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Need help with a circuit

ChickenNuggets

Sep 30, 2016
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I have two circuits, Circuit A that runs at 5 volts and Circuit B that runs at 48 volts. It is basically an arduino that is connected to a relay connected to power supply connected to fans. However when Circuit A turns off, Circuit B (the fans) are still running. I know that it is not the code of the arduino, and I do not think that it is the arduino is the problem at all.
How do I make it so when Circuit A fails, Circuit B turns off as well, so it is just not running "out of control" per se.
 

Harald Kapp

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A schematic could be helpful ;)
How is the aduino controlling the relay?
What does "when Circuit A fails" mean? In which way does the circuit fail, how does the failure show on the output controlling the relay?
 

ChickenNuggets

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I don't have one. The arduino is controlling the relay by having it be on for 3 seconds then off for 2 seconds. When I unplug the battery to the arduino the fans are still running. I need to make it so when the arduino gets turned off or fails, the fans stop too.
 

CDRIVE

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If the fan is still running when the arduino is powered down then you have the fans connected to the normally (NC) closed relay contacts.

Chris
 

HellasTechn

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That is correct Chris.

I don't have one. The arduino is controlling the relay by having it be on for 3 seconds then off for 2 seconds. When I unplug the battery to the arduino the fans are still running. I need to make it so when the arduino gets turned off or fails, the fans stop too.

You need to change your fan wiring to the Normally open contacts and then alter your arduino code so that it will disengage the relay when it was supposed to "engage" it and to "engage" it when it was supposed to be "disengaged"

In other words make the output of arduino controlling the relay go high when it would be low and low when it would be high.

does that make sense ?
 

CDRIVE

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I don't have one. The arduino is controlling the relay by having it be on for 3 seconds then off for 2 seconds. When I unplug the battery to the arduino the fans are still running. I need to make it so when the arduino gets turned off or fails, the fans stop too.
If it is cycling correctly ON - OFF while the Arduino is running then it's unlikely that you need to change your code. Not from the description above, that is. Just change your wiring to the Normally Open (N/O) contacts of the relay.

Chris

Edit: I just noted that your ON - OFF times aren't symmetrical. If the timing sequence is now correct then Constantine is correct. You'll have to change your code too.
 
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HellasTechn

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Edit: I just noted that your ON - OFF times aren't symmetrical. If the timing sequence is now correct then Constantine is correct. You'll have to change your code too.

That is why i suggested him to alter the code :) to keep timing !
 

CDRIVE

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Yes, that's why I corrected myself. "CYA"! :p

Chris
 

BobK

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Well, it doesn't have to be the use of NC contacts. It could be that whatever circuit is driving the relay needs to be either pulled up or down to open the relay.

Bob
 

CDRIVE

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When I unplug the battery to the arduino the fans are still running. I need to make it so when the arduino gets turned off or fails, the fans stop too.

Did you miss this?

Chris
 
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