LED current measures only 4.5ma

J

JPB

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aussiexmas said:
Hi Jon,
I presume you are intending to use these as chasing strings. I have found it takes a lot of time to reconfigure string wiring. I always spend 2-4 times longer on wiring projects than I expect at the start.

As you have several strings, an easy way to convert 2 to 4 channel is to zip tie 2 strings together taking care to match the correct bulbs. You can then control the 4 channels as required. The only difference is that the bulbs are closeer together. I recently did something similar with some C7 LED strings after a friend blew their controllers (& some bulbs) by connecting nominal 12V strings to 24V transformers. These were originally 2 channel, 4 colour strings which I have now converted by replugging bulbs & paralleling strings to give me a 4 channel chase capable string with each channel being a different colour.

By the way, be VERY cautious on relying on a DMM to get reliable (or even useful) measurements of DC voltages or currents in an AC powered controller string. While the controller typically includes a full wave unfiltered rectifier, the LEDs actually respond to the instantaneous voltage which resembles a half sine wave. They typically only light at the higher voltage period and are off for the regions near the zero crossings. If you swing a lit string around, you can see the varying light intensity (on-off) - see attached pic. The instantaneous LED currents will of course vary also.
Click to expand...

Thanks for the comments Geoff ( and I know I am actually a bit off topic seeing we should be talking about your LED test rig which actually looks great).

I know I am in for a lot of work to modify the strings but I have the time and I think the patience. Hopefully the end result will be worth it. I have done this on incandesent strings before.

In regards to the current that I am measuring, I thought 4.5mA was a bit low. In saying that, if I am measuring 4.5 now, as long as I end up at 4.5 after cutting down the string I should be right shouldn't I?

regards, Jon

And from previous post in other thread....

In the post Christmas sales I picked up a few box of LED icicle strings from Kmart. They are only 2 channel but I am planning to convert them to 4 and as the first step, I put a DMM into the string.
Each section of the icicle is only pulling 4.5mA which I have found surprisingly low.
Using a resistance substitution wheel I have worked out the values I will need to maintain the 4.5mA current when I cut each section into two.

Jon
 
Re: Re: My LED string Test Setup

AussiePhil said:
Guys

Would you like me to split this off to it's own thread?

Phil
Click to expand...

Thanks Phil, probably a good idea.
Sorry for hijacking a thread with my second post :-[

Jon
 
Re: Re: My LED string Test Setup

JPB said:
Thanks Phil, probably a good idea.
Sorry for hijacking a thread with my second post :-[

Jon
Click to expand...

Jon,

No dramas, i do it all the time just thought this deserved it's own thread.

Cheers
Phil
 
Now to your question..

I'm not overly surprised with a 4.5mA reading, need a couple of other bits of info

DC voltage used to drive string?
How many LED's in a section? and what colour?

Ta
Phil
 
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