Thread: Driving LED's in the workshop.

With LED's now quite common place I have found driving them can be problematic. I have come across this problem quite often with buying a ready made LED to install on a machine only to find getting DC od approproate voltage to it can be frustrating.

Old machines with 32V AC transformers for lights, a simple bridge rectifier and capacitor will convert to DC, but finding a ready to go LED array that can handle such a high voltage is not easy.

I am currently in the process of converting my optical comparator from incandescent bulb to LED. Due to the sort of light that has to be outputted I have to use a very high powered single die LED. I went with the now very old design SST-90 LED. It can handle up to 18 amps input with proper heatsinking for a massive 4000 lumens output in a 3mmX3mm chip size. All at only 3.6V.

Driving such a LED at such high amps for a reasonable price is not easy. My first attempt was a flashlight forum and the drivers they use. Well long story short, I fried the driver. Apparently feeding the driver 12VDC and it converting it to 3.5V with an output of 7 amps creates a huge amount of heat (it is the voltage differential between the input and output voltages that apparently does it)

So further exploration I have come across constant current buck converters. Obviously been on the market for a few years, but as some of them are CC they can be used to drive LEDs, often they can take a wide range of input voltages as well and they are low priced. $5 -$15 an example

DC 300W 20A CC CV Constant Current Adjustable Converter Step-Down Voltage Buck | eBay

You can pick them as they have two adjustable pots. There are youtube videos showing their use. I found this person have some very good videos on how to do it https://www.youtube.com/watch?v=piET0Biqo0I

I am now waiting on a buck converter to drive my LED to power my comparator again.

FWIW (not much for what you're attempting) I use quite a lot of LED lighting for the boat and it's all 12-24V as delivered. I think the actual range is 9V-32V input voltage.

Narva is one supplier I've used quite a lot.

An electronics friend of mine custom-made some LED lamps for my Kearns S type to light up the Optimetric scales. NFI on the details, that's why I have electronics engineers about the place. I'm a programmer, just bought my 5th Raspberry Pi and a nice new Arduino for the 5V A-D pins. I have a few projects in mind for the boat data system.

PDW

Hi RC,

I looked at the specs of that buck cc converter, and it's rated at a maximum of 40V input, if you drive it from a rectified 32V AC supply, you'll get a peak of 32*1.414= 45.2V which exceeds the maximum.

But it's not quite that simple, as you load it down you'll get ripple which will increase with current so the average DC voltage into the unit will be ok, but the peak of the half cycles will still be 45V

The maximum AC input voltage to match the specs would be 40/1.414 = 28V AC.

I'd still give it a try, and see how it goes, you don't have much to lose dollar wise if it goes bang.

I see there are plenty of 200W 60V max converters available, maybe one of these would be better?

Originally Posted by BobL

I see there are plenty of 200W 60V max converters available, maybe one of these would be better?

Or go for higher power, just to be on the safe side.

600W 10A DC Boost Step Up Power Converter CA CV Aluminum Base + Fan 10-60V Input | eBay

Or a cheaper buck version.

200W 15A DC-DC 8-60V TO 1-36V 12V Voltage Power Buck Converter module X2Y7 | eBay

Chinese ebay sellers tend to use their own custom version of SI units. Amps and watts are often based on a flexible marketting standard.

Originally Posted by RayG

Or go for higher power, just to be on the safe side.

that one looks like a step-up converter. I think RC is looking for 3.6V output?

Originally Posted by jack620

that one looks like a step-up converter. I think RC is looking for 3.6V output?

The other one I linked to is a buck ( step down )

I don't know what LED arrays RC is driving but the 10x10 100W arrays I use here are 33V input.

I think he's using this one:

Originally Posted by .RC.

Due to the sort of light that has to be outputted I have to use a very high powered single die LED. I went with the now very old design SST-90 LED. It can handle up to 18 amps input with proper heatsinking for a massive 4000 lumens output in a 3mmX3mm chip size. All at only 3.6V.

For my application of fixing my optical comparator I am using the buck converter like what I linked to above because I need a high amperage low voltage constant current device. This is because the LED I am using is a single chip LED Luminus Devices: SST-90 White LED

I have discovered a single LED needs around 3.5V to work. The large output LED's you commonly see are multiples of LED's chips all combined on a single die, this is why their voltage requirement is different depending on number of chips and what configuration they are connected in. Series or parallel or a combination of both.

I have had other issues with 20W floodlight LED's frying drivers, and trying to get reasonable priced replacement drivers. Now I know I can just buy a constant current buck converter which are far more versatile on the input voltage.

Many of us with newer machines might find the lights on them run off 24V AC. Rectified it will be somewhat higher. Try to find a prebuilt LED that will run off that voltage. With these CC buck converters it looks to be easily possible.

BTW the second one linked to in Ray's post is not a CC buck converter, you can see in the image there is only one pot to adjust. The CC ones have two. one to adjust voltage, the other current. Some others are all digital with a display.

I think LED lights are probably the future, but they are not as simple to run as just plugging it into a socket.

I put a 12v LED in my lathe light, but I power it using a spare 12v plug pack wired into the lathes electricals.

Dean

Yes I have done that as well, but never found it totally satisfactory.

Jaycar have a few 12/24 volt LED power supplies. Typically LEDs have fairly wide ranging power requirements, surely they would have something.

I use a 5 amp switchmode TV adapter to run an LED and a coolant pump on my lathe. Switchmodes, supposedly, aren't suppose to be run without a load so the LED is on permanently, the coolant pump via switch in the line. Switchmode adapters are superior to the linear PSUs in as much as they are much lighter and smaller.

I would imagine switchmode/linear adapters would be available in the higher voltage ranges, if not from Jaycar then perhaps from an o/seas supplier.