TV Backlight - Single Colour Led Strip - On/Off Problem

bertus

Joined Apr 5, 2008
22,270
Hello,

The SSR you are showing will not work, in your current setup.
It is supposed to be used with 100 - 240 Volts AC.
Your powersupply is 12 Volts.
An way to use it would be to switch the Mains with the SSR and connect the ledstrips directly to the powersupply.




Bertus
 

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Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
Hello,

The SSR you are showing will not work, in your current setup.
It is supposed to be used with 100 - 240 Volts AC.
Your powersupply is 12 Volts.
An way to use it would be to switch the Mains with the SSR and connect the ledstrips directly to the powersupply.




Bertus
Hi Bertus,

That's right unfortunately, and I've searched quite a few websites and couldn't fin any SSR (at least not an affordable one) that would work with a 5v - 12v DC current so it seems that if I want to use an SSR I will have to do it directly to the AC cable, which is the thing I wanted to avoid at all costs in this first small project, not that I don't trust my skills, but I'm aware that my inexperience can cause serious damage if I do something wrong on the main...I guess that the diode between the USB port and the normal relay would not be sufficient to guarantee a relative protection ?

In the event that the above answer is negative, I was thinking, some USB hubs have protections against short-circuits and spikes right ? If I used an USB Hub with these characteristics and connected the relay circuit to the HUB instead of the Tv USB port, wouldn't that produce the same effect? I'm guessing that even a passive 4-ports Hub would generate a minimum of 100-120mA per port which would be more than sufficient for the relay I indicated before. Just a thought worth asking I guess.

Thanks
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
Hello,

A heatsink as you are showing will not do anything against the spikes.
A diode will supress the sike generated by the unpowered relays.
Here is how to add it to your circuit:



Bertus
Hi Bertus,

I've been reading about diodes to conduct the excess voltage in circuits and I came across the zener diodes which apparently will divert the power when the voltage is above a certain level (for a short period of time), in this case I found some 5.1V zener diodes that might do the trick, given that the back-emf spike is for a really short period of time when the power suddenly drops, will they do the job ?
I also read about Flyback diodes exactly for the back-emf spike but I can only find them in higher voltages, the only one I could find approximate to a 5v circuit was the P6KE6.8A with a Working Peak Reverse Voltage of 5.8V, which one do you think that would make the circuit safer in terms of harming the Tv USB port (if any) ?

I'm learning a lot with only this simple circuit thanks to all of you, you have a really great community with great people here, hope to be able to help others in a few months like you do.
 

Alec_t

Joined Sep 17, 2013
14,280
The SSR you linked to should be ok. It is rated for 5V DC input (i.e suitable for USB) and has a 2A load at 240VAC, 50/60Hz rating. That would enable it to switch on the primary of the power supply.
Re the diodes, you don't want a zener or low voltage type for back-emf protection. In that role the diode spends most of its time reverse-biased but becomes forward biased by any back-emf voltage spike so drops only ~0.7V. A 1N400x type will be fine.
 
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bertus

Joined Apr 5, 2008
22,270
Hello,

How much current do the ledstrips take?
I have looked and there is an optocoupler that can switch on the 12 Volts side.
The CPC1979 of Clare is an optocoupler that has powerfets at the output that can handle 1 Ampere easely.
As the input is an IR led, a current limiting resistor is needed.
A resistor of 390 or 470 Ohms will do.
See the attached datasheet for more info.

Bertus
 

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Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
The SSR you linked to should be ok. It is rated for 5V DC input (i.e suitable for USB) and has a 2A load at 240VAC, 50/60Hz rating. That would enable it to switch on the primary of the power supply.
Re the diodes, you don't want a zener or low voltage type for back-emf protection. In that role the diode spends most of its time reverse-biased but becomes forward biased by any back-emf voltage spike so drops only ~0.7V. A 1N400x type will be fine.
Hi Alec,

So, zener diodes would be perfect for small voltage spikes under normal circumstances with the current flowing as it should, for back-emf spikes they are little to no good? Would a 1N4007 do the trick ? The maximum reverse voltage is 1,000V, would this be any good for such a low voltage circuit like the one I'm assembling ?

Thanks
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
Hello,

How much current do the ledstrips take?
I have looked and there is an optocoupler that can switch on the 12 Volts side.
The CPC1979 of Clare is an optocoupler that has powerfets at the output that can handle 1 Ampere easely.
As the input is an IR led, a current limiting resistor is needed.
A resistor of 390 or 470 Ohms will do.
See the attached datasheet for more info.

Bertus
Hi,

The LEDs are bright-white so at Full brightness they will consume between 35W and 38W (still need to take the accurate measurements of the Tv lenght) which at 12V means something between 2.9A and 3.2A.

My Calcs: 5050 300 LED/Roll, that's around 0.24W per LED and 3 LEDS per 5cm. My Tv is 47' (~119cm) so I'm counting with around 80cm for the Top, 80 cm for the bottom, and around 50cm for each side, giving me 2.6 meters in LED Strip, that's 156 LEDs X 0.24W = 37.44W. This will be the max, probably I'll end up taking a few centimeters off each side/top/bottom.

Now I got a little confused with one thing, for example, on THIS optocoupler/relay the maximum DC Load is 30V/10A, it would still work with a 12V DC line right ? I can't find that optocoupler (CPC1979) anywhere, and in Portugal if I can't find them online it's not even worth trying in the electronics stores. Will need go through it's specs later today to understand.
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
Just fine. Even a 1N4001 would do.
Odd enough, this was the cheapest one...Would have thought that sustaining higher Voltages the prices would be higher as-well.
Ok, so with the 1N4007 protecting the USB circuit from back-emf spikes, would it be safe enough to use a normal optocoupler relay (like this one) connecting both circuits (5V and 12V) ?

Once again, many thanks.
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
That relay should be ok (it's an SSR by another name). Since the input is an optocoupler you don't need the back-emf suppression diode.
Hi Alec,

Those are great news (for me), I made another sketch of the circuit (attached) with minor differences and with a bit more information, one of the changes was connecting the 12v negatives to the Optocoupler instead of the 12v positives, I believe this is the correct way of doing it?
Can you guys take a look and let me know if this will work?

You might correctly think that the Power Supply has much more amperage than needed but I will add some things to this circuit in the future that will consume a few Watts so I'm just planning ahead, when the time comes I will make another Thread here for sure.

Thanks a lot, will be waiting for your comments.

TV Backlight Circuit 2.jpg
 

Alec_t

Joined Sep 17, 2013
14,280
Your circuit in post #31 looks ok. If the "In" terminal of the relay module is connected to "DC-" as Bertus suggests, then logically the jumper should be to "L".
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
Hello,

I have downloaded the picture from the site and made some comments on it:



Bertus
Bertus and Alec, Many thanks to both.

It took me a while to research this (first time working with jumpers - low/high level triggers), all the explanations I found online are very well conceived in terms of how it works but none of them particularly talks about the wiring (at least not in a way that newbies can understand). Based on what I learned I believe the below image reflecting the wiring is Ok? If DC- is connected to the IN terminal, I will need to keep the flow going and wire the DC+ to the DC+ terminal (leaving the DC- terminal with no connections) and with the trigger set to L(ow); If DC+ is connected to the IN terminal, the exact opposite wiring and jumper, did I understood this correctly ?

If I did, are there any differences between each configuration that would lead me to opt for one instead of the other ?

Again, thanks a lot.

OptoCoupler Connections.jpg
 

Alec_t

Joined Sep 17, 2013
14,280
leaving the DC- terminal with no connections
No. Both "IN" and "DC-" should connect to the negative of the 5V supply from the USB. In the above circuit just add a shorting wire from IN to DC-.
The DC terminals are for powering the relay module optoisolator. The IN is intended for a logic-level trigger signal, e.g. from a micro-controller. Since you aren't using a trigger signal you just wire IN to one of the DC terminals. We've chosen DC- (arbitrarily, but IN happens to be right next to DC- so connecting there is easiest), so the jumper goes to "L" (logic Low).
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
No. Both "IN" and "DC-" should connect to the negative of the 5V supply from the USB. In the above circuit just add a shorting wire from IN to DC-.
The DC terminals are for powering the relay module optoisolator. The IN is intended for a logic-level trigger signal, e.g. from a micro-controller. Since you aren't using a trigger signal you just wire IN to one of the DC terminals. We've chosen DC- (arbitrarily, but IN happens to be right next to DC- so connecting there is easiest), so the jumper goes to "L" (logic Low).
Thanks Alec,

Now I understand why I was not being able to follow some of the "readings" I have been doing, most likely all of them were intended for a micro-controller as you mentioned and that was totally messing with my brain.
That sorted things out, and I believe that the initial objective of this thread has been achieved! :D As soon as I have all the material with me I can start assembling, test and make a final comment here with the end-result. Already have a new idea for a different project which will (obviously) lead to a New Thread, but I will have my eyes busy for a while to cover at least the basic schematics of the circuit.

Thanks to everyone that helped and took their time to comment, hope to be on the "helpers" side shortly.
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
I need the sets model number and make. ....
Hi Sheldons,

Still looking for a spare power supply with enough power but I am losing my hopes so I'll just buy a new one and get this done, been looking at THIS one (HD0638) which has more than enough power (should run at a max 50%-55% with all the leds at full brightness), don't really like Chinese stuff for mains but considering it will be running at about half of its capacity that shouldn't represent a huge risk should it ? Still going to look around my garage for the next couple of days so will order one (if needed) over the weekend, your insights on this are appreciated.

Many Thanks
 

Thread Starter

Carlos Almeida

Joined Jan 15, 2015
35
Hi everyone once again,

With the remaining materials of this project arriving shortly (with the exception of the power supply, but I'll get that this weekend) and the electric circuit apparently being in top shape, I started wondering about the LEDs temperature. I will be dealing with a max of ~37W and I've never been physically close enough to LEDs consuming that amount of power to know if they heat a lot or not, do you have any advise on this?

I believe that +30W can already emit a good amount of heat but given that each single LED doesn't consume much and that all of them spread across the strip facing outside on an open space, is this something I should worry about?

Thanks
 
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