Separate current measuring for each power line, similar to VP-X

Hello,
I believe the VP-X is a great product. I have developed dozens of electronic boards in my career, and current draw is probably the best way to realize without full functional tests that everything is intact.
However, I am finding it hard to put myself into a situation of being depended on a 3rd party, even though that by reading reviews and comments, seems like Chad is providing excellent support and planning on supporting this product for many years to come.
I wonder if someone here already developed similar system of measuring the various power lines.
If not, i thought about opening a shared open-source project.
Planning on using the following components:
1. High current sense resistor, or contactless current probe to enable easy retro fit, and to avoid the changes of grounding the system in case of a system failure.
2. Maxim seems to have the perfect device for it : https://www.maximintegrated.com/en/products/analog/amplifiers/MAX4210.html
3. Measuring the output and displaying it on a monochrome LCD by using Arduino Duo. I can easily modify it into extended temperature and add in-rush and over voltage protection.
4. coating with non-conformal coating.

Comments?!
has this already been done here and I missed it?

- Oren

Hi Oren,

I too thought the VP-X was a pretty neat solution, but was concerned given my remote location the resulting downtime if I ever had an issue. What I did instead was use the small klixon breakers, but put a shunt on the feed line from the battery to the main bus. This is in addition to the typical one from the alternator to the battery and at a glance lets me determine what the total draw is in the electrical system. Want to know what the specific draw from a component is, then just cycle the component and you will soon have a number. As much as I like the idea of knowing the individual current draw of every component all the time, one can not overlook the complexity and subsequent failure modes it introduces. Then again, this is the experimental game, so you can frankly do pretty much what you like.
Tom.
RV-7
With dual shunts.

I like Tom's approach (KIS), but have to ask...

Continuous current monitoring for every component has long been a key "functionality" of a well known all-in-one box I shall not mention.

Oren is looking for a DIY approach to the same function.

My question is why? What exactly does individual component current monitoring tell a pilot in flight, and what is the value of knowing?

DanH said:

I like Tom's approach (KIS), but have to ask...

Continuous current monitoring for every component has long been a key "functionality" of a well known all-in-one box I shall not mention.

Oren is looking for a DIY approach to the same function.

My question is why? What exactly does individual component current monitoring tell a pilot in flight, and what is the value of knowing?

Click to expand...

Hi
The overall current draw has too much a variance. for example, the G3X ( i am a Garmin guy) when CPU is at high utilization draws a much higher power consumption. in Addition, you can't enumerate various values to each of the possible scenarios , since there are too many options (strobes on/off, landing lights on/off? auxiliary pump?) , in fact, IMHO the current draw value is useless if measures the whole system, besides maybe showing battery charge/discharge. When you monitor only one function. you can narrow the valid range significantly, and from that point ANY(!) change, even minimal is alerting you that something is wrong. For example, a shortage between wires evolves in time, and doesn't happen immediately all at once, they get warmer at first. A burnt component in the G3X, that might no be in everyday use, can cause eventually to a system failure.
Even the fuel pump should consume same power everyday. if for some reason it consumes 30% more. you will know something is defected before it crashes....

I was developing electronics boards for 20 years. when we got a defected board from a client, first thing I did was comparing the board power consumption to what it was originally shipped. if power is same, in 99% all is well. And on contrary, when we test a board, if the power consumption is within range, most probably the functional test will pass as well.

BR,
Oren.

tgmillso said:

Hi Oren,

I too thought the VP-X was a pretty neat solution, but was concerned given my remote location the resulting downtime if I ever had an issue. What I did instead was use the small klixon breakers, but put a shunt on the feed line from the battery to the main bus. This is in addition to the typical one from the alternator to the battery and at a glance lets me determine what the total draw is in the electrical system. Want to know what the specific draw from a component is, then just cycle the component and you will soon have a number. As much as I like the idea of knowing the individual current draw of every component all the time, one can not overlook the complexity and subsequent failure modes it introduces. Then again, this is the experimental game, so you can frankly do pretty much what you like.
Tom.
RV-7
With dual shunts.

Click to expand...

Tom,
we can always use contact less current probes to measure current.
but i do believe that high-impedance, dedicated components to measure current with sense resistors are fail safe. Means that if it fails it will not affect the system, since we will add mili-amps fuses to those sensing nets (there should be no current running)

BR,
Oren.

Done that. Monolithic vs distributed power systems.

I see value in active power monitoring and gave a paper at Osh on this back in 2009. My approach was to create a distributed power system mitigating some of the single point failures that monolithic system can introduce. The system is based on CANaerospace (now a subset of ARINC825) and has been flying as a technology demo for 7 years. The legacy presentation and white paper are at http://jadsystems.com


The real challenge is getting in and out of the current crop of Exp EFIS systems. Several groups here have suggested a common interface/API for third party systems but to my knowledge no EFIS manufacture has implemented one. Without a way to fully integrate into an existing EFIS system I am concerned that installing a separate power 'alert' and LCD display could further divide a pilots attention during a critical phase of operation.

oren_rokach said:

When you monitor only one function. you can narrow the valid range significantly, and from that point ANY(!) change, even minimal is alerting you that something is wrong.

Click to expand...

So you're saying the value is the ability to predict future failure.

Light GA aircraft are relatively simple...or can be. Could you provide a list of components we might monitor which are flight critical, i.e. would constitute a legitimate emergency if they failed? Don't include anything routinely installed as a dual system.

DanH said:

So you're saying the value is the ability to predict future failure.

Light GA aircraft are relatively simple...or can be. Could you provide a list of components we might monitor which are flight critical, i.e. would constitute a legitimate emergency if they failed? Don't include anything routinely installed as a dual system.

Click to expand...

The only thing that I can think of would be the electric fuel pump in an EFI application. Higher current would indicate impending fuel filter clogging or just a motor about to go Tango Uniform.

As been mentioned, measuring current is not a requirement. The health of your electrical system is much better reflected by voltage. Recall that back in the day all cars had a ammeter and but no voltage meter. This was driven from the simplicity of how in line ammeters worked, and the premium cost (at the time) of voltage meters. Thus today if you have any gauges at all you will have a voltmeter.

I have not installed any current measuring device (like a shunt) in any of the three RVs I built. Voltage tells me everything I need to know:
- 14.2vdc, the primary alternator if on line, normal condition.
- 13.5vdc, the primary alternator is off line, but the standby alternator is running
- less than 13.5vdc, no alternator is on line, so now I?m monitoring for voltage drop as the battery discharges (2-3 hours in my planes depending on load).

I did use a regulated power supply to run the plane that has a current meter. This provided the one time data on current draw for different load configurations. Having continuous current measuring is more of an academic than practical exercise.

I never liked the current shunts as they are clunky, and unless you take steps you end up with exposed terminals.

Carl

Carl Froehlich said:

As been mentioned, measuring current is not a requirement. The health of your electrical system is much better reflected by voltage. Recall that back in the day all cars had a ammeter and but no voltage meter. This was driven from the simplicity of how in line ammeters worked, and the premium cost (at the time) of voltage meters. Thus today if you have any gauges at all you will have a voltmeter.

I have not installed any current measuring device (like a shunt) in any of the three RVs I built. Voltage tells me everything I need to know:
- 14.2vdc, the primary alternator if on line, normal condition.
- 13.5vdc, the primary alternator is off line, but the standby alternator is running
- less than 13.5vdc, no alternator is on line, so now I?m monitoring for voltage drop as the battery discharges (2-3 hours in my planes depending on load).

I did use a regulated power supply to run the plane that has a current meter. This provided the one time data on current draw for different load configurations. Having continuous current measuring is more of an academic than practical exercise.

I never liked the current shunts as they are clunky, and unless you take steps you end up with exposed terminals.

Carl

Click to expand...

Hi Carl,
The only occasion in which your voltage drops is when too much current is being drawn from your power source, more than it is capable.
For example, let use the strobe lights example, if it draws 8A at some point instead of 6A that it should, your 60A alternator will still show you 14.2 but you can end up with a fire in your wing, since you didn't realize that you have extra ~28W of power consumption that goes somewhere. Can be twisted hot wires. can be PCB which got burnt...etc.
Your brake fuse will also not break, since you have a 10A limit.

Same with the Glass cockpit elements, pumps, internal lights, flaps motor...etc

We need both to determine if system is healthy

-Oren

svyolo said:

The only thing that I can think of would be the electric fuel pump in an EFI application. Higher current would indicate impending fuel filter clogging or just a motor about to go Tango Uniform.

Click to expand...

For me, if a NAV/strobe light suddenly draws 2A (30W!) more than i should, its definitely a severe alert. I wouldn't pull the CAPS but would land as soon as possible to figure out what happened.

What is the Flap motors is drawing 1A when not even operated?

....etc

Oren.

oren_rokach said:

Hi Carl,
The only occasion in which your voltage drops is when too much current is being drawn from your power source, more than it is capable.
For example, let use the strobe lights example, if it draws 8A at some point instead of 6A that it should, your 60A alternator will still show you 14.2 but you can end up with a fire in your wing, since you didn't realize that you have extra ~28W of power consumption that goes somewhere. Can be twisted hot wires. can be PCB which got burnt...etc.
Your brake fuse will also not break, since you have a 10A limit.

Same with the Glass cockpit elements, pumps, internal lights, flaps motor...etc

We need both to determine if system is healthy

-Oren

Click to expand...

Sorry - does not work that way. How many cars do you know that had this happen? For that matter, using your example if you had a wire short in the wing, and your in line breaker did not work, the wires would indeed melt - and that would (in most cases) be the end of the event - but all this would happen before you knew you had something drawing excess current. The odds of a failure drawing ?just a little more current? is in the grass. Adding the cost and complexity (and risk) of all the stuff to monitor current of every component ends up (in my opinion) making your plane less reliable.

Carl

Failure modes

The primary function is always to protect the wire (harness). Most efuse devices have the ability give you current value for free. Having that value allows you to better quantify and quickly understand the issue while in flight. The use may be limited (from a pure flight safety standpoint) but still something I would like to have as I plan my reaction. I.E. land now, land at remote field, wait for a good town and hotel or simply continue on.


I look at this like ADSB weather. Did I need it (not really if I wanted to be ultra conservative) but it has saved me several nights in hotels by knowing more while I was in flight!

oren_rokach said:

For me, if a NAV/strobe light suddenly draws 2A (30W!) more than i should, its definitely a severe alert. I wouldn't pull the CAPS but would land as soon as possible to figure out what happened.

What is the Flap motors is drawing 1A when not even operated?

....etc

Oren.

Click to expand...

For the light, I will trust my life to the fuze. Same as every aircraft, on Earth. For the flap motor, if it isn't moving, same answer. If it is moving, big airplanes might have a warning for it.

If my fuel pump is about to die itself, or from overheating due to a clogged filter, it would be nice to know. Lots of big airplanes do have filter bypass lights or warnings for this reason.