Current through Control side of 3052 SSR board

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aro
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Current through Control side of 3052 SSR board

Postby aro » Mon Nov 12, 2012 11:49 am

Hi,

I'm working to setup an array of 10 relays (using the Phidget 3052 board) that are controlled from a digital output device (Arduino). The control circuit goes from a digital output pin of the arduino to the + side of the relay control side, and then the - side of the relay control side goes back to the GND of the arduino. However, this Arduino board only has two ground pins. As these pins have a max of 40mA, the current would need to be less than 8mA per ground wire if I split the 10 wires among the two grounds.

Is there a way to find out what the current would be through the relay (control side) or how to determine that it is less than 8mA?

Thanks,
Ayo

aro
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Re: Current through Control side of 3052 SSR board

Postby aro » Mon Nov 12, 2012 12:20 pm

Actually there are three ground pins, so it would need to be 10mA or less if I split the grounds among these three....

erik
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Re: Current through Control side of 3052 SSR board

Postby erik » Tue Nov 13, 2012 9:55 am

The control pin is connected to an LED and a resistor in series. The forward voltage on the LED is typically 1.2V and the resistor is 392 Ohms. So depending on what voltage your Arduino digital output is switching,

Current = (V - 1.2)/392

If it's a 5V digital output, the current will be 9.6mA, and if its a 3.3V digital output, the current will be 5.4mA.

Interestingly enough, we should probably have this included on our spec sheet for the device. I'll see what I can do to get it added there.

Additionally, I think you are misunderstanding the 40mA limit that Arduino's have on the pins. This applies to each digital output, and not the ground pins. So each digital output will be able to source or sink 40mA.

In short, you don't even need to worry about the current going through the ground pins.

aro
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Re: Current through Control side of 3052 SSR board

Postby aro » Tue Nov 13, 2012 11:09 am

Great, thanks for your help.


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