High Current, 100 Amp DC SSR- How do I pull ground?

This is my first post on this forum. I am a complete newbie to this world of micro controllers but I find it fascinating. I have zero coding experience, I am an engineer and I am willing to learn. I just need someone to help point me in the right direction.

I have scoured the internet to find a high current +50 amp DC relay that I can control with an Argon, Boron or Xeon. I came across this nifty device, it is a SSR in the form factor of an ANL fuse that is capable of 100 amps. In order to close the circuit you need to pull ground on the control wire.

For the life of me I cannot figure out how to do this. Is it possible? If so, what coding is required and is there any additional hardware needed.

Thank you in advance for your help.

The datasheet says that to activate the SSR, you pull the control pin low (ground) and to turn off, you leave the pin floating. The datasheet says you have to sink 21mA @ 12V and up to 24mA @ 15V. To be safe, I wouldn’t connect to a GPIO directly. I think you could use a MOSFET between control and ground. I’m not sure how to leave the control pin connected to the MOSFET purposefully floating though… You could certainly try it though if you have a spare lying around. The below circuit may work but you may have issues with the floating part (due to leakages, pin biasing, etc.)

For example:

image

To activate your SSR, you would drive your GPIO low, which in turn activates the MOSFET and connects GND to the SSR control pin. When you want to turn the SSR off, drive the GPIO high. You can add a pull-up resistor to the GPIO if you want to ensure the SSR is off during startup of the microcontroller.

Example to drive the GPIO (uses the D7 pin):

pinMode(D7, OUTPUT);  //Configures the GPIO pins as an output.
digitalWrite(D7, HIGH); //Turns the GPIO high (and SSR off).
digitalWrite(D7, LOW);  //Turns the GPIO low (and SSR on).

There should have been no need to scour the internet for this. A quick hop to Digi-key, or Mouser should have given you over a few hundred options to pick from. If your willing to say, what are you trying to control?
I ask because you have to really know the details of things when using a SSR or Fet to control something with certain loads. It might say it will handle 100A continually, (Ya right) 6 little smt pins are NOT going to handle 100A continually. Moreover if your controlling a motor, the inductive kick will fry them clean off the board. Let alone the startup inrush current will also likely melt them off as well.

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I have various applications I need this for. Motors, winch, battery disconnect, etc. I wanted something really small that can handle the load. I have tested the SSR that I mentioned in my first post and it will handle the load. It is one tough SSR.

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Thank you for your response. I will get myself a MOSFET and try that out. I did not consider that route.

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If you are unfamiliar, there are numerous types of MOSFETs that you might want to read up on. The one I depicted is an N-channel Enhancement-type MOSFET.

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Yep I read up on them, I am sure there are a million of them out there but I think I can figure it out.

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Hey, welcome to the forum! I’m with you on finding this world of microcontrollers fascinating.
I’m an engineer too that along the years started coding. But watch out, this is a one-way ticket, I can’t stop now!
There’s plenty of people around here willing to help, so keep on asking questions.
(just wanted to say hi and encourage you to post your progress on your projects).
There is a bunch of project to get inspired on here and here. There’s also the Hackster site in case you need inspiration!
Good luck,
Gustavo.

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Hi @dsb33

I just wanted to mention a few things about that SSR. By way of background, I have been a practicing electrical engineer for many, many years now.

  1. Nothing about the physical design of that part says to me that it can handle 100A continuous. It is just too lightly built.

  2. Replacing an actual fuse with this gizmo is a very bad idea. You can place it in series after the fuse but for safety don’t replace the fuse.

  3. The single control pin on this device relative to the ground or negative supply rail of the 12V system is very limiting in how you can use it. You are forced to connect the controller’s ground to the system ground.

  4. The device datasheet says it allows for 20V max between control and input. Automotive power is notorious for very high voltage spikes (google for “load dump”) and this specification is 3-4 times too low.

Do yourself a big favor and avoid headaches by buying a Crydom or other similar brand industrial quality SSR rated for at least 20% more than actual current (including inrush or locked-rotor current if you are controlling a motor). This will be a much larger and robust device.

Read the datasheet for your SSR about how to heatsink it since at 100A continuous, even a small on-resistance can generate a lot of watts.

A real industrial SSR will have two pins that you control which are optically isolated from the load so no grounds need to be tied together.

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