Battery charging voltage
 

For using an alternative charging power source I found out which voltage matches that the N810 (or a Nokia phone) charges and shows 'Charging' when plugging in and displaying the animating battery icon.

Using a 8.3 volts solar panel connected via a car charger does charge.
Using the same panel without car charger (i.e. the 8.3 volts directly to the N810) displays 'Not charging', which I think 8.3 volts is too high.
But when I put a single diode in series (0.7V volrage drop) does charge the N810 (and my 5800 XM phone).

Measuring the charge currents was in all cases 200-230 mA (battery was nearly full, all but one blocks in the battery icon was filled).

Does someone have experiences with charging voltages / alternative charge sources?

Re: Battery charging voltage
 

Well the wall wart is 5.0V. I've charged off of a USB port which is also supposed to be 5.0V.

I have a solar panel that puts out 5.0V but it does it in bursts, on for 2 seconds, off for 3 seconds and that just puts the tablet into a mode where the screen is always on and it's playing sounds for the start charge event and it ends up discharging the battery.

Frank

Re: Battery charging voltage
 

Skatebiker has the right idea, except I would use a solar panel that outputs 12 volts at full sunlight so that if it is somewhat cloudy it may still provide the 8.5 volts to the car charger. The 12 volt solar panel is very standard and used to keep a small charge on your car battery when parked for months at a time. For about $40 you can buy a 2.5 watt panel which will give you 200ma charge current.

Re: Battery charging voltage
 

No,the voltage is not dependant on cloudy or sunny sky. Mine outputs 8.5V @ full sunlight(500mA) or overcast sky (50mA).But many panels. output indeed 12 V.

Re: Battery charging voltage
 

Skatebiker, sorry I got confused. Solar panels contain "cells" that are wired in series to abtain the needed voltage. That voltage changes according to the amount of sunlight. Apparently the panels today contain voltage regulators such as yours. In the old days we had to add external regulators.

Re: Battery charging voltage
 

What you need is a solar charger with a "smart power controller". IE, no matter what voltage or amperage the cells are putting out, the unit always outputs the designed voltage and amperage. With the NITs, they need a steady voltage of either 12v, or 5v, and a minimum 400ma current to ensure charging. 800ma if you're doing something under load so that it doesn't start hitting the battery.

Re: Battery charging voltage
 

Anyone playing with non-standard charging should read this:

http://sw.nokia.com/id/3378ff2b-4016...on_v1_2_en.pdf

Anyways, the standard charger does not give 5V, it's more like 8V or so, less under load. Voltage should never exceed 9.3V according to that spec, in the N800, you'll risk tripping the built-in zener diode and then blowing the 2A fuse. I guess if a solar panel can't supply more than 500mA, it should be safe, just make sure there isn't a capacitor in line that could supply a short-duration high-current spike.

If the input voltage is around 5V, the N800 will see it as a "special" charger and never actually fully charge the battery. AFAIK, LiPol batteries are not very efficient to charge the last 20%, so it's better to just keep it at that level unless you have plenty cheap power available (that is, a wall charger), and can afford to turn most of it into heat.

Re: Battery charging voltage
 

Well that explains a lot to me. I'm kind of annoyed that the wall charger is marked as 5V though since that is clearly not the case. But to their credit, the pdf is awesome, I wish other manufacturers provided this type of information.

Frank

Re: Battery charging voltage
 

Each crystalline silicon cell is 0.45 V but the voltage does NOT change much dependant on sunlight. See the diagrams here:

http://en.wikipedia.org/wiki/Solar_c...ircuit_current

which confirm my measurements. Measuring the voltage of my small panel (loaded) it measures 8.4 V in full sunlight and 8.1 V in overcast sky. It contains of 18 cells in series which makes 18*0.45 = 8.1 V.
Here a picture of the panel :
http://misc.nicejewel.com/charging-n810.jpg
BTW, DealExtreme sells 6 V 200mA (maybe 5.4 V as they have 12 cells according to the image)
http://www.dealextreme.com/details.dx/sku.18168
for only $17 which can be switches parallel and be used as a USB or Nokia charger.

Re: Battery charging voltage
 

I've a wall wart for the nokia battery. The label says Output DC 4.2V 350mA. I get a full charge with it.

Re: Battery charging voltage
 

Is that charging the battery directly, or a supply for the tablet?

Re: Battery charging voltage
 

Charging battery directly.

Re: Battery charging voltage
 

Then those numbers make sense, since the (nominal) battery voltage is 3.7V (I think) so the charging voltage just needs to supply something higher than that at a controlled/fixed current. (Including _usually_ a temperature sensor to prevent flaming battery situations :-) Actually, a temperature sensor is usually built into the LiIon/LiPol battery packs, that's what the third contact tends to be there for)

As such, the device can't be compared with the tablet power adapter, but rather, the charging circuitry inside the tablet itself. The tablet power supply can be 'dumb': supply voltage X at current Y. A LiPol battery charger needs to have some brains: Supply current A until voltage at battery reaches B, then switch to supply current C until voltage is D, then shut off (or supply trickle current E); unless temperature reaches F in which case kill the current. Or some variation of this.

I think the battery charger would make a very poor general-purpose power supply :-)

Re: Battery charging voltage
 

I was wondering what the 3rd lead was for. My charger dosen't use it but has the necessary circuitry to indicate fully charged or charging via an LED.