DiyLightAnimation
Fun => The Porch => Topic started by: chrisatpsu on April 17, 2012, 12:04:54 am
-
how are you guys measuring the A or mA that a string of lights is using?
when i try to use my multimeter, i never get the result that i'm looking for. no where even close.
-
Kill-a-watt does it for me!
-
Current clamp works for me... this way you don't have to actually put your multimeter in the circuit
-
You can make your own DIY current clamp as well. However, don't have the link handy.
-
well, for example, when i try to measure the current used by the smart strings, i try to include the tester in the circuit, but i don't get high enough numbers when the string is on full white
-
What readings are you getting and where are you putting the meter?
-
i connect the multitester between the + connector, and the + lead on the end of the string, so that the tester is in series with the string.
-
when i'm expecting to see amps, it's reading a much smaller number in mA
-
You're not alone. I have issues trying to test amps as well.
If I test a single rectangular node connected to a 2010 controller, meter should read around 52ma, right?
-
You're not alone. I have issues trying to test amps as well.
If I test a single rectangular node connected to a 2010 controller, meter should read around 52ma, right?
Maybe the current is not constant? I wonder if you had an oscilloscope connected what it would look like.
If the signals are PWM maybe it looks something like this
http://www.youtube.com/watch?v=uj680hP9gGg
i speak as if i know anything about the electronics of pixels
-
First note - some answers might assume an AC string; AC current can be measured with current clamps (which essentially makes a tiny transformer). Doesn't work for DC, tho. In general, you will need to put something in line to measure DC current.
What I'd do first is use my old analog meter. It's a very old Radio Shack that was once probably $20. I've found it to work more reliably on circuits (current or voltage) with a lot of switching noise. If you don't have an analog meter, I recommend getting one; any time your digital meter reading seems a bit wacky or unstable (varying over time, or when measuring the same thing in different ranges), pull out the analog for a sanity check.
(If I had an oscilliscope I'd put that across the meter leads next and look at the waveform, but we'll leave that aside for now).
The smart strings have a highly variable current when doing PWM (Pulse Width Modulation). It's full on for a tiny fraction of a second and full off for another fraction, rinse and repeat often. That can drive a DMM to distraction.
It might measure better when at 100% brightness. You'd have to look at it with as scope to see if it really stabilizes to full on or if there is any off time. Try it.
If you really want to measure it with a DMM, you might be able to put an appropriate capacitor across the DMM leads to filter out the variations. Basically there is a small resistor (called a shunt if anybody cares) between the leads inside the DMM (and the analog meter) when measuring current. As current flows through the resistor it develops a voltage which is measured and scaled by the meter. A capacitor between the leads would smooth out the curve. I don't know the right value - it depends on the frequency of the PWM in the pixels, the amp range of the meter (which changes the shunt resistor used), and the current draw.
I would not be surprised if a really good DMM can handle all this in stride; I've never had a really good professional DMM.
-
Current clamp can in fact read DC current, thank goodness or it would make my life unbearable. However I never thought about PWM. Because of that you are getting an average.
-
The tough part is that your measuring something that is going to vary a lot anyways, so I'd be more interested in what the peak or average amps was.
I use a Watts Up, but same as a Killowatt ... and I hook it up to the extension cord that say feeds the PS for an active hub. Then I run some songs through it and measure what the peak, min, max, avg are.
In my mostly incand. world ... these things don't use much juice at all. Meaning, I could run two active hubs off a single 15a dedicated circuit and just forget about it.
I also use a whole house power meter, called the TED5000. I can watched the whole house usage in real time and was shocked how low it often was. Meaning these shows spike the power a lot, but its highly variable unless you sequence everything on and leave it for awhile.
It was helpful once, when I was blowing a GFCI ... I located an exact spot in a sequence and was able to turn off some lights that were supposed to be OFF, but were actually ON ... creating and overload on a circuit I was used ... by relying on used 2 colors at once but never 3.
-
The tough part is that your measuring something that is going to vary a lot anyways, so I'd be more interested in what the peak or average amps was.
I use a Watts Up, but same as a Killowatt ... and I hook it up to the extension cord that say feeds the PS for an active hub. Then I run some songs through it and measure what the peak, min, max, avg are.
In my mostly incand. world ... these things don't use much juice at all. Meaning, I could run two active hubs off a single 15a dedicated circuit and just forget about it.
I also use a whole house power meter, called the TED5000. I can watched the whole house usage in real time and was shocked how low it often was. Meaning these shows spike the power a lot, but its highly variable unless you sequence everything on and leave it for awhile.
It was helpful once, when I was blowing a GFCI ... I located an exact spot in a sequence and was able to turn off some lights that were supposed to be OFF, but were actually ON ... creating and overload on a circuit I was used ... by relying on used 2 colors at once but never 3.
You may have noticed the Nutcracker current meter is missing. I broke it in one of my code promotions and just havent gotten back to it.
When people build a target in nutcracker, i am going to prompt (or maybe just assume .3w) for the wattage of a single pixel.
Then for each frame i calculate the wattage each pixel is using , scaling it by the intensity setting.
It may not be perfect, but it will be a free meter showing power consumed during your show,
-
That's very cool.
-
when i'm expecting to see amps, it's reading a much smaller number in mA
With no intent of insulting your intelligence or any electrical knowledge , did you move the DMM lead to either the 300ma Fused or 20A non fused connector? When I get tired or distracted this is a mistake I have made from time to time.
-
At least with the Watts Up (more expensive versio of the Kill-o-Watt) ... a typical retail string of LED lights would barely register, so I finally just decided that it was such a small amount of amps that I wouldn't worry about it.
And now with smart strings, I'm just using a xxx watts ATX power supply and giving it plenty of power for the worst case and factoring a max of 70 or 80% of the power supply can be used by the smart string items ... and only using 80 PLUS or better (efficiency rated) single rail ATX power supplies.
The fact that the actual use is almost always highly variable, you might as well use the max or worst-case for planning and just be happy with it.
Just an opinion.
-
You may want to measure (or calculate an estimate for) amps for the sake of
(1) buying a large enough power supply or debugging
(2) checking the ampacity of your wiring
(3) checking the voltage drop of your wiring
If instead you are concerned about input power and your power bills, I agree that you would do better using one of the AC mains power meters like the Kil-o-watt - this can factor in the real power supply efficiency.
These are two different things, tho.
Also, regarding "varying current" this happens in two way on two timescales. When you are showing an individual pixel at 20% of max brightness (eg: at intensity 51 of a 0-255 scale) the chip next to the LED inside the pixel housing will be turning the LED on and off many times per second, perhaps hundreds so that you don't see flicker, so it can keep it on about 20% of the time. The high frequency is so you don't perceive it as flickering. The overall current draw will be a combination of these many individual and unsyncrhonized PWM current draws, so it'll be pretty jumpy on a millisecond time scale. Your DMM could be sampling that value at various points and not averaging it well, so it may have unstable or inaccurate readings. The analog meter (and maybe GOOD DMMs) will be more stable.
And of course, there is a different variance in that you will be turning pixels to various brightness levels during your sequences. Hopefully you realize that you would not want to be varying the lights while you are measuring them with the DMM, tho. This is the varying timescale that Nutcracker (or Vixen for that matter) could estimate for any given sequence step.
So there's input AC input power to pay for vs DC current to plan wiring, and there's PWM noise to confuse DMMs vs sequence controlled brightness changes. All are valid things to consider, but different.
-
so then i should find a fuse for my analog meter to get an average (since the needle cant respond THAT fast)
-
i should probably get my current meter turned back on within the next week or two (I am working a LOR export issue currently).
I will modify the current meter to be a power meter. That way i can use a univeral measurement irregardless of voltage of the strings.