Aura HD Charge battery without computer?

[Ken Maltby]

A similar discussion in part of another thread:
https://www.mobileread.com/forums/sho...211401&page=29

I get the impression that the Aura may be current limiting to 500mA, perhaps for a
slower, lower temp charging of the li batteries. I know that lower current/slow charging
of NiMH batteries will prolong their useful life.

Luck;
Ken

[DNSB]

Originally Posted by Ken Maltby

A similar discussion in part of another thread:
https://www.mobileread.com/forums/sho...211401&page=29

I get the impression that the Aura may be current limiting to 500mA, perhaps for a
slower, lower temp charging of the li batteries. I know that lower current/slow charging
of NiMH batteries will prolong their useful life.

Luck;
Ken

When I monitor the charging current for my Aura, it goes up to ~800mA if the adapter will support that much current. This matches up with the labelling near the USB socket.

Regards,
David

[FJames]

How are you measuring that without cutting into the charger cord on the DC side? I'm not sure a power reading on the AC side would accurately reflect the DC output.

You're right that the Aura USB input is labeled 0.8 amps, but so is the Touch. I always assumed that the maximum draw of both would be the normal USB limit of 500ma, but maybe they will both draw up to 800ma. Many computer USB ports actually will supply up to 800ma, so I'm not sure there would be any difference in charge time to be noticed.

[Ken Maltby]

I have a USB charger rated for 500mA on hand so I'll be using that even if it might
(hopefully) be slower at charging than a higher rated charger. I will keep a close
eye on the charger and its temp for any indication it is experiencing an excessive
draw.

Luck;
Ken

[DNSB]

Originally Posted by FJames

How are you measuring that without cutting into the charger cord on the DC side? I'm not sure a power reading on the AC side would accurately reflect the DC output.

You're right that the Aura USB input is labeled 0.8 amps, but so is the Touch. I always assumed that the maximum draw of both would be the normal USB limit of 500ma, but maybe they will both draw up to 800ma. Many computer USB ports actually will supply up to 800ma, so I'm not sure there would be any difference in charge time to be noticed.

I'm using a USB breakout box -- basically an A plug on one side, a A socket and a micro-B plug on the other with the 4/5 wires brought to jumperable test points. It comes in handy when I want to scope the data lines or check the voltages on the V+/V- lines. For current, I pull one of the voltage line jumpers and use the DMM to bridge the two pins. You can also add resistors across the data lines or from the data lines to ground.

The design is very similar to several projects on the internet with the added 5th pin connection for the micro USB port with a replaceable resistor to ground. Other than cutting up an USB extension cable for the A socket and plug and using the micro-B end of a damaged A to micro-B cable, the rest of the components were mounted to an old chunk of Vector prototyping board I had kicking around. Ugly as homemade sin but it works.

Regards,
David

[speakingtohe]

Originally Posted by TechniSol

I've charged my Glo with a variety of microUSB chargers. The lithium battery charging circuitry controls the current to the battery. Just because the adapter can provide the higher current makes no difference, it is wholly dependent on the charging circuitry in the device -it controls the current applied to the battery.

True in my world anyway.

Helen

[berklon]

Would it be safe to use the wall charger that comes with the Blackberry Playbook for the Aura? Or is it basically a no-no for a tablet charger to be used on such a device?

[FJames]

Interesting. So David's measurement shows that Kobo's labeling is accurate, and it will attempt to draw up to 800ma max if the charger supports it.

I guess it must attempt 800ma, and if the voltage supplied by the charger drops or cuts off, step back down to 500ma.

I know that on many computers even attempting to draw more than 500ma will trigger a shutdown of the USB port with a warning message. That doesn't happen with the Kobo, so it must recognize when it is connected to a computer USB port and limit the current to 500ma in that case.

[Ken Maltby]

Googling "usb charging current" provides some interesting articles including:

http://www.google.com/url?sa=t&rct=j...47244034,d.eWU

They usually talk about faster charging as if that little bit of convenience would be
everyone's goal. They seldom mention how it can reduce the lifetime of the battery.
All batteries (in civilian hands) have problems with heat in general and very high
temperatures can be a killer. Li Batteries have a special history with regards to
heat management and it's not pretty.

I'll trade the extra time charging for a longer lasting battery.

Luck;
Ken

The brands do their own thing with little regard for the standards, Apple & Blackberry
would take some looking at before I would use one of theirs. If they are reasonably
close to the spec. then there should be no problem.

[teija]

Originally Posted by Ken Maltby

They usually talk about faster charging as if that little bit of convenience would be everyone's goal. They seldom mention how it can reduce the lifetime of the battery.

...I'll trade the extra time charging for a longer lasting battery.

Maybe this is the reason that the iPad takes SOOOOoooo long to charge even when using the supplied wall charger. Good to know! I would rather my battery takes all night to charge but lasts longer.

[FJames]

The iPad takes a long time to charge, even with a high-capacity charger, because it has a much bigger battery capacity. Large tablets with color screens and fast multi-core processors and lots of memory need a big battery. Tablet chargers are generally 2 amps.

[Ken Maltby]

Originally Posted by teija

Maybe this is the reason that the iPad takes SOOOOoooo long to charge even when using the supplied wall charger. Good to know! I would rather my battery takes all night to charge but lasts longer.

Well, it would certainly go a long way to restoring my faith in corporate
America, if a company were making a decision to not try and pander to
the customer's wish for a rapid recharge, which would eventually cause
them to have to replace the proprietary batteries, and instead opt to
limit the charging rate, prolonging the battery.

Of course, the decision might have been made at about the time that
some Li Battery powered devices were being recalled, for catching fire,
I don't know.

Luck;
Ken

[DNSB]

Originally Posted by Ken Maltby

Well, it would certainly go a long way to restoring my faith in corporate
America, if a company were making a decision to not try and pander to
the customer's wish for a rapid recharge, which would eventually cause
them to have to replace the proprietary batteries, and instead opt to
limit the charging rate, prolonging the battery.

Of course, the decision might have been made at about the time that
some Li Battery powered devices were being recalled, for catching fire,
I don't know.

Luck;
Ken

I seem to remember reading that the laptop fires were tied to manufacturing defects in the Sony batteries used by Lenovo, Apple and Toshiba and nothing to do with the charging circuitry.

Regards,
David

[Skydog]

Originally Posted by DNSB

I seem to remember reading that the laptop fires were tied to manufacturing defects in the Sony batteries used by Lenovo, Apple and Toshiba and nothing to do with the charging circuitry.

Regards,
David

It's not only Sony batteries. It can be any lithium battery particularly from manufacturers with lack of QC (China for one). I have seen lithium batteries ignite simply while sitting in a flight bag.

[Ken Maltby]

My understanding was that "a rapid discharge" was the most common factor uncovered.
Pushing a chemical reaction either way, will create heat management problems.

In any case I wasn't suggesting that a higher charging rate will cause a fire with modern
Li batteries, just that it can reduce their lifespan.

Luck;
Ken