Resistance value to get 1.5 v output form a 2.8 v adapter?

Thread Starter

meghama

Joined Jun 11, 2010
1
I have a 2.8 V ,150 mA charger . I need the out put voltage of 1.5 V . What is the value of resistance need to get 1.5 V output Voltage , Pls give the color code of the resistor.
 

Papabravo

Joined Feb 24, 2006
21,158
There is no value of resistance that will give you that voltage for all possible loads. Familiarity with ohms law would reveal this salient fact.
 

oidium45

Joined Apr 24, 2010
138
There is no value of resistance that will give you that voltage for all possible loads. Familiarity with ohms law would reveal this salient fact.
This is correct.
However, If you are going to use the adapter for one item. (hopefully not your cell phone or anything too important!) You could use ohms law to determine the value needed for the voltage drop. But keep in mind that as the current requirements change so will the needed resistor values unless you use a voltage regulator.There are a few 1.5v voltage regulators out there and the required circuits are pretty small, cheap, and simple. Search google for "1.5v voltage regulator".

Good luck.
 

SgtWookie

Joined Jul 17, 2007
22,230
If it's a constant current charger, a 2.8v 150mA charger will overcharge a 1.5v battery.

The charger will supply current at a controlled rate until the chargers' output voltage reaches the limit.

A resistor in series with the charger will slow the rate of charge, but it will still overcharge the battery.

You need the correct charger for your battery.
 

Externet

Joined Nov 29, 2005
2,200
Instead of using a resistor, connect a couple of 1N4001 diodes in series and test if the voltage is close enough to your satisfaction when the unit is working.

+2.8V---------|>|------|>|--------+1.5V
 
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