Trouble with a SSR - Page 1
Forum section: electronics / beginners

author: Bootalito
author_rank: Unknown
timestamp: April 22, 2018, 03:30:05 pm
content: I'm having some admittedly embarrassing trouble with a SSR I'm using for a reflow oven with an ESP8266, MAX31856 I'm slapping together. No matter what I do, the SSR is not passing currentHere is a schematic of the SSR from BigClive:The SSR is on the low side of the circuit: 120+ straight from the wall -> Resistive elements -> SSR terminal 1-> SSR terminal 2 -> 120V- straight back to the wall. I've verified that when I connect the wires connected to the two SSR terminals manually (and safety), power is passed through, the elements get hot, and everything is fine. So its just the SSR NOT triggering. I've tried 4 different SSRs albeit from the same AliExpress order. I've tried swapping the AC leads (not that it should matter), and I've tried putting the SSR on the high side (120+ -> SSR terminal 1-> SSR terminal 2 -> Resistive elements ->Ground.).I'm using PWM from an ESP8266. Default setting from the Arduino toolchain is 10bit at 1Khz frequency. But I've also tried 10hz frequency. I've also of course just set the output on (PWM 100% duty cycle). I've verified the PWM is functioning with an oscope. The SSR also has an in-built LED that is dimming with response to my inputs, so I know its getting a signal. I haven't tried just giving it input side off the SSR like 10V or 24V from a bench power supply. But it shouldn't matter....?All I can think right now is that I got a bad batch of SSRs from AliExpress. I mean...its not complicated, this should just work. What am I missing? Is there something I'm missing.

author: picandmix
author_rank: Frequent Contributor
timestamp: April 22, 2018, 04:11:18 pm
content: Hi,Can you specify the type of SSR , one like this ? What is the SSR current rating and what is the current /wattage of your heater ?https://www.aliexpress.com/store/product/solid-state-relay-SSR-10DA-10A-actually-3-32V-DC-TO-24-380V-AC-SSR-10DA/2021064_32606149138.html?spm=2114.12010612.0.0.2bbe24a58CUGMjTo Test , best to apply DC + 5v direct to the input side, that should trigger the output .When using such 'unbranded' SSR is best you overrate by a large margin, eg 100% and if passing heavy current you need a solid heat sink.

author: wraper
author_rank: Unknown
timestamp: April 22, 2018, 04:18:15 pm
content: Quote from: Bootalito on April 22, 2018, 03:30:05 pmThat 99% of the the cheap SSRs on aliexpress and ebay are counterfeits and outright dangerous.QuoteSSRs are not supposed to be PWMed. Once fired, generally they cannot switch OFF before AC voltage goes through zero cross as they are triac based. Most of them even intentionally prevent random turn ON and will switch ON only when voltage on it's power terminals is close to zero crossing.http://www.crydom.com/en/tech/newsletters/solid%20statements%20-%20ssrs%20switching%20types.pdfAlso, I think ESP8266 will output only 3.3V which is not enough for many SSR, not to say it likely cannot output enough current and voltage will drop even more.

author: Bootalito
author_rank: Unknown
timestamp: April 22, 2018, 05:00:50 pm
content: I'm using the same ssr that bigclivedotcom used in his video. The circuit does have zero Crossing detection and like all Triacs won't actually turn off until the sine wave crosses 0v. However if I use pwm with a frequency of 10hz, or even 1hz, this is good enough for analog heating control.Ive applied 3.3v to the input and its just 2 leds in parellel and bigclive measured only 2ma. So a direct uC output should be fine.Either way I'm going to try a higher voltage(from a bench power supply) as this is the most likely culprit

author: wraper
author_rank: Unknown
timestamp: April 22, 2018, 06:43:30 pm
content: You are thinking it's the same SSR which big clive tested, but most likely it's not. There are tons of internally different counterfeits made by many different people. Not to say that SSR tested by big clive was dangerous counterfeit crap as well, dunno what were you thinking when buying them. 2mA is not enough to activate optocoupler in most cases, more like 10+ma is required.

author: Bootalito
author_rank: Unknown
timestamp: April 22, 2018, 07:26:31 pm
content: It was the voltage. SSR triggered between 4.6 and 4.8V. Not the 3V listed on the SSR...

author: wraper
author_rank: Unknown
timestamp: April 22, 2018, 08:18:30 pm
content: Quote from: Bootalito on April 22, 2018, 07:26:31 pmYet another reason to open the disput against seller for selling counterfeits. In any case, it is almost guaranteed to have too weak triac inside which is unsuitable for reflow oven powered at 120V. Eventually it may fail short and fry the board(s) you will be reflowing.

author: Bootalito
author_rank: Unknown
timestamp: April 22, 2018, 08:21:45 pm
content: Quote from: wraper on April 22, 2018, 08:18:30 pmYup. I'm going to use 2 ssrs, one for each of the elements. It's only 8amp total, so each ssr passing 4 amps should be fine

author: Kjelt
author_rank: Super Contributor
timestamp: April 22, 2018, 08:52:38 pm
content: Most SSRs are OKish but indeed buy one extra and open it up to see if it is crap (small isolation space, bad solderjoints, space between triac and heatsinkplate etc.)Better safe than sorry.