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Author Topic: Why isn't resistor affecting voltage read on multimeter?  (Read 615 times)
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Wales
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I'm trying to reduce 4.5v to 2.8v with resistors. No matter what resistor I use, and even if I use a few in parallel, the voltage measured with my multimeter remains the same as the input voltage - 4.5v.

It's been a few days since I messed worked on my project - am I going mad?

I've tried 10kohm, 2.2kohm and 560ohm resistors - and even these in combination as I said.


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+               -    in
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+               -    out
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probe          probe
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Thanks
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Poland
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Hi Dane,
it would be better to redraw this circuit, because I'm not sure what are you doing.
For me, it would be much simpler to use a simple voltage divider.

So, you should use, for example R1 = 1,7k, R2 = 2,8k.


* voltage_divider.jpg (11.15 KB, 371x359 - viewed 11 times.)
« Last Edit: March 24, 2012, 06:39:18 am by Rubid » Logged

Coventry UK
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Hi Dane, Have you got the circuit completed? You won't get any voltage dropped until you have a current flowing.

Martyn.
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This might be helpful: http://en.wikipedia.org/wiki/Voltage_divider
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Modern multimeters draw incredibly little current when measuring voltage - they closely approximate an ideal voltage sensor.

If no current flows through a resistor then both ends are at the same potential, so you won't see any voltage change.

Go with the resistive divider, a circuit where current actually flows.
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Left Coast, CA (USA)
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Quote
I'm trying to reduce 4.5v to 2.8v with resistors.

Also you might let us know what you are going to wire the 2.8vdc to, as the amount of current draw of the 2.8v would determine the best method to reduce the voltage from 4.5v.

Lefty

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Cumming, GA
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Voltage dividers do not make good power sources... they are better used as reference voltage sources for sensors or to lower the potential on signals whose load current is constant.    IE; I have used a voltage divider to allow my Meter tor read the output of  a voltage multiplier circuit that generated 1500V... higher than my meter would normally measure.

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