Teardown of an eBay 25A Solid State Relay. (SSR)

A solid state relay is an industrial component used for interfacing low voltage control signals to high current mains voltage loads.
They sell them on eBay at a ridiculously low price, so it's time to see what's actually inside one of these eBay units.

[dannywood]

Thanks for this tear down Clive.

I have the exact same part from an ebay seller that I intended to use in a Kiln controller (~3KW max output).
So after watching this I stripped mine down to reveal that it also contains the BTA12-600B, obviosuly not quite sufficient for my application.

I have now ordered a BTA24-600B to uprate this to its original spec of 25A, at least I will now be operating its safe area.

Thanks again for your entertaining and interesting videos!

[frank]

Thanks Clive! I change out CryDom HD4890 SSR (480Volt 90Amp) Solid State Relays that run 7K watt heater bands on a PVC extrusion lines on a pretty regular basis. About 30 of them are used per line to heat "zones" controlled by Telemachique controllers. Always wanted to see inside one but the Crydom's are potted! Great video! Hate that the Crydom's sometimes fail in a closed gate state and burn up heater bands!

[Starchface]

I have considered these relays but avoided them because of safety concerns. I have no problem piling on heaps of dubious low-voltage components that are practically free, but it is a different situation when a component is to be connected to the mains. I don't want to burn down the house or electrocute someone. Even though yours seems reasonably good, I think I'll pass. When certification markings are false and no one is accountable, it is hard to have confidence in a part.

This is the first video of yours that I've watched Mr. Clive, and it is simply fabulous. First class. Thanks for doing this.

[thoragn]

Bought a few "FOTEK" SSR-25DA a few years ago, used them to control approx. 1kW heaters at 230V. A very light load, only 4-5amps and I have had no problems. Fortunately they are also mounted on a decent heatsink, enclosed in a metal box and controlled by a PLC so there is no human contact with the input.

Had some leftovers so after watching this video I cut one open and found a single BTA20-600 inside. A bit bigger than the one in the video but still only rated for 20A, not the full 25A.

The input circuit is different and actually quite nice, it has a LM337 regulator connected as 12mA current limiter, which supplies constant current to the optocoupler for the full range of 3-30V.

However the PCB is horribly badly designed, input and output traces very close (1-2mm) for the whole width of the board, there is quite enough space to do this properly, really makes one wonder why they had to screw it up.

After some thought I got more curious and two weeks ago I ordered a few more SSR-25DA and SSR-40DA from different China ebay sellers just to check them out. Shipping was unusually quick, they all arrived here in Iceland 7-10 days after ordering.

First I noticed that none of the items looked exactly like the pictures in the listings, minor difference like "Taiwan made" changed to "Made in Taiwan" and "Solid State Relay" becomes "Solid State Module".

Next I split them open and found a single BTA12-600 inside the SSR-25DA type as in the video. So only a 12A TRIAC in a 25A rated module, not good!

The listing pictures for the 40A show a module with two screws on the bottom, indicating it might have two power-components, one could even dream about two antiparallel SCRs which is the proper way to make a 40A SSR.

Unfortunately they sent a different type with just one screw and a single BTA16-600 in the SSR-40DA. 16A instead of 40A, even worse than the 25A one!!

Also the RC filter across the TRIAC was completely missing, no components, just empty holes on the PCB!!!

The PCB of the 25A type is exactly like the one in the video, but the 40A has a much better PCB, with SMD components, good clearance and a milled slots between input/output traces. The 40A is also filled with more resin, the space below the PCB was almost completely filled on the output side and the components on top of the board well covered. A real shame they then ruined the whole thing with a 16A TRIAC.

Some used heat conducting paste when mounting the TRIACs, some had no paste.

It is possible to disassemble those SSRs without much damage, first pry the top cover with sticker up using a small screwdriver. Next use a fine tipped soldering iron to melt/burn the resin from the head of the TRIAC-fixing screw. Then remove the screw and finally the metal heatsink. The TRIAC will stay in place and hopefully not tear any traces on the PCB.

Reassembly is also possible, but hardly recommended.

After this experience I will try to avoid those SSRs.
They are only good for appox. 25-30% of rated load.
They should not be used where humans (or any other live creatures) might come in contact with the input wires, the insulation between input/output is not to be trusted.

[AppliedScience]

I have a few of those in my shop. Thanks for the helpful teardown.

[davidanderson]

I took apart an old 1980's vintage USA made 10Amp 140V ssr and it is indeed fully filled with dense black compound. The lid is a full cover and they have little legs that extend into the potting compound to hold the lid on. Much more robust construcutib than what is shown above.

[trustthewater]

Thank you! You've been very helpful.
I've been eyeing some of those for a project. Every time I hovered over the checkout button I would get a little voice telling me, "You get what you pay for."

[hassanburrows]

Wow! Thanks for such a quick response. I am pretty much still in the electro-mechanical era so this type of thing is new to me, but still interesting.Pity most schools can't make subjects as interesting as you do.Fantastic work!

[cplsyx]

Stumbled across this whilst going through your older videos - and I just happen to have one of these sat on my desk! Very useful teardown and glad to see they aren't all that bad.

[footstepsinchina]

SSRs are really intended for fast switching that would wear out a contactor (controlling temperature on a heater, switching in a VFD) If you want something to be left on for long periods your usually better off with just a contactor. Best for resistive loads, they don't handle inductive surges well.

[cbcdesign]

I cant get my head around the concept of faking a 25A SSR and selling it for a couple of pounds on ebay when they could sell it for the same price rated and labelled as an 8A device instead. It would still be a very competitive price but legitimately rated.

[pcfred]

Always nice to see what you're really getting in these modules.

[tiger]

I messed around with some triac circuits some years ago which were basically schematic equivalent to this thing. Had no difficulties powering incandescent lights, occasionally some difficulties with compact fluorescents (the holding current you mentioned).

One thing that I think would be extremely good advice is to be VERY CAREFUL about powering heavy loads and/or heater loads with these devices. When the triacs got warm, they tended to self trigger, so that even when the opto-isolator circuit was turned off, they would still pass current. (negative temperature coefficient of solid-state devices)

If you are thinking of controlling a heating device with one of these, I strongly recommend using an electromagnetic relay instead -- especially given clive's teardown results showing you can't trust the printed current rating.

[PeterScargill]

Years ago we used to build home control boards and in one of them we used a similar arrangement but simpler as the input voltage was known - hence resistor into the zero-crossing opto-triac then the same components on the right. We used 15A triacs on heatsinks and controlled 2KW heaters no problem.

[d.jensen]

It's fascinating to see what I've been using for the last six years! I'm glad now that I acted on impulse and used them conservatively, and only for personal projects. But they have worked without complaint.

[braddofner]

This is one I needed to see, but I didn't know that till I saw it. This is amazing to see the insides of something I have used so many of!

[davdsmth]

Just got one of these to control the heated bed on a 3d printer I'm building.  It was a relief to hear your verdict that it may be up to the job.  Fingers crossed.

[Greebstreebling]

Thanks for posting, it's good to see the insides. I used an SS40DD (to switch a DC 3A load) controlled by an arduino GPIO pin. I was using it well within spec, but it got very hot indeed and all the case melted and twisted. I built my own after that :) :)

[garbo]

Have used 25 amp solid state relays but when load was more then 3 amps would mount it on a heat sink and use heat conducting paste. Have just used a 6 by 6" aluminum plate that was 1/4" thick for loads up to 50% of label. Nice vid.

[fcmacken]

OMRON tops there SSRs all the way with sealant. Very seldom have any problems with their components, but they are quite pricey.