13 VDC switch

This is starting to smell very much like the upcoming November Kitplanes
column.

Jim


"cavelamb" wrote in message
k.net...
abripl wrote:
Since its so trivial for you, how about a basic indication of the
components hookup or reference to the circuit elsewhere?

Anybody (else) know of a finished product source of this trivial
product? Kit?

RST Engineering wrote:

Trivial to design and build.

Jim



Nope.

That's mostly a roll yer own.

Sounds like a relay circuit to me.

Off the shelf automotive supplies?
Wally World?

You mean I started a new idea? It sure would be handy to plug in
portable devices into the cigarette lighter socket source and not drain
the battery with engine off. OR in case of charging system failure
some non-crucial devices could be turned off automatically. We need
this before November.

RST Engineering wrote:
This is starting to smell very much like the upcoming November Kitplanes
column.

Jim

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.

There will be about a milliampere of quiescent current for the sensor that
will still be on-line when the output shuts off.

Jim



"abripl" wrote in message
ups.com...
You mean I started a new idea? It sure would be handy to plug in
portable devices into the cigarette lighter socket source and not drain
the battery with engine off. OR in case of charging system failure
some non-crucial devices could be turned off automatically. We need
this before November.

RST Engineering wrote:
This is starting to smell very much like the upcoming November Kitplanes
column.

Jim

"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.

There will be about a milliampere of quiescent current for the sensor that
will still be on-line when the output shuts off.

Jim


One-chip solutions designed for this purpose that can detect both
undervoltage and overvoltage are available from several vendors, such as
Maxim.
Example: http://pdfserv.maxim-ic.com/en/ds/MAX6457-MAX6460.pdf

These offer very low quiescent current when off (couple of uA). The output
can be used to activate a relay (maybe needs an extra transistor). I think
you can request free samples.

Rob

A. Maxim is very poor on production delivery.

B. Joe Sixpack in East Undershirt Ohio can't go down to the corner Maxim
store and buy onesie-twosies on Sunday afternoon.

C. One milliampere out of a 25 amp-hour battery will run the battery down
in 25,000 hours (1040 days, or a little less than 3 years). If you don't
fly your airplane but once in 3 years, that's not my problem.

D. Why would you use an unreliable electromechanical device like a relay
when a FET is half the price and a thousand times more reliable?

Jim




"Rob Turk" wrote in message
news:Y7_gg.1536$YI3.268@amstwist00...
"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.

There will be about a milliampere of quiescent current for the sensor
that will still be on-line when the output shuts off.

Jim


One-chip solutions designed for this purpose that can detect both
undervoltage and overvoltage are available from several vendors, such as
Maxim.
Example: http://pdfserv.maxim-ic.com/en/ds/MAX6457-MAX6460.pdf

These offer very low quiescent current when off (couple of uA). The output
can be used to activate a relay (maybe needs an extra transistor). I think
you can request free samples.

Rob

"RST Engineering" wrote in message
...
A. Maxim is very poor on production delivery.

That's not been my experience, but maybe I've just been lucky. Also, when
they offer samples then the chips are available at least in sample
quantities. That may not mean much if you want to order 100.000 of them, but
for us one-off builders this is fine.

Besides, Maxim was just one example. Linear Technologies has similar chips
and similar sample programs.


B. Joe Sixpack in East Undershirt Ohio can't go down to the corner Maxim
store and buy onesie-twosies on Sunday afternoon.

The samples ship worldwide. If I can get them easily in Hoevelaken, The
Netherlands, Europe then I'm sure they'll ship to East Undershirt Ohio as
well.


C. One milliampere out of a 25 amp-hour battery will run the battery down
in 25,000 hours (1040 days, or a little less than 3 years). If you don't
fly your airplane but once in 3 years, that's not my problem.

Agree, and if you leave your plane for 3 years without flying I'm sure there
will be other issues to worry about..

D. Why would you use an unreliable electromechanical device like a relay
when a FET is half the price and a thousand times more reliable?

Agree again, it's whatever makes you feel happy. I've had luck with either
device. Automotive relays seem pretty reliable, and so are FET's.


Jim

Rob

Yeah,

13V cuttoff sounds right. Most charging systems go to at least 13.5
volts and batteries seldom settle near 13 when not charging. 1 ma is
fine. FET? is that what it takes? Its gota work for low and high loads
same...

RST Engineering wrote:
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.

There will be about a milliampere of quiescent current for the sensor that
will still be on-line when the output shuts off.

Jim

"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