Solid State Relays.

[Robin GrahamParticipant @robingraham42208]

I want to make an Arduino controlled LED strobe light (for serious workshop purposes, honest guv, nowt to do with Halloween) and I thought I could just buy an SSR rather than making an amplifier myself. Foolishly I clicked ‘buy now’ on this four channel device:

As shown it’s hooked up to 5V (DC+,DC-) .Off camera is another power supply set at 5V with a current limit of 1.0A connected to the red/black output terminals. When I touch the white wire to the CH1 trigger terminal (ie pulling it down) the relay conducts, the voltage on the other PSU drops to about 1V and the current limits at 1A. However the relay then latches closed – I have to remove the ‘load’ from the output to make it open again.

I’m sure that I’ve blundered – the blurb doesn’t make it clear, but I suspect the device is designed to switch an AC load and needs the output to cross zero before it changes state. Is that reasonable?

Another strange thing is that if I set the off-camera PSU to 6V or higher then ground the trigger terminal the onboard LED comes on indicating the relay has ‘closed’ but no current flows in the output circuit.

Any elucidation welcome!

Robin.

 

 

 

 

 

[Michael GilliganParticipant @michaelgilligan61133]

A tiny flicker of elucidation from me, Robin …

I think the SSDs are SCR based; so yes they expect to be switching AC

… explanation beyond that requires a better night’s sleep, and then Coffee.

MichaelG.

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Ref. https://en.wikipedia.org/wiki/Silicon_controlled_rectifier

[Michael GilliganParticipant @michaelgilligan61133]

This might help:

https://docs.rs-online.com/1f69/A700000009611095.pdf

MichaelG.

[RobinParticipant @robin]

Inside an SSR you would expect an opto-isolated TRIAC and a big fat power TRIAC. All wired up to switch AC.

If you wanted to switch DC then there would be one component, a big fat MOSFET. Bit hard to sell packaged single components no matter how fancy.

The tricky bit is switching heavy inductive or capacitive loads. It’s like closing a blade switch in Frankenstein’s laboratory to connect up the lightning bolt. You must expect to be hurled across the room.

The AC switch can wait for zero volts before it closes. Might have a bit of a wait with DC.

Good luck

Robin

 

[Michael GilliganParticipant @michaelgilligan61133]

Data-sheet for the Omron device: https://docs.rs-online.com/d4d0/0900766b814048ef.pdf

Interesting to note that RS lists this as discontinued … which might explain why there are so many around at very modest prices.

MichaelG.

[Robin GrahamParticipant @robingraham42208]

Thanks for replies. The mists have cleared.

Robin – points taken. Since posting I have found that packaged DC-DC SSRs are available – their selling point seems to be that they are opto-isolated which I don’t need. I have also found a box of IRLZ34N MOSFETs in a drawer which I must have bought for an Arduino project a while back, then promptly forgot about. Doh!

Michael – thank you for your research.  The relays I bought appear identical to those you found except that they don’t bear the Omron mark. So designed to switch AC. Unfortunately that wasn’t clear to me when I bought the unit through Amazon. I’m planning to make a spooky display using those ‘spotlight’ LED arrays which you drew attention to earlier in the year and I’m sure the IRLZ34Ns will do the job.

Robin.

[noel shelleyParticipant @noelshelley55608]

AH yes ! the 42 led array from I think plessy ? I have one on the mantle shelf with a pin fin heat sink and a boost converter to give the 40 ish voltage and current limiting so that I could make a super dooper 12v torch. I have a 12V 7Ah gel cell for power and am thinking of something like the old “6v hand Lantern” of the 60s. A friend had spent about £140 on an LED one and I felt that “just for fun ” I could put him in the shade for about £20. As yet I have not found the time but will watch your progress with interest – keep me posted. Noel

PS can I get back to the original thread that michael and others commented in ?

[Michael GilliganParticipant @michaelgilligan61133]

Here you go, Noel

https://www.model-engineer.co.uk/forums/topic/some-very-interesting-led-modules/#627304

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Fortunately, the site Search did quite well using the word Plessey

MichaelG.

[noel shelleyParticipant @noelshelley55608]

Thank you Michael, just reread it all ! Still wonering if I should put a thermal pad between the leds and the heatsink ? The heatsink is anodised. Noel.

[Robin GrahamParticipant @robingraham42208]

Noel – I ended up putting thermal grease between back of the array and the (anodised) heatsink despite the dire warnings on the data sheet. I’ve not had any problems. To get maximum brightness (subjective!) they seem to need  43-44V – but at 44V they take about 35W, so they do need a substantial heatsink.

I too wondered about a flashlight and found a converter

which does the job of driving the array from a 12V lead acid battery. Ten quid though! What did you use?

Robin.

 

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