Author Topic: Charging cellphone battery  (Read 3846 times)

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Denis710

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Charging cellphone battery
« on: February 15, 2010, 09:58:48 pm »
I'm working on a protect that involves PIC micro and a cellphone (Motorola c168i). I need to keep the phone charged.

Do I need a charge control ic or its embedded in a cellphone and 5VDC on the phone's charger input will do the trick.
 

Offline desolatordan

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Re: Charging cellphone battery
« Reply #1 on: February 16, 2010, 06:17:30 am »
Is it charged by a USB connector or some base station dock? It's most likely embedded, but it's possible it doesn't have a charge regulator if it uses a base station to charge and moniter battery health.

If you don't need battery operation you could just rip it out and apply power directly.
 

Denis710

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Re: Charging cellphone battery
« Reply #2 on: February 16, 2010, 10:43:49 pm »
It charges from a typical wall charger. The connector is a small barrel power plug. Getting rid of the battery, so its not really an option.
I would think that the charge controller is embedded but I want to make sure. Is there a way to test it? I do have the original wall charger.
 

Offline DJPhil

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Re: Charging cellphone battery
« Reply #3 on: February 17, 2010, 05:47:23 am »
It charges from a typical wall charger. The connector is a small barrel power plug. Getting rid of the battery, so its not really an option.
I would think that the charge controller is embedded but I want to make sure. Is there a way to test it? I do have the original wall charger.

I checked amazon for replacement chargers for that model, at least a few had something in the description that suggested charge control but I suppose that's not conclusive. Fortunately it appears that the battery for that phone (Motorola BT60) is Lithium Ion, and there's not much variety in how they can be charged. There's some good info here, as well as a charge current vs. battery voltage chart.

I mention all this because after a spin around the internet and some brainstorming I can't think of a slick way to be sure the circuit's not in the charger. I'm sure it's simple, but it's eluding me at the moment. I will continue thinking on it, and will post back if I think of something.

If all else fails I suppose you could use the voodoo method: bang the charger on a rock until it breaks and read it's entrails for clues. :)
 

Denis710

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Re: Charging cellphone battery
« Reply #4 on: February 18, 2010, 03:21:23 am »
voodoo method: bang the charger on a rock until it breaks and read it's entrails for clues. :)

You are right, the charger case is glued together and cannot be open other than by the voodoo method.

I think I will do an experiment - apply 5v to the phone and see what will happen.
I guess I can monitor current and if it will drop significantly over some time (according to the link above) then the charge control circuitry is NOT embedded in the phone.
Can anyone comment on my logic?

« Last Edit: February 18, 2010, 03:29:07 am by Denis710 »
 

Offline DJPhil

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Re: Charging cellphone battery
« Reply #5 on: February 18, 2010, 04:21:58 am »
This stuff's still fuzzy for me, I've been breaking up drywall all day but I'll give it a go.

Operating under the assumption that the battery is a single cell, which fits the 3.7v rating on the battery, the max voltage that any charger can safely apply to the battery is 4.2v, and is more likely to be around 4.1v. This is a very tight specification, so odds are fairly good that if you can find 4.05-4.2v coming from somewhere, it's a regulated charge current. What trips me up is how to measure this with the battery present in the circuit. I can't conceptualize the whole thing well enough to be able to predict what you should be measuring at any given point to know what's happening.

If you apply 5v to the charger input I suppose you risk letting some smoke out, but if you try it and see more than 4.2v at the battery terminals you'll know the charge circuit is in the wall wart. A proper lithium charger circuit should be able to protect the battery from overvoltage charging as a matter of safety.

Another way might be to see if you get continuity between the battery terminals and the charge input jack. That would indicate that it's just a pass-through, and probably in parallel with the phone's Vin, so that it can charge and operate at the same time.

I'm assuming you aren't opening up the phone, I suppose you could just follow the traces in the phone and see where they go.

I hope that helps some, gonna go shake the dust out of my brains. :)
 


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