Re: Low battery voltage level

Thanks Jim.

I'm an electronics designer, I have been asked by my customer to provide a
warning when battery volts drop below 12.5V. I already measure voltage with
a data logger. The logger has an accuracy of +/- 2% on bus rail voltage
monitoring (this is around +/-0.25V at 12.5V). My customer wants a warning
when battery voltage goes below 12.5V irrespective of whether the engine is
running or not. To achieve this the threshold must be set at 12.75V to
guarantee catching 12.5V, but it could of course be the other way round and
we'll actually warn at 13V. All a bit hairy really.

Given the inherent inaccuracy, I'm concerned that this voltage warning will
be triggered un-necessarily and is essentially impractical when set to
12.75V. Personally I'd put the threshold to 12.5V nominal and have a large
time constant filter on it to catch glitches and momentary dips - this would
trigger at a minimum of 12.25V, max 12.75V. I can also measure engine speed
with the logger and inhibit warnings under 50% rpm when the alternator is
not charging, this is currently what the prototype sytem does and is
reliable, but my customer wants warnings below 12.5V regardless.

Any comments welcomed!

Regards,

Mark


"Jim Macklin" <p51mustang[threeX12]@xxxhotmail.calm> wrote in message
news:22mqf.30260$QW2.2267@xxxxxxxxxxxxx
> The 12 volt generator/alternator will be at 14-15 volts
> nominal when within the working range of RPM. The voltage
> regulator should keep the voltage within that range without
> any significant variation.
>
> Just what are you intending to be warned against? The load
> meter gauge shows the load being carried by the generator
> system, the ammeter shows whether the generator or battery
> is supplying the power being used, An ammeter should be
> showing only a slight charge all the time as it keeps the
> battery "topped off." If the battery is any good, the
> ammeter will return to low indicated charge within a few
> minutes after starting the engine. At a low idle, the
> battery will show a discharge because the generator is not
> carrying the load and the battery is discharging to carry
> what the demand is at the time. This is not a problem in
> the short term, such as a power-off landing or glide, but
> anytime that the engine is in the power range, the generator
> [alternator] should be carrying all the load.
>
> Power relays need about 10 volts to stay engaged. If you
> are building a home-built airplane, you could have a yellow
> warning light at less than 13.9 volts and a red warning at
> 12.8. Open cell no-load voltage is 2.2 volts or 13.2 volts
> on a lead/acid battery.
>
> Certificated aircraft require certificated parts. You can
> get a cigarette lighter plug-in monitor.
>
>
> --
> James H. Macklin
> ATP,CFI,A&P
>
> --
> Merry Christmas
> Have a Safe and Happy New Year
> Live Long and Prosper
> Jim Macklin
> "markp" <map.nospam@xxxxxxx> wrote in message
> news:40u6omF1bk76mU1@xxxxxxxxxxxxxxxxx
> | Hi All,
> |
> | I'm looking for recommendations for a low battery warning
> voltage level. I
> | was going to use 12.8V - is this liable to be triggered by
> noise/dips in the
> | bus voltage? My guess is when heaters or motors kick in
> there could be a
> | momentary drop due to high current that could trigger my
> low voltage
> | indicator. Also it it worth putting a long time constant
> filter on this?
> |
> | Thanks!
> |
> | Mark.
> |
> |
> |
>
>


.

Relevant Pages

  • Re: 12 volt power source?
    ... and Greg Procter instead replied: ... A 12 volt battery will never be at a 13.8 volt potential. ... The nominal voltage is the one you want. ... volts safely for long periods of time for keeping the battery ...
    (rec.models.railroad)
  • Re: Outboard Motor Charging System.
    ... >>> Since the terminal voltage of a good lead acid 12 volt battery doesnt ... >>> missing in the description of the voltage. ... >>> terminal voltage might go as high as 17 volts while the battery ...
    (rec.crafts.metalworking)
  • Re: Low battery voltage level
    ... a warning should ... the battery, about 13.5 volts with a steady yellow light, ... but I'd want to have a flashing red if the voltage was below ... I like the airplane to have a volt meter and a load meter. ...
    (rec.aviation.ifr)
  • Re: voltage low on car battery
    ... What is the CHARGING voltage at 2.5 amps after several hours? ... A typical auto battery these days has six cells each, nominally, 2 ... Hence such systems are called 12 volts systems. ... Also one bad cell in the series of six can spoil the battery. ...
    (alt.home.repair)
  • Re: voltage low on car battery
    ... What is the CHARGING voltage at 2.5 amps after several hours? ... A typical auto battery these days has six cells each, nominally, 2 ... Hence such systems are called 12 volts systems. ... Also one bad cell in the series of six can spoil the battery. ...
    (alt.home.repair)
Loading