13 VDC switch

"Steve Foley" wrote:
"jmk" wrote in message
oups.com...

I believe it was "Interesting proof."

I remember it as being 'trivial'. I have always looked with skepticism on
anything called trivial ever since.

I suspect you are all thinking of Fermat's Last Theorem, which states that:

x^n + y^n = z^n

has no non-zero integer solutions for x, y and z when n 2. Fermat had
written the rather infamous note on this theorem:

"I have discovered a truly remarkable proof which this margin is too small
to contain."

And didn't someone finally work
it back out a couple of years ago?

Probably. I've been away from math class for many years now.

A proof for the theory is presumably now worked out, thought its length is
so long and complex that most doubt that Fermat had a valid proof.

http://en.wikipedia.org/wiki/Fermat's_last_theorem

"abripl" wrote in message
oups.com...
Others can do what they want. Personally I want a finished "plug-in,
easy to use" product and not a lifetime hobby of playing with
alternator circuits, or whatever.


Ok, then it sounds like the best solution is something simple like
connecting the stator output from the alternator (on many brands, that't the
terminal with the "S") to a relay.

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

"RST Engineering" wrote in message
...
What do you want the cutoff voltage to be? Personally, I'd pick 13.0
volts, but it is child's play to do any voltage you want.

That's about right, but here's a couple lessons learned the hard way:

I'd like to see some hysteresis in the switching -- say power on at 13.1V
and off at 12.9V.

It would also be a good idea to have some limitation on inrush current or at
least a delayed response. I've seen too many cases where it goes into
oscillations when a device with a hefty inrush pulls the detector voltage
below the switch point which shuts down the power at which point the voltage
recovers and it turns back on and the cycle starts over.

Gerry

"Gerry Caron" wrote in message
.. .

"RST Engineering" wrote in message
...
What do you want the cutoff voltage to be? Personally, I'd pick 13.0
volts, but it is child's play to do any voltage you want.

That's about right, but here's a couple lessons learned the hard way:

I'd like to see some hysteresis in the switching -- say power on at 13.1V
and off at 12.9V.

I never do a comparator without hysterisis.



It would also be a good idea to have some limitation on inrush current or
at least a delayed response. I've seen too many cases where it goes into
oscillations when a device with a hefty inrush pulls the detector voltage
below the switch point which shuts down the power at which point the
voltage recovers and it turns back on and the cycle starts over.

I was sort of figuring on about a ten second loop constant.

Thanks. How you been, Gerry? Long time no type. Who you working for now?

Jim



Gerry

"RST Engineering" wrote in message
...

"Gerry Caron" wrote in message
.. .

"RST Engineering" wrote in message
...
What do you want the cutoff voltage to be? Personally, I'd pick 13.0
volts, but it is child's play to do any voltage you want.

That's about right, but here's a couple lessons learned the hard way:

I'd like to see some hysteresis in the switching -- say power on at 13.1V
and off at 12.9V.

I never do a comparator without hysterisis.

I figured you probably would. I raised the issue to enlighten the less
experienced.



It would also be a good idea to have some limitation on inrush current or
at least a delayed response. I've seen too many cases where it goes into
oscillations when a device with a hefty inrush pulls the detector voltage
below the switch point which shuts down the power at which point the
voltage recovers and it turns back on and the cycle starts over.

I was sort of figuring on about a ten second loop constant.

Thanks. How you been, Gerry? Long time no type. Who you working for
now?

Jim

Been doing pretty well. Have made a few posts, but mainly lurk. Work's
been keeping me real busy. I'm still at Rockwell Collins in Melbourne.
Been working on a new integrated surveillance (transponder, TCAS, WxR, and
TAWS) system for the heavy iron.

Gerry