Hey Everyone. I apologize up front, this is a Raspberry Pi question. I know this board is primarily about Arduino, but I know MANY of the people here have cross tech experience in this area.
The RPI4B detail is important because I only have 3.3 (3.1) volts to work with in a GPIO output.
Here's the setup
Pump to move liquid. 230v AC @50hz and rated at 13 amps continuous draw. The pumps are rated for continuous duty, so the mechanism needs to be able to handle long runtimes.
We are working with an industrialized Raspberry PI 4B and we need to trigger a relay that can handle these kinds of volts / amps. My experience in the past says this isnt as easy as it sounds. There's MANY 3-240v solid state relays, just doing a search, but the mA draw will burn a GPIO right up.
I've sucessfully prototyped the whole solution using a transistor to trigger a higher power relay, that turns the pump on. This works just fine, but it's not industrial, or hardened at all?
Can someone recommend either a relay trigger board, or component, or a relay capable out of the box of doing what I want? Even a MOSFET that could directly power the pump would be fine. Just looking for an elegant solution to this problem. Ultimatly we'll be running 8 pumps, so it has to scale sideways also.
Any suggestions from the people out there WAY smarter than me?
How many GPIO pins will burn up when feeding a single LED? All SSR that have an input voltage of 3 volts or more, already have a resistor in series with their LED. With a heat sink, single SSR will do the job for you. If you want "industrial rated", buy from a recognized distributor and a known brand name.
I have burned a few GPIO's up on relay switching, but I think I mis-spoke, that was switching a traditional relay. Switching traditional relays with a switch voltage of 3(ish) volts, and can support 230 / 20 on the other side, aren't easy to find, usually draw to many mA or don't actually switch at 3v even though they're are rated that low. Especially when you start to account for voltage drop across the GPIO pins of 0v1 or 0v2.
I have not found a single SSR that can be switched on actual 3 volts. Can you suggest one?
This one (or similar) should work. These "industrial style" SSRs are easy to wire-up with screw terminals and easy to mount, but they are bulky.
That should work fine. You shouldn't need any special "electrical hardening" as long as the Raspberry Pi is "protected". Environmental & physical protection is a different story.
A regular bipolar transistor is better than a MOSFET because a transistor turns fully-on with less than 1V. MOSFETs usually need at least 5V with most needing more.
Thats a great suggestion. These are exactly the type I've been looking at all morning, but the trigger voltage was always above 4v sometimes as much as 7v. This one appears to be in the 2.4v range, which is fantastic.
I found the issue with transistors to be the current draws on them. I was burning them up trying to flip what I thought were standard latching type relays in this same volt / amp range. It was a while back that I was messing with these though, so my memory on the "why" isn't relevant anymore without rebuilding the circut.
Hey Jim! Glad you jumped in here. Can you give me a little more details on this? I looked up that IC, and I haven't used it before.
The idea would be to host the IC on a daughter board, and use the IC gates to flip 5v high and low, and just drive regular old 5v trigger relays? Do you happen to have a schematic laying around that would show me how to utilize that?
It adds a bit of complexity but a high-power shift register would do the job nicely. It can control 8 relays out the box while only using 2 or 3 pins and best of all, you can daisy-chain them to get more outputs while still only requiring the same number of pins.
The TPIC595 is a popular device. Handles up to 150mA @ 50V! I don't know of any boards with them that come ready to use, but if you look around I'm sure you can find one.
The datasheet mentions it's suitable for switching "non-saturated inductive loads".
I wonder what that means? I've never seen "non-saturated" mentioned when it comes to inductive loads. OP is switching a 13A pump. That's inductive, but "saturated" or "non-saturated"??
@techypants you'll need a heat sink. The relay linked above has a 1.6V drop so 13A*1.6V = 21W dissipation in the SSR.
In order to increase reliability, I decided it would be best to only connect 4 relays to a single 244. That way, if each relay should draw 25mA the maximum current used will only be half of the maximum rating for the IC.
So you will need two of the circuits shown below to control 8 relays. Actually the wiring will be much easier since all the inputs are on one side of the IC and and all the outputs on the opposite side.
