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[aprssig] Re: D7 battery

Stephen H. Smith wa8lmf2 at aol.com
Fri Mar 24 20:32:46 UTC 2006


pagreen at gmail.com wrote:
> When you get to that low of voltage, it gets distorted at lower 
> volumes than when you are running 9.6 and higher.  I definitely notice 
> more distortion on the lower voltage battery than on the high power 
> ones at the same audio levels.  Sounds to me that you are getting a 
> dead cell and it's getting lower than it used to.
>

This is an issue of using rechargable NiMH batteries in the drycell AA 
holder
instead of non-rechargeable AA alkalines.

The alkalines are 1.5 V per cell for a total of 6 volts.

The rechargable NIMH cells are only 1.2 V per cell for a total of
only around 4.8 volts  *FRESHLY CHARGED*.  This causes the
5VDC regulators in the radio's logic circuits to start dropping out. 


This is a chronic problem in devices with 5VDC logic circuits, normally 
powered
from 4 non-rechargeable alkalines.   Low-dropout regulators can barely 
produce
5 VDC from a 6-volt source. The rechargeable AAs, Cs, and D cells simply 
aren't
an alternative as a direct one-for-one replacement for alkalines, since 
they don't
produce a high-enough voltage for the 5VDC  regulators to work.  

Unless of course, you use 5 or more cells in series.  Or if the device 
has a more
sophisticated DC-DC converter that can produce a constant output voltage 
from
a supply voltage higher or lower than the output.   

I have found this issue very frustrating with the Kenwood VC-H1 SSTV 
device. It
runs on 4 AA cells (i.e. 6VDC) which it eats in about 2 hours. I would 
love to use
rechargeable NI-Cd or NiMH cells in it but they simply won't work -- it 
thinks that at
at 4.8 VDC are already dead. 







Stephen H. Smith    wa8lmf (at) aol.com
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