# 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 ....????

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lemonie5 years ago
Tell us why, i.e. what you want the 800mA for / to go through.

L
5 years ago
Its his phone charger. He doesn't understand that the phone does the limiting.
kartik negandhi (author)  steveastrouk5 years ago
i understood wat u r trying to say,but if there is no current only then how will the phone limit the current......????
5 years ago
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 ?
kartik negandhi (author)  steveastrouk5 years ago
without the resistor,it shows 0.4A....
5 years ago
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"
kartik negandhi (author)  steveastrouk5 years ago
can i use 2 5v voltage regulator??but then too i wil hav 2 connect resistances,rite?can u tel me hw much R should i conect 2 get around 6.7v,0.8A from a 10v battery.
5 years ago

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

Steve
kartik negandhi (author)  steveastrouk5 years ago
wat to use along with lm317....????
Can u plzz give me the circuit diagram
can u plz do me that favour....???
5 years ago
http://www.reuk.co.uk/LM317-Voltage-Calculator.htm
kartik negandhi (author)  steveastrouk5 years ago
can u plzz tell me wat value of resistances should be used along with lm317 to obtain the desired value.....ie.6.7v,and 0.8A
5 years ago
I gave you a link to a calculator ! Use it.

Steve
kartik negandhi (author)  steveastrouk5 years ago
but will i get the required cureent????
the is nothing such for calculating the current
5 years ago
You already said this circuit can give you up to 1A, that will be fine.

Steve
kartik negandhi (author)  steveastrouk5 years ago
but that was using the earlier circuit.and i destroyd that circuit as it was using ic 7805 which could produce only 400mA max..
5 years ago
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
5 years ago
I prefer the straightforward questions over cryptic ones...
He wants an LM-something?

L
5 years ago
He's got one, only he's buggered it around with an extra resistor, which freaks the phone's charging circuits out.
kartik negandhi (author)  lemonie5 years ago
i want it to go trrough my cellphone to charge it with a 9v battery,but when i connected the entire circuit,i am not getting the required current.the multimeter showz no current in the circuit,however if we calculate using v=ir,the required resistance shud be around 12ohm
5 years ago
You should use a voltage regulator, do you know what the phone's charger gives in volts?

L
kartik negandhi (author)  lemonie5 years ago
my phone charger gives 5v output....
i hav used ic 7805 ie. 5v voltage regulator,but i dont get the desired output current
i require a current of 800mA,but i dont get any current at the output.wat i get is only 5v output voltage.....
5 years ago
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