LED power supply

alahol2

alahol2

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www.troppo.co.uk
A couple of years ago I experimented putting some led strips up under the sidedecks to provide ambient lighting and was very pleased with the results. Two years on a lot of the LEDs have died and the strip is losing its 'stick'.
I now want to do it properly so will get some proper ally channel with frosted cover strip to hold the LEDs. I also want to add some voltage regulators which I hope will prevent the LEDs from burning out. The two main lights are about 2 metres long and it appears that 5050 SMDs at 60 per metre need around 15 Watts/metre to run them. I've found these power supplies which look like they will handle the power OK.
http://www.ebay.co.uk/itm/161303594673?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Can anyone see a problem with these or suggest a better (but not too expensive) way of doing it?
PS I don't want to rewire the boat thanks.
 
Hi, I've been looking at these for the same purpose. It doesn't say in the ad what the "voltage overhead" is (sorry, I know there's a proper name for this but can't think of it 0- I mean how much higher the input voltage has to be than the output. For example would this still produce 12 v out if the input dropped to 12.5 v without any adjustment).

This might be better
http://www.ebay.co.uk/itm/12-VOLT-R...1901304?pt=UK_Light_Bulbs&hash=item3f447bc378
I bought something similar from this supplier a couple of years ago and it was fine - he doesn't do the same circuit any more but I think I'll go for these, even though they're more expensive

Let us know how you get on if you buy one of the others to try.

David
 
Thanks OldSalt, yes I've had a look at that thread and found it very useful.

DRA said:
This might be better
http://www.ebay.co.uk/itm/12-VOLT-R...1901304?pt=UK_Light_Bulbs&hash=item3f447bc378
I bought something similar from this supplier a couple of years ago and it was fine - he doesn't do the same circuit any more but I think I'll go for these, even though they're more expensive
Click to expand...

I was going to go with those until I worked out the potential power consumption. My 2 metre strip is liable to use around 30 watts.
 
alahol2 said:
Thanks OldSalt, yes I've had a look at that thread and found it very useful.



I was going to go with those until I worked out the potential power consumption. My 2 metre strip is liable to use around 30 watts.
Click to expand...

The ones I have here have a 130ohm resistor for ever group of 3 diodes, so at 12V, I'd expect about 23mA per 3 diodes. 3 diodes= 50mA, so that's about 5.5W per metre.
Say 1A per 2m?

The minimum 'overhead' by which a regualtor's input must be above its output is called the 'dropout voltage', try looking for an LDO low dropout regulator.
It's mostly aterm in linear regulators not switchers.
 
Last edited:
lw395 said:
The ones I have here have a 13ohm resistor for ever group of 3 diodes, so at 12V, I'd expect about 23mA per 3 diodes. 3 diodes= 50mA, so that's about 5.5W per metre.
Say 1A per 2m?

The minimum 'overhead' by which a regualtor's input must be above its output is called the 'dropout voltage', try looking for an LDO low dropout regulator.
It's mostly aterm in linear regulators not switchers.
Click to expand...

Are your LEDs 5050s?

I was going by this table (and others that seem similar)... http://www.ledlightsworld.com/page.html?id=32

Using 5050 leds at 60/metre that gives me about 30W for 2 metres.
 
Alahol2, You're right about the higher power consumption of the 5050 LEDs, I am using the 3528. The 8 watt device that I bought drives a 1m length happily - I think 10 watts would be OK for about 2 metres. It will be interesting to now if the device you suggested can drive a full 5m strip of 5050s.

LW395, thanks for reminding me about dropout voltage. Te device I bought was a linear device and your calculations tie in with mine for 3528 LEDs

David
 
alahol2 said:
A couple of years ago I experimented putting some led strips up under the sidedecks to provide ambient lighting and was very pleased with the results. Two years on a lot of the LEDs have died and the strip is losing its 'stick'.
I now want to do it properly so will get some proper ally channel with frosted cover strip to hold the LEDs. I also want to add some voltage regulators which I hope will prevent the LEDs from burning out. The two main lights are about 2 metres long and it appears that 5050 SMDs at 60 per metre need around 15 Watts/metre to run them. I've found these power supplies which look like they will handle the power OK.
http://www.ebay.co.uk/itm/161303594673?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
Can anyone see a problem with these or suggest a better (but not too expensive) way of doing it?
PS I don't want to rewire the boat thanks.
Click to expand...

This power converter is quite a clever device in that low voltage drop out is not a concern. It will buck or boost as necessary to give the desired output. So if you set it for 12v output it will give that from about 6 up to about 30 volts. It is a switch mode transforming type device. Do check the current of your LEDs however to ensure you don't overload the supply.
Re light strips yes they are great. I have some of the 3528 type where there have been multiple failures. I use them at home in cupboards. I suspect that the voltage of the 240 to 12v supply rises with less current so more failures the more liekly to fail. Or perhaps it is just the construction.
Last one I bought was 5050 type and i am optimistic this will last better. good luck olewill
 
Big John said:
I think you should go for this unit as you can adjust the current as well as the voltage. http://www.ebay.co.uk/itm/DC-Buck-S...03594673&tpos=top&ttype=price&talgo=undefined
Click to expand...

I think you are right. It does more than my suggestion and at a cheaper price (including postage on mine), go figure. Thanks for that.
And thanks William_H for the extra info. I think I shall now go for the later suggestion which looks like it can control the current also. Really don't understand how the voltage AND current can be controlled at the same time but it sounds a good idea.
 
alahol2 said:
Are your LEDs 5050s?

I was going by this table (and others that seem similar)... http://www.ledlightsworld.com/page.html?id=32

Using 5050 leds at 60/metre that gives me about 30W for 2 metres.
Click to expand...

no, not 5050's.
Can you read the resistor values on yours?
The ones I have in front of me were only about 3 quid for 5m, I'm putting them in the garage and garden shed. No more shadowy corners....

I think the bigger leds like 5050's may be more sensitive to bumping up the current and voltage.
 
Actually I am now having second thoughts about using 5050 LEDs. I want background lighting and the 3528 LEDs I used last time were about right. The 5050s are going to be too bright I think and certainly use a lot more power if I'm running 4 metres of them (2 metres under each side deck). I suppose I could use 5050s at 30 per metre. Oh decisions, decisions.
 
I did my dissertation which included looking at failure modes in LEDs intended for long term lighting applications a few years back. The reason these cheaper LED strips tend to fail is actually a result of moderate, long term overheating. While this is related to how much current is driving them, it's more to do with actual package design. The 5050 / 3528 type packages - and other similar packages such as PLCC2 (that I focussed on) were developed as surface mount indicator LEDs - not illumination LEDs. They therefore do not have sufficiently low internal thermal impedance to the substrate to which they are mounted to keep the silicon P-N junction cool enough when the LEDs are driven at anywhere near their maximum 'If' (forward current). In fact, a PLCC2 running at about 80% maximum If will probably run at about 120-150° at very localise, microscopically small points in the junction.

In genuine long term applications, these things are normally run at about 10-20%, with more diodes being used to give the required luminous flux. Unfortunately, these cheap LED strips tend to have a log going against their reliable, long-terms, manufacturer stated credentials.

- Use of polyamide PCB (fleximble) mounting substrate further reduces the heatsinking effect of the board to which they are mounted.
- All diodes are created unequally, and are 'binned' based on their performance. The diodes that make their way into the £10 type strips tend to be the lowest, cheapest, crappiest binned diodes - which probably should have stayed in the bin!
- To make the most of the 'potential maximums', even with a resistive shunt, they're normally set up for being driven at about 60-100% If, and therefore run (internally) hot.

Anyway, my point is, the actual driver isn't so important, but if you want a fit and forget solution that'll last years - forget the £10 LED strips - they have a good chance of failing after as little as 20 hours or so (as I have experienced myself).

Ideally, LED strips that have loads of diodes and no shunt resistors, driven from a constant current driver at around 2-3mA, will last a lot longer, but even then it's many times more expensive.

One other word of warning - if the regulator (especially buck+boost switchers) is going to cost you <£5, then there's just as much likely hood that this'll go wrong in similarly short periods of time! Hopefully, when it does go wrong it'll go open circuit, but it may well not... and take your LED strips with it!

Not sure the drivers with adjustable current and voltage are required. If you strips have shunt resistors, then they will regulate current (and then by changing the output voltage you change the current seen by the LEDs proportionally), and you can leave the current setting up at maximum anyway. An extra potentiometer in a circuit is an extra potentiometer to go wrong, IMO!

Personally, and contrary to everything I have said, we will be fitting some £10ish strips to the cockpit of our boat this winter ready for the season. We will also be using an El Cheapo eBay special of a driver. It's many times cheaper than doing it 'properly' and we will therefore just make it so the whole set is as easy as possible to replace as and when it does go wrong - even if it does mean £30 of LEDs and half an hour of tinkering every season or two.
 
Thanks Annageek, very interesting.
I was hoping that mounting the LED strip in an aluminium channel might help to keep them cool. From what you are saying, would it be better to use 5050 strips and run them at, say, 11 volts rather than use 3528 strips running at 12 volts? Or would it be better to use the current limiter than the voltage limiter?
 
alahol2 said:
Thanks Annageek, very interesting.
I was hoping that mounting the LED strip in an aluminium channel might help to keep them cool. From what you are saying, would it be better to use 5050 strips and run them at, say, 11 volts rather than use 3528 strips running at 12 volts? Or would it be better to use the current limiter than the voltage limiter?
Click to expand...

In reality, for these types of LED strips, the alu channel is unlikely to make that much difference. Although they do look hella cool, and it means that if you do end up having to replace the LED strips, then you have a semi concealed area, behind a nice frost bezel, so you can't see any crappy bits of adhesive tape that may still be leftover or anything - making the whole swap to new strips much easier.

The trouble with getting closer and closer to the head room of the LEDs is that small fluctuations in supply voltage (and forward voltage drop, 'Vf', of the LEDs) will have a proportionally much bigger effect on the current regulated by the shunts. Furthermore, as the resistances of the different shunts will vary, you'll also get some dimmer patches of LEDs. Add to this that we're talking about a few amps of current through some conductors that are just copper foil PCB tracks (probably only 0.05mm^2 of cross sectional copper area) and so voltage drop over the length will be more noticeable with lower head room - and you may notice that the LEDs at the input end of the strip are brighter than those at the other end. If this effect is noticeable, you could half the problem by connecting the end of the loops's conductors to the start of the loop's conductors, thereby making a ring circuit. You could also remove the problem by creating the right circuit and sourcing the positive supply exactly half way around the length of the LED strip when compared to the negative (balancing the current seen by each 'series system' of three LEDs and shunt resistor. But then, this is all adding to the faff that will need dealing with when it comes to replacing the strips.

I think the Vf for these LEDs will be about 3.3V at average forward currents. Therefore, going from a regulated 12V source to a 11V source should give you about half as much current (which will probably appear something like 70% as bright - when you factor in the response of the human eye, and the non linear response of LED luminous flux vs forward current).
 
For the record. It's problems like these why PWM (pulse width modulation) is used for controlling LEDs.

Essentially, you are always driving LEDs at 80-100% whenever they are illuminated, and so their characteristics always stay the same. To change the brightness, you just alter the time they spend illuminated vs the time they spend not illuminated (deluminated?), at say 200Hz (so the human eye doesn't notice) and all's well and good. Generally a bit more expensive and complicated though,

This is the method used in most consumer applications and why if you dim the screen on your phone and wave it about in front of you quickly, you can notice it flickering.
 
Thanks again Annageek.
I've now changed my mind again to go back to the 5050 LEDs and drive them off a lower voltage to reduce the power usage and reduce the illumination.
It's all good fun isn't it:rolleyes:?
 
The 5050 LEDs are an interesting device. They have 3 diodes in the package which collectively excite a phosphor to provide the white light. The LED diodes seem to emit a blue green. The diodes are each accesible on the back but are usually wired in series for 12v with a current limiting resistor added. The device is clearly made for providing lighting as opposed to Annageek sugesting some are made for SMD indication. Regarding getting too hot and insufficient heat dissipation well this may be so. Heat is a function of current so any additional series resistance to reduce the voltage/current will reduce the heat and light output. But improve reliability. However I suspect that some reliability will be lost in the corrosive environment on a boat.
Just as an excercise in time wasting fiddly things. I had one of those little candle lanterns used for Christmas decorations. I got 4 x5050 chips. Removed them from the base printed circuit and rewired them in parallel. The 4 face outwards in a square mounted on copper wire. With a suitable series resistor they run on 3 x1.5v cells and provide as much light or more as the candle. But no fire risk. Definitely fiddly. A winter project for the insane. olewill
 
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