Nokia 5500 emergency charger

[ketas]

At first, I thought about building MintyBoost-like circuit for this, but then I actually measured Nokia charger's voltage. With no load, both old ACP-7E and new AC-4 SMPS charger puts out 6-7(8)V. No idea what happens under load. It probably drops. Old is labeled 3.7V and new 5V.
Actually I should retrieve my somewhat better multimeter and drop that poor 1V resolution current clamp to see correct results.

Well, at first I tried to charge my phone with 12-24V car charger and cheap 2*9V batteries. Not so good results. I guess that more than half of energy went to heat. Batteries were very warm and charger was also a little bit warm (no wonder, because of the current). And per-battery voltage dropped from ~10V to ~3V. Poor batteries.
Well, I even managed to charge a phone little bit. According to not very accurate battery charge indicator, I calculated that I managed to squeeze out about 150mAh. Then I disconnected it. I don't know what was charger's output voltage, but probably under 5V. I also tested it without load. Outputs ~6V if input is >=6V. But phone was still showing that it's charging until I disconnected it.
Second time I connected my poor charger solution again, because there was still energy in those batteries. This time, I let it run for hours. When I finally checked what it's doing I saw that charger LED was very dim (yeah, I know that LED isn't voltage measurement device, I'll use multimeter next time) and phone charge indicator was acting very weird. It seems like it's "half-charging". Indicator rolls to half and stops there. Then repeats.
I have no idea, if undervoltage can damage something in phone. Currently I expect that it can. Or it's just not very good.

Then... I thought that, oh wait... there are actually emergency chargers based on 9V, or better, on 4*AAA batteries.
I thought that maybe I can build a charger with just 4*AA batteries. Or C/D size 1.5V batteries. Just 4 batteries and one inline shottky diode, which gives me about 0.5V voltage drop and also protects my phone from wrong polarity. Which, I guess can surely damage it. And it's a little bit over month old too...
And what about undervoltage? Can it damage my phone or not? Any ideas? I also heard that some 1.5V cells can have voltage up to 1.7V when not under load. But that's not very much and will drop.

Well, so, I though that I can make charger out of 4*1.5V batteries, a shottky diode and according to some reports, I also need current limiting resistor. Some Nokia's wont charge when they receive too much or current. Example was Nokia 6610. So maybe I need about 10-15 ohms resistor.
BTW, can anyone confirm if it's true that alkaline cells maintain their nominal voltage until they're almost empty, but regular zinc-carbon ones just continue to drop voltage through their lifetime, until it's zero? Haven't measured it yet.
I guess that alkalines make better charger because voltage is correct for longer period? But I also read that I can't draw too much current from alkaline because then large part of precious energy dissipates as heat. Is about 355mA too much for them? Actually, it's value on charger, I have no idea how much it actually takes.
And of course I can'd design a emergency charger that runs only on alkalines.
Or I should forget this idea and go for boost converter because of dangerous undervoltage?

But, when using some high-power D-size (alkaline) cells I must have a lot of power. They're heavy, I know... but not so much when in backbag.


So, there are my ideas... Just some random ramblings... :( I guess it will fit to this category.

[ketas]

No replies...


But I found out that Nokia has finally thought about it. Now they have portable power supply DC-1 which can do about 3*950mAh charges and it's charge time is 10h with AC-4 charger.
DC output is 5.7V.

That's what they say.
No wonder people need it, as N-series drains batteries much.


Pretty impressive storage. So they have little less than 3Ah there.
But I'm wondering when I can have car battery amount of energy in phone. Like 70Ah. I haven't look for that, but I'm sure it's possible.

1TB HDD was once impossible too :)

[ketas]

Hmm... I tried to charge my phone with following circuit:

http://kodu.neti.ee/~madis555/tmp/phone_charger.png

I know it's overly safe, but something weird is happening.
Seems like that I'm actually discharging the battery. It was connected for hours, all the time phone reports that charger is connected and indicator shows charging. However, hours later when disconnecting charger for a few seconds, phone wasn't saying "charging" on connect. However, still reports that charging is in the process. I guess that voltage is too low. About 4-5V (still no good multimeter :P)

What's interesting is that battery level went from 100% to 85%... to 71% to 57%!
While not doing anything.

After several connects/disconnects, I even experienced scary issue, backlight refuses to turn on. Luckily reboot fixed that.

[richms]

Nokia chargers have a resistance inline with them, they are not a simple voltage source.

If you go to your dollar store you should be able to find a USB charging cable for nokias. Those have the resistance in them and the hard to get plug, or else look inside your car charger and see what resistance they have inline with the cable to the phone.

IIRC the charge current is set by that too, but its been a while since I have charged a battery on my phone, I have several and use a desktop charger.