Voltage Measurment locaton with a diode

[dbuds2]

I followed the Bob Nuckols design with a diode between my main and essential buss. The diode definitly drops the voltage to about 12v with fully charged batteries. My EFIS power supplies are on the essential buss and I measure voltage on the essential buss. I've been flying with both the main and essential busses switched on to show the true system voltage and charge the BU battery.

Since the SV needs >12.25 to start charging, i'm beginning to think I need to put the SV power connections and EMS voltage measurement on the main buss. What do you recommend?

 

[jdubner]

I also have an E-buss à la Bob Nuckols and wired my SV to the E-buss.  My backup battery stays charged.

The SV should still see >12.25 volts on a normally operating electrical system (~14.2 - 14.6V) even after a diode-drop.  You'll be OK if you want to keep it on the E-buss.

I wired the Voltmeter1 input (pin 1 of the EMS 37-pin connector) to the master buss.  I used Voltmeter2 (pin 2) to monitor the E-buss voltage (just for grins).

--
Joe

 

[dynonsupport]

What Joe said.

 

[dbuds2]

Thanks guys, I just went and looked at data from a couple recent flights. Measuring 13.8-14.1 with both Main and E buss switched on Only 11.8-12 when thru the diode.

Should I be putting out over 14V to still show >12,25 thru the diode?

 

[dynonsupport]

A diode should drop a maximum of 0.7V, so something else is up. I'd look for thin, loose, weak, or corroded connections.

 

[jdubner]

What Dynon Support said.   

But also check that you're feeding your E-buss through just one diode and not two.  It would be easy to inadvertently have two diodes in series when using a bridge rectifier for the diode.

If using a bridge, check that the connections are made to two adjacent terminals, not two opposite ones. 

--
Joe

 

[dbuds2]

great suggestion Joe, going to verify using only one diode today.

 

[Carl_Froehlich]

Schottky diodes are good for this application. Many choices, here is but one: http://www.alliedelec.com/images/products/datasheets/bm/VISHAY_SEMICONDUCTOR_ITALIANA/70078779.pdf