Energizing a relay using the expansion header

Muhammed

Hi,
I want to control an MT2 Relay that has this datasheet using the 50-pin expansion header on my Duet 2 board. The relay works fine when directly connected to a 3.3V output. However, when I try to control it using a heater output, such as exp.heater3 it does not get energized. Any ways to control it?

Thanks for your help.

infiniteloop

@Muhammed

I want to control an MT2 Relay that has this datasheet using the 50-pin expansion header on my Duet 2 board.

In the ”Coil Data” section of the data sheet, several versions (from ”High sensitive” to ”Standard”) are specified. The „Rated voltage“ values of all but the first two versions do not qualify for 3.3V, only the 150 and 200 mW versions act on 3V. The required wattage, however, exceeds the power of the expansion header by an order of magnitude - in short: won’t work.

Either you attach a suitable driver circuity, or you use one of the dedicated IO-pins of the Duet, e.g. for heaters or (PWM) fans.

Muhammed

@infiniteloop Yes, its a 400mW coil, sorry for not mentioning that.

I need to turn it on and off multiple times within a short period of time. Can I use the E1 heater output for coil pins?

Thanks

infiniteloop

@Muhammed

Can I use the E1 heater output for coil pins?

That depends. The E1 heater output switches to GND, but provides VIN on the other pin by default. So return to the data sheet and assure that your relay’s version has a matching ”Coil code”: ”24” for a VIN of 12V, ”25” for a VIN of 24V.

A note of caution from the documentation:

There are no on-board flyback diodes on these outputs, so if you connect a high-current inductive load, you must use an external flyback diode.

Muhammed

This post is deleted!

Muhammed

@infiniteloop said in Energizing a relay using the expansion header:

@Muhammed

Can I use the E1 heater output for coil pins?

That depends. The E1 heater output switches to GND, but provides VIN on the other pin by default. So return to the data sheet and assure that your relay’s version has a matching ”Coil code”: ”24” for a VIN of 12V, ”25” for a VIN of 24V.

A note of caution from the documentation:

There are no on-board flyback diodes on these outputs, so if you connect a high-current inductive load, you must use an external flyback diode.

I forgot for a second that the E1 heater output doesn't match the coil requirements for this relay, which operates at 5V. Are there any suitable pins on the board that I could use instead? If not, I'll need to consider using a different relay.

Thanks for the note as well.

infiniteloop

@Muhammed

Are there any suitable pins on the board that I could use instead?

Have a look at the Duet 2 WiFi and Ethernet Hardware Overview, especially the "Description of Connections". There, you'll find two options:

Always On Fans, FAN0, FAN1, FAN2
2 always-on fan connectors, 3 PWM-controlled fan connectors. Voltage selectable between VIN, 5V or external supply (all fans together). Total current draw not to exceed 1A. From board revision v1.02, PWM fan outputs are protected by on-board flyback diodes.
5V_PS
Used to turn on and off an external 12/24V supply

To check the available voltages, you might also want to refer to this diagram.

Just as a sidenote: It is always a good idea to check the extensive documentation. That's what I have to do in order to answer your request, so you can do it by yourself, too No offence intended, just a hint on how to access a wealth of information 'bout the Duet controller you own.

dc42

@Muhammed the PS_ON pin could be used for this purpose, but you must connect a flyback diode (the right way round!) in parallel with the relay coil, to protect the output from the coil back emf when you turn the relay off.

Alternatively, use a relay module instead of a bare a relay, then you should be able to drive from one of the pins on the expansion header.