RE: Indicated Voltage Problem

RE: Indicated Voltage Problem

I am just about to put my RV7A in the air but....I have one minor problem to solve. The Dynon EMS D-120 is not indicating TRUE voltage output both with the engine in operation or when running on the battery.

My electrical architecture is Z13/8 modified to have the B&C 40 amp alternator regulated by LR3C-14. The amp/current pick off shunt is in location A position as found in the Dynon EMS D-120 install manual page 3.12When the Master Battery/Main Alternator switch is actuated the Dynon shows 10.8 volt. When the Essential bus is actuated the voltage climbs to 12.8 with or without the Master on.

Every possible connection point has had a continuity check/voltage check completed. We have also followed the B & C LR3C-14 trouble shooting guide which had no neitive results so the LR3C would SEEM to be OK . All grounds have been checked for problems...one found.

But all (except using B&C trouble shooting guide)roads seem to lead to a bad LR3C-14.....but Bill at B&C thinks there has to be another problem....................In short every connection up to the regulator are 12.8 volts with the master on but once past the LR3C it read 10.8 at the power pin location #1 on the D-Sub. This indicated two things the problem is at the LR3C and the Dynon D120 is isolated showing it isn't the problem....................

We know the altenators ..... both main and aux SD8 are doing there thing because when we have ground run the engine the battery charge has been maintained

So where do I check next??????????????????????????????

Frank @ 1L8 ...RV7A... ready to fly?????maybe

Frank,

I haven't looked at drawings to see exactly what you have here, but you may just be seeing the forward voltage drop across the diode you have isolating your essential bus. Unless you're using a power schottky to isolate your E-buss, you should see an ~1.5V drop due to that diode.

When you flip the E-buss switch, you're bypassing the main-to-E buss diode and the voltage reading comes up.

Measure the voltage each side of the diode protecting your E-buss and see what you get.

Guy

This is exactly what happened to me

Guy Prevost said:

Frank,

you may just be seeing the forward voltage drop across the diode you have isolating your essential bus. Unless you're using a power schottky to isolate your E-buss, you should see an ~1.5V drop due to that diode.

When you flip the E-buss switch, you're bypassing the main-to-E buss diode and the voltage reading comes up.



Guy

Click to expand...

I had designed my electrical system with a split bus, but decided later not to install a backup alternator or battery. I found low voltage reading on the EMS 120, which was higher when the E-bus was turned on. Since my EFIS has a backup battery, and I have a 696 in the panel, I figured I could do without the E bus, given the type of flying I do. So I just did away with the diode and installed a jumper across the two buses, thereby creating one larger power bus. The voltage was a good 1.5 V higher.

If my alternator breaks, I'll know it immediately from the voltage drop, and I can just start turning things off.

I guess the alternative would be to adjust the voltage regulator so that you get the voltage you want on the downstream side of the diode, but that would leave you with over 15 volts when the e bus switch is flipped. It still might not be an issue since you would probably only do that if you had an alternator failure.

mine reads low too

My d100 says my alt volts is 13.7..But I measured it at the bettery and its 14.2. I have a shotkey so i don't think there is appreciable FWD voltage drop.

Creepy, sam problem, same airplane and same first name!

Maybe we'll adopt the same solution..I.e forget about it..

Frank

frankh said:

My d100 says my alt volts is 13.7..But I measured it at the bettery and its 14.2. I have a shotkey so i don't think there is appreciable FWD voltage drop.

Creepy, sam problem, same airplane and same first name!

Maybe we'll adopt the same solution..I.e forget about it..

Click to expand...

My Garmin 696 will show 13.9, while the volt meter reads 14.2.

I'm forgetting about it also.

L.Adamson