Kill Power To Motor Controller With A Small Relay

[rs14smith]

Hi,

I have a 24v Sabertooth 2X25 motor controller that is capable of supplying up to 25A to 2x24v motors. I am wanting to install a relay that will turn the motor controller on and off, and the relay would be controlled by a microprocessor that will supply it 5v when the relay needs to activate.

Currently, the space for this project is limited, and I would like to use the smallest relay (in size) possible for my application, but I'm not sure what all is out there that I can use. I've seen solid state relays, but I was wondering if anything smaller might exist?

 

[Electronics4you]

If space is an issue, why not use a PMOS load switch?
It requires only a few components to be controlled directly from the MCU, but may need a heat sink in your 25 A case

 

[rs14smith]

If space is an issue, why not use a PMOS load switch?
It requires only a few components to be controlled directly from the MCU, but may need a heat sink in your 25 A case

Well I've always had issues with isolating the controlling circuit from the circuit I'm trying to switch ON/OFF with the MOS. I'm sure it's probably something I'm doing wrong, but I'd like for the MCU to not be apart of the same circuit as the motor controller, as I've fried MCU's because the load or whatever was too high. Again, I'm sure I'm probably doing something wrong, but solid states, and other types of relays seem a bit easier to work with for me.

 

[Electronics4you]

Well I've always had issues with isolating the controlling circuit from the circuit I'm trying to switch ON/OFF with the MOS

You can always use optocouplers to isolate the controller circuit from the load circuit


I don't know your relay size requirements, but here are a few suggestions:

Regular relay
SSR (requires heatsink)
SSR (including heatsink + 4VDC control voltage)

 

[dr pepper]

Can you switch the 240v side, aassuming ts mains powered, 25a at 24v would only be 3a or so at mains voltages.

 

[rs14smith]

You can always use optocouplers to isolate the controller circuit from the load circuit


I don't know your relay size requirements, but here are a few suggestions:
SSR (requires heatsink)
SSR (including heatsink + 4VDC control voltage)

I never seen a relay like the last 2 you linked to, and those look really small and probably perfect for what I need. Is there some type of mount they are suppose to sit in so you can mount it to something, or how do you normally install these types of relays?

SSR (requires heatsink)
SSR (including heatsink + 4VDC control voltage)

I also see the output side of the relay is for AC circuits, but my load circuit is DC based, so is that going to be an issue?

 

[Electronics4you]

They are all through-hole components and can be soldered to a PCB like any other component. The second one though must be mounted to a heatsink as well, and must be located close to the PCB edge for that reason (if the heatsink is not going to sit on the board itself). Just use some thermal adhesive to stick it to the heatsink.

The third option just requires a good air flow, so not in an enclosure without proper ventilation (see datasheet for more properties).


EDIT: Regarding the AC/DC issue, the technology is not mentioned in details the datasheet, but in case it is a TRIAC, it will not work. However, the circuit diagram shows SCR's.

 

[Wade Hassler]

Those are both AC-only relays. There are some DC units on that same Farnell search, but some sticker-shock comes with them: a 40A/100VDC part is £53.75 / singles.

 

[KMoffett]

From the 2x25's manual:

"Emergency Stop:
In Packetized Serial mode, the S2 input is configured as an active-low emergency stop. It is pulled high internally, so if this feature isn’t needed,
it can be ignored. If an emergency stop is desired, all the S2 inputs can be tied together. Pulling the S2 input low will cause the driver to
shut down. This should be tied to an emergency stop button if used in a device that could endanger humans."

I didn't see it, but I assume that your µC just sends it a command to restart the controller.

 

[rs14smith]

From the 2x25's manual:

"Emergency Stop:
In Packetized Serial mode, the S2 input is configured as an active-low emergency stop. It is pulled high internally, so if this feature isn’t needed,
it can be ignored. If an emergency stop is desired, all the S2 inputs can be tied together. Pulling the S2 input low will cause the driver to
shut down. This should be tied to an emergency stop button if used in a device that could endanger humans."

I didn't see it, but I assume that your µC just sends it a command to restart the controller.

Oh wow! How did I miss that! I will review the manual right fast and take a look, as if that's the case, this problem just became easily solvable.

Edit: However, I am not using my motor controller in Packetized serial mode, so I'm not sure if that will be an issue or not.

 

[rs14smith]

Late tonight I tested disconnecting power to the radio receiver, and as a result, the sabertooth instantly stopped my motors. This is exactly what I need. So now I plan to let the micro processor control the power going to the radio receiver at all times, and mission accomplished!