yojo98
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Re: Power Explanation

Sun Apr 15, 2012 8:55 pm

Hello.

Could someone please just explan in simple terms:

A: What interface the power is.

B: How/Where to buy these.

C: If it could give enough power for a Model B with a 7" 800x480 Mointor and a USB Hub, and A keyboard and mouse.

D: How long the life owuld be with all that.

le4thab
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Re: Power Explanation

Sun Apr 15, 2012 8:58 pm

1 is micro usb (most new mobile phone chargers)

2 is ebay

3 would all be dependent of the items powered by the hub.some devices need more power and would require a powered usb hub

4???

faqs would be a good start mate

spurious
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Re: Power Explanation

Sun Apr 15, 2012 9:02 pm

A: micro USB

B: Mobile phone stores.. lots of places online

C: no idea.. you would need to check the screen's power requirements

D: life?.. if you're connecting batteries it would depend on what you used, but mains supply would be the norm, so not relevant.

There is lots of info in FAQ

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mahjongg
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Re: Power Explanation

Sun Apr 15, 2012 9:21 pm

The pinned (permanent) FAQ of the beginners section shows you how a micro-USB looks like, in fact its the miniature one with the rounded (not pinched in sides), these are more or less standard now.

Adapters with a regular (model A) outputs are a (mainly Chinese) standard now, but choose one with a regulated 5.0 Volt output, that is, not a charger. And use a USb to micro-usb cable with it, or use a regulated one with a directly connected cable ending in micro-USB,

Many devices you buy today come with such power supplies. Also see my answer to your For your fourth question (about expected battery live) see your original question about "battery life when playing starcraft". Check your local electronics shop and explain what you want, they should be able to help you. Explain you want a powersupply that generates 5 Volt (+- 10% accurate) with a micro USB output, and the ability to source about 750mA.

The USB outputs of the R-PI are for connecting a keyboard and mouse, not for connecting "power hungry devices", it can deliver no more than 100mA or so, if you need more power, or more outputs, use a powered USB hub.

For the battery life expectancy see my answer to your original (battery/startcraft) post.

yojo98
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Re: Power Explanation

Sun Apr 15, 2012 10:07 pm

I meant like, how long in hours would the device last? Also for mahjongg, I will be using the hub for everything I plug in (Monitor, Keyboard and mouse, wifi card) and then the one on the board for my 32GB usb.

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jbeale
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Re: Power Explanation

Sun Apr 15, 2012 11:28 pm

for how long in hours would it last, are you asking for MTBF (mean time before failure) that is, expected device lifetime before something breaks?

Normally such single-board computers last longer than anyone is interested in using them. The failures that happen are usually connectors wear out (if you force them, or use them a lot) or failure from mechanical or electrical abuse (put high voltage on GPIO, cause electrical short circuit, etc.)

yojo98
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Re: Power Explanation

Mon Apr 16, 2012 1:33 am

Well, I plan on using it as a cheap way to play old games on the go (Doom, the original StarCraft, Battlefield 1942). I meant how long I would get on a charge.

colin B
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Re: Power Explanation

Mon Apr 16, 2012 2:53 am

yojo98 said:


Well, I plan on using it as a cheap way to play old games on the go (Doom, the original StarCraft, Battlefield 1942). I meant how long I would get on a charge.


What type of battery were you thinking of using?

I believe the Pi by itself will use 700mA – if you take a worse case, standard AA cells (Alkaline) are 1000mAH = 1 hour 25 minutes of use of just the Pi itself.

You"ll need 4 in series which is 5v5, which i think is 0v25 higher than the maximum allowed. A Schottky diode between the battery pack and the Pi +V terminal would bring that down to approx 5v2 (schottky = 0v3 drop approx) . Diode terminal with the black or silver band around it would connect to the Pi end, battery + end to the other.

If you intend to use a rechargeable battery then depending on the chemistry the amount of batteries and the mAH figure will differ.

If you want to use a Lithium mobilephone battery then something like   this http://www.mikroe.com/eng/cate.....ly-boards/ recharge and regulate your battery power.

Sparkfun/Dontronics/RapidOnline/Maplin will possibly have something similar.
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plugwash
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Re: Power Explanation

Mon Apr 16, 2012 5:33 am

Running the Pi directly off batteries is a bad idea. The power circuitry is simply not designed to handle the wide swings in voltage over a battery's lifetime. Brand new AAs can be as high as 1.6V which means four of them would give a total of 6.4V which is too high for the Pi (and is likely to trip the protection) while four nearly flat AAs could be as low as 4V which is low enough that USB stuff will flake out.

If you must run the Pi off AA batteries my advice would be to put 8 of them in series and then use a step down converter module. (Something like http://uk.mouser.com/ProductDe.....QqJQ%3d%3d )

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Gert van Loo
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Re: Power Explanation

Mon Apr 16, 2012 12:15 pm

plugwash said:


Running the Pi directly off batteries is a bad idea. The power circuitry is simply not designed to handle the wide swings in voltage over a battery's lifetime. Brand new AAs can be as high as 1.6V which means four of them would give a total of 6.4V which is too high for the Pi (and is likely to trip the protection) while four nearly flat AAs could be as low as 4V which is low enough that USB stuff will flake out.

If you must run the Pi off AA batteries my advice would be to put 8 of them in series and then use a step down converter module. (Something like http://uk.mouser.com/ProductDe.....QqJQ%3d%3d )



Right on! I am the hardware lead of his thing and please, please let everybody out there who wants to run it off batteries realize the following: IT HAS NOT BEEN DESIGNED FOR BATTER LIFE! I have posted in several places already that even if you put a 5V DC-DC converter before it, which solves the above listed problem of the battery voltage range, the board will burn away 50% of your battery life in the regulators. For efficient battery operation you should replace the regulators on the board with SMPS ones.

XAPBob
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Re: Power Explanation

Mon Apr 16, 2012 12:31 pm

For those of us who are daft enough (and probably therefore not in this forum) have you any suggested regulators?

I might look at this for a project on an "A" in a while....

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mahjongg
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Re: Power Explanation

Mon Apr 16, 2012 4:51 pm

IMHO the easiest, and probably cheapest way to go about is to use a 12V battery and to simply buy a "cigarette lighter adapter for USB". These are meant to charge your iPod while driving in your car. and are very common and therefore cheap. They normally put out a stabilized 5V @ 750mA or more (often 1000mA), but check before you buy.

Normally they are also efficient as (especially the small ones) contain a "switched converter". Do not buy the large boxes that replicate the cigarette plug several times, if you want your batteries to last long, these often very cheap devices contain a simple regulator that converts most of the energy to heat.

A good converter keeps working if the input voltage drops considerably, even as low as 7 Volt or less, and efficiency is mostly in the range of 80%.

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mahjongg
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Re: Power Explanation

Mon Apr 16, 2012 5:31 pm

XAPBob said:


For those of us who are daft enough (and probably therefore not in this forum) have you any suggested regulators?

I might look at this for a project on an "A" in a while....



Well, its not really a "beginners topic", but if you are talking about regulator IC's, then I'm quite fond of the AP1530 IC, it uses minimal parts and has good overall specs. There are many others like it, and perhaps its not the most common or cheapest one, but this is one of the better ones IMHO.

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mahjongg
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Re: Power Explanation

Mon Apr 16, 2012 9:06 pm

P.S. there is also a cheap "chinese copy" of the AP1530, the XL1530 (had to look it up hence the postscript), which is even easier to use, and will also suffice.

Both these devices are SMT.

If you want to use a device that is often used in most of the cheap converters, but works, and is available in a DIP package then the MC34063A is the "canonical" choice.

colin B
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Re: Power Explanation

Mon Apr 16, 2012 10:06 pm

The MC34063A is often the SM chip in mobile phone power adapters for cars.
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mahjongg
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Re: Power Explanation

Mon Apr 16, 2012 11:57 pm

bodgyuk said:


The MC34063A is often the SM chip in mobile phone power adapters for cars.


Yes, thats what I said, in the "cigar plug adapters" used in cars, the AP/XL1530 is used in high end versions. Many modern cigar plug adapters have an USB (type-A) connector, so you can plug in you ipod charger cable.

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