"Martin Gregorie" wrote in message
...
On Sat, 16 Aug 2008 11:16:47 -0600, Bill Daniels wrote:

I have a Microair and, as long as you feed it 11.5V, it works fine. Up
and down the flightline it seems that every radio brand has it's share
of problems. Gliders are a harsh environment for complex electronics.
Be thankful radios work at all.

Has anybody tried putting a solid state DC-DC converter in the Microair's
power supply?

Devices exist that can easily supply a constant voltage in the range
12-14v at whatever current the radio requires, even when the battery
drops to 10v. It seems to me that these devices could solve many of the
problems people have discussed on r.a.s when attempting to run
electronics designed for 12-14v off an SLA. The main drawback would
appear to be a slightly reduced battery life because the conversion won't
be 100% efficient. A side effect is likely to be that the radio will work
OK until the battery is completely drained, at which point it will
suddenly drop out; a voltmeter upstream of the converter might be useful.

As an example of what these converters can do, I installed a T&B about a
year ago. Its a powered aircraft type designed for a 28v supply which has
been fitted with a solid state DC-DC converter to step up the voltage. As
a result it runs happily off 12v.

Maxim sell a huge range of DC-DC converter chips for step-up and step-
down use. These handle currents of at least 2 amps: maybe higher, but I
haven't needed anything more so haven't looked. A low-power example is
the MAX666, which supplies 5v at 40 mA from an input in the range 2-16v.

Disclaimer: I have no connection with Maxim.


--
martin@ | Martin Gregorie
gregorie. | Essex, UK
org |

Good idea, Martin.

I've looked (not very throughly) for one that would output 13.8V (typical
regulated voltage in "12V" aircraft systems) from something like 6 - 18V
input. I'd like 95% efficiency but most are ~85%. It would also me nice
to have one with a low voltage cutoff on the input side that would prevent
damage to the battery from deep discharge.

I suspect most gadgets would work better with regulated voltage.