Switching a relay from ESP8266. Issue with voltage & current

Thread Starter

Jean Roux

Joined Feb 21, 2016
4
Hi, my first post, so be gentle please !

I want to switch my pool motor, 0.75Kw, I bought a 25A 220V solid state relay. Make Kudom - Model: KSI240D25-L, spec sheet here: https://www.rapidonline.com/pdf/546290_v1.pdf

It seams the most important info to take care of in the spec sheet is:
Max Input Current = 25mA.
Min Turn-On Voltage = 4VDC
Min Turn-Off Voltage = 1VDC

I drive it from digital pins from an ESP8266 12F, as the output is 3.3V, and the min turn-on for this relay is 4VDC. I use a level converter, 3.3v to 5v for this, like this one: https://www.sparkfun.com/products/12009

Although, if I do not connect the Kudon relay, it pushes out a nice 5v, when I connect it, the V drops to 2.65v, and thus does not switch the solid state on. My calculations using R=V/I with an incoming V's of 5V says I need to use a 200 Ohm resistor in parallel over the 5V and GND to the input of the Relay. I tried different R's, but without any luck.

Anybody with advice?
 

JWHassler

Joined Sep 25, 2013
306
Solid-state relays don't need a series (or parallel(?)) resistor: they have one internally to limit current.
Just hook the ESp8266/level-shifter to the relay
 

Thread Starter

Jean Roux

Joined Feb 21, 2016
4
...
Just hook the ESp8266/level-shifter to the relay
Thank you for your response, that is what I did, and the LED of it glows only very softly, but it does not do any switching....

I also changed the polarity of the incoming V to the relay, (obviously only works with V+ incoming to its +)
 
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JWHassler

Joined Sep 25, 2013
306
Thank you for your response, that is what I did, and the LED of it glows only very softly, but it does not do any switching....

I also changed the polarity of the incoming V to the relay, (obviously only works with V+ incoming to its +)
Aw, heck.
Does the relay switch when the 5V supply is directly connected to it? - with proper polarity, of course.
 

Thread Starter

Jean Roux

Joined Feb 21, 2016
4
Okay, just tested that, working, if applying 5v directly to the relay. Thus, I think it does not get enough power. I think I am going to through out the level shifter, and replace that with an opto coupler.
 

EM Fields

Joined Jun 8, 2016
583
Okay, just tested that, working, if applying 5v directly to the relay. Thus, I think it does not get enough power. I think I am going to through out the level shifter, and replace that with an opto coupler.
Since the input side of the relay is just an IRLED, all you have to do to turn it on with a 3.3 volt signal is this:

SSR switch 2.png
 
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