Re: NIMH issues
- From: "CWatters" <colin.watters@xxxxxxxxxxxxx>
- Date: Thu, 13 Oct 2005 08:26:03 GMT
"<RJ>" <baranick@xxxxxxxxxxxx> wrote in message
news:0gunk1h2sofrdtj0a7dk0nb8k66bgca69u@xxxxxxxxxx
> QUESTION;
> a. How do we know the batterys are "fully charged" ?
Depends on the design of the charger. NiMH cells exhibit a characteristic
"bump" in the voltage when they are full after which the voltage actually
goes down slightly. Many chargers look for this bump or the negative slope
or the change in the slope. See diagram at..
http://www.digibattery.co.uk/nimh_tech.html
>
> b. When the camera says "not enough power",
> How can we verify this ?
Logic devices (including those used in cameras) need a minimium votlate to
work. The camera manufacturer will know what that is and design in a citcuit
to detect when the battery voltage falls below this level. It's not quite
that simple in practice but that's the idea. You can't just measure the
voltage of the battery because batteries "recover" when the load is removed.
You have to measure them on load. A NiMH cell is generally considered empty
when the voltage on-load falls below about 0.9V per cell but remember the
camera might need 1V per cell.
> I've put my trusty SIMPSON meter
> on a fully charged nimh battery.
> It reads 1.3 volts,
> and about 2.1a using the 10 amps setting.
Cell voltage is NOT a good indication of charge state because the curve is
very flat. See this article...
App Note 121: Inaccuracies of Estimating Remaining Cell
Capacity with Voltage Measurements Alone
http://pdfserv.maxim-ic.com/en/an/AN121.pdf
Quote..
Data is provided that demonstrates the high degree of error introduced when
implementing voltage measurement as a fuel gauge method when the battery is
subjected to real world conditions of varying temperatures and discharge
rates.
End Quote.
This is one reason why some battery meters are very inaccurate or next to
usless particularly as cells age.
.
- Prev by Date: Re: small voltage converter 5v -> 50v
- Next by Date: Re: due to some kind of interference, monitor display is "shaking"
- Previous by thread: Re: NIMH issues
- Next by thread: Re: NIMH issues
- Index(es):
Relevant Pages
|
