OT: Powerbank & air travel question

[newshound]

I thought they now had insulated boxes big enough to take a laptop.

[The Natural Philosopher]

You do, That's the AH of the raw cells...

[John Rumm]

The 12Ah seems a little suspect in the first place - they may well be marketing Ah rather than electrical ones!

They are probably adding together the cell capacities even though they are most likely wired in series.

Say it has 3 cells at 3.6V, and each cell is 4Ah (probably less), that gives 14 odd Wh per cell, or a tad over 40 for the whole pack.

[newshound]

Good point, they might have done that too. WE JUST HAVE NO WAY OF KNOWING WHICH OF THREE CALCULATIONAL METHODS THEY HAVE USED.

[Dave Plowman (News)]

Be interesting to know what it weighs. Should be possible to do a rough calculation from that as to the true capacity at a nominal 12v.

[Dave Plowman (News)]

Just been looking at a variety of these on Ebay. Most are very coy about quoting the battery part in amp.hr. Preferring to quote maximum current to start an engine - but not for how long.

One of the most expensive is the Sealey. That gives the weight as 1 kg, so don't see that being 12 amp.hr at 12v. More like 5 amp.hr by my reckoning.

Another does give a figure - 13,600mAH/ 50.32WH Also claims to be suitable for jump starting diesel or petrol engines.

But 13.6 amp.hr at 12v gives 163 watt.hr, so they are quoting the 5 v output.

[The Natural Philosopher]

I doubt they did.

Its clear its a three cell pack of 4000mAh cells. These are not uncommon these days and so the pack will be around 40-45Wh, and capable of delivering > 200A at 12V for short bursts. Just what a car needs to start.

[Tim+]

Maybe I should give it to Big Clive to tear apart. Bet he could tell me. ;-)

Tim

[John Rumm]

The main problem is the marketers being fast and lose with the tech specs. If the total battery capacity genuinely is 12Ah, and the voltage is 12V then energy content is 144Wh, and we don't care how many cells there are.

Since we expect there is some slight of hand going on to arrive at the

12Ah figure, knowing the number of cells (and their chemistry) means we can make a more meaningful stab at estimating the actual true energy density.

[newshound]

Yes! And charge it up and short it out afterwards, please!

:-)

[Dave Plowman (News)]

Car batteries are only the stated voltage. And the capacity as marked on them generally accurate.

For some reason, other types of batteries tend to be more the subject of fraud. And a power pack with a variety of output voltages just gives an unscrupulous maker a chance to confuse even more.

[John Rumm]

Couple that with the need of sellers on eBay to be able to one up the competition selling basically the same thing, there is always a desire for a bigger number.

[Vir Campestris]

In the cabin.

One, you'll be gentle with it (compared to baggage handlers) two, if it does catch fire you'll tell someone and they'll stick it in a metal food trolley or something while they do an emergency landing.

Andy

[Andrew Gabriel]

Yes, you're right - was thinking of something else.