# Voltage Divider

Discussion in 'The Projects Forum' started by jons, Feb 17, 2012.

1. ### jons Thread Starter New Member

Feb 17, 2012
2
0
Hi,

I need to monitor a DC charging voltage and have a 4-20ma and a 0-10V input available on my PLC. The charging voltage will flucuate but I'm mainly interested in between 20 and 30 Vdc.

My question is would a simple voltage divider with a pair of resistors to drop the max 30v down to max 10v (I calculated 10K and 5K would take me there abouts) or would these resistors just sit and get excessivly hot?

Any other suggestions?

Cheers

Jon

2. ### chandrashekhar New Member

Feb 17, 2012
1
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you can also use op-amp as comparator.

3. ### Brownout Well-Known Member

Jan 10, 2012
2,375
998
P=V^2/R = 30^2/15,000 = 60mW. That's not much power. You only need to make sure that the pin your reading from has much higher resistance. A typical input pin should by > 1M ohm, so usually that's not a problem either.

4. ### luvv Member

May 26, 2011
186
31
Love using this http://www.falstad.com/circuit/ as a litmus test for simple circuits.

It is no pro simulator...but what it lacks in accuracy it makes up in simplicity.

Just hover the mouse over the resistor it will show you all the info including power dissipated.

-luvv-

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Feb 17, 2012
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