DC SSR half cycle

Thread Starter

Barbibulle

Joined May 24, 2020
9
Hi everyone,

short version:
I've been struggling to find an optocoupler for my application. I think this one could work: Crydom DR06D03 but the datasheet lists the turn-on and turn-off times as "1/2 Cycle" and I don't get what it means since it's all DC on both input and output side. Crydom's support service is not answering my emails.
1590371124698.png
long version:
I'm an industrial vision engineer. I'm trying here to strobe an LED light called LFVX-200SW (40W) using the output of my vision controller.
The light is powered with 48VDC instead of 24VDC to get a brighter strobe. This is allowed by the manufacturer as long as the duty cycle is less than 7%.
As you can see, the on/off time of my opto is critical to avoid damaging the light.
I've tried using a Crydom DRA1-MPDCD3, which ticks all the boxes except it keeps getting damaged. I've replaced it twice in my machine already and the same thing happens: when the controller's output is ON, the light turns ON which is great. When the controller's output turns OFF, the optocoupler doesn't turn OFF completely and "leaks" about 10VDC on the output side, leaving the light dimly lit. The opto never shuts off entierly even after I've disconnected everything on the input side.
The wiring couldn't be more straightforward:
1590371431662.png

Anyway, any help will be greatly appreciated, either in understanding that 1/2 cycle thing or fixing my leaky opto.
Thanks!
 

Thread Starter

Barbibulle

Joined May 24, 2020
9

Thread Starter

Barbibulle

Joined May 24, 2020
9
Wow, thanks for the quick reply about the half-cycle! I think I'll have to read that a couple more time to fully understand it.

As for my current Crydom SSR, to make sure there was nothing weird on the controller side, I completely disconnected it. The opto is still "half open" with absolutely nothing connected to its input side. I'm stumped.
 

Thread Starter

Barbibulle

Joined May 24, 2020
9
Thanks Les! I did see the notes but I wasn't sure what applied to my situation. I had never heard of Cycle Control and I was worried it would be a bit too convenient to ignore that part of the datasheet and only take the notes into account.

So you reckon the datasheet means "if cycle control is used, then turn on/off time is half cycle. If DC control is used, then turn on/off time is <1ms" ?
 

LesJones

Joined Jan 8, 2017
2,696
I can't find the term "cycle control" in the data sheet so I don't understand what you are talking about. My understanding is devices for AC output use SCR or TRIACS so they will latch on to the end of the cycle. If they were used with DC output they would not be able to switch off. Notes 9 and 10 give the turn on and turn off time for DC output devices.

Les
 

ericgibbs

Joined Jan 29, 2010
10,756
hi B,
Try this simple check.
Disconnect the SSR input leads from the Controller, then link the input leads together, so effectively short out the internal emitter diode of the SSR.
The Light should be Off.
Ref this image.
E
AAA 352 10.50.gif
 

strantor

Joined Oct 3, 2010
5,329
Your opto is rated 3A.
Your LED is rated 60W @ 24V. That's 2.5A.
You're powering it with 48V instead.
Assuming the V:A curve is linear, you can expect it draw 5A. If nonlinear, then even more than that.
You're utilizing a solid state device at 166% (min) it's rated capacity.
This is not like a mechanical relay where it takes some time to heat up before it burns. Solid state devices fail closer to "instantly" - that is why we protect them with ultra fast-blow fuses.
Use the LED at its rated voltage or get a bigger opto.
 

ericgibbs

Joined Jan 29, 2010
10,756
hi strantor,
He has already cleared this point with the SSR manufacturer, ref his opening notes.
E
Clip:
The light is powered with 48VDC instead of 24VDC to get a brighter strobe. This is allowed by the manufacturer as long as the duty cycle is less than 7%.
As you can see, the on/off time of my opto is critical to avoid damaging the light.
 

Thread Starter

Barbibulle

Joined May 24, 2020
9
Your opto is rated 3A.
Your LED is rated 60W @ 24V. That's 2.5A.
You're powering it with 48V instead.
Assuming the V:A curve is linear, you can expect it draw 5A. If nonlinear, then even more than that.
You're utilizing a solid state device at 166% (min) it's rated capacity.
This is not like a mechanical relay where it takes some time to heat up before it burns. Solid state devices fail closer to "instantly" - that is why we protect them with ultra fast-blow fuses.
Use the LED at its rated voltage or get a bigger opto.
Hi Strantor,
Thanks for your reply. I assumed that P = V x I so 40W powered with 24V draws 1.66A and the same light powered with 48V only draws 0.83A. I have to confess I didn't even check how much power it was drawing at 48VDC. *facepalm*
(The datasheet of the light says it uses 40W max btw.)
 

Thread Starter

Barbibulle

Joined May 24, 2020
9
hi B,
Try this simple check.
Disconnect the SSR input leads from the Controller, then link the input leads together, so effectively short out the internal emitter diode of the SSR.
The Light should be Off.
Ref this image.
E
View attachment 208070
Thanks Eric,
I've just tried that. The light stays dimly lit with the input of the SSR shorted. I don't have anymore brand new SSR to test unfortunately. I fear Strantor is right and my light draws more power at 48VDC than at 24V. I didn't see that coming.
 

Thread Starter

Barbibulle

Joined May 24, 2020
9
Alright, I just measured the current drawn by my light while increasing slowly the power supply. The current definitely goes up. My SSR is way underspecs and I'm an idiot.
Thank you all for your help!
Barbara
 

Thread Starter

Barbibulle

Joined May 24, 2020
9
Also for future reference for myself. I got confused by the "half cycle" mention in the datasheet because I wrongly assumed that all the models DRxxDxx were DC only. But the DR24D12, for example, switches AC loads.
In my case, the DR06D06 switched DC loads and the turn-on/off times that apply are the ones listed in the notes like LesJones pointed out. Pfew!
Thanks again everyone!
 

ericgibbs

Joined Jan 29, 2010
10,756
hi Barbara,
That simple shorting test showed the SSR was leaking/failing.
Would be interested to hear how the project goes, say with a higher power SSR or lower supply voltage.
E
 

LesJones

Joined Jan 8, 2017
2,696
I think you need to provide some data on the LED device you are using. I tried to find a datasheet on the LFVX-200SW but only found one in Chinese. (I think.) I suspect it is just an LED array with no proper current limiting. If so it will take very much more than double the current at 12 volts when supplied with 48 volts.

Les.
 
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