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Topic: what kind of battery for 5V 5A output? (Read 4449 times) previous topic - next topic

bodtx

Hello I'd like to make a lighsaber with adressable strip led:
144 led/m

I'd like to take the 144 led/m strip to get a unified color in the saber.
my problem is that I need 288 led/m as I have to make front and back inside the saber
The saber will be a 90cm tall so I have to output:
288 * 0.9 (meters) * 0.017 A (only bluecolor at full power for one led) = 4.40 Amp
I need a battery who could deliver this.
I've seen that most lipo battery van deliver 0.5 - 1C. Some cans deliver up to 10C but I cannot find a shop for that.
Or maybe NiMh battery would be a better choice?

I don't need big capacity, 15 minutes would be great. I need only Big power and small size to fit in the saber like max LR20 diameter :)

thx for help

MarkT

4 x NiMH would give 5.2V or so, quality brand C or D cells (find ones for which there is a datasheet
if at all possible).
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Noobian

#2
Dec 19, 2015, 02:35 pm Last Edit: Dec 19, 2015, 02:49 pm by Noobian
You could put 2x CR123A camera batteries in series and you would get 2x3v=6v at 1500mA
Then you could simply use a tiny resistor to reduce that 6v to 5v.

The reason I pick CR123A batteries is because they are small enough, round shape(perfect for lightsaber), easily available and cheap, packs lot of power, and lightweight when compared to NiMH AA cells.

Just make sure you buy lithium CR123A and not Lithium-ion. Lithium is 3v whereas Li-ion is 3.6v.
If you buy Li-ion, then you get 2x3.6v = 7.2v, so you will have to use different resistor value.

Also buy from quality brands like Energizer or Duracell, the "FIRE" series Chinese clone ones pack very little power.

NOTE: you could also get 12v led strips from alibaba

Zapro

You could put 2x CR123A camera batteries in series and you would get 2x3v=6v at 1500mA
Then you could simply use a tiny resistor to reduce that 6v to 5v.
NO!
You *cannot* drop voltage with resistors with a varying load. Also, assuming that OP has a circuit that draws 5A constantly, you would have to dissipate 5 Watts in the resistor - not tiny by any means.

// Per.

bodtx

Indeed to go from 6 to 5V I need a 5V regulator. The problem is that for 5W I need also a dissipator , don't know if it fit in.

12V led => car battery could be the solution but a little too big ;)

I'll take a look at thoose CR123A ih they can draw 5A

Noobian

#5
Dec 20, 2015, 06:17 am Last Edit: Dec 20, 2015, 10:00 am by Noobian
Indeed to go from 6 to 5V I need a 5V regulator. The problem is that for 5W I need also a dissipator , don't know if it fit in.

12V led => car battery could be the solution but a little too big ;)

I'll take a look at thoose CR123A ih they can draw 5A
Yep, my bad, you do need a buck and sink, but you could use the light saber handle as one, if it it made of aluminum or similar metal.

There is a type of battery called A23, which is 12v and tiny in size.Commonly used for remote control of garage doors and wireless door bells. But the problem is that they have only 50mA.

If you're going for the 12v LED strips, then I would suggest connecting 4x CR2 Lithium batteries in series. They would give 4x3v =12v at 750mA. These batteries are also easily available and cheap.
The most interesting thing is that they have only half the size of a AA battery. So if you stack them, 4x CR2 batteries will only take the height of 2x AA betteries.
imo, 12v led strips are more common than 5v strips, i believe the reason they make 5v strips is to attach to a USB port to fit behind tv or monitor .

on the plus side, a 12v strip need only less than half the Amps than a 5v one.


bodtx

CR2 is nice indeed but I will have a problem with the discharge current it is 1A max
http://data.energizer.com/PDFs/CR2_AP.pdf

I think I'll take a look with the nimh battery hobby for RC car or drone. There are lot's of type with a 10C discharge which is enough for me.
The hardest part will to find the good size for 5 cells (6v)

yes about the regulator and dissipater I was thinking about the handle of the light saber !

Noobian

 :smiley-cool:  How bout LiFePO 26430 batteries? They have ~8A discharge current and are about the size of a 'C' cell.
So you can stack up 3 of them in series and get 10.6 volts if you are planning to wire them 5v strips in series.

http://www.nexcellglobal.com/LiFePO4.htm



zoomkat

Go on ebay and get a 5a UBEC voltage regulator and you have a large range of battery input voltages. These regulators are small, inexpensive, and have good efficiency.
Google forum search: Use Google Search box in upper right side of this page.
Why I like my 2005 Rio Yellow Honda S2000  https://www.youtube.com/watch?v=pWjMvrkUqX0

dwightthinker

If your running 288 blue LEDs in parallel, at 5 volts and assuming
each light is using a resistor, almost 30% to 40% of your power is
wasted in heating dropping resistors.
LEDs are best driven from a constant current source.
This is more efficient if you have a switcher supply to power them,
that is run in a constant current output mode.
No more high power series resistors.
If it were my design, I'd use a simple flyback voltage booster
and run 10 or 15 LEDs in series, parallel.
I would use a small sense resistor in one of the strings as a
feedback for the flyback duty cycle.
A small resistance in each string would help balance them.
Run the switcher with about 12V worth of batteries. A one
amp-hr pack would last at more than 15 minutes.
Dwight

bodtx

#10
Dec 24, 2015, 03:09 pm Last Edit: Dec 24, 2015, 04:12 pm by bodtx
Ok I think liFePO4 battery is a good start.
My problem is that I tought I could drop the 6.4V (2*3.2 battery) to 5V with a LM7805 ^^ but I've read the data sheet and I've seen that it can output a maximum of 1A :o

Damn!

Well so I'm looking for high Amp regulator but it seem not to be a good idea, what could be a good way to do that? May be a stepDown converter like this, but it could be great if I can avoid big sizes, I have to fit it in the saber:
http://fr.aliexpress.com/item/DC-DC-10A-CCVC-CVCC-4-32V-12v-to-1-2-32V-5v-Step-Down-Buck/32373565914.html

@dwightthinker I would really like to keep the ws2812 strip entirely and not divide it.
I do not understand how the current is regulated at 5V in your exemple

dwightthinker

#11
Dec 24, 2015, 06:38 pm Last Edit: Dec 24, 2015, 06:43 pm by dwightthinker
The only reason that I can think of that it requires 5 volts
is because it uses resistors to drop the additional voltage.
If the resistors are removed, then a constant current source
makes sense.
LED are not 5V without some other power wasting device connected.
You seemed to indicate that you were to use individual LEDs.
I reread your post and realize that you expect to be using these strips.
What an inefficient way to run LEDs. One can see the individual resistors.
Dwight

Zapro

I reread your post and realize that you expect to be using these strips.
What an inefficient way to run LEDs. One can see the individual resistors.
He's using WS2812 which is "intelligent" LED's.

They have internal current limiting for the integral LED-dies.

// Per.

Wawa

#13
Dec 24, 2015, 08:58 pm Last Edit: Dec 24, 2015, 09:00 pm by Wawa
2C or 3C LiPo and two micro buck converters. One for each strip.
Higher voltage and switching regulators keeps battery current down.

Older style lineair regulators have a large dropout voltage (~2volt).
Assume an equally large dropout voltage with buck or boost converters, unless documented.
https://www.pololu.com/category/131/step-down-voltage-regulators
https://www.pololu.com/product/2850
https://www.pololu.com/product/2851
Leo..

bodtx

#14
Dec 25, 2015, 11:07 am Last Edit: Dec 25, 2015, 11:54 am by bodtx
OK as you've said if i go for power more than 5v I need one or more step down converter.

But I've discovered that:
https://learn.adafruit.com/battery-power-for-led-pixels-and-strips/about-batteries
So with four NiMH batteries I will have 4.8v which seems to be in the range for the strip ans the mcu
I think it is the cheaper solution. I hope it will be enough stable
There is an exemple here https://youtu.be/KxMFyPtARYY and the Guy is running it below 5v, see thé comments

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