Question about Nokia's charger
 

It's not easy to find (it's embossed in the plastic), but Nokia's charger says the output voltage is 5V. So why does my multimeter claims the output voltage is 12.65V?

Re: Question about Nokia's charger
 

I’m guessing it is because you’re measuring the voltage while the charger has no load attached to it. It’s designed to output 5V with the battery charging circuit drawing some current.

If you were able to somehow measure it with a load resistor in parallel to your multimeter terminals I’m pretty sure you’ll find it drops back to around 5V.

Re: Question about Nokia's charger
 

It's normal for it to be a little high under no-load conditions, but that's way too high. You might have a defective charger. Mine read 6.16VDC (OEM) and 7.22VDC (aftermarket, rated 6.5VDC ideal). I would test them under load, but all I have on hand are 1/4 watt resistors (would need 5 watt resistors to test).

Re: Question about Nokia's charger
 

Nevermind, folks. Defective multimeter, got stuck on AC no matter what I do with the switch, which doubles the voltage readout apparently. I tried with a friend's one and the voltage is a little over 6V.

Sorry to have wasted anyone's time.

Re: Question about Nokia's charger
 

Additionally, read this:
http://www.forum.nokia.com/info/sw.n..._2_en.pdf.html

It's NOT 5V. Otherwise, the tablet would think it's an "emergency charger" and never charge the battery fully.

Re: Question about Nokia's charger
 

Interesting. So if I were to put a switching regulator (like this one) between my 4AA charger and my N800, and up the output voltage to 6V, I could fully charge my tablet from the AAs?

Re: Question about Nokia's charger
 

I measure 6.4 V unloaded.
With 12 volts you might damage your n810 or phone.
I can even use a block of 4 NiMH AA's (5 V, 2.5Ah) to charge the N810. The internal battery is only 3.7 V (3 cells).

Re: Question about Nokia's charger
 

When the internal battery is down to 3.7 V the device has probably auto-shutdown already. My Palm shuts down at 3.79 V (on the Palm there's software available to tell you which voltage it shuts down, which voltage it starts to give you warnings, which voltage it stops charging etc. Some of these can even be changed with software).

A fully loaded battery will be somewhere between 4.10V and 4.20V, depending on the device and its configuration. My Palm goes up to 4.24V while charging, but not above.
Chargers typically provide around 5.2V, the charging circuitry in the device does the rest.

Re: Question about Nokia's charger
 

Oooh, that's a nice device. However, I don't think you really want to _fully_ charge your internal battery from AA's. The way I understand Li-Ion batteries, they charge fast (and efficiently) up to to 80% or so, but then the remainder is difficult to get in and goes really slowly. I think Nokia has designed it such that in "emergency charger" mode you always stay in the "efficient" region and don't try to charge the battery to the full capacity unless you're on a mains charger.

A proper battery expert can probably tell you that I'm completely wrong and talking out of my a**, but that's the way I understand it. :-)

Re: Question about Nokia's charger
 

Ah, but I also have this huge beast of an external LiPol battery, designed for laptops. It has oodles of amp-hours on board and with my regulator I can step down the voltage from 16 to 6 easily and, because it's a switching one, with rather good efficiency (80%+) as well.

Also, the idea is not so much to recharge the tablet, but to give it extra juice running. Like, when I'm way out in the wild, far (like, more than four steps :cool:) from any AC outlet, I could plug the tablet in and let it run off the external battery. Some claim it's even more efficient to run of an external battery with a fully charged device than to recharge the internal battery with external battery power.

Re: Question about Nokia's charger
 

Hmmm, wouldn't the most efficient way to get power into the device then to fix the regulator to 3.7V, and feed the power into the battery terminals? Maybe even build a (almost) hollow "fake battery" with cables out to your LiPoly battery. Of course, you really want to make sure the connection is stable else suffering sudden, complete, and filesystem-chewing poweroff. :D

Else I would agree, having a full battery should make the tablet only take power from the charger input, so overall, your idea is probably pretty good.

Re: Question about Nokia's charger
 

I really wouldn't even think of doing that.. fiddling on that level is for RC enthusiasts, and they're prepared to blow up the battery now and then, so they wear protective gear. It's safer and good enough to just go through the intelligent charging circuitry of the device itself.

Re: Question about Nokia's charger
 

What he ^ said...

Re: Question about Nokia's charger
 

Oh, I think I was misunderstood. I meant to feed the 3.7V directly into the tablet, not the battery. In fact, no battery would be involved except for the external one: feed its output through your 3.7V regulator into the contacts inside your tablet, bypassing the internal battery (in fact, keep it somewhere else). (Yes, I realise it's still a risky stupid idea :-) but no battery charging would be involved.

Though I don't know what the third terminal of the battery does, or how the tablet uses it. Current sensor? Temperature sensor?

Re: Question about Nokia's charger
 

Although I do like the idea of pushing efficiency to the limit, I don't think I want to play guinea pig on this one. I'm pretty happy with the efficiency I'm getting at the moment, but feel free. Also, this involves taking out the battery, which means rebooting, which is something I do only very rarely on my computers and don't like at all.

And no, I don't know what the third terminal does either, part of the reason why I'm passing.