My latest unhappy discovery - my 12V 2801 pixels draw over 5 ma each

My latest unhappy discovery - my 12V 2801 pixels draw over 5 ma each when off. Apparently they use a zener shunt regulator. That means the SLA battery powered string of a 100 I was planning to use at a campout next week draws half an amp even when off, and with no signals going out to them, ie: when battery voltage drops below 10.5v I send all dark and then stop calling LEDS.show() - and the battery keeps draining and the voltage dropping, since by then the battery is in the steeper decline region so even half an amp drops it to 8 volts after a few more hours. (Nominal 12 Ah SLA).

I mention this because it may be an unexpeted factor for other pixel library users; I wish I had known about it before switching to 2801s.

So, among the characteristics that a comprehensive page on pixel chips and strips/strings should describe, is the quiescent current - which along with PWM rate is generally not advertised and must be dug out or measured.

I’ve ordered some relays to cut power to the string when then battery voltage cutoff triggers. At first I was going to get latching relays, but then I realized that the current cost of keeping the relay activated while the string was on is not so important, so a conventional relay should be fine.

Aside - a current of half an amp is awkward for me to measure accurately with tools in hand - it’s above the 400 ma range of my multimeters, and the 10/20A ranges don’t have much resolution. I’m thinking to get some hall effect current sensors, and integrating those in some displays, even if only during development. It would be one way to self test whether all the LEDs are apparently working, or even count the length of a string. (Tho in this case, lighting a pixel full on only adds 30 ma to the 0.54A off current).

Ug. Yeah, the quiescent power consumption is definitely an issue for battery powered applications. Dan has some numbers that he measured about WS and TM parts, but I’m not sure how universal they are.

I wonder if a MOSFET could be used to switch the power to the strip instead of a relay. A little out of my expertise here, but it might be an option. Perhaps you could do the fail-safe version of the circuit that way, too.

One fancy solution would be to use a solar charge controller with Low-Voltage Disconnect, eg a Morningstar Sunsaver L10 (or L20)


The LVD cutout has totally saved my battery biscuits on multiple occasions, both on my small (60W!) home solar rig, and out in the desert at Burning Man. If you’re doing solar charging anyway, I’d recommend something like this. If not, it’s definitely more expensive (~$75?) than just a relay or MOSFET.

The ever-awesome Battery University has lots of relevant information on what happens when lead-acid batteries are over-discharged, and the ensuing “non-reversible sulfation”, which is what you’ve got to avoid as much as you possibly can.
http://batteryuniversity.com/learn/article/sulfation_and_how_to_prevent_it
I had two LA batteries give up the ghost due to accidental overnight (or multi-day) irreversible over-discharge-- before I installed charge controllers with low-voltage disconnect.

As for measuring power, i just LOVE the Watts Up WU100 from Tenergy.


It’s also in the ~$70 range, but has turned out to be one of the best diagnostic tools I’ve used for this. It measures in 0.01A, up to 50A. I attached barrel plugs and SAE quick disconnect plugs to mine and BAM!: quick easy answer to “How many Watts does this animation draw?” Or “if I let this run for fifteen minutes, how many Ah does it eat?”

For bench testing, there’s also this slick USB power monitor, which is not yet available in the US (I think) – just Japan.


I don’t have one in my hands yet, but reliable sources seem to have found it useful.

-M

TM1809’s appear to be 0.6ma@12v/ chip (3 led pixels per chip), and the WS2811s appear to be about 1ma@5v per chip (1 led pixel per chip). 5ma for the ws2801 seems really really high - sure it isn’t .5ma per? or was that 5ma for the entire string? I’ll see what else I can get measured/documented.

Locus Lux Liquida (the large project I was doing for the 4th, which ended up not being completed in time, so only a partial install was doing - next time, I have to cut off the non-project related work sooner) draws over 1 amp@12v sitting idle doing nothing :frowning: Cutting off power to the strips when they’re off is the next hardware mod that I want to do to it (as well as putting fuses in place on all the power lines, and maybe something that I can use to measure power draw/voltage drops - but fully lit up, this thing could end up drawing as much as nearly 30A@12v:)

Yeah, I do mean 5 ma/pixel for the 12v 2801. Measured 0.55 A for 100, minus about 50ma for the controller.

I have been told that this is because the 2801 has only 6v tolerance and thus there is an inefficient zener shunt regulator on the tiny pixel pcb (bullet style pixels) to supply the 2801 chip’s power, which makes sense. A 5V 2801 might use much less power, but this may be typical of 12v 2801’s.

And some chips chips (eg:180x) may not need the external shunt regulator to run on 12v. This is one of the things I would have loved to know about the chips before buying. Let’s work together to make your chip reference a definitive source for all this info; or I can put something online if you want to focus on the software.

I have 12v 1804’s, but I got the 12v 2801’s because I don’t like their slow PWM rate (this is for a mellow hang-out space). It’s too late to get any other option for this event, but now I’ll be looking at both dark power drain and PWM rate as considerations for some projects in the future.

Tonight i’ll see about adding the power information i’ve collected to the website - as well as the bits about the 2801 that you have. And I hear you on power draw, i’m starting to get to the point where i’m doing large enough projects that even dark power draw is becoming significant. Thanks for the ws2801 info (as if I needed any more reasons to not use the ws2801s anymore at all for anything).

I’m also building out a checklist for things to find/get for new led chipsets as I add support for them, including measuring dark power usage, digging out the PWM rate info from the data sheets if I can, etc…

Great. If you want to use a wiki format, I can help with some of the pixel info organization. Or I’m happy to let you do it all - tho I particularly want you to have enough time for the stuff only you can do!

I suggest normalizing the dark current as ma/pixel rather than per chip. (let’s define pixel = one individually controllable element; in some 12V strips three visually distinct RGB LEDS are stacked in series between the power and the chip but still represent one logical pixel).