USB 'Power Banks'

JohnW2 said:

I'm certainly not going to buy any product based on a guess at its specification, that guess itself being based on the appearance/size/weight of the product.

We know that these eBay-listed things don't have a capacity anything like 100 Ah at 5V - I'd be surprised if (m)any have a capacity greater than 10Ah (at 5V)
I certainly don't - the product I want would be tiny. However, if the listings meant what they say, they certainly would be enormous (and very expensive) - 2,000,000 mAh at 5V is 10,000 Wh, (i.e. 10 kWh) which, in energy terms, would be roughly equivalent to 550 Ah at 18V (i.e. over 100 times bigger than your power tool battery!!

Kind Regards, John

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Ok, were talking a completely cross purposes, I'll leave it at this. Anything claiming over 20,000 mAh has got to be big, unless they employ a different battery chemistry with a much higher energy density. I don't know of any such commercial offerings. So with that in mind a 10-20,000 mAh power pack is always going to be roughly 3-4 times the volume of the phone.

Isn't this just the modern day equivalent of the ads for PC speakers from a few years back?

You know, the ones that claimed to have a "250W music power" output.... yet were run from a 500mA 9V DC walwart?

EddieM said:

Ok, were talking a completely cross purposes, I'll leave it at this. Anything claiming over 20,000 mAh has got to be big...

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Exactly, and all of those I've seen are tiny (per stated dimensions/weight) and many have photos of them sitting on someone's palm.

I presumed that we are all agreed that none of them are going to be >20,000 mAh (and some probably a lot less than that). However, the problem is in knowing what capacity they actually ARE, given the silly numbers they claim. As I said, even if I were otherwise happy (about safety etc.) I would not buy on the basis of a guess of its spec!

Kind Regards, John

Ok, so a bit of digging seems to suggest that at max a Li-Ion battery is capable of 36,000mAh per Kg at 5V.

EddieM said:

Ok, so a bit of digging seems to suggest that at max a Li-Ion battery is capable of 36,000mAh per Kg at 5V.

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It looks as if that may be somewhat of an under-estimate. Most Belkin 20,000 mAh ones (and a number of other makes) are about 400g (total) weight (hence around 50,000 mAh per kg) but there is at least one Energizer 20,000 mAh one which claims to be only 225g total weight - which, if true, would imply around 89,000 mAh per kg.

Kind Regards, John

2 years ago a friend purchased a 'battery bank', quoted as 22000MaH with switchable output of 5, 12, 24V. 5V on USB and 1.3mm DC socket and 12/24V on something like Powerpoles and 2.5mm DC socket. this is a device about 3"x 2"x 5"

Included was a jump start lead finishing in insulated crocodile clips which didn't open far enough to clip on car battery terminals let alone the connecter on them.

So when he produced it for a demonstration we laughed. Fair do's it started a 2litre deisel engine twice but not a third time. The same test using the original 3 year old 55Ah Battery started the engine 20 times without silly drop in performance.

Recharge from a 5v USB [rated 4A but not measured] took about 27h before the internal auto charge light went out. 10Ω resistor on 12V o/p the starting voltage something like 10.5V dropped to 6V in about 8h, estimated as something like 6 to 8Ah. 24V on 30Ωohm load gave a capacity of about half of that but the 5v o/p with 10Ω started at 5.1V [1/2A] and 4 days later was still 4.9V so an estimation of something over 30Ah.

These figures are from memory so sorry a bit vague.

The interesting part about this device is using it to operate 2 way radio kit gives a very reduced time, something like half compared to a 7Ah gel battery.

More recently a USB battery bank of 10000mAh and 6.803Ω 10W resister, starting voltage 5.031 lasted for 14.43, 14.67, 14.11 & 14.37 hours to 4.9V starting at 8pm on alternate evenings with a recharge from noon to 7pm [31h]. Now that battery is exactly the same shape and size of the disposable lighters about 15mm diameter x 70mm long, it even has the squared lump on one side.

SUNRAY said:

2 years ago a friend purchased a 'battery bank', quoted as 22000MaH with switchable output of 5, 12, 24V. 5V on USB and 1.3mm DC socket and 12/24V on something like Powerpoles and 2.5mm DC socket...

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Well, for a start, as Detlef pointed out, in the case of a multi-voltage output, to quote the capacity in mAh (or (Ah) is obviously essentially meaningless. One imagine/suspects that the 22,000 mAh probably related to 5V but, if so, that would mean only around 9,200 mAh at 12V and around 4,600 at 24V.

However, I'm not attempting here to discuss here how actual performance relates to the claimed (when 'sensible') 'nominal' capacity (which is a different question), but how one can even tell what the 'nominal' capacity is when the seller it claiming something ridiculously high, and clearly incorrect.

Kind Regards, John

JohnW2 said:

Well, for a start, as Detlef pointed out, in the case of a multi-voltage output, to quote the capacity in mAh (or (Ah) is obviously essentially meaningless. One imagine/suspects that the 22,000 mAh probably related to 5V but, if so, that would mean only around 9,200 mAh at 12V and around 4,600 at 24V.

However, I'm not attempting here to discuss here how actual performance relates to the claimed (when 'sensible') 'nominal' capacity (which is a different question), but how one can even tell what the 'nominal' capacity is when the seller it claiming something ridiculously high, and clearly incorrect.

Kind Regards, John

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Measured figures are not far off those.
Well how about just buy the biggest possible on ebay then demand full refund when the product does not come up to spec?
Then keep going until you get what you want.

SUNRAY said:

Well how about just buy the biggest possible on ebay then demand full refund when the product does not come up to spec? ... Then keep going until you get what you want.

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... because it's very likely that none of them would prove to be 'what I wanted', so it would be a pointless hassle keeping on trying to 'get full refunds'. I previously though that "2,000,000 mAh" was the 'biggest possible', but I've just found a couple of hundred like this ...



5,000,000 mAh is, of course, 5,000 Ah, which equates to 25 kWh at 5V (a bit more than my average total domestic electricity consumption)!

From the price, I would suspect that these are probably nowhere near the 15,000 - 20,000 mAh (at 5V) that I really want (maybe only ~5,000 mAh) - so, as above, I could spend my whole life trying to get refunds without ever getting one that I actually wanted!

Kind Regards, John

JohnW2 said:

Indeed. There are countless suppliers of reasonable-sounding branded ones - but this discussion is about trying to make some sense of the listings (for 'unbranded' ones) on eBay.

Kind Regards, John

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Th

JohnW2 said:

Indeed. There are countless suppliers of reasonable-sounding branded ones - but this discussion is about trying to make some sense of the listings (for 'unbranded' ones) on eBay.

Kind Regards, John

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Sorry - I wasn't clear - this is not a supplier of reasonable-sounding branded ones - this is a specific individual trader who will (in my experience) talk to you on the phone about your particular needs and sell you something reasonably priced that does what it says on the tin.

StephenStephen said:

Sorry - I wasn't clear - this is not a supplier of reasonable-sounding branded ones - this is a specific individual trader who will (in my experience) talk to you on the phone about your particular needs and sell you something reasonably priced that does what it says on the tin.

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Fair enough - recommendations like that are always worth having.

However, as I thought I had made clear, I have absolutely no need to talk to anyone on the phone about my needs. I know exactly what I want, and the only problem is that, even if I were otherwise happy (about safety etc.), there would be no way I could tell whether any of the ridiculously-described products on eBay corresponded with what I wanted.

Kind Regards, John

ok not in the least scientific
dewalt 18v 5ah powertool battery not including lumpy bits for connectors is100mmx45mmx75mm
now if we assume a battery pack 1/3 the size at 6v that would give a package 100x75x15mm would give you around 6 or 7ah max with present generation lion batteries
now dewalt seem to be on the verge off doubling capacity so perhaps up to 12-15ah but any bigger claims off energy stored would seem fancy full

big-all said:

ok not in the least scientific .... dewalt 18v 5ah powertool battery not including lumpy bits for connectors is100mmx45mmx75mm .... now if we assume a battery pack 1/3 the size at 6v that would give a package 100x75x15mm would give you around 6 or 7ah max with present generation lion batteries ... now dewalt seem to be on the verge off doubling capacity so perhaps up to 12-15ah but any bigger claims off energy stored would seem fancy full

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Yes, we all know that the claimed capacities I've been illustrating are ridiculous, leaving no clue as to what the actual capacities might be.

However, as for your "... so perhaps up to 12-15ah but any bigger claims off energy stored would seem fancy full", that's over-stating the situation a bit, since there are countless reputable 20,000 mAh (i.e. 20Ah) (at 5V) power banks on the market.

Kind Regards, John

just trying to give some sort off baseline for reasonable expectations so being 20-30% out is fairly good

big-all said:

just trying to give some sort off baseline for reasonable expectations so being 20-30% out is fairly good

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Sure, I understand that - but given that the claimed capacities appear to be anything from 500% to 25,000% 'out', I think that we have already worked out what 'expectations' are (and are not!) reasonable

Kind Regards, John