Hoping for some advice if I can simutaneously drive 10 SSR Relays (SSR-40DA-H pdf, SSR-40DA-H Description, SSR-40DA-H Datasheet, SSR-40DA-H view ::: ALLDATASHEET :::) with an ESP32. Dev Kit C board. I'm trying to control 10 exhaust fans in a greenhouse. The input voltage on the SSR is 3-32VDC and the ESP32 puts out 3.3vDC so no problem. My questions is most of the time the relays will be activated and on. Can I pull 3.3v on 10 GIO pio pins from the ESP32 continously? I'm powering the ESP32 with a 5vdc power supply.
I'm a novice at the ESP32/Arduino stuff and do not completely understand how to read the datasheets. The SSR says it draws 7.5mA / 12VDC. So I assume if 10 of the SSR are activated it draws 75mA / 12 VDC? How does that 12 VDC extrapolate to the ESP32 power at 3.3vdc? Any direction would be appreciated. Also, so no one is worried about me eloctrocuting myself the SSR are just providing the input signal to driving large mechanical contactors, so no high voltage in this setup. Thanks for any advice!
Probably a little better than a quarter of the 75ma. The best way to know is to measure it. Hook up one SSR to the power source, put the meter (in current measuring mode) in series with the SSR and see what current it draws at 3.3V.
Hi,
You would be best to drive a MOSFET with the ESP32 and the MOSFET controls the SSR input.
That way you will not be putting stress on the ESP32 and you can use 12V to switch the SSR reliably.
I find anything over 5V is a good SSR input voltage, 3V3 can produce inconsistent results.
What is the exact model number of your SSR?
What are the specs of your fans?
The SSR is FOTEK SSR-40 DA 3-32VDC input and 24-380VAC output. I'm not sure of the specs on the fans they are large 220v industrial fans, I'm just driving the mechanical contactor and the electricians hook the fans up to the mechanical contactor. Any chance you have an example or specific MOSFET part number you would recommend and I can try and firgure that out? Thank you!
Thanks Tom, I have my reading cut out for me. The load will be irrelevant because the the SSR is behind a mechanical contactor. I'm an amateur at electronics but I have built an automated brewery control panel and a few other cool items. I've just never driven so many relays attached to a single ESP32. As long as I can fire the relays everything downstream is handled no prioblem. I'll start searching into on incorporating a MOSFET to get the 3.3v up to 5v like you suggested. Thanks again for pointing me in the right direction.
Not from 3.3V. The threshold voltage for the IRF520 is 4V, so it won't consistently work... the specs say you may need to drive it with up to 4V. The other option is to drive it via another driver... buy the right mosfet and keep it simple.
I figure the circuit in the upper left is the easiest to implement and understand:
when the Base goes HIGH then the "─" terminal is taken LOW and the SSR turns On.
Same thing with a mosfet, except you can dump the base resistor and it creates less heat... Either will work, but transistor do not have a 'low' on resistance in the mili-ohm range like a mosfet.
If your analysis is correct, then the worlds automakers have it all wrong since billions of these are used in cars, not transistors.
You can think of them the same was as a transistor, at least as a switch.
The advantages are a low on resistance and a high input impedance... There is no need for a large current flow from the gate to the source like there is from the base to the emitter.
They were created to allow switching with low current draws and a low 'on' resistance to be driven by logic circuits in many cases.
You'll find they are far superior for this than a transistor. Don't be afraid of them, they are much easier to work with.
Same thing with a mosfet, except you can dump the base resistor and it creates less heat... Either will work, but transistor do not have a 'low' on resistance in the mili-ohm range like a mosfet.
So many straw men.
("Less heat". . . Good Gravy.)
It seems to me the transistorizing is over-complicating the matter. If the datasheet is reliable, the ESP32 should be fine without (est. 1mA).
The datasheet says 40mA for source/pin and 29mA sink/pin. Max of 1200mA...
The datasheet for the SSR-40DA states trigger is 7.5mA/12V...
The problem is the esp32 is a 3.3V system.. You can't source a high enough voltage to turn on the ssr from the device, the only other option is to 'sink' it, but you will exceed the devices voltage rating.
The esp32 does trigger the SSR with a 3.3v pin. My concern is that I need to drive 10 SSR's at the same time (from a single esp32) and they will most often be on. So the current draw maintaining 10 of the SSR's in an active state is what I was concerned with. After researching all of the advice it seems the IRF520 Mos Module would be perfect (https://www.amazon.com/gp/product/B07F7SV84V/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1)
I have a regulated 12vdc power source in my control panel. My plan is to fire off the mos module with the esp32 and pass 12vdc onto the SSR. If I'm understanding it correctly, this way no chance of overloading the esp32 it's just firing the mos module. For curiosity I'mm probably test it with and without the mos module to see if an esp32 can hold up. Thank you for all of the advice.
Should the SSR modules need >3.3volt to work, then two TPIC6B595 shift registers could be a better solution than a bunch of mosfet modules. Saves on ESP pins too.
Leo..