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Electronics Forum / Basics / February 2007



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Differential Amp

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Michael - 28 Feb 2007 20:24 GMT
Hi,

I have a bank of 6 6V batteries and I'd like to be able to measure the
voltage across each one. Would the best way be to use a diff amp as the
voltage won't be relative to ground?

If so, could someone please suggest a suitable IC that will won't go into
saturation round the 45V area?

Cheers,

Michael
chuck - 28 Feb 2007 09:30 GMT
> Hi,
>
[quoted text clipped - 8 lines]
>
> Michael

The batteries are in series and connected to a load? You can't
disconnect the load and simply measure the voltage of each battery with
a simple DMM?

I'm a bit confused by what you are trying to do, Michael.

Chuck
Michael - 28 Feb 2007 22:00 GMT
>> Hi,
>>
[quoted text clipped - 22 lines]
> ----= East and West-Coast Server Farms - Total Privacy via Encryption
> =----

Hi,

I'm building a robot that has 6 6V batteries as its power source and I'd
like to monitor each battery when the robot is operating.  As it's designed
to work from some distance, I need to read the voltage and input it into the
onboard computer computer so it can be transmitted (IE I can't just use a
DMM as I won't be there to read it.)

Cheers,

Michael
Michael A. Terrell - 28 Feb 2007 22:13 GMT
> >> Hi,
> >>
[quoted text clipped - 34 lines]
>
> Michael

   Resistive dividers, and a mux to an A/D converter.  BTDT, and its in
orbit.

Signature

Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

john jardine - 28 Feb 2007 23:31 GMT
> Hi,
>
[quoted text clipped - 8 lines]
>
> Michael

For one diff' measurement it's simple to just use a standard opamp and
resistors to knock the voltage down and increase the common voltage range.
This example would put out 1/10 of the diff' voltage in. Ie 0.60V for a 6.0V
battery. That 6 volts could be sat on top of anything from 0V upto about 45V
                                  10k
                                   ___
                             ,----|___|---,
                             |            |
                             |            |
                             |      5V    |
                             |     -o-    |
                     100k    |      |     |
                     ___     |    |\|     |
    ( - ) in o------|___|----o----|-\     |     Out
                     ___          |  >----o------o
    ( + ) in o------|___|----o----|+/              0-5V
                             |    |/|            o
                     100k   .-.     |            |
                            | |    -o-         --o--
                         10k| |    0V           0V
                            '-'
                             |  Opamp is a 'rail to rail' in&out type
                           --o--
                            0V

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