[TenTec] emergency back up power

[Dr. Gerald N. Johnson]

On Mon, 2007-03-05 at 18:31 -0700, Eric F. Richards wrote:
> At 06:49 PM 3/5/2007 -0600, Dr. Gerald N. Johnson wrote:
> >On Mon, 2007-03-05 at 17:21 -0500, Gary Hoffman wrote:
> > > I'll bet that the battery voltage, as delivered to the actual radio, is a
> > > little low.
> > >
> > > Going to a sine converter and 115 VAC power fixes this issue totally.
> >
> >At a cost of anywhere up to 50% of the battery's power from the
> >inefficiency of the inverter and the linear Tentec power supply.
> 
> Most inverters today -- including a properly designed sine-wave inverter -- 
> are 85% efficient and up.  The power supply is a different matter.  This is 
> based on running a 500 W space heater and measuring the DC current.

An 85% efficient switching supply with that inverter gets you 72%
overall. Nearly 30% losses. A common linear supply isn't that efficient
with the unregulated voltage over 20 volts. At best 65% efficient. I do
have a linear supply that I've measured 92% efficiency but it is picky
about its input voltage and has no tolerance for low line voltage when
loaded heavily. The FETs in it regulate down to .020 volts drop. They
they go out of regulation. But the typical multiple transistor bipolar
regulator has to have 4 to 8 volts drop to make the equalization
resistors work.
> 
> 
> >Sometimes it is more effective in the long run to let the radio struggle
> >with 12 volts and to run 25 watts and to run for many hours than to run
> >high power inefficiently for a few minutes. Then it helps to select the
> >radio that will run from the battery that isn't being charged.
> >
> > >
> > > Gary
> >
> >--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
> >
> >_