Subject:
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RE: Battery Status
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 4 May 1999 04:05:45 GMT
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Original-From:
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Mike Jones <michaelj@wt*spamcake*.net>
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Reply-To:
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MICHAELJ@WTavoidspam.NET
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Viewed:
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818 times
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Has anyone ever tried having a small offline battery that can be kicked in via
sofware? When the main power source is nearly exhausted it can be put online
and you know approximately how long that emergency supply will last.
Mike
> I have quite a few battery discharge curves lying around, and one
> thing I can tell you is that they are all different. Generally they start • at
> a high voltage, quickly discharge to a normal operating voltage, hold that
> voltage for a majority of their life, and finally roll off around a "Knee."
> There is a slope in the normal operating voltage region of the curve, but it
> is very small especially compared to the other operating regions. It is easy
> to tell when the battery has reached its knee, but once the knee shows up you
> have very little battery life to work with. The big catch with all this is
> that these battery curves are all made under constant current conditions. • (I
> have a device called "The Battery Tool" which places a programmed current
> load on the battery, and measures the voltage every second. The computer
> program on the controlling computer, plots the curves, and computes useful
> information.) A robot uses everything except a constant current.
> I get the impression that you would like to know the status of the
> battery so that your robot can do something about the battery (seek a
> charging station) when the battery reaches a certain level. I think that you
> will have a hard time doing this with the Handy Board as it is currently
> made. Measuring the battery terminal voltage will certainly tell you more
> than you currently get (nothing). But you will have to jump through some
> extra hoops to get useful information out of if. The first thing you will
> need to do is to find a way to "idle" the robot while you make your voltage
> measurement. You don't have to remove the load, just make it the same for
> each measurement. Second you will need a history of typical behavior.
> Finally you will need a way to update that typical history as the battery
> ages. You could probably do the last two parts in the same algorithm if you
> can set the initial conditions right.
> I personally feel that the right way to go is with a smart power
> source. This is where your NiCads are packaged with a microcontroller and
> current sensor. The Micro keeps track of the charge taken (and the current),
> the last time and amount of charge, and can respond to a host (serial or I2C)
> clearly stating the expected remaining battery life.
> It would be nice to hear from the satellite people. They have to be
> real battery experts. (You can't just go up and change a battery.)
>
> Later,
> Pherd
>
>
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Message has 1 Reply:
 | | RE: Battery Status
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| Sort of, I've had a FET driving a solid state relay that allowed me to connect the motor batteries to the system to preserve the system in the case of system battery failure. However the robot wouldn't move under that situation since the reason the (...) (25 years ago, 4-May-99, to lugnet.robotics.handyboard)
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