Relay driver for USB 6210

[knowlittle]

I need to run 24V DC 8W solenoid from 5V digital out ports. Digital Out can source 18 mA max. I need a driver in between. Does NI sell such a board? I am not skilled enough to fab a MOSFET circuit. Thank you.

[soonxaf · Accepted solution]

Assuming you have a 24 VDC power source, a USB-6525 has 8 channels of Solid State Relays (SSRs) that can switch +- 60VDC. This unit can only handle 500mA per channel though, so you would need to share channels and assume the current would divide evenly.

A less expensive solution if you feel up to it would be to purchase a SSR so you can use your existing Digital Out. If you choose this option, you might look to Crydom as a supplier, and consider using a Flywheel Diode if the SSR needs it.

A third option would be to find a Reed Relay that can handle the 24V power requirements. Typically you can switch a Reed Relay with a digital out.

[knowlittle]

Thank you for the advice. Option 1 seems to be the simplest. Since I have 2 more options to choose from, I will see which fits the project schedule best. 

[RavensFan]

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@soonxaf wrote: If you choose this option, you might look to Crydom as a supplier, and consider using a Flywheel Diode if the SSR needs it.

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That is a "flyback" diode.

[knowlittle]

Thank you for the clarification.

The suggested board USB-6525 is not going to work. I need both analog input and digital output. USB-6525 does not have analog input. So I need to build a MOSFET circuit that will go between my digital out and 24VDC 8W solenoid.

My output is from USB-6210 Digital Out Port 1 Line 1, 16mA max. I plan to do the following:

1. Select a logic level N-channel enhancement FET.

2. Digital output connects to Gate. Do I need a resistor there?

3. Source is Grounded.

4. Solenoid goes between +24VDC and Drain.

5. Connect grounds together; USB-6210 Digital Ground, 24VDC power supply ground, and FET Source.

6. I will use a flywheel/flyback diode across the solenoid. 50V 1A.

[AnalogKid2DigitalMan]

I'd use a diode rated at several hundred volts just to be safe. You'd be surprised at how much voltage can be generated- easiest way is to connect and oscilloscope across the coil without a diode present.

-AK2DM

[soonxaf]

I won't tell you to not build a FET circuit, however I would choose to use a SSR. One like this might work for your application.

The diode is used to suppress the voltage spike caused by opening the circuit of the inductor (solenoid winding), which can be quite large, but with basically no current. I generally use one with a rating of at least 1 kV, something like this.

[knowlittle]

Thank you for the suggestion. Since the board was powered by USB, digital output could even turn on SSR. Solution was to connect an external 5V DC to +5V and DGND. This enabled digital out to turn on SSR.