andyohare
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Cheap battery at B&M

Mon Dec 09, 2013 4:05 pm

went to my local B&M store today and picked up a USB battery for £4.99. Box states it's 2500mAh, max output 800mA. Will post back when I've done some timed tests so I don't know how long it will actually last, but seems to happily power my Model B with wifi, wireless keyboard and four LEDs connected to the GPIO. I can't find it on the B&M website but it looks very similar to this one. Fortunately mine doesn't smell!

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DougieLawson
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Re: Cheap battery at B&M

Mon Dec 09, 2013 7:28 pm

I bet it won't run your RPi for more than a couple of hours if that.
The problem comes as the batteries die and the voltage drops, that WILL cause SDCard corruptions.
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jbeale
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Re: Cheap battery at B&M

Mon Dec 09, 2013 8:09 pm

I used a similar device: Tenergy Model 51038 5V,1A USB power pack. It ran a Model A + RPi Camera + USB wifi for 3 hours, see this post: http://www.raspberrypi.org/phpBB3/viewt ... 64#p450157

The Model B will have a shorter runtime- it takes a lot of current to keep that USB/ethernet chip up to temperature :-).

andyohare
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Re: Cheap battery at B&M

Mon Dec 09, 2013 9:59 pm

DougieLawson wrote:I bet it won't run your RPi for more than a couple of hours if that.
The problem comes as the batteries die and the voltage drops, that WILL cause SDCard corruptions.
I wasn't expecting it to - and it didn't. 2.5 hours on the first go, with x running and some fairly heavy wifi use. You're right about potential problems when the power suddenly dies. Not bad for a fiver though!

realworldnumbers
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Re: Cheap battery at B&M

Fri Dec 13, 2013 7:52 pm

I have succesfully powered my Pi and done a test on how long it can survive using only 4AA batteries :D
http://realworldnumbers.com/how-to-test ... batteries/. I got about 8.5 hours and there was no damage when pushing 6.52Volts until fully drained.

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jbeale
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Re: Cheap battery at B&M

Fri Dec 13, 2013 10:28 pm

realworldnumbers wrote:I have succesfully powered my Pi and done a test on how long it can survive using only 4AA batteries :D
http://realworldnumbers.com/how-to-test ... batteries/. I got about 8.5 hours and there was no damage when pushing 6.52Volts until fully drained.
Impressive, I would not have guessed it would last that long. By the way, according to http://en.wikipedia.org/wiki/AA_battery an alkaline AA ranges between 1800 and 2600 mAh. The best NiMH AA cells do a bit better (up to 2850 mAh) and although nominal 1.2V instead of 1.5 V, they usually have lower internal resistance (NiMH AA: 30 mOhms, Alkaline AA: 150 mOhms) so voltage under heavy load holds up better. Also, you don't have to throw them away after one use :-).

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mahjongg
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Re: Cheap battery at B&M

Fri Dec 13, 2013 10:39 pm

theoretically at 6.0V the PI's "over voltage triggered Thyristor" should have triggered to protect the PI, by shorting the 5V line. :shock:
I assume you must have been lucky. :o

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redhawk
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Re: Cheap battery at B&M

Fri Dec 13, 2013 10:47 pm

realworldnumbers wrote:I have succesfully powered my Pi and done a test on how long it can survive using only 4AA batteries :D
http://realworldnumbers.com/how-to-test ... batteries/. I got about 8.5 hours and there was no damage when pushing 6.52Volts until fully drained.
Model A or Model B??

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simplesi
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Re: Cheap battery at B&M

Fri Dec 13, 2013 10:53 pm

I've been using v similar spec ones from Scan for my Robots for the past year - if you just use them to power your Rpi and have a separate motor battery then they easily exceed 2 hours on a model B

They'll even totally power a little stepper motor bot on their own for a 1 hours after school club :)

Good find as the ones I got from Scan for £5 are no longer available :(

Simon
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