240C Cylon effect problems

[fritz42_male]

Hi all,
This isn't strictly a Picaxe issue but I hope someone can help.

I created a 'Frankenmachine' for a Halloween Mad Scientist lab. Part of the effect is 6 240V bulbs that flash in a 'Cylon' sequence (1-6 then 6-1 and so on).

I used a 14X and Axe117 with LEDs to test and got it all working nicely. Speed is controlled by a 10K pot. Now it all works fine with LEDs - the problem is when I go to mains bulbs. I am using 6 SSRs to drive the bulbs. All works fine until the speed gets up to a certain point then....nothing - all the bulbs stop flashing - no random blinks just nothing.

Now the SSRs are ones picked up of eBay and are Huntleigh Technology SMT2000/4 and others are working fine in other projects. The speed of the light sequence could be approaching a 60hz flash but unlikely.

Anybody got any ideas why they stop flashing at a certain speed?

I do have some Xmas light boards (SSROZ) that I could use for the same things but these SSRs were otherwise just right for the prop.

 

[Michael 2727]

Anything faster than around 10 Hz will look like it is ON constantly.

At 60 HZ you will be lucky to see even a flicker and even then only
out of the corner of your eye where you detect it best.

Try driving the SSR Input / LEDs a bit harder, some inputs require up to 50mA
to guarantee switching.

Are your units Zero Crossing or Phase Angle switching types ??

 

[MPep]

Do a search for "Persistence of Vision" on Google.
Above a certain rate, everything looks ON, even though only one output may be ON at any one time.

no random blinks just nothing.

Actually, what exactly happens when 'just nothing' happens? Do the lamps not come on at all? If that's the case then it can also be because the filament needs time to warm up. One method I have read that tries to overcome this is to have a permanent low value of AC current flowing, in order to maintain heat in the lamps. Not high enough to make the effect visible, of course.

 

[Dippy]

I think we need a data sheet on this Ebay sourced device.

I can't find any SMT2000 from Huntleigh using Google.
Was the Manufacturer's name written on using felt tip pen?
Were these the cheapest on the planet?

I'm sure you imagine for yourself what will happen at high switch speeds if it is zero cross. Well, hopefully you can.

 

[fritz42_male]

Sorry, I'm obviously not being clear. Once the speed goes above a certain point (which is actually only about 1/4 sec per bulb the bulbs stop lighting up at all). No dim glow, no random flashing, nothing. Turn the flash speed down a bit and all is fine.

If I plug the LEDs back in, they work fine so it is obviously a problem with the SSRs. Load shouldn't be a problem - the SSRs are rated at up to 4A on the 240V side and need a switching input of 3-32V. The bulbs I'm using are 25W. All the info on them is printed and they are a professional package in appearance.

I couldn't find a datasheet when I bought these and the company although still in operation, no longer has anything to do with SSRs. In appearance, they are like this one:

http://www.jaycar.com.au/productView.asp?ID=SY4080&keywords=relay&form=KEYWORD even down to the pin spacing and encapsulation dimensions.

Yes, these were dirt cheap - I got 10 of them for about 12 quid. I'm using them elsewhere with no problem but they are just switching things like fog machines so the cycle time is in seconds.

No problem using something else instead for this project but I'm curious as to why an SSR would behave like this.

 

[Dippy]

Oh I see, they just don't switch on.

Have you just tried a single one to determine the frequency/duty at which point they misbehave? You may get some idea if it's a switching issue from that. Are they all the same? Are you driving them properly?

Personally, I'd have driven a triac circuit and then you know where you are.

Maybe you've just bought some less-than-ideal-economy Fleabay Fodder with a made-up name?

Are you confident that they are safe?

Sadly, there's no point comparing them to others. These devices have a fairly standard physical appearance.

 

[hippy]

Once the speed goes above a certain point (which is actually only about 1/4 sec per bulb the bulbs stop lighting up at all). No dim glow, no random flashing, nothing. Turn the flash speed down a bit and all is fine.

You will probably have to take a step back and implement a program which controls a single SSR with variable on and off times to analyse what is happening to determine where any issue is.

Without a datasheet you don't know if there is a fault or the SSR's are doing exactly as they are meant to. Perhaps they are smarter than imagined and have internal electronics which limit maximum switching rates ?

To analyse what's actually going on you need to look at the trigger, the mains and the load drive and that is not easy. You need to take special precautions in doing that as you would be working with live mains - we recommend against this unless qualified in this field, have appropriate equipment, and an appropriate environment approved in which to undertake such work.

I think the moral is that without a datasheet you cannot tell if a component will perform as hoped for. If that's the case then you just have to shrug and move on to using something else.

 

[John West]

What exactly are you referring to as "mains bulbs?" There are a whole lot of bulb types that run on mains. Some of them won't turn on and off within a quarter of a second.

 

[fritz42_male]

These are authenticated devices - Huntleigh just discontinued them a LONG while back when they upgraded to become a Medical Technology company.

I'll just go to a Triac circuit when I rework the design and use the existing SSRs for simple switching projects for which they work fine.

Dippy/Hippy, I'll have a play over the Xmas break just to expand my knowledge - I may even try deconstructing one of them (which will mean killing it due to the epoxy encapsulation).

JW - I'm just using ordinary 25W incandescent mains bulbs, I know they take time to heat up and cool down but the point at which they stop working is VERY marked. I would have expected some variance between the SSR components which would mean that some would stop working whilst others continued to flash but they ALL go off at the same point - this is what intrigued me.

 

[MPep]

Maybe try using the Jaycar devices. Good luck.
Very strange symptoms though.

 

[Dippy]

Odd.

If they ain't up to the job best you buy ONE of a modern design and see how fast you can run it.
OR , if you are 'up to the task' then use TRIACs.

I really can't be bothered to list all the warnings, I just hope you are careful and that you realise that TRIACS and SSRs are not perfect switches..

XMas break? That's miles away. Obv no urgency then?

 

[Michael 2727]

FOG MACHINE !
They can draw many AMPS.
As a rule of thumb I'd never drive a Triac or SSR to more than 60% of it's rated capacity.
Why - because they fail regularly if pushed to their limit.

What current are you driving the SSRs LED with.

Just because you can see the LEDs on the outside working does not mean
the IR (Optocoupler LED) LED on the inside is getting enough current to work correctly.

 

[fritz42_male]

Dippy: I already have some lighting controller boards using optocouplers and triacs - a set of 4 per board and I have 2 boards. These are from a Xmas light forum and will do the job perfectly - it's just that I had the Huntleigh SSRs handy, unused and ideal for the job (I thought).

I'm aware of the need to avoid inductive loads without changing the design and so on.

And no, there is no urgency - it worked well enough for Halloween - I just want it improved for next Halloween. My Jacob's ladder gave a bit of trouble though - every time a kid touched the electrodes, there was a bang and puff of smoke and I got a new 'dead person' prop! (no, only kidding - I made sure that one wasn't running and am looking at making a kiddysafe EL wire Ladder simualtion for next year.)

Michael, my fog machine is a wimpy home one and rated at 2A - 50% of the rating on the SSR.

As for the current drive on the optocouplers in the SSR - should be ample as the Axe117 uses a ULN2003A Darlington to drive the outputs.

 

[Dippy]

Ah well, if your circuit drives the SSRs adequately, and your programme works and your mains side is good and your power supply is good and your PICAXE is happy then there can only be one bit which is a bit dicky.

Are any mains switching spikes getting to PICAXE?
Have you used any decoupling/filtering to prevent this?

My first steps would be to check PICAXE supply is good and buy ONE new SSR from a proper supplier. Buy a type that has a data sheet (which you read before purchase) and a warranty. Then give it a good thrashing.

There comes a time when you have to stop penny-pinching.

THEN you can see what is ideal for the job.

Just think , you saved a dollar on the device, but you'll soon be getting a bill for $500 from the Forum Consultancy team... and it didn't get solved
God Bless Ebay and all that sail in her.

 

[fritz42_male]

Nope - no supply issues, I ran out of power supplies so powered this prop off a 3xAA battery pack (& before you ask, yes, fresh batteries)

Nope, I'm fairly certain it's the SSRs as the root cause - I'll try my Triac boards next as they are designed for lighting with fast switching.

Penny-pinching? Hmmm nothing wrong with that in these hard economic times. Yes, I'll probably pick up a 'good' SSR from Jaycar to play with. I was just curious as to whether anybody could shed light on why these SSRs were exhibiting this symptom as I had assumed(yes, I know) that they were a typical optoisolator/triac config/

Consultancy charge? Sorry mate - I believe in no fix/no fee - but I'd buy anybody who replied a beer quite happily. Mind you, you will have to get to Perth to drink it!