SSR cooling - Page 1
Forum section: electronics / beginners

author: mushroom
author_rank: Regular Contributor
timestamp: September 16, 2022, 04:57:47 pm
content: Hi,I got a SSR : FOTEK SSR-50 DA (maybe fake...) ;https://datasheetspdf.com/pdf-file/789344/ANV/SSR-50DA/1There's no information about the triac junction(s) -> air thermal resistance, so I can't do the math.It is intended to drive a 97.7R pure resistive load using PWM (3D printer bed).  : more bang bang than PWM !Mains = 230V, PWM ratio = 100% and 1.6V drop -> I = (230-1.6) / 97.7 = 2.34 A. P = 1.6 * 2.34 = 3.74 W. Let's say 5 W.According to your experience, will it need a heatsink, if in direct fan airflow, and most of its socket in contact whith moving "cold" air (45x62mm = 28 cm²) ?Long ago, I've been driving 100-200W flood light bulbs (scene lights) with TO220 triacs, no heatsink, and never fried any !A TO220 being able to dissipate 0.5-1W with it's poor 1 cm² or so, it doesn't sound too bad to me...Of course I could experiment and measure temperature... if I had a 100R/230V load by hand. But I don't have such a load (hair driers and electric heaters are far too much, it wouldn't be realistic in the context).

author: Jackster
author_rank: Frequent Contributor
timestamp: September 16, 2022, 08:38:01 pm
content: I actually sell these in the UK. We advise our customers to go by the guide on the PDFRight at the bottom of the PDF,https://www.fotek.com.tw/en-gb/download/61Don't know if the numbers are there that you want but it should help.You can make use of metal enclosures for the 10A one if there is enough metal and ambient cooling.

author: mushroom
author_rank: Regular Contributor
timestamp: September 16, 2022, 08:54:31 pm
content: Perfect numbers : up to 10 amps with the fan.Thanks !(3D printed enclosure, wanted to avoid a heatsink, and the SMPSU cannot be used as a heatsink because the required M4 bolts would interfere with the transformer)

author: wraper
author_rank: Unknown
timestamp: September 16, 2022, 09:07:21 pm
content: If you bought it on ebay or aliexpress for $10, there is no chance it's a genuine thing. Usually you get something with a triac rated for a half of the current that SSR supposedly should be able to handle. For some stupid reason there seems to me 100 more times more fake FOTEK made than the real thing. Like it became a go to name how to call a counterfeit SSR.

author: mushroom
author_rank: Regular Contributor
timestamp: September 16, 2022, 09:34:18 pm
content: Yes, I watched some videos about these things before I ordered a few years ago ! Reason why I chose 50 amps hoping it will be good enough for 5A. Got it from eBay or Ali. Most likely fake, see poor quality markings and QR code. I knew it.I also have a couple genuine (but salvaged) 18A CRYDOM SSR's (EZ240D18) but they come with Faston connectors that don't really make them low profile. And some brand new Omron's, but 3 amps only ; not enough.

author: floobydust
author_rank: Super Contributor
timestamp: September 16, 2022, 10:13:17 pm
content: I use the ballpark value of 1W/A to estimate SSR heatsink/cooling requirements.Crydom does have advanced thermal design mounting the triac to the back slab, which is essential if you are in the say 50A club. One reason for why they are expensive.Fotek are ordinary, many counterfeits and some even dangerous with poor spacings/isolation.For 5A it should hold OK, vanilla TO-220 triac poorly mounted to the back slab.

author: james_s
author_rank: Super Contributor
timestamp: September 16, 2022, 10:20:36 pm
content: Quote from: mushroom on September 16, 2022, 09:34:18 pmI wouldn't bet on the 50A rated ones being any different internally than the 20A rated ones. Either way I don't know why people buy these stupid fake SSRs, it is only encouraging further counterfeiting. If you are willing to be a bit of a jerk though you can get them for free by putting in a refund claim of item not as described, ebay will refund you and you won't have to send it back. A used Crydom is infinitely better than a fake Fotek.

author: mushroom
author_rank: Regular Contributor
timestamp: September 16, 2022, 10:49:34 pm
content: Quote from: james_s on September 16, 2022, 10:20:36 pmbecause I didn't want to spend useless money ; it's just for a test rig. When I'm sure it works, the SSR that came with the modded printer will be reused. A OctoPrint / Marlin controller that emulates the RepRap 12864 display on the HDMI monitor, in a dispmanx overlay window. 99% funtionnal, time for real world testing. The counterfeit SSR will probably never be reused. For now, I can't take the printer apart : egg and chicken problem.(the 200mm Mitutoyo calipers are genuine, from an authorized reseller ; same for the Meanwell PSU even if it's crappy, with no PFC AFAIK)

author: thm_w
author_rank: Super Contributor
timestamp: September 16, 2022, 11:27:21 pm
content: Quote from: mushroom on September 16, 2022, 09:34:18 pmCould very carefully bend the fastons sideways.

author: mushroom
author_rank: Regular Contributor
timestamp: September 17, 2022, 01:05:52 am
content: Yes, you are right ; one of the two Crydom SSRs had its 4 Faston terminals at an angle when I salvaged it. Straightened them up later, maybe it can be seen on the picture. The terminals look like they are made to be bent (length = 0.5" insteed of 0.32" in the Mouser datasheet ; the difference being nearly equal to the distance to the package edge). They were salvaged from a 1.5 kW autoclave with two heaters. Old equipment (eighties), high quality, made in the USA, "A brand", not some noname crap : 100% sure bending the terminals is not some stupid trick on these ones, and that they were designed for.But... When possible, I avoid Fastons (except when reaaly needed : IEC sockets, loudspeakers, full bridge rectifiers, automotive, etc. and I always use dual crimp female terminals + slip-on rubberry boots). The problem with Fastons is they cannot be properly crimped to smaller gauge wires, and they are difficult to disconnect (most of the time). Great in automotive environment, a pain when tinkering with electronics. And Fastons are more expensive than ferrules.Knowing they are not made for inductive loads, I even used a Crydom anyway, with no snubber, crossing fingers, to turn on/off a 500VA transformer (audio amp). It did it for a couple years, several times every day, with no problem ! (didn't find a SSR intended for reactive loads - I was told it existed with zero crossing current, but didn't find any... BJT based ? MOSFET based ? IGBTs ? AFAIK, a triac cannot do that...).

author: Jackster
author_rank: Frequent Contributor
timestamp: September 19, 2022, 10:08:52 am
content: I got a response from Fotek.If it is marked "3 ~ 32VDC" then it is a knockoff.Real Fotek SSRs are "4 ~ 32VDC".Some fakes do show "4 ~ 32VDC" but the vast majority, from the sounds of it, are "3 ~ 32VDC".

author: mushroom
author_rank: Regular Contributor
timestamp: September 19, 2022, 11:09:45 am
content: Yes, it is these markings. Retrieved BligClive's video :Also retrieved the order : the thing was 1.72 € including P&P at this time ! (2020-11-11).It will have to work a few minutes only.Funny fact : there's a 3D model on 3D Content Central or GabCad ; the model shows 3-32VDC ; the exact same SSR that Big Clive took apart !

author: james_s
author_rank: Super Contributor
timestamp: September 20, 2022, 05:13:37 pm
content: Quote from: Jackster on September 19, 2022, 10:08:52 amThat's surprising, if they're going to make a copy, why not scan the label from a genuine one and make accurate looking copies of that too?

author: mushroom
author_rank: Regular Contributor
timestamp: September 20, 2022, 08:18:37 pm
content: Elementary ! Because it will (or will be supposed to) work with 3.3V logic. Why would they divide the customer base by two ? Testing the SSR with DC instead of AC. Just remenbered there's no reason it wouldn't work with DCpushing 6.2A (8.5W according to the PSU display), the Fostek knockoff turns on at 1.67V. After 15mn, with zero cooling the socket is at 80°C, and 55°C with a 12V fan undervolted at 6V. Ambiant 23°C.Conclusion : no problems.