Current sensing can be done in one of two ways. One way is what you already do for your ammeters - you use a shunt designed to produce a small but measurable voltage drop across the line. Most of these are designed to produce "full scale" drops of 50mV for their rated current flow, and can be had in a variety of

A voltmeter would then allow you to measure current flow. If you want to "trigger" at a certain voltage, a comparator will allow you to do this. Two useful books if you just want a bunch of useful circuits are those by Forrest Mims sold by Rat Shack, and the "Encyclopedia of Electronic Circuits" volumes (there are like 6 or 7 these days). Both a 555 timer and an op amp, both sold by Rat Shack, can be used to make these.

Let me know if you want a schematic. I haven't looked into the specs to see voltage and current flow, so if you want me to draw one up I'll need to know the expected run voltage (is it 14V, or regulated, like to 12V or similar?), the full-scale current flow (what was this, 7 amps?), and the trigger point (the amount of current flow you want to trigger something). The easiest thing would be to light an LED - you can drive a relay for other tasks if you please.

The second way is more complex, but not invasive. You wrap a coil of wire around one of the power feeds to the motor, and use inductive measurement to determine current flow. This isn't really hard either, but it's hardER, so you may as well go for option 1 above if it's possible.

> -----Original Message-----
> From: Jim Sower [mailto:canarder@frontiernet.net]
> Sent: Wednesday, October 15, 2003 9:23 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: EWP - series pumps and wacky ideas
>
>
> A device like that would be interesting to have in a lot of
> places.  Like
> measuring current to fuel pumps as a take on their state of
> repair.  Wouldn't
> it be nice to have several of these and other sensors working
> in "background"
> on another "page" of my engine monitor that I could peek at
> from time to time.
> Ain't technology wonnerful ... Jim S.
>
> John Slade wrote:
>
> > > It would be relatively trivial to design a circuit that
> uses current
> > > sensing to detect pump failure. Current to the pump that
> falls either
> > > above or below the design window can be used to trigger
> an alarm or
> > > activate the backup. Response would be nearly instant.
> >
> > Relatively trivial to you, perhaps. Current sensing sounds
> like a great way
> > to spot a fuel or water pump failure, or even potential for
> failure. I
> > managed to build an RST intercom that sorta works. Could I
> build one of
> > these gizmos? What would be involved?
> > John Slade (electronically challenged, but keen to learn)
> >
> > >>  Homepage:  http://www.flyrotary.com/
> > >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>
> --
> Jim Sower
> Crossville, TN; Chapter 5
> Long-EZ N83RT, Velocity N4095T
>
>
>
> >>  Homepage:  http://www.flyrotary.com/
> >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
>