LEDs ... The Good, The Bad, and The Ugly

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Sorry, the Red lead broke at the solder joint before I could cut it.

Removing the outer sleeve revealed a very nicely executed Heat-Shrink sleeve inside, covering the dropper resistor:

... Which makes me think they bought-in the LEDs with the resistors attached.

It certainly looks like two different standards of workmanship.

MichaelG.

Just to let everyone know, B &Q have boxes of 5 x 4 watt led lamps gu10 fitting for £16.00, that is £3.20 each.

They seem to use 1 x 4 watt led rather than multiple led of lower rating.

Supposed to be equiv to 35 watt halogen but both the wife and myself think they are brighter than the 50 watt halogens they have replaced..

Energy saved = 4 watt x 10 lamps replacing 10 x 50 watt = 460 watt saving

Hi Michael,

The USB limit is only 150mA for USB1 and 500mA for USB2.

A proper USB controller will only let each device use an allocation of 100mA 'units' if it is 'asked' for permission.

I imagine that your MAC implements this strictly and the LED is not an intelligent device.

Neil

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Neil,

May I suggest that you check Apple's specifications ... The USB2 ports on the MacBook Pro [and several of the other machines] were upgraded to deliver up to 1000mA, so that they were capable of charging the iPad.

Agreed, the LED lamp is not an "intelligent device" and so the USB port should limit the current ... but the point I was making was that the LED lamp had an internal short ... and [as an aside] I was pleased to find that the Mac not only protected itself, but informed me how and why it had done so.

MichaelG.

I have made up 2x 4 foot LED strip lights double row from a 5 meter flexi strip. I have stuck them on to a strip of aluminium flat bar to act as a heat sink. When I first turned the one above the lathe it didn't seem that bright and the heat sink didn't get warm. The power supply was an old PC unit. The 12 volts was rated at 8amp. When I measured the voltage under the load of the lamp it was 9.5v! Bought a 20amp PSU now the heat sink gets warm and the LEDs are bright. The garage temperature is 13.6C and after 45 mins the heat sink is 34.7C. Something to warm my fingers on in the cold!

Cheers Michael.

Hi Michael,
PC power supplies need a reasonable amount of current to be drawn from the 5 volt output (And possibly the 3.3 volt output on modern ones.) before the 12 volt output will give the correct voltage.

Les.

I have added a way to drive a string of LEDs that require between about 13 volts and 30 volts with constant current drive from a 12 volt supply to my Weebly website. It uses one of the cheap LM2577 based step up regulators that are sold on Ebay.

Les.

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Very interesting, Michael

If you have the opportunity ... Could you please check what current these strips are now drawing at 12volts.

Also maybe the dimensions of your heatsink.

Many thanks

MichaelG.

I doubt it makes much difference; it depends on what the joint connects to rather than the composition of the joint itself. A lot of power ICs have thermal pads underneath that are inteded to be connected to internal, or external, planes with vias to spread the heat. It's all about copper area.

Andrew

Edited By Andrew Johnston on 26/10/2014 11:02:38

1.9 Amps!

That will teach me to assume! I was expecting 8 Amps!!

So it looks like Les was on the money!

Well at least the PSU's will run cool and I will have plenty of juice to drive other things.

The aluminium strip is 4 foot by 1 inch by 1/8 inch.

Cheers Michael.

Les,

I cannot find your LED driver on your website

regards

Geoff~

Hi Geoff

Try the link below. He has 2 web sites!

**LINK**

Cheers Michael.

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Thanks for that, Michael

MichaelG.

Hi Geoff,
Sorry. I intended to put this link to the LED driver on my last post.

Thanks Michael (H) for posting the link to my Weebly website.

Les.

Les/Michael Horner

many thanks for the link

Geoff~

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W.

Many thanks for running the test, and posting the results ... impressive indeed.

Apologies if you have already done so, but; would you please check the device number for the controller chip in that lamp ... it's obviously one to look for.

MichaelG.