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Is this Maplin Power Bank 4000mAh pwerful enough to power the Pi with all of the peripherals below? This is useful as I cannot order online, and it is currently £15.

I have a Raspberry Pi Model B, which I plan to use build a small two-motor robot. The motors are powered externally by 4 AA batteries, and are to be controlled by at first by two large NPN transistors, and then a small also externally powered motor controller board (I found a working one lying around in a box). The Pi is to be controlled over a now-working wi-fi hotspot that it creates through a USB Ralink RT5370, and I may later want to add a USB webcam to give a view of what it is doing.

The reason I ask is because I have not bought the battery yet, and though it says that it has a 1 Amp output, I emailed Maplin and had the reply:

Thanks for contacting Maplin technical support This product would struggle to power the pi reliably however N95LH would be suitable for this'.

Is this true, or are they just trying to sell a more expensive product? Searching this forum and elsewhere, I have found stuff about 5200mAh batteries being used reliably.

N.B. I have already built a power supply with several AA batteries and a 5 volt regulator, which works OK, but runs out really quickly, and only work reliably with alkaline batteries, and repeatedly buying batteries cost a fair fortune. That is why I am considering this lithium-ion battery instead. I did try a 9V with the regulator, but it did not provide the Pi enough power to boot.

If you do suggest any other products, try to keep to stuff available in the UK please.

Works now - here is a picture: Raspberry Pi And Battery

Do not know how it will work on low battery, but it works OK now. Here is a link for anyone interested. (Last updated 17/11/2013)

Another update, works very well with a USB camera (was an integrated one removed from an old laptop) and wifi AND ethernet (for downloading) - even when the last blue light is flashing (I got VERY nervous then -but I could not stop it as it was running updates...) confused

(Last updated 22/11/2013)

Link may not work occasionally, just hit reload if needs be.

http://www.maplin.co.uk/maplin-power-bank-4000mah-853747

(Last updated 26/11/2013)

(Update 2017) Battery now virtually useless with anything (won't charge properly etc). Be careful of cheap ones ;)

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2 Answers 2

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Either would power the pi and your peripherals. The pi could draw between 0.5A and 1A (depending what camera and how much wifi), so the 4Ah battery should last 4 to 8 hours and the 10Ah battery 10 to 20 hours. Choose the one which gives you the duration you want, or a smaller or larger as required.

A standard 9V non-rechargeable PP3 has a high internal resistance so the voltage will drop a lot at these sort of loads.

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  • Great, I should be able to get this sorted tomorrow. Should I mark this as solved now, or until I manage to get this done? Having it work for 20 hours would be great, but it would be too heavy, too big, and too pricey - hence I will go for the 4Ah. Thanks Anyway.
    – Wilf
    Commented Nov 14, 2013 at 18:51
  • @wilf: if the question is answered to your satisfaction, you should accept it. If not, you can wait for more responses or ask for a clarification. Up votes are good as well!
    – Jacobm001
    Commented Nov 14, 2013 at 19:43
  • Jacobm001 - I cannot upvote anyway (Not enough reputation again). I should hopefully have this done by tomorrow, and if it works OK I shall mark it as solved. One question though @PeteKirkham - how can I measure the resistance of a battery, or find out what it is, using a conventional multi-meter or the internet?
    – Wilf
    Commented Nov 14, 2013 at 20:08
  • @wilf there are some tables on the net with typical values, but it will vary between different battery models. With a multimeter and suitable load (e.g power resistor) you can measure voltage at no load, then voltage and current at load. The drop in voltage divided by the current gives the internal resistance to a first approximation (it may not be constant, and won't be constant if the battery temperature changes, so you can take multiple measurements to find the gradient dV/dI for a better approximation at given operating temperature).
    – Pete Kirkham
    Commented Nov 15, 2013 at 19:26
  • I have bought the battery, spent ages charging it, and it works! Boots fine, and works fine as a wi-fi hotspot. I do not know the performance of the battery when it gets to low power, but the signal strength is brilliant. Shall mark as answered.
    – Wilf
    Commented Nov 17, 2013 at 16:29
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I've powered the Pi with cheaper battery packs than that and it's fine. With motors though there are a couple of extra considerations. First is that they have a very high current draw when the start up. The high current draw could potentially damage some of the circuitry in the battery pack. Secondly, motors don't just "stop". The process of stopping is what might charitably in other industries be called a sort of "regenerative braking"---that is to say that there is a slight back charge along the wires when the current cuts off as the motors cut-off. Make sure you include a diode to protect in this case both the Pi and the battery pack as every cut-off effectively becomes a temporary short-circuit due to the current reversal. This is usually taken care of with a diode, which most robotics add-ons include.

The current drop over a linear regulator is very high as it actually uses the energy to do the conversion. Since a 9V battery doesn't have much juice to start out with, it drops too quickly to stably power the Pi. Even if you can't order it now because of your age, in the future it might be worth checking out MoPi though as this would get around some of the power problems. Specifically, it features a much more power efficient switched mode regulator, which is the same sort of thing they use in cell-phone chargers and PC power supplies.

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