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Re: Voltage Readings

PostPosted: Thu Apr 13, 2017 1:08 pm
by Sportsman
Hmmm... That's exactly what I have done, Jeff. I probed with mcro-probes inserted into the back side of the d-sub connector pins and measured a voltage that's pretty darned close to one diode drop higher than the voltage reported by the EFIS. I only have two buses supplying power so have only done this on two of the three inputs. Each of those two inputs shows a consistent 0.6VDC higher than EFIS-reported voltage.

Heaven help me if I'm dropping 0.6V across a DB25 connector...

Re: Voltage Readings

PostPosted: Thu Apr 13, 2017 5:36 pm
by Bobturner
I wonder what sort of internal failure could cause this? My HX reads the buss voltage within round off error (0.1 volt). IIRC I used 18 gauge wire for power and ground.

Re: Voltage Readings

PostPosted: Fri Apr 14, 2017 4:07 am
by GRT_Jeff
It sounds like the calibration is bad. The power input voltages are measured before the diodes and the board has a calibration probe point there on input 1. I don't think it could be any hardware failure, although I have seen one board where the ADC was inconsistent from one boot to the next (bad self-calibration during power on I suspect).

Re: Voltage Readings

PostPosted: Sat Apr 15, 2017 1:22 am
by Sportsman
Interesting... Today I was again playing with our instrument panel and the HX was showing a voltage input value much closer to what I was reading - within a tenth or two of a volt. This is quite different from what I had previously seen. Jeff's suggestion of varying display brightness to see if reported voltage tracks changes in input current demand is a good one and in our case I was able to see some correlation between reported input voltage and brightness. Higher brightness settings consume more current, thus there is greater voltage drop across wiring etc, and a lower input voltage reported.

I'll monitor to see if the reported voltage changes after power-cycling the HX.

Re: Voltage Readings

PostPosted: Wed May 24, 2017 12:32 pm
by psychose
hello folks,

Sorry about the long delay, but I finally was able to measure voltage difference on EIS vs Battery, with and without engine running.

engine running: batt voltage: 14.5 v, EIS indication: 14.1 diff=.4 volts
engine not running: batt voltage : 12.5 v, EIS indication: 11.8 diff=.7 volts though this difference can vary +/- .1 volts.

A type of bias function, even if accurate only within a certain current range, would be nice, or some other way to get a more accurate measurement.

For now I will account for the difference in my EFIS alarm settings.

Normand
C-GNGN

Re: Voltage Readings

PostPosted: Thu Feb 07, 2019 9:23 pm
by psychose
Hello Folks,

Many moons later, I finally got around to adding the 240 ohm resistor from the battery bus to the EFIS.
I now get an EFIS voltage reading within +/- 0.01 of the battery voltage, so I'm very satisfied. Thanks to Jeff DeFouw for his support.

To convert an analog input into a voltage with tenths:

Analog # Function: Aux (EIS compatible)
Analog # Internal Pull-Up: Off
Analog # Scale Factor: 25
Analog # Offset: 0
Analog # Sensing: Forward
Analog # Integer/Decimal: Decimal
Analog # Aux Function: Aux
Analog # Aux Name: Batt Bus (Give this input a name for alarms and bar graphs)
Optional:
Analog # Remote Channel: (pick an unused channel 1-16 if you want to send this input to another display)

After this is configured, the aux name ("Batt Bus" for example) will be an option on bar graphs and data boxes.

Normand
RV8 C-GNGN

Re: Voltage Readings

PostPosted: Wed May 29, 2019 4:23 pm
by BillinDurham
I assume this is still valid. Having had the same set of problems with accurate voltage displays, I'm intend to configure 2 analog inputs as described below to display bus voltages on my 2 bus, 2 batt, 2 alternator Z-14 system.

Confirmations or comments welcome. Thanks.

psychose wrote:Many moons later, I finally got around to adding the 240 ohm resistor from the battery bus to the EFIS.
I now get an EFIS voltage reading within +/- 0.01 of the battery voltage, so I'm very satisfied. Thanks to Jeff DeFouw for his support.

To convert an analog input into a voltage with tenths:

Analog # Function: Aux (EIS compatible)
Analog # Internal Pull-Up: Off
Analog # Scale Factor: 25
Analog # Offset: 0
Analog # Sensing: Forward
Analog # Integer/Decimal: Decimal
Analog # Aux Function: Aux
Analog # Aux Name: Batt Bus (Give this input a name for alarms and bar graphs)
Optional:
Analog # Remote Channel: (pick an unused channel 1-16 if you want to send this input to another display)

After this is configured, the aux name ("Batt Bus" for example) will be an option on bar graphs and data boxes.

Normand
RV8 C-GNGN