lworbey
Posts: 41
Joined: Tue Dec 20, 2011 12:39 pm

Re: Battery power

Fri Jan 06, 2012 11:37 am

It lists


Output Power: 75mA @ 5.5V


so I would think it would not be suitable as the A Model need 500mA and B Model 700mA.

This does seem quite low though and I am not convinced that this isn't the power output of the solar cell that charges the battery and the battery might give out more power but you would need to contact Maplin to confirm this.

Mp4
Posts: 9
Joined: Fri Jan 06, 2012 11:08 am
Contact: Website

Re: Battery power

Fri Jan 06, 2012 11:40 am

lworbey said:


It lists


Output Power: 75mA @ 5.5V


so I would think it would not be suitable as the A Model need 500mA and B Model 700mA.

This does seem quite low though and I am not convinced that this isn't the power output of the solar cell that charges the battery and the battery might give out more power but you would need to contact Maplin to confirm this.



Thanks ill ask them

geomore
Posts: 1
Joined: Fri Jan 06, 2012 12:30 pm

Re: Battery power

Fri Jan 06, 2012 1:05 pm

Having read through this thread felt compelled to register and comment...
I have been considering in the back of my my mind how I might power my berry on batteries.
I remember reading somewhere that the 5V supply needs to be carefully regulated as it is fed directly to USB ports etc. As someone mentioned, in theory providing no peripherals are used, you could get away with a coarser voltage, as the SOC runs off its own 3.3v regulator. However It is proabably not designed to work off a noisy or unregulated supply. In my opinion you really want to regulate the 5v input. Usb Devices expect a regulated 5v supply (+-0.25v i think) so anything designed to power a "generic USB device" should in theory be fine to use. However USB chargers designed for a specific make or model phone MAY not follow these rules, for example if the phone only needs 3.7v. So when chosing a pre-made "battery booster" or similar, I would look for one designed for generic use e.g "for all smart phones". Smart phone ones would be a good choice as smart phones expect a lot of current to charge their big battery packs. A solar charger is unlikely to cut the mustard unless it has a backup battery (and would proabably need a fair size solar panel - if you are in scotland forget it).

For those that want to self build, I"d stay away from Heath Robinson voltage drop resistors and diodes - they appear to work in basic theory,but are not going to give a stready voltage. Look up "5 volt voltage regulator" for some circuits that either use a single regulator IC (3 Pin device costing about £2) or a more complicated (but interesting) circuit relying on a zenner diode. The downside is you will loose some efficiency, and would need to make sure the voltage from the batteries does not drop below about 7(?) volts (it"s a long time since I made one) so think 5 or 6 AA"s. You would also need to think about removing spikes (capacitor) and low voltage protection, to stop the device from switching on and off rapidly whn the batteries are flat. I"m sure there"s lots of websites full of info.

Generalkidd
Posts: 26
Joined: Thu Jan 05, 2012 5:28 pm

Re: Battery power

Fri Jan 06, 2012 3:47 pm

Just out of curiosity and this may sound like a stupid question, but how do you turn on the Raspberry Pi. Based on the pictures and schematics I've seen so far, I don't seen any power switches for turning it on or off. Does it just turn on automatically when connected to a power supply?

stormy1
Posts: 60
Joined: Fri Jan 06, 2012 3:44 am

Re: Battery power

Fri Jan 06, 2012 6:23 pm

geomore said:



For those that want to self build, I"d stay away from Heath Robinson voltage drop resistors and diodes - they appear to work in basic theory,but are not going to give a stready voltage. Look up "5 volt voltage regulator" for some circuits that either use a single regulator IC (3 Pin device costing about £2) or a more complicated (but interesting) circuit relying on a zenner diode. The downside is you will loose some efficiency, and would need to make sure the voltage from the batteries does not drop below about 7(?) volts (it"s a long time since I made one) so think 5 or 6 AA"s. You would also need to think about removing spikes (capacitor) and low voltage protection, to stop the device from switching on and off rapidly whn the batteries are flat. I"m sure there"s lots of websites full of info.



A switching voltage regulator as opposed to using a linear regulator would be a good idea:

http://www.dimensionengineerin.....lators.htm

example:

http://www.pololu.com/catalog/.....oduct/2177

spamel
Posts: 196
Joined: Sun Jan 01, 2012 8:43 pm

Re: Battery power

Fri Jan 06, 2012 6:35 pm

Wwould I be correct in thinking the charger for my Blackberry will also power a Raspberry? Such fruity excellence if this is so!

netomx
Posts: 80
Joined: Tue Oct 11, 2011 4:06 am

Re: Battery power

Fri Jan 06, 2012 6:57 pm


nichobb
Posts: 82
Joined: Sat Nov 19, 2011 10:34 am

Re: Battery power

Fri Jan 06, 2012 6:57 pm

I plan to use the circuit from a phone charger that runs from a cars cigarette socket and splice it into a cable. I"ll be doing a number of power checks to ensure nothing excessive goes through (and they have fuses in there I may keep).

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abishur
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Location: USA
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Re: Battery power

Sat Jan 07, 2012 3:40 am

Just for the record, the r-pi does come with voltage protection features (self resetting fuse, polarity protection, and over-voltage latch).  You will need to give it the 5V it needs or it won't work of course, but that is part of the reason why they did go with the USB form factor PSU.  In powering from batteries, my plan is to use a grouping (specific number to be determined) of AA batteries in conjunction with an voltage booster.  Wire a couple of these groupings up to double (or triple) the mAh.  The voltage booster would keep it at a steady 5V and I'd get a nice long battery power from the r-pi.  Throw in something like the Maxim DS2715 and I can use rechargeable batteries possibly in an automatic battery backup for power loss applications

Also originally they were going to use a switching regulator, it was (for a myriad of reasons) replaced for the linear regulator we have now.  I know every little bit adds up, but we're talking 3.5W under full steam.  My guess is to see a normal operating level of 2.5 watts (500 mA power drain) or even 1.7ish for the model A depending on the application.
Dear forum: Play nice ;-)

marc
Posts: 48
Joined: Fri Jan 06, 2012 6:40 pm

Re: Battery power

Sat Jan 07, 2012 10:59 pm

Just finished building a circuit for using 8 AA batteries.

Battery depletes in 0.1v over time and stops running at required voltage after some time.

4x. 1.2v is 5v 1.1v x4 is 4.4v below. .5 tol.
8x 1.2 is 10v 1.1v x8 is 8.8. way above tol.

regulated to 5v +-0.3 v leakage.

minimum deplete level for each cell will be 0.6v to get 5v less with the lower tolerance.

it works. charging 1500ma samsung phone battery on 5v usb charge port.

i guess building your own is best way.

marc
Posts: 48
Joined: Fri Jan 06, 2012 6:40 pm

Re: Battery power

Sat Jan 07, 2012 11:18 pm

To answer other questions here about packaged emergency chargers for phones.

They run off 3.7v li ion cells and use a circuit known as a jeule thief that uses an transistor and coil to boost voltage level which settles at max output of whatever it is plugged into. Some use a diode on the output this diode is an zenor diode that has a designed breakpoint of 5v. when placed in circuit in reverse.

not the best things to use but work well in the short term.

pico from freeloader uses similar circuit and a 6v panel to charge internal battery.

there is a new device in maplin that has an 4000ma battery and dual solar panel to charge it.

4x AA doesn"t last long as i have discovered. even with a zenor diode leakage is 0.3v. standard diode 0.7v. so upto you what you use.

marc
Posts: 48
Joined: Fri Jan 06, 2012 6:40 pm

Re: Battery power

Sat Jan 07, 2012 11:33 pm

Would like to improve on this one i built and use more cells but its getting big as it is. I just completed phone charge too 100% it notified to remove charger this never happened with 4 AA setup. so should be capable to run rpi for a while?

jwatte
Posts: 203
Joined: Sat Aug 13, 2011 7:28 pm

Re: Battery power

Sun Jan 08, 2012 6:31 am

spamel said:


Wwould I be correct in thinking the charger for my Blackberry will also power a Raspberry? Such fruity excellence if this is so!



The Blackberrys I've owned have all used MINI-USB. The Androids and cameras I've owned have mainly used MICRO-USB. IIRC, the RPi wants MICRO-USB.

However, this is just a physical difference. There are adaptors. And if the charger has a regular USB host port on the wall end, you can just use the right cable. And if Blackberry switched to MICRO-USB in the last 3 years or so, I wouldn't know about it, and you'd be good anyway.

jwatte
Posts: 203
Joined: Sat Aug 13, 2011 7:28 pm

Re: Battery power

Sun Jan 08, 2012 6:39 am

netomx said:


How about MAX786 ?

http://www.maxim-ic.com/datash.....vp/id/1187


I bet that would work, but it looks expensive.

If you want simple to wire, and have 7V available (two Li-Ion cells, say), you could just use a 7805. Or, if you have 5.7V or more, an LDO version might be the TL750M05C. That's a buck 26 cents at digi-key.

If you worry more about the power draw of the regulator, then you need a switcher, and all the trouble that comes with that. You probably want to buy an integrated package, rather than design the circuit board yourself at that point. Integrated switcher regulator + LiIon charger circuits are starting to become quite affordable.

foobar
Posts: 9
Joined: Sat Dec 17, 2011 10:00 pm

Re: Battery power

Sun Jan 08, 2012 8:51 am

If you want to simple and cheap use a LM2574 or LM2575. Works on a breadboard and gives a reasonable efficiency.

spamel
Posts: 196
Joined: Sun Jan 01, 2012 8:43 pm

Re: Battery power

Sun Jan 08, 2012 11:26 am

Cheers Jwatte, thinking on it I also have a plug thingy for my Galaxy Tab so I should be able to use that with the correct usb cable. Cheers!

yehnan
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Contact: Website

Re: Battery power

Sun Jan 08, 2012 12:01 pm

Hello,

Originally my power plan is: computer – USB cable – Raspberry Pi

However, after reading some posts, I think this scheme is kind of not stable and not good enough.

I found a power adaptor of my old Mxtx V3. It says:

Input: 100-240V ~ 50/60Hz 0.2A

Output: 5.0V  500mA

Can I use this to power up RPi?

Power rating of Model B is 700 mA(3.5 Watt), so I can't power up Model B?



Thanks.

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

Re: Battery power

Sun Jan 08, 2012 12:45 pm

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

t = C/ I^n

assuming good 2100mAh NiMH batteries, with a Peukerts constant = 1.3.

The model B rasPi runs at 700mA

so t= 2.1 / 0.7^1.3 = 3.33hrs if Peukerts constant is worse at 1.1 it gives 3.1hrs

If we assume now the 11000mAh trent Icruser with model B, and again assume a good 1.3 Peukerts

t = 11/0.7^1.3 = 17.48 hrs

This is better, but still in my use a couple of days. Assume always connected to the network. This means it could drain quickly. Someone mentioned trickle charging with a solar cel, which for the most part might help. But before committing you might want to fully consider the reality.



PatrikL
Posts: 5
Joined: Fri Dec 23, 2011 11:03 am

Re: Battery power

Sun Jan 08, 2012 1:37 pm

I do not understand at all why is it necessary to use "Peukerts constant" I have read something here http://www.39pw.us/car/peukert.....ffect.html about it, but still I do not think it is necesessary to use it, because good li-ion batteries have almost the same capacity if they are discharged at different rates

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

Re: Battery power

Sun Jan 08, 2012 4:48 pm

@PatrikL

True Li-ion will, in general be better, but still Pukerts is a factor. What I was demonstrating is that the length of time the RaspPi will run on such a battery, be it Li-ion, NiMh or Alkaline for a relatively short time.

Pukerts also has an effect on said length of life- even for Li-ion, true less effect (in general) but to exclude it from calculations would be a lie.

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

Re: Battery power

Sun Jan 08, 2012 4:53 pm

Update to calculations:

Just realised I substituted the wrong answers! (three posts up)

2100mAh battery, best case: 2.9hrs worst case: 2.7hrs

11000mAh battery (i.e. the Li-ion one) best case: 15.2hrs

Sorry everyone!

PatrikL
Posts: 5
Joined: Fri Dec 23, 2011 11:03 am

Re: Battery power

Sun Jan 08, 2012 5:31 pm

I still have some questions, with your calculations, five 2100mAh NiMH batteries should provide about the same runtime like one 11000mAh li-ion battery (or four 2800mAh 18650, three 4000mAh 26650 batts...), or am I wrong? But there is big difference in voltage between these technologies... Five 2100mAh NiMH batts will have total energy about 5*2,1Ah*1,2V = 12,6 watt hours. Combined energy of x li-ion batts, or total energy of one 11Ah pack will be 11Ah*3,7V and that is more than 40 watt hours... (calculated with nominal voltage 1,2/3,7V of NiMH/Li-ion cells).

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

Re: Battery power

Sun Jan 08, 2012 5:54 pm

it would be more correct to consdier 'cells' and 'battery'

for the NiMH/Alkalines we are most likely considering a number (say 4) of AA 'cells' (each 1.5v theoretically, or 1.2v realistically after initial drop off) that equate to one 'battery' of cells totalling a capacity of 2100mAh (2.1Ah), at approximately 6v.

The fact you have multipule cells does not increase the mAh as the multipule cells are in series to uprate the voltage to the required voltage.

The Li-ion in this case, would be best considered as a single cell battery. So has 11Ah capacity in it own right.

white74
Posts: 6
Joined: Thu Dec 29, 2011 12:19 am

Re: Battery power

Sun Jan 08, 2012 10:29 pm

ldo regulator would be good

i wonder if a 7805 would have enough amps to run main system

powering your usb externally would help as well

using a usb hub and adding a 7805 for each port

most rf usb devices are power hogs

jwatte
Posts: 203
Joined: Sat Aug 13, 2011 7:28 pm

Re: Battery power

Mon Jan 09, 2012 2:27 am

white74 said:


i wonder if a 7805 would have enough amps to run main system



Depends on which "7805" you get. Most of them do at least 1A, though, and many do 1.5A.

Search for "ldo regulator 5v" on digikey.com to find a long list of parts that might work.

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