powering 3 meter led strips with DC
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powering 3 meter led strips with DC

by mohawkpiper on Wed Oct 31, 2012 8:47 pm

hey all,
im new to arduino and leds but have a project im currently working on that ive been wanting to do for a while... putting some controllable leds in a monowheel (7ft diameter wheel that you ride inside.)
the wheel frame is plastic and hollow so th leds show through.
(here is a test on one sixth of the wheel...)
http://www.moonlitmethod.com/addressable_leds_LOW.mp4

anyhow, i have 3 meters of Digital Addressable RGB LED w/ PWM strips totaling 96 leds. http://adafruit.com/products/306

was wondering if anybody has any good ideas about how to power them with rechargeable batteries?
i would like to use something along the lines of say a cell phone battery, where i can just plug a wall wart into it to charge it. the power source is going to be inside the bike frame, so it will be really hard/annoying to get to to swap batteries out or anything like that and they need to be small.

i was wondering if something along these lines would work...
say two 3.7V cell phone batteries (cheapish on ebay and the perfect size for what i need them for...)
maybe something like this..
http://www.ebay.com/itm/Samsung-Android ... 48437b2bc8

and a step down converter like this...
http://www.pololu.com/catalog/product/2110

thoughts? input? better ideas?

thanks in advance
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Re: powering 3 meter led strips with DC

by adafruit_support_rick on Thu Nov 01, 2012 1:10 pm

The very first thing you need to decide on is how long you want them to run for. The RGB PWM strips take up to 2A@5V/meter. So, you need around 6A, not counting any current losses in your voltage regulator. Those cell phone batteries are rated at 1.5Ah, so they would give you a run-time of maybe 15 minutes.

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Re: powering 3 meter led strips with DC

by adafruit_support_bill on Thu Nov 01, 2012 1:55 pm

2A per meter is the theoretical max (all leds on 100%). In practice it is often less. Partly due the pattern programmed, and partly due to voltage losses in the strip. But Driverblock's formula still applies. Even at 1A per meter, your runtime would be only 30 minutes with that battery.

This thread has some experimental data on the subject:
viewtopic.php?f=47&t=24275&p=135754
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Re: powering 3 meter led strips with DC

by mohawkpiper on Thu Nov 01, 2012 2:09 pm

forgive me i am new to all of this and trying to wrap my head around V vs A vs resistance (ohms?)

id like it to stay on a few hours... 2 to 4, closer to 4 if possible.

so sounds like those batteries wont work. a few other questions just to understand this a little better...
1. if i were to connect two of those batteries together, each being 3.7V 1.5A, that would double the volts to 7.4V but the amps would still stay at 1.5? or do the amps double also?


2. i am cutting every 2 leds and putting about a foot of wire between them. how does this play in voltage loss? does the guage of wire affect this and if so, what guage wire should i use?


3. if i were to find some sort of battery that would work.. would it be possible to connect one battery at the beginning of the entire strip powering the arduino and half the strip, and connect a second battery halfway through the strip to power the second half of it to help keep voltage loss to a minimum at the very end of the entire strip?

thanks for all the help and the link!
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Re: powering 3 meter led strips with DC

by adafruit_support_bill on Thu Nov 01, 2012 2:17 pm

Wiring two batteries in series, the voltage doubles and the amps stay the same. Wiring two batteries in parallel is not a recommended practice.

However, you can power sections of the strip with separate batteries. Just connect the ground and signal wires between sections. Then connect power between ground and +5v on each section.

Wire gauge for your connections between strips can make a difference (heavier is better). But voltage drop will be less of an issue if you distribute power over several shorter sections instead of one great long one.
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Re: powering 3 meter led strips with DC

by mohawkpiper on Thu Nov 01, 2012 2:29 pm

adafruit,
i am a little confused.

to power sections with separate batteries....
on the strip there are four wires, ground, clock, data, and 5V.

so you are saying...

connect GO of strip one to GI of strip two,
connect CO of strip one to CI of strip two,
connect DO of strip one to DI of strip two,
connect 5VO of strip one to negative of battery, and connect positive of battery to 5VI of strip two?

and wire gauge can get too heavy no?
it looks like the guage wire used for jumpers and stuff for breadboards is 24g.

i have a roll of 18g and 20g wires at home from a previous project (unrelated to arduino and leds). these are not too big of a guage are they?
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Re: powering 3 meter led strips with DC

by adafruit_support_bill on Thu Nov 01, 2012 2:51 pm

connect 5VO of strip one to negative of battery, and connect positive of battery to 5VI of strip two?

No. The 5v for each section will be isolated from the other sections. You will have one 5v power supply (battery plus regulator or DC/DC converter) for each section. The negative terminal of each power supply connects to ground. The positive terminal of each power supply connects to the +5v of it's designated section.

18 gauge should be fine for interconnecting sections.
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Re: powering 3 meter led strips with DC

by pburgess on Thu Nov 01, 2012 3:01 pm

This tutorial on battery power for LED strips might be helpful.

All grounds from all strips will be connected one way or another (it doesn't necessarily need to be end-to-end...branching or "fanning out" works too). If you have one jumbo 5V supply for everything, you can do the same thing with the 5V connections...but if using multiple smaller battery packs or power supplies, these should be routed to sub-sections with no connection between them.

When running wire for power, heavier gauge is always better as there's less resistance. The signal lines (data and clock) are fine with smaller wire.
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Re: powering 3 meter led strips with DC

by mohawkpiper on Thu Nov 01, 2012 3:57 pm

thanks for the info guys, you have just made me much more knowledgeable and this really helps.
paul, i saw that link and have been through it several times. i know it says to add a power tap for every meter but i wasnt sure HOW to add a power tap (what connects to what etc) and i couldnt find that info. all this answers that though.

thanks again,
ill figure this out!

G
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Re: powering 3 meter led strips with DC

by mohawkpiper on Thu Nov 01, 2012 5:12 pm

k so it seems regular rechargeable batteries will be best. i can strap the battery holder(s) to the outside of the frame and the project will still work, just will look a bit cluttered but i guess thats ok.

so been browsing batteries and just noticed sometimes they say mWh instead of mAh and so i looked it up.... just wanna be clear i have this right...
mWh = mAh * V correct?

so these for example...
http://www.tmart.com/2pcs-16V-9000mAh-A ... 42037.html

i could put three together to make 4.8V (meaning no resistors needed) but it claims in the title its 9000mAh which sounded awesome but then i noticed in the pic on the actual batteries it says 9000mWh so that means they are 5625 mAh yes?
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Re: powering 3 meter led strips with DC

by adafruit_support_bill on Thu Nov 01, 2012 5:19 pm

Nizn batteries are the only ones that advertize mWh. The general consensus among regular users seems to be that their capacity degrades quicker than NiMH after repeated recharge cycles. If this is a one-time sort of project they may serve you well. If it is expected to have a long life with many recharges, I'd stick with 4xNiMH cells for the same voltage.
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Re: powering 3 meter led strips with DC

by pburgess on Thu Nov 01, 2012 5:29 pm

They probably meant 900 mAh. Even decent AA cells seldom exceed 2500 mAh, and these are dinky AAAs. And then the whole special NiZn 1.6-1.8V thing...I wouldn't touch these with a 3-meter pole.

You have a lot of LEDs, you're going to need a lot of power. I'd suggest 4 big hankin' D cells in series (split the output 6 ways, each with its own diode if using alkaline cells), or multiple AA battery packs. Alternately, consider RC car batteries and a beefy DC-to-DC converter.
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Re: powering 3 meter led strips with DC

by mohawkpiper on Wed Nov 07, 2012 2:14 pm

just wanted to say thanks again for all the help.
i went with 3 separate sets of 4AA batteries in each set. i bought these batteries...
http://www.newegg.com/Product/Product.a ... 6817355039

so here is where i am at so far...
http://www.youtube.com/watch?v=rCym-rWtDnI
(its a 7 foot diameter wheel where the frame is hollowed out plastic and the leds are inside the frame)
this is 2/3rds of ONE side, which is an entire 1-meter strip of the LPD 8806s (32 leds).

so i was planning on powering each meter with i set of 4 batteries.
i tried it out when i got the batteries. it lasted barely an hour at full power, and by the next half hour was barely visible. that was with the exact light patterns you see in the youtube video.
i lightened up the power consumption in the code (more blacks, no full white brightness) and tried again. it gave me maybe another 15 to 20 minutes.
i was thoroughly disappointed then i remembered rechargeables rarely come fully recharged. so i recharged them and tried again with the lightened code.
it ran for 8 hours!!! so far and looks the same as the batteries fresh from the charger. i had to go to work so i pulled the batteries and will finish them off tonight when i get home.

so im going to do some more tests, gonna run a pretty power intensive light pattern through it and see how long it lasts.

im really only looking for 3 hours, 4 max, and id like to minimize the batteries used,

so im going to test it to see how long it lasts if the battery pack is running a meter and a half (48 leds, which would be one whole side of the wheel). if 48 leds can handle a somewhat power intensive light pattern for at least 3 hours, and not dim very noticeably at the end of the strip, im going to go with 2 sets of 4 batteries each, but if not ill stick to the 3 sets.

just got excited so i wanted to share, and say thanks again for all the help. you guys are wonderful.

G
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Re: powering 3 meter led strips with DC

by pburgess on Thu Nov 08, 2012 1:53 am

Cool beans! Glad to see you're making good progress with this, can't wait to see video of it zipping around. Should be quite the spectacle!

I'm a total bike nerd, so the Monovelo pertains to my interests even before the LEDs get involved. :D
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Re: powering 3 meter led strips with DC

by adafruit_support_rick on Thu Nov 08, 2012 10:22 am

That looks terrific! Can't wait to see the whole thing. Looks like a Burning Man project?
How are you constructing the drive/seat/etc.?

Might I suggest some sort of zero-crossing sensor so that you could synchronize the lights to the rotation? If you time it right, you could flash the lights to make it appear as if the wheel isn't rotating.

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