How to determine the power consumption of pixels

[BundyRoy]

I have inherited some lights that I don't know any details of other than they are 12V and ws2811. I also have some 5V ws2811 as well. I'm trying to work out the power requirement to run these strings. I only have a multimeter at my disposal but I have a mate who is an electrician and into solar power so I can probably borrow whatever is required. Can I hook up a string of lights through a controller on full white and somehow measure the current draw or power consumption to get a better idea of the actual use/pixel for the pixels I have.

 

[darylc]

Check out http://www.da-share.com/calculators/led-strip-string-current/

 

[scamper]

I would suggest hook them up to a larger supply than you expect them to draw. Get hold of a multimeter with a 10amp setting on it (or similar) you hook that up in series with your power supply and set the pixels to all white at 100% brightness and read the meter.
Making sure the voltage is set correctly of coarse.

 

[BundyRoy]

Thanks Daryl, I had looked at the calculator but was wondering if I could measure the actual current to check. There seems to be some variability on the current draw with the cheap lights.


Thanks Scamper. I didn't realise I could hook my multimeter up in series to measure current. I was thinking I may need one of those meters that form a loop around the cable (without touching it) and I don't have one of them.

 

[i13]

I agree it is best to actually measure it.

I am sure this is what scamper meant but you should be measuring the current for the low voltage power supply output - not its input.

Also ensure that you don't confuse the settings/plugs on the multimeter when changing between measuring current and measuring voltage. You can blow a fuse if you have it set up to measure current when you're actually tyring to measure voltage.

 

[BundyRoy]

Thanks All. I've been doing a bit of googling which is always dangerous. If I can borrow one of these clamp meters, are they any good. Or is it better to use my multimeter in series to get the best reading.

 

[scamper]

don't know if it is 100% accurate, but I think a clamp meter will only work on AC.
I would use a meter on current setting.
And yes, on the dc side. There is no point knowing the ac current... I don't think.

 

[darylc]

Thanks Daryl, I had looked at the calculator but was wondering if I could measure the actual current to check. There seems to be some variability on the current draw with the cheap lights.

Sorry, didn't read closely enough. I attached some 3 pin pigtails to one of these for real life monitoring:

http://www.ebay.com.au/itm/VOLTAGE-CURRENT-METER-12v-electrical-solar-battery-test-0-60V-0-100A-Analyzer-/221733237003?hash=item33a054b10b:g:64kAAOSwnDZT~DG1

 

[Phrog30]

don't know if it is 100% accurate, but I think a clamp meter will only work on AC.
I would use a meter on current setting.
And yes, on the dc side. There is no point knowing the ac current... I don't think.

That is not correct, you can use an amp clamp on DC, assuming the meter supports it.

$50 for a decent one.

James

Sent from my SM-G900V using Tapatalk

 

[fasteddy]

If you don't have access to a amp meter then you can assume these will run at approx max of 60mA per light, you will find they will most probably draw less than this once you get them on a meter.
If the 12vdc has been made correctly then you could assume that these would be approx. 30mA but then Ray has some that are 12vdc and draw much more than that.

A multimeter in series will have a current rating, many meters vary in this rating, so ensure you either use a meter with a high enough current rating for the load or you will blow the fuse in the meter. Or just test 1 or a couple of pixels that have been cut off from the string, because if you test a full string with only 1 or a couple of lights on then you will get incorrect readings because the IC chip will draw a small amount of current when on standby

 

[BundyRoy]

Thanks for all the tips. Good to know I need to have all the lights connected turned on as well.

I gather if I blow the fuse in the multimeter I can replace it. I gather it entails opening the case of the multimeter. Or is a case of if the fuse blows it's cheaper to buy a new one. I looked at my multimeter and it says it can go to 20A so should be right but just checking in case the worst case scenario happens.

 

[fasteddy]

Yes its just a fuse you would have to replace inside the meter, but at 20 amps then load should be no issue and you wont blow a fuse if testing a string

 

[scamper]

Thanks for all the tips. Good to know I need to have all the lights connected turned on as well.

I gather if I blow the fuse in the multimeter I can replace it. I gather it entails opening the case of the multimeter. Or is a case of if the fuse blows it's cheaper to buy a new one. I looked at my multimeter and it says it can go to 20A so should be right but just checking in case the worst case scenario happens.

You will most likely find that you have to move the probe lead to a different socket on the meter to measure 20a. They often have a shunt on the high current input.

 

[BundyRoy]

Thanks for the tips. I finally got a chance to do some measurements. The strings I tested had 42 ws2811 nodes on each. I have 48 strings but I only tested 4 as there seemed to be very little variation. They came in at 2.22 to 2.26 A. This is 0.054 A per pixel when on white. So very close to the 60 mA you allowed Eddy but not very close to the 30 mA of the better quality lights. That's 1.8 time the power consumption due to poorer quality equipment.


Also thanks to David for the DA_E131 program. Without that, getting all the lights on full white would have been a lot more onerous.

 

[fasteddy]

That's very close to the output spec for the 2811/2812 as they are rated at 18.5mA per colour. But at 12vdc there is a lot of wasted energy and very little advantage over 5vdc lights