Can a 3V relay with 70mA draw be used with the relay port for lights?

I know electrical mechanical relays are not OK for motors, but can they be used for a light with the relay port? I can’t see if the RoboRio 2 can drive 3V, 70mA relay coils, but I imagine it must. Is it legal to light lights this way?

As far as legality, lights are not actuators and therefore fall under custom circuits. So you can control them just about any way you want.

Here’s the roboRIO datasheet.

You can see that the relay outputs are on the 5V bus, which can provide a total of 1 Amp (across the whole bus).

Thanks! This is what I was hoping to hear.

Oh-wait a minute…the Relay current max listed is only 7.5 mA , so this might actually be a problem even for my small 3V relay with a maximum 0.36W activation power. I see now why MOSFET solid-state relays are recommended.

Are you sure about this? That is a ridiculously small amount of current to switch with a relay. Most GPIO ports on any microcontroller could source that. I suspect you are looking at the holding current for keeping the relay closed?

Got specs?

1 Like

Yes, I’m absolutely sure that my tiny little relay needs 0.06 A to stay closed. I just measured it with the student this morning. As far as electromagnetic coils go this is not a lot but it is nearly 10 times the 7.5 mA on the Robo Rio spec sheet from national instruments.

Right, those outputs are not meant to drive relay coils directly. They’re meant for controlling things like the original IFI Spike, or one of the little opto-isolated relay boards that can be had for very cheap (look for “relay module for arduino” or similar). Trigger current on those is just a few mA.

This topic was automatically closed 365 days after the last reply. New replies are no longer allowed.