[ARC5] adventures in battery ops

[AKLDGUY .]

Arduino seems a bit overkill for battery level warning.
Why not configure a $2 op-amp in a window comparator circuit?

I set one up years ago to monitor the falling voltage of my cellphone's
NiCad battery, when discharging in my homebrew discharger
(remember how we had to ensure NiCads were fully discharged before
charging?). The window comparator's output operated a high-pitched
buzzer via a cheap transistor of the BC108 class.

For those who don't know, a window comparator makes use of the
way the op-amp's output rapidly switches from ground to + rail (or vice
versa) when one of its input voltages crosses the threshhold voltage on
the other input.

With a voltage divider or pot, you set the desired battery minimum
voltage (eg. 11.5 volts) on the appropriate input of the op-amp and
connect the battery to the other input. Nothing happens 'till the battery
discharges to the preset voltage, when the op-amp abruptly turns on
(or off), triggering the buzzer.

73 de Neil ZL1ANM


On Mon, Apr 6, 2015 at 9:46 AM, Bill Cromwell <wrcromwell at gmail.com> wrote:

> Hi,
>
> I have been running my command receivers on pure DC battery power. For the
> heater strings I have been running a pair of '12 volt' gel cells - 7.5 A-H
> - in series to give me the required voltage. I periodically measure the
> terminal voltages and a couple of days ago I thought I was getting close to
> needing a charge cycle. This morning I went in to turn the radio on
> (BC-455) to play with it a little more and it wouldn't come up. I shut
> everything down and applied the voltmeter again. One battery was dead! That
> is not good. The remaining battery can force the weaker one into reverse.
> The battery in question seems to be okay.
>
> This incident set me to thinking that I should rewire all my 24 volt
> heater strings to 12 volts so there won't be this possibility of a reversed
> battery. I think I would rather setup an Arduino to monitor the battery
> voltage and give me a warning when it gets to the minimum useable point.
> The same thing can happen to a single 12 volt battery when one cell get
> discharged before the rest.
>
> By the way, using batteries has kept the crap that can be conducted into
> the radio via the power line *OUT* of my radios. That's why I initially
> tried it. I'm working to make the AC line operated power supplies cleaner
> but meanwhile the battery operation has been an eye opener. Besides cleaner
> power I can take the radios out to the park for field operations. Sealed
> lead-acid batteries on the heaters and ten 9-volt batteries in series for
> the B+. The little 9-volt batteries have surprised me by how long they
> last. I use the cheapest alkaline batteries I can get and I'm paying just
> under a dollar each in six packs.
>
> 73,
>
> Bill  KU8H
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