to help me out.

Mageek
 
Posts: 5
Joined: Thu Jul 15, 2010 3:13 pm

Re: SPDT Relay NC switching but NO not

Post by Mageek »

According to Sparkfun:

"We had a bit of a mix-up with an order and ended up with these Omron relays. The relay is a SPDT sealed style relay with a 5V coil. It can switch up to 5A @ 250VAC, so these can be used for quite a bit of applications. Get them while we still have some!"

Oh well. I guess sometimes you just end up with something other than what you expected.

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