# wat resistances shall i connect with a 9v battery to obtain a current of 800mA???

wat resistances shall i connect with a 9v battery to obtain a current of 800mA???i tried with 12 ohm but the multimeter does not show any current..,anything else shud be connected with the resistances ....????

sort by: active | newest | oldest
Dec 25, 2011. 1:37 AMlemonie says:
Tell us why, i.e. what you want the 800mA for / to go through.

L
Dec 26, 2011. 1:35 AMlemonie says:
You should use a voltage regulator, do you know what the phone's charger gives in volts?

L
Dec 27, 2011. 2:02 AMlemonie says:
You won't increase it with a resistor, 800mA is quite high load for a PP9; you're probably at the limit of what it will give.

L
Dec 25, 2011. 2:04 AMsteveastrouk says:
Its his phone charger. He doesn't understand that the phone does the limiting.
Dec 26, 2011. 12:01 PMsteveastrouk says:
You haven't said there is no current before.

All you have said is you seem to be insisting the resistor is needed, and I am quite sure it is not.

Have you measured it ? Have you measured it with your resistor removed ?
Dec 27, 2011. 2:44 AMsteveastrouk says:
Ah, so not 1.2 A as you were predicting....

Play with the voltage a little bit, and you will establish the right vltgae for the charging circuits to say "yes, we can charge with that"
Dec 27, 2011. 4:56 AMsteveastrouk says:

You CANNOT use a resistor to control current and voltage for your phone charger. It is NOT POSSIBLE

Steve
Dec 27, 2011. 9:25 AMsteveastrouk says:
http://www.reuk.co.uk/LM317-Voltage-Calculator.htm
Dec 29, 2011. 3:17 AMsteveastrouk says:
I gave you a link to a calculator ! Use it.

Steve
Dec 29, 2011. 6:01 AMsteveastrouk says:
You already said this circuit can give you up to 1A, that will be fine.

Steve
Dec 30, 2011. 4:13 AMsteveastrouk says:
THIS circuit uses an LM317. A standard 7805 will deliver 1A, if its heatsinking is done correctly. THe current limit is determined by the regulator. It will automatically close down if you try and take too much from it, if its heatsinks are OK

Steve
Dec 25, 2011. 7:17 AMlemonie says:
I prefer the straightforward questions over cryptic ones...
He wants an LM-something?

L
Dec 25, 2011. 7:42 AMsteveastrouk says:
He's got one, only he's buggered it around with an extra resistor, which freaks the phone's charging circuits out.