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LED controller
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Andy Davies



Joined: 09 Dec 2014
Posts: 97

PostPosted: Tue Jul 24, 2018 3:39 am    Post subject: LED controller Reply with quote

I can remember somone posting an image of a desktop LED controller that had knobs for controlling current and voltage with a digital readout. Can anyone recommend such a device?
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Justwalking



Joined: 10 Jun 2018
Posts: 137
Location: Russia

PostPosted: Tue Jul 24, 2018 5:56 am    Post subject: Re: LED controller Reply with quote

Andy Davies wrote:
I can remember somone posting an image of a desktop LED controller that had knobs for controlling current and voltage with a digital readout. Can anyone recommend such a device?


Hi, Andy.
Without a knob it's easy to find small DIY devices (cost about $2) but need to solder few wires to LED power. Adding the knob probably will higher the price more than cost of LED.
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Saul



Joined: 31 Jan 2011
Posts: 1208
Location: Naperville, IL USA

PostPosted: Tue Jul 24, 2018 8:31 am    Post subject: Reply with quote

Ebay items
292091996180
253240124377
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Andy Davies



Joined: 09 Dec 2014
Posts: 97

PostPosted: Thu Jul 26, 2018 5:18 am    Post subject: Reply with quote

Many thanks Saul.

The controller I am looking for is an LED controller as well in a box about the same size as an oscilloscope I used to use in school!

Cost was around £40.
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1068
Location: Stockholm, Sweden

PostPosted: Thu Jul 26, 2018 6:14 am    Post subject: Reply with quote

Andy Davies wrote:
Many thanks Saul.

The controller I am looking for is an LED controller as well in a box about the same size as an oscilloscope I used to use in school!

Cost was around £40.

Perhaps you mean a bench power supply, like eBay item n. 321862408895. There are cheaper as well as (much) more expensive ones. It all depends on the precision, power rating, availability of a communication interface, programmability etc. To use it as a LED supply you need one with adjustable maximum current (adjustable voltage is also nice, but adjustable current is what you really need), enough power, a reasonably precise current readout, and nothing more.
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Andy Davies



Joined: 09 Dec 2014
Posts: 97

PostPosted: Thu Jul 26, 2018 4:05 pm    Post subject: Reply with quote

Yes, that is what I am looking for! Need one that does 39V for the new COB LED I have just bought.

Most seem to go to a max of 30V.

I will mostly be doing video so need one that does not create flicker when powering the LED. Can the LED be driven directly by the unit?
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ChrisR
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Joined: 14 Mar 2009
Posts: 7832
Location: Near London, UK

PostPosted: Thu Jul 26, 2018 4:40 pm    Post subject: Reply with quote

There are loads of them on ebay which go to 38V or so.
First I found: 263577248109

Some dimmable.
150W?
221727121668
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1068
Location: Stockholm, Sweden

PostPosted: Thu Jul 26, 2018 9:19 pm    Post subject: Reply with quote

Andy Davies wrote:
...

I will mostly be doing video so need one that does not create flicker when powering the LED. Can the LED be driven directly by the unit?

Good ones have very little voltage/current fluctuations at 50/60 Hz. It is just a matter of choosing one good enough.

The analog supplies tend to have low noise if the 50/60 Hz and their harmonics are smoothed out adequately, and for this use it does not really matter if their output is slightly sluggish. The switching ones, if cheaply made, may have a high-frequency noise (usually, somewhere between 20 and 40 KHz).

The idea is to feed the LEDs (connected in series to feed the same current through multiple LEDs) directly from the regulated power supply. If you are using a cob, typically the connections among individual LEDs have already been made for you, and you cannot choose. If the LED or cob package already has built-in regulating electronics, it will probably interfere with the functioning of the constant current supply and you may not be able to get the dimming you want. Also, dimming is likely not linear in any case (a bench power supply is not built to be used as a LED dimmer, strictly speaking).

Connecting multiple LEDs in parallel can cause some of them to conduct a higher current than others, and the ones with higher current warm up more and can enter a self-destructing thermal runaway process. Even with a constant current source.

If you must connect LEDs in parallel, each of them should at least have a significantly large resistor in series to reduce the risk of thermal runaway. This will of course waste much of the power.
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Andy Davies



Joined: 09 Dec 2014
Posts: 97

PostPosted: Sun Jul 29, 2018 7:01 am    Post subject: Reply with quote

At the moment I use a DC unit connected to this http://www.luxdrive.com/products/flexblock-a011/

Would I be able to use the bench power supply connected directly to the LED and dim it?
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enricosavazzi



Joined: 21 Nov 2009
Posts: 1068
Location: Stockholm, Sweden

PostPosted: Sun Jul 29, 2018 7:08 am    Post subject: Reply with quote

Andy Davies wrote:
At the moment I use a DC unit connected to this http://www.luxdrive.com/products/flexblock-a011/

Would I be able to use the bench power supply connected directly to the LED and dim it?


If you mean swapping out the DC unit and LuxDrive driver and replacing them with a bench regulated current supply, yes. You still need to know the maximum safe operating current of the LEDs, and not exceed it with the bench power supply. You also need to know the approximate voltage needed by the LEDs, since bench power supplies usually have limits of 24 or 48 V. If you cannot get the voltage high enough, you cannot get the current you need, either.

The LuxDrive driver you mention, however, already has a constant current output and a dimmer input. What is the reason you want to replace it?
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Andy Davies



Joined: 09 Dec 2014
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PostPosted: Sun Jul 29, 2018 7:15 am    Post subject: Reply with quote

I've already bought a 6V, 12V and 24V power supplies and now need to be able to drive a 39V 2.8A LED and have burnt out one of the Luxdrives so wanted to have more control with readouts as to what is going on.

Also bought 4 LED cheapo drivers from China with readouts but these induce LED flicker on video.

Have also experimented with Peltier cooling.
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enricosavazzi



Joined: 21 Nov 2009
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Location: Stockholm, Sweden

PostPosted: Sun Jul 29, 2018 10:35 am    Post subject: Reply with quote

Andy Davies wrote:
I've already bought a 6V, 12V and 24V power supplies and now need to be able to drive a 39V 2.8A LED and have burnt out one of the Luxdrives so wanted to have more control with readouts as to what is going on.

Also bought 4 LED cheapo drivers from China with readouts but these induce LED flicker on video.

Have also experimented with Peltier cooling.

One thing that sellers are sometimes not careful to explain is that these potted regulators typically need to be glued/bolted on quite large heatsinks to avoid overheating. They may have built-in temperature protection, but if they heat up very fast the protection may not cut the supply power fast enough. They should in theory not burn out if overloaded or overheated, but obviously the one you lost did just that, or was defective to start with.

With a programmable power supply, in principle you could set the maximum current so that this value will not be exceeded. With an ordinary power supply you must instead keep watch on the current readout and avoid turning the current knob too high, but it is also easier to dim the LEDs just by turning down the analog current potentiometer.

In general, a bench power supply should be sturdy enough to provide the nominal current without overheating, and should also have effective short-circuit and overcurrent protection.
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Andy Davies



Joined: 09 Dec 2014
Posts: 97

PostPosted: Mon Jul 30, 2018 3:36 am    Post subject: Reply with quote

It was my fault that the Luxdrive burnt out as I shorted it whilst trying to determine which way the wires should be connected to the pot!
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mjkzz



Joined: 01 Jul 2015
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PostPosted: Wed Aug 01, 2018 1:08 am    Post subject: Reply with quote

Andy Davies wrote:

Have also experimented with Peltier cooling.


Not sure if Peltier device will help because these devices are not very efficient, you could end up with more heat sink and fans than without as they themselves generate more heat.

Unless, you need to have a particular spot cooled and do not care more heat generated by Peltier device.
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enricosavazzi



Joined: 21 Nov 2009
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PostPosted: Wed Aug 01, 2018 2:01 am    Post subject: Reply with quote

mjkzz wrote:
Andy Davies wrote:

Have also experimented with Peltier cooling.


Not sure if Peltier device will help because these devices are not very efficient, you could end up with more heat sink and fans than without as they themselves generate more heat.

Unless, you need to have a particular spot cooled and do not care more heat generated by Peltier device.

Agree, Peltier cooling is not meant for power devices but mainly for cooling down components like sensors where thermal noise is significant. The main advantage of Peltier elements is that they can cool down a component well below ambient temperature.

Heat pipes are probably most effective for cooling down power components, and they use no extra energy. They just redistribute heat around, so they also need efficient heat sinks at one end. An advantage is that the heat sink does not need to be directly attached to the power device but can be a short distance away.

If one needs a stronger cooling, forced water circulation is more effective than heat pipes. Open-ended forced water circulation requires no heat sink, since you are going to discard the heated water (but tap water leaves calcareous and/or rust deposits that foul up the heat-exchange element rather quickly).
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