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Burngate
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Location: Berkshire UK Tralfamadore
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Re: Battery power

Mon Jan 09, 2012 12:47 pm

7805s quoted at 1A will only give that on a heatsink. That series of regulators is actually thermally limited, so in free air, and with more than the minimum of voltage drop across it, you may only manage ~100mA. Switch-mode chips, while being more complicated, may be more satisfactory

Wooloomooloo
Posts: 92
Joined: Fri Nov 25, 2011 10:52 am

Re: Battery power

Mon Jan 09, 2012 1:22 pm

Burngate said:


7805s quoted at 1A will only give that on a heatsink. That series of regulators is actually thermally limited, so in free air, and with more than the minimum of voltage drop across it, you may only manage ~100mA. Switch-mode chips, while being more complicated, may be more satisfactory



Basically you're right, one will need a heatsink if one wishes to use a 7805 up to its 1A rating - but the specifics don't quite sound right. I'm looking at a National Semiconductor spec right now that states cca. 2W of dissipated power for no heat sink and a generic TO-220 capsule (which is the usual package for the 1A range) at room temperature in open air. That would mean one could in theory actually get all 1A out of the regulator at the minimum voltage drop (Vin=7V) or conversely, one should go up to a Vin of 25V to get limited to 100mA without a heat sink.

For Pi purposes though, indeed a heat sink would pretty much be needed on that capsule.

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Burngate
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Location: Berkshire UK Tralfamadore
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Re: Battery power

Mon Jan 09, 2012 1:38 pm

Yes, you're right - I exagerate for the sake of emphassis!

Though where I've used them in the past, on linear PSUs, and with largish ripple going in, it's quite easy to hit that 2W limit.

Maybe I should be more careful about putting figures in on this forum - get it wrong & you get jumped on &-)

peterbailey
Posts: 2
Joined: Mon Jan 09, 2012 1:54 pm

Re: Battery power

Mon Jan 09, 2012 2:11 pm

Hi, I"ve been watching this thread with interest,

I am hoping to get one of these Pis and put it into an existing case that I have. I would like to have a laptop style "plug it into the mains to charge and run it at the same time, or run it off the battery" functionality.

Does anyone know of any circuit that can be bought off the shelf to do that? My googling hasn't turned up anything so far that could handle the 700mA of the Pi model B, but to be fair as I don"t know exactly what such a thing would be called I am struggling a bit.

I'm happy enough to up/down voltage as necessary as long as I can get reasonable run time and a small-ish package.

I've considered trying to cannibalise a laptop, but the battery space I've got to work with in the case I'm intending to use is 4xAA (so just over 2" square, could be hollowed out slightly), so a laptop battery would be too big.

I guess the ideal would be a charging circuit for 2xCR-V3 batteries, if such a thing exists, or a circuit for charging a couple of the flat 3.7V polymer li-ion 2000mAh 5.8x54x54mm packs.

Any ideas appreciated…

Wooloomooloo
Posts: 92
Joined: Fri Nov 25, 2011 10:52 am

Re: Battery power

Mon Jan 09, 2012 5:14 pm

Burngate said:


Yes, you're right - I exagerate for the sake of emphassis!

Though where I've used them in the past, on linear PSUs, and with largish ripple going in, it's quite easy to hit that 2W limit.

Maybe I should be more careful about putting figures in on this forum - get it wrong & you get jumped on &-)



No worries, I wasn't trying to prove you wrong, sorry if I sounded too dry. The numbers just got me a bit puzzled, is all...

hellsing
Posts: 7
Joined: Thu Jan 05, 2012 4:11 pm

Re: Battery power

Mon Jan 09, 2012 6:21 pm

I'll probably use a 12V, 1.2Ah battery with a DC/DC downconverter for car, it will be perfect when i move it. Or one of my big 3.7V li-ion battery from a old mp3 player but it wiil need a power up circuit and a charging one...

And I think i will power it with my screen usb switch the rest of the time.

vrana54
Posts: 4
Joined: Tue Jan 03, 2012 7:00 pm

Re: Battery power

Mon Jan 09, 2012 6:44 pm




peterbailey said:


Hi, I"ve been watching this thread with interest,

I am hoping to get one of these Pis and put it into an existing case that I have. I would like to have a laptop style "plug it into the mains to charge and run it at the same time, or run it off the battery" functionality.

Does anyone know of any circuit that can be bought off the shelf to do that? My googling hasn't turned up anything so far that could handle the 700mA of the Pi model B, but to be fair as I don"t know exactly what such a thing would be called I am struggling a bit.

I'm happy enough to up/down voltage as necessary as long as I can get reasonable run time and a small-ish package.

I've considered trying to cannibalise a laptop, but the battery space I've got to work with in the case I'm intending to use is 4xAA (so just over 2" square, could be hollowed out slightly), so a laptop battery would be too big.

I guess the ideal would be a charging circuit for 2xCR-V3 batteries, if such a thing exists, or a circuit for charging a couple of the flat 3.7V polymer li-ion 2000mAh 5.8x54x54mm packs.

Any ideas appreciated…



I think you are looking for something like this. I plan on using this as well. It takes care of all the necessary interfaces in one package.

http://tinyurl.com/72poep3

mobeyduck
Posts: 173
Joined: Tue Nov 29, 2011 6:39 pm

Re: Battery power

Mon Jan 09, 2012 7:17 pm

I wonder if you can charge and use those Mobile Power Supply USB Battery Charger 18650 Box at the same time, like with laptops they charge while you can use them.

so that the R-Pi normally runs from the power net and when theres a power failure or when your going on the road that you just unplug the box and go

peterbailey
Posts: 2
Joined: Mon Jan 09, 2012 1:54 pm

Re: Battery power

Mon Jan 09, 2012 9:02 pm

mobeyduck said:


I wonder if you can charge and use those Mobile Power Supply USB Battery Charger 18650 Box at the same time, like with laptops they charge while you can use them.

so that the R-Pi normally runs from the power net and when theres a power failure or when your going on the road that you just unplug the box and go


That is what I need. vrana54, have you used this device, and do you know if it will be possible to use the output with 700mA draw while charging? Thanks

vrana54
Posts: 4
Joined: Tue Jan 03, 2012 7:00 pm

Re: Battery power

Mon Jan 09, 2012 9:18 pm

peterbailey said:


mobeyduck said:


I wonder if you can charge and use those Mobile Power Supply USB Battery Charger 18650 Box at the same time, like with laptops they charge while you can use them.

so that the R-Pi normally runs from the power net and when theres a power failure or when your going on the road that you just unplug the box and go


That is what I need. vrana54, have you used this device, and do you know if it will be possible to use the output with 700mA draw while charging? Thanks



I have not tried it so I am not sure if it can do both. If it can't, then I would just install a slider switch which would let me pick between wall power and battery.

I am going to contact the seller to make sure and will report back when I know more.

error404
Posts: 351
Joined: Wed Dec 21, 2011 11:49 pm

Re: Battery power

Mon Jan 09, 2012 9:38 pm

macbadger said:


While battery power would be excellent, please bear in mind capacity.


700mA is, as ever, a worst case specification. Basing battery life estimates on it is going to be very misleading unless you're planning to keep the thing at 100% CPU and the GPU fully active all the time, and even then there's probably some margin.

bbaasje
Posts: 5
Joined: Mon Jan 09, 2012 11:05 pm

Re: Battery power

Mon Jan 09, 2012 11:37 pm

Is it possible to use a USB to power cable? like the one in the image?

because then I could connect it to my TV, via USB .

XBMC on it, PS3 remote, usb Dongle, wifi adapter, and it's a success!!!!

http://www.ps3toothfairy.com/s....._cable.jpg

mobeyduck
Posts: 173
Joined: Tue Nov 29, 2011 6:39 pm

Re: Battery power

Thu Jan 12, 2012 9:22 pm

No the R-Pi does not use that connection it uses micro usb for the power.

you can still connect it to your tv if it gives enough power on the usb port.

If you want to know if you can power that Mobile Power Supply USB Battery Charger linked earlier, it probably wont fit that tooth-fairy said it needs 2.1mm standard DC barrel input connector, 3.3-12VDC, center positive and the mobile power 1,35mm

Byron
Posts: 11
Joined: Mon Jan 23, 2012 1:05 pm

Re: Battery power

Wed Jan 25, 2012 9:09 pm

Really easy to build a 5V regulator on a stripboard etc. Components cost: about £1.50.

Plenty of simple circuits online.  Advantage? Use a 9v battery and the Pi will keep running even when the battery has lost 40% of its voltage.

.......dont forget to include a diode eg 1N4001 on supply line to protect the Pi from reverse polarity connection.

mcookie
Posts: 1
Joined: Wed Jan 25, 2012 11:30 pm

Re: Battery power

Wed Jan 25, 2012 11:54 pm

I'm no electrical engineer, but will the classic "mintyboost" altoids thingy work?

http://www.ladyada.net/make/mi.....power.html

It supplies 5v, and is quite cheap. Integrating what they already have there into one's own power supply couldn't be too hard, could it? My devised plan for the RasPi I get won't involve that much portability, so would 3 D-Cells work (or 4, with the whole subtract .7V thing...). All those mAh (60,000 total, according to the table on the mintyboost link) would run a RasPi for quite a while.

Corrections? Anyone?

Liest_dk
Posts: 1
Joined: Thu Jan 26, 2012 9:42 am

Re: Battery power

Thu Jan 26, 2012 9:51 am

stormy1 said:


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 aren't that much cheaper than buying one.


I would have to agree with stormy1 on this. But you can find a lot of UBEC/BEC online on eBay and such for as little as £1.6

This is one I have for a RC at home and give it any battery from 5.5 V to 23 V and it will give you 5V at 4A.

Now use any number of batteries and format and it will power the Pi for you. Even if it is in a car or for at portable settup.

Link to one cheap on eBay.

http://tinyurl.com/UBEC-BEC

error404
Posts: 351
Joined: Wed Dec 21, 2011 11:49 pm

Re: Battery power

Thu Jan 26, 2012 6:09 pm

mcookie said:


I'm no electrical engineer, but will the classic "mintyboost" altoids thingy work?


The DC-DC converter in the mintyboost is only rated for 600mA. It will probably work, at least most of the time, but it's a bit under-rated.

As far as capacity, it is better to think about watt-hours than amp-hours for this, since the DC-DC converter basically converts amps to volts, and will mess you up if you don't take that into account. It'll also account for the battery voltage dropping over time.

So a Duracell D-cell seems to hold about 8Wh at 1W load, down to 1V. 3 of those is 24Wh. Not totally sure exactly what the Pi power consumption will be, but I've seen 2.5W thrown around, so that's ~9-hours. Say your DC-DC converter is 90% efficient and you'll get about 8 hours out of it. Rechargeables will be considerably less.

macbadger
Posts: 6
Joined: Sun Jan 08, 2012 12:32 pm

Re: Battery power

Thu Jan 26, 2012 7:24 pm

error404 said:


macbadger said:


While battery power would be excellent, please bear in mind capacity.


700mA is, as ever, a worst case specification. Basing battery life estimates on it is going to be very misleading unless you're planning to keep the thing at 100% CPU and the GPU fully active all the time, and even then there's probably some margin.


I think it would be safe to assume if you watching a video over a network connection it would be fairly close to the 700mA hours especially as the none network version does not have a much lower rating.

macbadger
Posts: 6
Joined: Sun Jan 08, 2012 12:32 pm

Re: Battery power

Thu Jan 26, 2012 7:33 pm

mcookie said:


I'm no electrical engineer, but will the classic "mintyboost" altoids thingy work?

http://www.ladyada.net/make/mi.....power.html

It supplies 5v, and is quite cheap. Integrating what they already have there into one's own power supply couldn't be too hard, could it? My devised plan for the RasPi I get won't involve that much portability, so would 3 D-Cells work (or 4, with the whole subtract .7V thing...). All those mAh (60,000 total, according to the table on the mintyboost link) would run a RasPi for quite a while.

Corrections? Anyone?


Please remember, as previously posted 4x D cells rated at 15,000 mAh does not equal a capacity of 60,000 mAh. The four batteries are connected in series to get upto the required voltage. Only batteries conencted in Parallel increase the effective mAh capacity.

Thus in this case you connect four in series to reach ~6v, none in parallel, thus total 15,000mAh capacity.      -[Dcell][Dcell][Dcell][Dcell]-

IF...

you connected four in series, (to give ~6v)

then

another four in series to this

it would give supply of 6v 30,000mAh (8cells)

{ [Dcell][Dcell][Dcell][Dcell] }

- { [Dcell][Dcell][Dcell][Dcell] } -

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