Keep it safe..!

[Dr_Ju_ju]

10 minutes ago, Gina said:

Surely the SSR will switch at the next zero crossing point after the change of DC input.  Or aren't these SSRs that clever?

who knows the circuitry that's buried inside...  and as will all things, you get what you pay for.....

[Chriske]

1 hour ago, Dr_Ju_ju said:

It will depend on where in the frequency cycle the switching occurs, if you are switching at the mid point of frequency cycle, you'll be ok, as you'll effectively be switching 0v, but if you are switching at the peaks, then you will be switching at full voltage, which then could have high voltage\current switching transients, very much dependent on load type, i.e. resistance\inductance etc. 

For it to always to be switching at the mid point, would require some form of frequency synchronisation, which isn't available in these 'simple' systems, although I have used it in broadcast equipment for certain type of equipment.

Hey guys,

How do I know this : It will depend on where in the frequency cycle the switching occurs.

[Dr_Ju_ju]

Ahh, it takes me back a looong way, & it involves differential calculus, which I'll readily admit, is now well buried in the grey matter.....  But a starting point for you would be https://en.wikipedia.org/wiki/Alternating_current

[tekkydave]

Looks like I have a fake. I'm only drawing ~3A (750W silicone heater) so theoretically well in spec.

It doesn't even feel warm to the touch in use but I think I'll invest in a genuine part and up the spec a bit.

 

[Dr_Ju_ju]

Looks like I've been a bit more luckier, the AC one on the left is genuine, whereas the DC one isn't.

Note that both types were bought from the same eBay supplier, who probably doesn't even realise whether they sell genuine or fakes (or may not even care...)

 

[tekkydave]

I bought a new SSR from a reputable supplier (RS)

Its a zero-crossing type which Duet recommends and is also the correct type to use for mostly resistive loads.

It should fit in the existing case on my D-Bot but the LED will be in the wrong place. A drill should fix that

 

[tekkydave]

Now fitted into D-Bot's Mains Distribution Enclosure. It is a drop-in replacement for the FOTEK although the indicator LED is in a slightly different location and it is overall slightly deeper (front to back).

I made a temporary mod to the front panel for the LED. I'll print another one at some point

 

[Dr_Ju_ju]

Although we can't see inside, but as an additional safety measure, I'd recommend\ensure that the rear metal plate, of the SSR, is connected to ground, such that any 'internal' failure, will blow the fuse...

[Chriske]

On 19/03/2020 at 10:23, tekkydave said:

I bought a new SSR from a reputable supplier (RS)

I'll order in UK because only companies can buy from RS-BE

[Chriske]

On 19/03/2020 at 10:23, tekkydave said:

I bought a new SSR from a reputable supplier (RS)

As I said I'll buy these,

But aren’t these also made in China...?

[Dr_Ju_ju]

If not China, it would be Thailand, Vietnam, Philippines, Mexico etc.  even the 'big' brands don't make anything local anymore.  

[Chriske]

Stupid question I know Julian, but why would 'things' in general be made better in other countries then in RC..?

[Carbon Brush]

1 hour ago, Chriske said:

Stupid question I know Julian, but why would 'things' in general be made better in other countries then in RC..?

What is more important is control over the manufacturing process and manufacturing traceability.

Any semiconductor device (SSR, microchip, logic gate, transistor) may actually be partly made in several different factories in different countries.
Not all of them owned by the company who stamp their name on the semiconductor at the end of the day.
If you have good control over your subcontrator activities, you generally end up with a product of known quality.
The days of shovelling sand (silicon) into one end of the factory and getting transistors out of the other end are long gone.

A few years back a 'big brand' laptop manufacturer had a recall bill of a few million ££££££ because the battery packs had a habit of catching fire.
The chinese assembly factory used the wrong sort of cardboard to separate the individual cells in the battery packs.
The individual cells were though good quality devices, made in Japan.

A former work colleague moved to another job and found himself sorting quality issues with a chinese sub contractor.
Visit 1 to resolve failed connections in wiring. Crimp tools were found to be poor quality and worn out.
He explained this and the tools were thrown in the bin.
Visit 2 a few weeks later on a different issue. Looking at the assembly line, the old crimp tools had been fished out of the bin!

While we all look to pay £1 less for a product, the manufacturers will chase down whoever can build for less.
Governments will offer grants and other incentives to bring in work. This happens worldwide.

If you buy a semiconductor device marked as one of the 'proper' names, it will be good, provided it is not a fake.
If you buy through proper distribution channels, for example RS, the parts are traceable so you know the parts are genuine.
If you buy from a grey market supplier, or the bay, it might be a fake

If you buy a semiconductor device from the Ying Ting manufacturing company (I don't think they exist, but apologies if they do) there is no quality history.

Moving to telescopes. If you ship parts to an assembly factory and specify that the finished product has to meet a specification, then you get a product of known quality.
But what happens to the lenses with bubbles or poor coatings. Or the wobbly focussers. They go in the bin. Or do they?
You know that a particular scope (lets assume SW ED80) performs well and they are sold through an approved dealer network.
Then a scope appears from a different dealer. It looks just like the SW ED80 but is badged WS ED80 and is half the price.
Is it a good scope without the SW dealer network price mark up? Or is it made from leftover parts?

HTH, David.

 

 

m

[Dr_Ju_ju]

Its not a case of being made 'better', its always a case of where a part can be made for the lowest cost, so it all comes down to maximising profit....

[tekkydave]

14 hours ago, Chriske said:

As I said I'll buy these,

But aren’t these also made in China...?

Yes, but I trust RS as a decent and responsible reseller. The fake I bought on ebay was untraceable really.

[Chriske]

Well, same in UK, you need to fill in the name of company.
So there's no way I can buy from RS in UK, same as in BE

[Chriske]

Reply from RS-UK

Thank you for your e-mail and your order.
Unfortunately it is not possible for us to deliver to individuals without VAT number. We are a business to business supplier and therefore we cannot proceed your order.

[Chriske]

I had another three in stock

One that didn't work at all(left) and another Chinese copy.
The third, also made in Taiwan, is now installed.

[pete_l]

If RS don't want to take your money, you could always try Rapid

[Chriske]

37 minutes ago, pete_l said:

If RS don't want to take your money, you could always try Rapid

Thanks a lot Pete.
I already ordered at Conrad.
 

Apparently some of the readers here do have a VAT number

[Chriske]

Dam... Chinese rubbish...!... 😡    I thought I had replaced all SSR's.  Seems I forgot one SSR swap...

[D33P]

In my experience SSR's always fail closed.

I'm a controls engineer, and seen plenty of dead SSR's over the years. Don't recall ever seeing one failed open.

My printer is in an enclosure with heat and smoke detection. It will isolate and raise the alarm if anything goes wrong. As yet untested, and I hope it never gets tested! I do leave it running unattended in the garage, but never leave the house so I'm around to hopefully catch any failures before it gets out of hand.

[Viktiste]

On 26/08/2021 at 22:13, D33P said:

My printer is in an enclosure with heat and smoke detection.

That is a very good idea. Although I have a bought a printer rather than made one I think I will make an enclosure for it and install detectors. A 3D printer is not much use for anything but tiny parts unless you can run it unattended and still sleep well.