How do portable USB power banks make their mAh claims? (Lazer PB-CJ12000)

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Forums › Finance and wealth management › How do portable USB power banks make their mAh claims? (Lazer PB-CJ12000)

raytaylor

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#204617 9-Oct-2016 18:36

I bought a large portable USB power bank from harvey norman today.

On the manufacturer's website, it says its 12,000 mAh of capacity.

http://www.laserco.com.au/PB-CJ12000-universal-portable-battery-rechargeable-12-000mah-with-usb-car-jumper-cables?search=PB-cj12000K

When I got it home i decided to open it up. I found the battery pack is only 44.4 Wh at 12v. Thats only 3.7 Ah or 3700mAh

Even trying to stretch the figures by assuming its 12,000mAh at 5v for the USB output, this is still only a capacity of only 8,888 mAh (74% advertised capacity)

Has anyone else noticed similar problems with these sorts of products?

I can imagine the battery cell producer claiming more than the chemical capacity of a battery, but when the capacity is printed plainly on the battery pack, I think its quite audacious of Lazer to go and claim 3x the actual capacity on the outer packaging.

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#1648136 9-Oct-2016 18:40

Q. How do portable USB power banks make their mAh claims?

A. Think of a number and double it.

About as accurate as claimed peak power levels in cheap hi-fi gear.

Sideface

richms

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#1648139 9-Oct-2016 18:46

They list the total cell capacity, not the output capacity. So 4000mAh per cell will give the 12000 rating, if its a 3S, but saying 12v might be a 4S of a lithium iron phosphate cell, which has a 3.2v nominal voltage. so it would be 3000mAh per cell.

See heaps of angry people that dont understand that when they find they cant get 1A for 2 hours out of their 2000mAh packs. I find that its about half of the cell capacity you get at 5v from powerbanks, which allows for the step up and also the inefficiancy of the converter.

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jarledb

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#1648142 9-Oct-2016 18:50

And the reason is they measure the mAh at 3.7 Volt, not 5 Volt.

About powerbank capacity

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gregmcc

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#1648156 9-Oct-2016 19:31

It's seems like a whole lot of fudging of numbers to me, but at the end of the day the fair trading act must be complied with, take it back and ask for a refund, or make them "Aware" of the problem so the can adjust their marketing to reflect actual capacity.

richms

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#1648178 9-Oct-2016 20:00

Also only phones with a buck converter charger (most now) will be getting anywhere near efficient with the charge. Most cheap slow charging things will have a liner regulator doing the charging, so there goes another 30-40% of the power as heat from the regulator rather than into the cell in the device. That is why its often more effciant to have a lower voltage charging things with a linear regulator doing the charging - anything between the cell voltage and the supply voltage just gets lost as heat.

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sleemanj

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#1648692 10-Oct-2016 18:30

44.4 Wh / 3.7v nominal Lithium Ion Cell = 12 Ah , so that's where they got that number.

Of course it is a stupid way to measure the capacity, but chinese marketers don't care, and since all their competitors do the same, they don't want to be the ones giving a "low" number even if it would be more useful.

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gregmcc

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#1648745 10-Oct-2016 20:12

sleemanj:

44.4 Wh / 3.7v nominal Lithium Ion Cell = 12 Ah , so that's where they got that number.

Of course it is a stupid way to measure the capacity, but chinese marketers don't care, and since all their competitors do the same, they don't want to be the ones giving a "low" number even if it would be more useful.

As the OP stated, markings on the cell are 44.4wh, using known and proven electrical formulas it works out to 3.7Ah, bet they wouldn't accept their logic if it was used to calculate the number on cents in a dollar so they could be paid

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sleemanj

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#1648840 10-Oct-2016 23:22

gregmcc:

As the OP stated, markings on the cell are 44.4wh, using known and proven electrical formulas it works out to 3.7Ah.

Yes, if you work on the basis of the mAh capacity at 12v, but I bet they didn't say that.

There is no argument from me that the marketing of this sort of product is misleading, but it is however not surprising, the defacto measurement unit of these "power bank" products has become the mAh at 3.7v (and that's for the honest ones), regardless if the "power bank" contains a series or parallel combination of cells, or outputs 5v, or 12v, or whatever.

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sbiddle

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#1648870 11-Oct-2016 07:19

It's really just like router vendors like Linksys, Netgear and so on who claim things like "5 Gbps WiFi" which is a case of adding up the maximum PHY layer throughput of the different technologies they incorporate. It's not actually possible to get speeds like this.

neb

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#1649253 11-Oct-2016 14:56

raytaylor:
I bought a large portable USB power bank from harvey norman today.

On the manufacturer's website, it says its 12,000 mAh of capacity.

When I got it home i decided to open it up. I found the battery pack is only 44.4 Wh at 12v. Thats only 3.7 Ah or 3700mAh

They're rated at the nominal cell capacity at 3.7V. So if the cell claims 3000mAh then you can draw somewhat under 3A at a nominal 3.7V (depending on charge) for an hour or so. With an 80% efficient DC/DC converter that's about 800mAh at 12V.

(NB: Back-of-the-envelope/mental calculation, all figures are approximate to illustrate what you're getting).

neb

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#1649257 11-Oct-2016 14:59

gregmcc:
It's seems like a whole lot of fudging of numbers to me, but at the end of the day the fair trading act must be complied with, take it back and ask for a refund, or make them "Aware" of the problem so the can adjust their marketing to reflect actual capacity.

I don't think it's unfair, if you've got 4 x 3000mAh cells then that's a nominal 12,000mAh of capacity. They never claimed it's 12Ah at 5V or 12V. You can certainly try to return it, but I don't know how far you'd get, I don't know if anyone's ever managed to return a 5000W PMPO AA-battery radio for false advertising. A better option would be to write to Fair Go and get them to make consumers aware of the issue.

gregmcc

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#1649294 11-Oct-2016 16:08

neb:
gregmcc:

It's seems like a whole lot of fudging of numbers to me, but at the end of the day the fair trading act must be complied with, take it back and ask for a refund, or make them "Aware" of the problem so the can adjust their marketing to reflect actual capacity.

I don't think it's unfair, if you've got 4 x 3000mAh cells then that's a nominal 12,000mAh of capacity. They never claimed it's 12Ah at 5V or 12V. You can certainly try to return it, but I don't know how far you'd get, I don't know if anyone's ever managed to return a 5000W PMPO AA-battery radio for false advertising. A better option would be to write to Fair Go and get them to make consumers aware of the issue.

And if those cells we arranged in parallel then that would be correct, but the markings state 12V so they are arranged in series giving a mAh of 3700

richms

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#1649394 11-Oct-2016 18:14

That would make comparing the capacity very hard for people that do not understand that.

Imo there is that total amount of cells in it and it makes it comparable to 2s or 3s power bank by number alone.

Richard rich.ms

neb

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#1649416 11-Oct-2016 19:01

richms: That would make comparing the capacity very hard for people that do not understand that.

Maybe we could come up with a simple conversion formula, 3.7/5 * 0.8 (boost 3.7 -> 5V with 80% efficiency) or something, so multiply by about 0.6 to get the actual capacity in mAh at 5V.

Edited to add: I'm assuming 18650s here, obviously things will depend on what's actually in there. The OPs power bank looks like it has some custom battery pack.

richms

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#1649417 11-Oct-2016 19:03

Or watt hours which is what you need to know for air travel etc. Also the reason that chinese sellers are lying in the other direction now.

Richard rich.ms

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