Power banks for tramping
Lately I've been updating electrical devices (torch, gps, camera are my main three). More and more they're trending towards charging and/or running straight of USB, whether or not they have replaceable batteries. I used to try and always get stuff that ran off AA batteries to make it simpler to manage spare power between them, but now it's making more sense to have lighter devices and carry a power bank instead. I presume many people here are already doing something like this. I haven't bought one for a while, though. With a tentative look there seem to be lots of power banks out there, but much of which also looks very consumer grade and aimed at people are are just hanging around town and worried about their phone battery running out. Are there any favourites out there for tramping purposes, or thoughts on what might be good value for money? In my mind I'd like something reliable and reasonably durable, like if I knock it or if it got a little wet then I'd want it to keep working. Weight's always of interest, as is having a decent charge and some kind of indicator of remaining charge. I'm not expecting to get it perfect first time, but I might as well try. Any thoughts?
Re slow-charging: Yes. The power bank i'm using has capacity of 1A output which it happily delivers to other usb equipment. I'm testing on a miboxer power bank as that has a built in ammeter. But I note that samsung phones drop to a trickle charge when using non samsung chargers. Likewise on my 2.5A usb wall socket the samsung slow-charges. === Regarding 85% efficiency - where does that figure come from? I can see that 5v usb dropped to 4.2v charging voltage across an ideal voltage regulator will give you 84% of the supplied power delivered to the battery. But there is also loss before that stage: at what's delivered to the USB wire by the powerpack. The measured usb output for the full discarge cycle of my 2600mAh battery is approx 6.3Wh-7.3Wh at the usb compared to 9.36Wh nominal for the battery (The range is because I have only a range for the time it ran for of 3-3.5hr). So thats 67%-78% efficiency across the voltage step-up stage. If this is achieved with a voltage doubler follower by regulator - I'd expect a max theoretical efficiency of that setup to be 69% (5/(3.6*2)) due to the power/voltage dropped across the regulator. So my theoretical max efficiency across the supply and charging circuits is .69*.84=57.9% So what wrong assumptions have I made @bernard?
Good topic, I've come to the conclusion I'm going to go with a power bank because my phone provides more entertainment and has more function than any other single thing: - camera - watch - Video - notepad - recording my voice, notes - apps for the trail - podcasts - e books I've more or less landed on the Belkin 10,000, which I'm assuming will do 3 charges, so that's 4 charges from the time I leave the car https://www.dicksmith.co.nz/dn/buy/belkin-pocket-power-10000mah-power-bank-silver-f7u039btslv-belkin/?utm_source=google&utm_medium=product_listing_ads&gclid=CjwKCAjw9dboBRBUEiwA7VrrzVTOnp2Zb3eMNg7kfjkUQEzqCWwPL2r8UoqocVJ9GZZY3PHSBMnMhxoCbxAQAvD_BwE
@madpom, the formula is this: Labeled capacity of the power bank x 3.7 / output voltage of power bank) x 0.85 / battery capacity of device = Total number of recharges
1 deleted post from madpom
Well ... were pretty close to agreeing. By your formula: (3.7/5) x .85 = 0.74 x .85 = 62.9% By my calculations based on the components I believe the circuit uses: (5/(3.7*2)) * (4.2/5) = .67 * .85 = 57.9% Either way the max theoretical charge you will get out of a usb powerbank is around 60% of its labelled capacity, and experience shows you might not even get that. Buyer beware.
Charging any battery is subject to lots of variables not least of which is the type, e.g. sealed lead acid, NiMh, NiCd, lithium and so on. Not withstanding the stretched claims that some of these power pack manufacturers may be making, lithium batteries need to be constant CURRENT charged. So,depending on how the charging circuit applies voltage potential to the cells, as long as the constant current parameters are met then the lithium battery should recharge at a proper curve with minimal heat. Battery quality and internal resistance will vary from manufacturers so these claims aren't even necessarily misleading, just highly subjective.
there is enough electronics in most bat packs and I would hope most other devices to take care of the constant current charging
@madpom the formula doesn't give you the efficiency, but [the number of charges](https://techzillo.com/power-bank-recharges/). If we assume a 6000 mAh battery, you can charge your phone 1.5 times. That's an efficieny of 75%. I.e. the naive calculation is 6000 mAh / 3000 mAh (size of power bank divided by size of phone battery). So you would expect 2 charges. But we get "only" 1.5.
@bernard. Your formula does not give the result 1.5 times (75% of expected charge). For a 6000mAh pack charging a 3000mAh battery it gives: 6000x(3.7/5)*.85/3000 =1.258 charges Which is 62% of nominal charge
@madpom, sorry, should have added I used 4.2V for charging. That's the value you mentioned as you seem to have measured that. But yes I agree with your value if you take 5V.
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