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Author Topic: Help Making 5V @ 6A from Battery  (Read 1164 times)
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I've searched, lurked, and read tons of information on getting 5V from battery as long as you only need ~500mA or less.  I need up to 6A though and just can't find anything like this.  I'm not a very strong hardware guy and I'm running out of keywords to search and need some real practical usage info to point me in the right direction.

Requirements:
1) 5V
2) 2-3A typical (theoretical max of 6A)
3) Circuit (not including cells) must fit inside 5/8" inner diameter tubing (no really big components)
4) Descending order of importance: Size, Efficiency, Simplicity, Weight, Cost
5) Circuit will be somewhat confined and cannot generate a huge amount of heat
6) Li-ion preferred (even with the hassles of charging and protection) but am open to information here if this is an issue

Questions (given the requirements above):
1) Is it more efficient to use under-voltage pack (e.g. 3.6v) and boost or over-voltage (e.g. 7.2V) and regulate/buck?
2) Where should I start?  Buck converter, switching regulator, linear voltage reg, something else?  I believe I've generally listed them from best to worst but don't understand which works best given my requirements above (especially size?).
3) Can someone point me to a reference design, IC, etc somewhere for this kind of high current usage?  I can't safely build this circuit without something to work from.  smiley

Here is an example of a perfect circuit... except I need up to 6A (and this, like most others, max at 600mA):
http://www.sparkfun.com/products/10255
« Last Edit: October 30, 2011, 06:06:48 pm by CraigKC » Logged

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Search ebay for UBEC to find the high current voltage regulators. They usually have selectable output for 5v or 6v, and probably require the 7.2v or higher battery inputs. Generally inexpensive. Online hobby sellers like hobbyking and hobbypartz also sell them.   
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Consider the daffodil. And while you're doing that, I'll be over here, looking through your stuff.   smiley-cool

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Quote
Circuit (not including cells) must fit inside 5/8" inner diameter tubing (no really big components)

That is the deal breaker, I don't think you find it is possible to pack any kind of 6 amp regulator circuit in that size tubing. Your better off maybe building a 4 cell high current ni-cad or nimh pack that would generate close to nominal 5vdc. What is your duration target like?


Lefty

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@zoomkat: WOW!  I had no idea I could get such an affordable already assembled solution.  So I start looking into physical size... which brings me to retrolefty's post.

@retrolefty: It looks like you're right.  I don't see a single one that's even close to 6A and <17mm.  I did, however, already find some 3A continuous / 5A peak that are 17mm wide.  I think zoomkat may have hit as close to a perfect solution as I can find.  If I modify the design to include 3/4" inner diameter and settle for less current I could be in business here.
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2-3A typical, for how long? Is this intermittent? Continuous? How long do you want it to run before you have to swap out batteries?

You mentioned Li-Ion, but LiMn is a better chemistry, available in the same form factors, and can source higher current. You might have also found Li-Poly batteries at those hobby sites, which have advantages.
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 Upon thinking on the subject, the smallest 5 volt regulators tend to be the switching ones designed and sold to the R/C hobby where size and weight is very important. They are called in that hobby "BEC" modules, and they were developed to power the R/C receiver and servos on an existing electric motor battery voltage rather then requiring the flight package to have a seperate 4 cell ni-cad pack for the 5 volt radio system.
They have models that will generate 5v @ 5amps or so when powered by higher voltage Li-po battery packs.

 Why don't you can the specs and see if any could be fitted in your project. But still not sure one can be stuffed down a 5/8" tube.  smiley-wink

http://www.hobbyking.com/hobbyking/store/__112__182__ESC_UBEC_VR-VR_2F_UBEC.html

Lefty
« Last Edit: October 31, 2011, 12:30:34 am by retrolefty » Logged

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can you use 3 batteries, and 3 5v 2A voltage regulators instead of one ?

some of the rc stuff is very powerful and 30a from 7.2 volts is possible

look at the LiPo batteries

are you switching a solenoid or electric motor ?

can you run more than 5 v ?
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You guys have been really helpful... I finally have a direction here and feel really good about your suggestions.

First, I did some real world testing yesterday and it looks like I won't actually need over 3A.  This is for a 10' RGB LED strand that can actually be powered from both ends if I need.  It gets brighter and draws about 3.5A if I do it that way but I'm satisfied at a peak of ~2.25A powered from one end.

The BEC or UBEC regulators suggested by a couple of you look like they're going to work perfectly.  Playing to find out if I need 1 or 2 is all I need to do now.  My research shows that a BEC is linear and UBEC is switching.  I'm not sure if that's standard or if it just happened to be the models I looked up?  In any case I may just try both to see if there's significantly higher efficiency in a switching unit to justify the extra size.

I looked into LiMn but their capacity is up to 50% lower per given form factor it seems.  Runtime/capacity is pretty critical here since I'm already looking at struggling for much over an hour on 3 cells at full brightness/load.  Li-po seems to be out as I need 14500 size that also has to fit inside the tubing (probably going to be 3/4" ID now).
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