Odd voltage reading

[PhantomPholly]

I have an odd scenario with my D180.

When running on ship's battery power (not the internal D-180 backup battery), voltage at the EFIS reads only about 11.1 volts.  If I remove the Female D-25 connector and measure the voltage across pins 1 & 3 (Primary Power & Ground) I read 12.8 (only 0.1v less than right at the battery terminal).

If I attach a battery charger to the main bus, or if I run the engine with the alternator on, it reads around 13.6 (expected voltage).

I have re-checked the main power and ground leads, and have added a case ground to the main ground bar (connected to the heavy battery ground cable, and the same place the wire from pin 3 is grounded).

Any thoughts on why voltage might be reading low when just on ship's battery power, or what other leads I might check to understand why this could be under reported?

 

[PhantomPholly]

Ok, I know I'm being impatient and it's Sunday...

What could cause my D180 to read a low voltage when the current at the primary pins is ok? Does it look at some other pin that I'm not checking that might have a bad ground?

 

[dynonsupport]

When the D180 is reporting the lower voltage (11.1), what is the voltage directly across the battery?

Also, does the voltage change if you pull the 37 pin connector off?

 

[PhantomPholly]

When the D180 is reporting the lower voltage (11.1), what is the voltage directly across the battery?

12.9v at the battery (fresh charge, and nothing else running but the D180 and 3 green gear lights). 12.8v measured at the connector (removed from the D180). The battery voltage does not change when I turn on the Master & Avionics switches - brand new Odyssey battery, fully charged.

Also, does the voltage change if you pull the 37 pin connector off?

I'll have to check that - I presume you are asking if the battery voltage changes, not the Dynon reading.

All other things being equal, am I correct in believing that if pins 1 & 3 show 12.8v then the Dynon should indicate 12.8v +/- 0.1v?  As a side thought, I'd think the + wire had a weak connection if the voltage didn't come up when the alternator is on or the charger is running.  But, that doesn't make sense if the Dynon reports the higher voltage with power increased to the same bus.

 

[PhantomPholly]

When the D180 is reporting the lower voltage (11.1), what is the voltage directly across the battery?

Also, does the voltage change if you pull the 37 pin connector off?

Ok, battery voltage is 13.0 when Dynon reports 11.7. Measures 12.9 at pins 1 & 3 on the primary power (other small connector, not the 37 pin). Pulling the 37 pin connector has no effect on reported voltage. Turning on a charger raises the bus voltage to 13.7, and magically the Dynon starts reporting within 0.1v of the bus voltage.

Take the charger off, back to 11.6/11.7. Shut the main battery power off and silence the acknowledgements - NO CHANGE!!!!

:-/

Sounds like the D180 doesn't read system voltage until it goes above 13v (maybe the charging circuit?). This is not correct.

 

[PhantomPholly]

Bump - Did I mention that once voltage gets up to about 13.5 that the Dynon reading matches the bus voltage exactly? So, it is apparently not a calibration issue.

 

[dynonsupport]

We're a little stumped at the moment. The fact that it "get's better" at higher voltages makes us think that it's less likely the unit and more likely that it is something that we're missing. Do you have the ability to hook the unit up to a variable voltage power supply outside the airplane, and see is you can reproduce the issue that way?

Also, which voltmeter are you looking at? The EFIS info item, or the EMS display? If the EFIS info item, you're looking at the "M" line, right? What are the other line items displaying?

 

[PhantomPholly]

We're a little stumped at the moment. The fact that it "get's better" at higher voltages makes us think that it's less likely the unit and more likely that it is something that we're missing. Do you have the ability to hook the unit up to a variable voltage power supply outside the airplane, and see is you can reproduce the issue that way?

I could hook it up to my battery charger with a light dimmer and measure the resulting voltage with my volt meter. When the Dynon gives what I will refer to as an accurate reading, it is within 0.0v of my meter.

Also, which voltmeter are you looking at? The EFIS info item, or the EMS display? If the EFIS info item, you're looking at the "M" line, right? What are the other line items displaying?

I am looking at the EMS page with all the CHT/EGTs. I haven't noticed voltage on any other page, but haven't looked hard either.

 

[PhantomPholly]

Bump - heading out Saturday to have another look.

I would like some clarification on your question about which page I'm looking at the voltage info on. Does it matter which page (e.g. is it displaying some different value on other pages)?

 

[airguy]

Dynon - what is the voltage sampling rate on your unit, and do you do any smoothing across samples? Could this be related to ripple output and sampling frequency?

 

[dynonsupport]

It's the same voltage being reported, but on the EFIS-page info-item, there are three voltages being reported, and I wanted to make sure you were looking at the right line-item.

We sample at 4Hz, and there is some basic very short term filtering. So if you had real voltage fluctuations, they would be apparent, but there's nothing going on over multiple seconds, for example.

 

[PhantomPholly]

It's the same voltage being reported, but on the EFIS-page info-item, there are three voltages being reported, and I wanted to make sure you were looking at the right line-item.

We sample at 4Hz, and there is some basic very short term filtering. So if you had real voltage fluctuations, they would be apparent, but there's nothing going on over multiple seconds, for example.

Ok, dove into the manual.  I am not displaying any of the optional voltages on the EFIS screen.  I AM seeing the analog/digital voltage meter on the full EMS page.  

Is it possible that the voltage being displayed on that page is the internal battery voltage instead of the bus voltage?  The manual says this is not possible, but I just cannot understand why it would jump up and down when my voltmeter clearly indicates 13v at Pin 1.

I will configure both voltages (Master Bus; Internal Battery) on my EFIS screen and see if this throws any illumination (so to speak...) on the problem.

 

[dynonsupport]

It really isn't possible to display anything but the master input voltage on the EMS page. There just isn't code to do this anywhere in the unit.

Your voltmeter uses a capacitor to average voltage over a second. Voltmeters are slow to respond and average out all fluctuations. The EFIS/EMS samples only a few times a second, with less capacitor averaging, so it's possible for us to see fluctuations that are real while your voltmeter doesn't show them.

 

[PhantomPholly]

On Saturday I turned on the 3 voltage readings on the EFIS screen and confirmed that the voltage reading on the EMS screen was mean to be bus voltage. I also figured out my analog volt meter reads about a volt high (read 15+ when the electronic charger was running, and 13.5 at the battery terminals) as compared with a digital meter which read 12.5 / 14.1 under the same conditions.

Still, the Dynon reads about 1/2 to a volt low (11.1v battery only; 13 on the charger that I'm guessing runs about 14v when the battery is fully charged).

I'm not too awfully concerned about it, as it will always read "in the green" when the alternator is working and I actually like the fact that it will provide low voltage warning if the alternator quits - just would prefer it to be a tad more accurate.

Is there a way to calibrate it, and if so what would be the procedure?

 

[dynonsupport]

There isn't a calibration routine.