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Karel Jansens is offline Karel Jansens
2009-02-22 , 23:56
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#1
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?
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j d is offline j d
2009-02-23 , 00:40
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#2
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.
 
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jellotherat is offline jellotherat
2009-02-23 , 01:02
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#3
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).
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Last edited by jellotherat; 2009-02-23 at 01:09.
 
Karel Jansens's Avatar
Karel Jansens is offline Karel Jansens
2009-02-23 , 11:46
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#4
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.
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jthiemann is offline jthiemann
2009-02-24 , 03:09
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#5
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.
 
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Karel Jansens is offline Karel Jansens
2009-02-24 , 12:03
Posts: 3,220 | Thanked: 326 times | Joined on Oct 2005 @ "Almost there!" (Monte Christo, Count of)
#6
Originally Posted by jthiemann View Post
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.
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?
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skatebiker is offline skatebiker
2009-02-24 , 13:36
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#7
Originally Posted by Karel Jansens View Post
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?
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).
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Last edited by skatebiker; 2009-02-24 at 13:40.
 
TA-t3 is offline TA-t3
2009-02-24 , 14:00
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#8
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.
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jthiemann is offline jthiemann
2009-02-24 , 15:09
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#9
Originally Posted by Karel Jansens View Post
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?
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. :-)
 
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Karel Jansens is offline Karel Jansens
2009-02-24 , 15:33
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#10
Originally Posted by jthiemann View Post
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. :-)
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 ) 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.
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