Voltage Readings

Sportsman
Posts: 13
Joined: Tue Mar 19, 2013 12:04 am

Re: Voltage Readings

Post 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...
Bobturner
Posts: 420
Joined: Mon Mar 11, 2013 6:34 pm

Re: Voltage Readings

Post 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.
GRT_Jeff
Posts: 634
Joined: Tue Dec 11, 2012 12:11 am

Re: Voltage Readings

Post 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).
Sportsman
Posts: 13
Joined: Tue Mar 19, 2013 12:04 am

Re: Voltage Readings

Post 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.
psychose
Posts: 17
Joined: Fri Apr 19, 2013 11:14 pm

Re: Voltage Readings

Post 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
psychose
Posts: 17
Joined: Fri Apr 19, 2013 11:14 pm

Re: Voltage Readings

Post 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
User avatar
BillinDurham
Posts: 35
Joined: Sat Mar 16, 2013 10:53 pm

Re: Voltage Readings

Post 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
Bill Watson
8NC8 Durham, NC
RV10 HX, G430w, NavWorx, EIS
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