Zvanochek
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Re: Battery power

Thu Jan 05, 2012 2:13 pm

It is great to see that the Pi can be run from 4xAA batteries, but could someone point me in the right direction to connect it up? Is there an off the shelf cable that I can clip into my battery pack or will I need to do some bodging/DIY soldering?

Sorry if this has come up before, but most power/battery topics end up in in-depth conversations about various modules power useage......which is over my head!

Zvanochek

shaurz
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Re: Battery power

Thu Jan 05, 2012 2:17 pm

You can get back-up batteries for mobile phones with microUSB connectors. Those will probably work with the RPi. Some have extra USB ports that could be used to power a hub, etc.


julianrich
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Re: Battery power

Thu Jan 05, 2012 2:49 pm

The power supply proposed for the Rpi has an output set at 5v with a tolerance of + or - .5v. to connect a 6v battery pack you need to lose .5v.

The simplest method is to use a resistor in the cable to reduce the voltage to 5.5v maximum.

Ohms law gives a value of 1.66 ohms for model A at 300mA and 0.71 ohms for a model B at 700mA, 2w rating should allow the resistor to run cool.

You just have to solder the resistor into the cable somewhere on the + side

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meltwater
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Re: Battery power

Thu Jan 05, 2012 3:12 pm

shaurz said:


I found this: http://www.amazon.co.uk/Backup.....B004A9I2CA


A phone backup Li-ion battery would give you far better mileage for your money, with the added bonus of containing charging and protection circuits too.  That is my plan anyway.
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lewmur
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Re: Battery power

Thu Jan 05, 2012 3:12 pm

If you use rechargeable AA batteries, you will be within the .5v tolerance and won't need a resistor.

shaurz
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Re: Battery power

Thu Jan 05, 2012 3:23 pm

@meltwater - I agree

@lewmur -  Good point, 1.2v * 4 = 4.8v

lewmur
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Re: Battery power

Thu Jan 05, 2012 3:30 pm

julianrich said:


The power supply proposed for the Rpi has an output set at 5v with a tolerance of + or - .5v. to connect a 6v battery pack you need to lose .5v.

The simplest method is to use a resistor in the cable to reduce the voltage to 5.5v maximum.

Ohms law gives a value of 1.66 ohms for model A at 300mA and 0.71 ohms for a model B at 700mA, 2w rating should allow the resistor to run cool.

You just have to solder the resistor into the cable somewhere on the + side


That assumes that the current is constant and it isn't.  It will vary widely with usage.  Neither is the output voltage of the batteries as they discharge.  As I said, using rechargeable AAs will bring you within the .5v but a better solution would be to use a higher voltage battery and a 5v regulator chip.  I don't know about the UK but RadioShack in the USA has those chip for a couple of bucks.

julianrich
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Re: Battery power

Thu Jan 05, 2012 3:32 pm

Just bear in mind that phones and other devices have internal batteries and power management devices to control everything Rpi has none of these.

Get it wrong and you will fry your pi

Zvanochek
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Re: Battery power

Thu Jan 05, 2012 3:52 pm

So if I had something along the lines of the following:

http://cgi.ebay.co.uk/ws/eBayI.....0392422292

How easy would it be to wire it into a micro-usb? Ultimately I plan to hook up my Pi  power supply to a solar panel to drip feed my battery as it would only be on for a couple of hours a day at most, but right now I am just looking at logistics etc.

Yes I know other options might be better, and that the running costs of the Pi are low, but this is for the fun of it. A nice little fun project

I will look into the regulator - should be easy enough to wire in-front of the battery, although this is my first bit of electronics since school (10 years ago maybe?)....

Warringer
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Re: Battery power

Thu Jan 05, 2012 3:56 pm

julianrich said:


The power supply proposed for the Rpi has an output set at 5v with a tolerance of + or – .5v. to connect a 6v battery pack you need to lose .5v.

The simplest method is to use a resistor in the cable to reduce the voltage to 5.5v maximum.

Ohms law gives a value of 1.66 ohms for model A at 300mA and 0.71 ohms for a model B at 700mA, 2w rating should allow the resistor to run cool.

You just have to solder the resistor into the cable somewhere on the + side


No, the simplest thing would be to use a diode. You will always loose 0.7 Volts and you don't have to do any math, combined with the integrated security that it will prevent damage of you put the battery in the wrong way.

I'd suggest a 1N4004 just to be on the safe side.

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S0litaire
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Re: Battery power

Thu Jan 05, 2012 4:44 pm

I was looking at something like this :

http://www.amazon.co.uk/New-Tr.....f_dp_p_t_1

Only issue (apart from it's as big as a brick!*) is that it only puts out 3.7v as far as I can tell.

*ok might not be a brick but it's at least the size of 4 stacked CD cases!
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arm2
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Re: Battery power

Thu Jan 05, 2012 4:52 pm

almost all batteries start off at a higher voltage than there nominal voltage and gradually lose voltage as they discharge. How long rechargeable batteries would be withing the +- 0.5V range, who knows!

Also what happens if it is overvoltage at the start I don't know. Damage to chips, just not work or not work reliably...?

For extended battery use and if you did not need to use USB & HDMI (Which IIRC needs 5V according to an authoritive post) what batteries could be used to power it via the 3v3 pin on the GPIO?

PatrikL
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Joined: Fri Dec 23, 2011 11:03 am

Re: Battery power

Thu Jan 05, 2012 5:06 pm

meltwater said:


shaurz said:


I found this: http://www.amazon.co.uk/Backup.....B004A9I2CA


A phone backup Li-ion battery would give you far better mileage for your money, with the added bonus of containing charging and protection circuits too.  That is my plan anyway.


+1 for Li-Ion batteries  Like I wrote here http://www.raspberrypi.org/for.....-2/#p23317 , one 18650 cell has more energy than three rechargeable AA batteries…

And here are some measurements http://budgetlightforum.com/no.....ent-105444 (and other options are in that thread too)

S0litaire
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Re: Battery power

Thu Jan 05, 2012 5:08 pm

Done a bit more digging about the New Trent iCruiser IMP1000 battery.

it DOES output at 5v (It's just the internal battery is 3.7v)

Running as a headless file server it could power it for between 1.5 - 2 days in a full charge. (assuming it pulls on average 300mAh or unless my maths have left me over the Holiday period...)
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mas
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Re: Battery power

Thu Jan 05, 2012 5:16 pm

You could just use the MintyBoost http://www.adafruit.com/products/14

Hmm… A battery pack and a computer both in Altoid tins. Thats interesting …

PatrikL
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Re: Battery power

Thu Jan 05, 2012 5:20 pm

That "Trent iCruiser" is a bit expensive

lewmur
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Re: Battery power

Thu Jan 05, 2012 5:30 pm

I'm curious.  What applications are there for the R-Pi in a portable environment?  Even the A model would go through AA batteries at a horrendous rate.  Even high quality alkaline batteries are good for only about 2.4 ah.

Personally, I'm planning on building a giant screen portable computer.  But I plan to power it with 12v 12ah SLA batteries.  Those will power my 22" LED monitor directly and then, with a 5v regulator, the R-Pi and USB wireless mouse, keyboard, 16gb USB hdd and wifi dongle.

error404
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Re: Battery power

Thu Jan 05, 2012 8:13 pm

Perhaps your definition of 'horrendous' doesn't match other users'. I don't think too much power consumption information is available yet, but I would guess at an idle consumption under 1W for the MPU. That's 200mA at 5V, giving you over 10 hours on your AAs.

stormy1
Posts: 60
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Re: Battery power

Fri Jan 06, 2012 3:57 am

The safest way is a 5V 3A BEC Step-Down Voltage Regulator

The can be found for about $10-12 on several sites from a google search.

You could also build one but the parts arent that much cheaper than buying one.

jamesh
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Re: Battery power

Fri Jan 06, 2012 8:50 am

error404 said:


Perhaps your definition of 'horrendous' doesn't match other users'. I don't think too much power consumption information is available yet, but I would guess at an idle consumption under 1W for the MPU. That's 200mA at 5V, giving you over 10 hours on your AAs.


Not sure about the Arm, but I believe the GPU is <10mw at idle.
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Re: Battery power

Fri Jan 06, 2012 9:01 am

julianrich said:


Just bear in mind that phones and other devices have internal batteries and power management devices to control everything Rpi has none of these.

Get it wrong and you will fry your pi



The power input on the Pi includes a resettable fuse and voltage regulators so a badly behaved battery setup might result in a temporary outage but nothing permanent.  In many ways, a battery setup would be preferable to a cheaper 5v USB power adaptor as they can and do crap out, frying anything connected to them!

If I could afford one of the eBayed Pi's and wanted to use them, I'd power them by battery to prevent any untoward damage!
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error404
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Re: Battery power

Fri Jan 06, 2012 10:51 am

Jongoleur said:

 In many ways, a battery setup would be preferable to a cheaper 5v USB power adaptor as they can and do crap out, frying anything connected to them!
This is actually a very good point I hadn't thought much about. I've seen USB wall warts that aren't even isolated properly, and far more that have such shoddy internal construction that the isolation is nearly worthless. Not only dangerous for the hardware, but dangerous for the user as well.

lworbey
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Re: Battery power

Fri Jan 06, 2012 10:54 am

I plan on using a phone charger as you can pick up genuine manufacturer ones that generally are very reliable (they don't really want you frying your £500 contract phone too often).

I can get a replacement charger for my phone for about £3.50 on amazon and then I also have a spare charger for my phone as well...

Can't say I haven't considered a battery setup though to make the device portable!

Mp4
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Re: Battery power

Fri Jan 06, 2012 11:10 am

Would one of these work?

http://www.maplin.co.uk/freelo.....ger-354195

Powers all portable electrical devices with a maximum voltage of 5.5V

Built-in USB socket also allows connection via any devices sync / charge cable

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