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Draining phone batteries

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Screech

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Can I use a resistor to safely drain phone batteries?
nokia 3210 and ericsson 624.
What ohms would safely drain most phone batteries?
 
Screech said:
Can I use a resistor to safely drain phone batteries?
nokia 3210 and ericsson 624.
What ohms would safely drain most phone batteries?

Yes you could use a resistor, but you shouldn't drain rechargeables below a certain point.

To work out the value simply apply ohms law, you already know the battery voltage, decide on the current you require, and calculate the resistor.
 
I wonder if a zener diode in series with a resistor wouldn't provide the discharge capability and some protection from taking the battery down to nothing. Resistor would have to be selected with the power handling ability of the zener - don't forget the power rating of the resistor itself.
 
Nigel , is the safe discharge for batteries worked to a percent of full charge ( eg . a new car batt fully discharged a few times seems to wreck them ) ,,?? .. Also a mate of mine got a mobile phone the same as mine ,(same shop, one day later , and his batt died a few months ago and mine's still goin strong ),(touch my head)..
 
simoV8 said:
Nigel , is the safe discharge for batteries worked to a percent of full charge ( eg . a new car batt fully discharged a few times seems to wreck them ) ,,?? .. Also a mate of mine got a mobile phone the same as mine ,(same shop, one day later , and his batt died a few months ago and mine's still goin strong ),(touch my head)..

The spec for rechargeable batteries usually specify the minimum recommended discharge point. As for phones, they usually don't treat the battery very well, so it's quite easy for the battery to fail fairly early.
 
stevez said:
I wonder if a zener diode in series with a resistor wouldn't provide the discharge capability and some protection from taking the battery down to nothing. Resistor would have to be selected with the power handling ability of the zener - don't forget the power rating of the resistor itself.

I'm not sure about this, but I think the reason behind only discharging to a certain point is so that cell reversal won't occur which can permanentl affect the cell. If that's the case, I think discharging down to several hundred millivolts would probably be ok. Instead of the zener just put a silicon rectifier diode in series with the resistor and you could discharge down to about 0.7 volts. Or depending on what the spec sheet says, just several diodes or one zener like Stevez suggested.
 
you guys have put me off it now, but if I decide to do it then:

Next time when my phone battery goes flat, I'll check what that voltage is(when flat).
That way I will have a minimum voltage reference to drain to.

I will check too, what the current is when I'm using the phone, when sending my voice.
then I'll know what resistor to use.

Hope that works.
 
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