Battery to Buss Voltage Drop

[Rjmvmi1998]

I have an interesting problem here, looking for some advice on where to trouble shoot. RV10 with two earth X batteries. Electrical systems designed for two batteries, 1 main and 1 standby (which is continuously tied to the main under normal conditions when system voltage is above 12V and then automatically disconnects when voltage drops below 12V). The batteries power 1 main buss which in-turn powers 1 endurance buss. The main and endurance buss is connected with a diode (a four prong transformer rectifier) to allow main buss voltage to power the endurance buss but prevents the endurance buss from powering the main buss. Endurance buss is connected directly to standby battery via a direct feeder circuit to the standby battery and switched on/off in cockpit

So I hope I explained that well enough to understand the basic architecture.

So here is my problem, I’m experiencing voltage drop on the endurance buss during normal operation. I removed the standby battery to start my trouble shooting, so all voltage into the system is coming from one battery and it is is fully charged reading 13.28 volts under a small load, probably 3 amps. With the battery switch on, the main buss voltage is reading 13.25 volts, and the endurance buss is reading 12.48 volts. With the battery switch off and the endurance switch on, the endurance buss is reading 13.25.

So I’m getting a voltage drop of .75 volts between my two busses under normal operating conditions. The obvious suspect is something in the diode pack connecting the two busses is causing this but wanted to put it out there to see if anyone else has a suggestion.

Thanks

Robert
.

 

[JonJay]

Standard voltage drop through a diode is .7v.

 

[Avanza]

I see no problem here.
It is normal to see a voltage drop over diodes of 0,7 V.

Good luck

 

[Rjmvmi1998]

Standard voltage drop through a diode is .7v.

Thanks,

What concerned me was Earth X states a Lithium battery 12.5 volts is very depleted and should be charged before engine start. My engine monitor is powered from this E buss and I was seeing 12.48 volts on the monitor. I will have to make a mental note of this .7 difference and do the mental math. Thanks for the reply, hopefully this will help someone with a similar concern.

Robert

 

[dmattmul]

So here is my problem, I’m experiencing voltage drop on the endurance buss during normal operation. I removed the standby battery to start my trouble shooting, so all voltage into the system is coming from one battery and it is is fully charged reading 13.28 volts under a small load, probably 3 amps. With the battery switch on, the main buss voltage is reading 13.25 volts, and the endurance buss is reading 12.48 volts. With the battery switch off and the endurance switch on, the endurance buss is reading 13.25.

I have a similar set-up and has been said 0.7 is a normal voltage drop through a diode. You don't mention your alternator(s) (one alternator per bus?) set-up or your bus voltage when your main alternator is supplying output to the main bus voltage on your endurance bus. Earth X recommends charging their batteries at 14.2 volts. What is the charging voltage of your endurance battery?

 

[Rjmvmi1998]

I have a similar set-up and has been said 0.7 is a normal voltage drop through a diode. You don't mention your alternator(s) (one alternator per bus?) set-up or your bus voltage when your main alternator is supplying output to the main bus voltage on your endurance bus. Earth X recommends charging their batteries at 14.2 volts. What is the charging voltage of your endurance battery?

I have one alternator. The B terminal is connected to the main buss bar which sends charging current to the batteries.

You do bring up a good point and one I didn’t think about. I haven’t changed the output voltage of my alternator since installing the Earth X batteries. The current output is mid 13V range. I confirmed with Earth X that these batteries like 14.2V for charging.

 

[dmattmul]

I have one alternator. The B terminal is connected to the main buss bar which sends charging current to the batteries.

Just for clarification. If your B lead is going to your main bus and that sends a charging current to your batteries seems that might allow the main bus to pull down your endurance bus. My guess is to protect your endurance bus your charging voltage is going through a diode and if your alternator is outputting 13.5 volts your endurance battery is trying to charge at 12.8 volts which will not charge an Earth X battery.

 

[kms001]

Hi so you need approximately 14.4 volts to charge both batteries. If the backup battery is on the other side of the diode, that could be a issue. A drawing here would be really useful, just the batteries, the two busses diode and alternator.
Where did you get the wiring from Vans , Bob N ?

 

[Rjmvmi1998]

I have a similar set-up and has been said 0.7 is a normal voltage drop through a diode. You don't mention your alternator(s) (one alternator per bus?) set-up or your bus voltage when your main alternator is supplying output to the main bus voltage on your endurance bus. Earth X recommends charging their batteries at 14.2 volts. What is the charging voltage of your endurance battery?

During normal operation, the E bus can only receive power from the main bus through a feeder which goes through a diode. Power can only flow one way, Main Bus to EBus. The EBus is essentially a dead end not independently connected to the batteries.

During emergency operation the EBus cockpit switch is manually closed and the EBus becomes powered from a feeder directly off the standby battery. The same diode would prevent the EBus from powering the main bus if the main bus has lost power. So the only scenario I can think of where charging current could pass through the main bus diode to the EBus would require operating the alternator with the EBus switch turned on. Charging current could potentially flow from main bus through EBus back to the battery. The EBus switch should only be on when you experience alternator / electric failure so I can‘t imagine a scenario flying in this configuration with the alternator working. Let me know if you see it differently, I’m far from experienced with this stuff.

 

[Rjmvmi1998]

Hi so you need approximately 14.4 volts to charge both batteries. If the backup battery is on the other side of the diode, that could be a issue. A drawing here would be really useful, just the batteries, the two busses diode and alternator.
Where did you get the wiring from Vans , Bob N ?

I will try to draw something up tonight. I didn’t build the airplane. I know that a professional installed the electrical system and I believe it to be a Bob N design.

 

[dmattmul]

I will try to draw something up tonight. I didn’t build the airplane. I know that a professional installed the electrical system and I believe it to be a Bob N design.

Perfect, provide the Bob N design-Z number. He is the master design aircraft electrical engineer. It sounds like you might be using Z-14 and that uses a cross over switch but then that requires 2 alternators, likewise Z-12.

 

[blaplante]

0.7 volts drop is standard for a Silicon rectifier, which is the common item.
A Shottkey rectifier will be around 0.5 volts.

What's your current requirement?

 

[Rjmvmi1998]

Perfect, provide the Bob N design-Z number. He is the master design aircraft electrical engineer. It sounds like you might be using Z-14 and that uses a cross over switch but then that requires 2 alternators, likewise Z-12.

I am traveling and this is the best I can do with pencil and paper in the hotel. 1 alternator, 2 batteries, 2 main buses, 1 endurance bus, and a low voltage monitor/switch. If the resolution isn,t good enough I will draw it up on the computer when I get home. Thanks for you interest!

Robert

 

[rolf]

Robert,
Your system sound very much like mine, and suffered a similar drop thru the diode charging the E-batt.
So, used a relay to to control the path from the main buss to the E-buss. (for better charging of the E-batt)
A 3 position switch allows selection of relay position ON AUTOMATIC OFF
The AUTOMATIC position uses a voltage sensor such that OLNY when voltage is above 14.2V the relay closes.


Rolf
N9EY

 

[downundarv8builder]

I have an interesting problem here, looking for some advice on where to trouble shoot. RV10 with two earth X batteries. Electrical systems designed for two batteries, 1 main and 1 standby (which is continuously tied to the main under normal conditions when system voltage is above 12V and then automatically disconnects when voltage drops below 12V). The batteries power 1 main buss which in-turn powers 1 endurance buss. The main and endurance buss is connected with a diode (a four prong transformer rectifier) to allow main buss voltage to power the endurance buss but prevents the endurance buss from powering the main buss. Endurance buss is connected directly to standby battery via a direct feeder circuit to the standby battery and switched on/off in cockpit

So I hope I explained that well enough to understand the basic architecture.

So here is my problem, I’m experiencing voltage drop on the endurance buss during normal operation. I removed the standby battery to start my trouble shooting, so all voltage into the system is coming from one battery and it is is fully charged reading 13.28 volts under a small load, probably 3 amps. With the battery switch on, the main buss voltage is reading 13.25 volts, and the endurance buss is reading 12.48 volts. With the battery switch off and the endurance switch on, the endurance buss is reading 13.25.

So I’m getting a voltage drop of .75 volts between my two busses under normal operating conditions. The obvious suspect is something in the diode pack connecting the two busses is causing this but wanted to put it out there to see if anyone else has a suggestion.

Thanks

Robert
.

I have a similar system on my RV8 which has the EFII System 32 so it's electrically dependant. I have 2 ETX-900 ventilated batteries, one for the main bus and one for the essential (endurance) bus. The buses are connected via the standard diode and, as has been mentioned by many posters, it's completely normal to have a voltage drop of .7V - .8V across this type of diode. I found the voltage drop problematic so I got some inspiration from my days flying the Falcon 900 which ran 24V DC busses. After engine start, the DC busses were tied (so theoretically one generator could supply the entire aircraft if necessary) so I decided to incorporate a bus tie relay into my system. For engine start, the busses are connected via the diode as per normal and the bus tie switch is in START (relay open). After start when the alternator is doing its thing (and those ETX batteries are really thirsty), the busses are connected by placing the bus tie switch to NORM (which closes the relay by providing a ground to the coil) and allows the essential bus to see the full 14.2V from the alternator. The system is redundant because if the relay fails, power still goes via the diode but the essential bus will just see a reduced voltage. In normal operation, the essential bus battery is fully charged. In practice, after start, the bus tie switch goes to NORM and after a few minutes, both batteries are stabilised at 14.2 -14.3V and they stay that way. If the alternator fails and you wish to separate the busses, the bus tie switch goes back to START and the essential bus is isolated once again and powered by its own battery. The system has worked flawlessly from day one. I have attached a hand drawn pdf if you're interested. I suppose you could wire it so that power from the alternator closes the relay so it's all automatic but Bob Nuckolls always uses a ground to control a relay so that's good enough for me. I can remember to turn off a switch in an abnormal hopefully! The relay is the standard one from Steinair and my system when the EFII is going full power puts a max of about 12A through it - it's good for 40A I think. So, for my mental health, no criticism please - I'm just a dumb pilot. I read Bob's book, Dassault use it and it works perfectly in practice. Please feel free to adapt/use/ignore as required. Best of luck.

 

[Mich48041]

downundarv8builder, the B&C diode is backwards in your drawing.

 

[Rjmvmi1998]

I have a similar system on my RV8 which has the EFII System 32 so it's electrically dependant. I have 2 ETX-900 ventilated batteries, one for the main bus and one for the essential (endurance) bus. The buses are connected via the standard diode and, as has been mentioned by many posters, it's completely normal to have a voltage drop of .7V - .8V across this type of diode. I found the voltage drop problematic so I got some inspiration from my days flying the Falcon 900 which ran 24V DC busses. After engine start, the DC busses were tied (so theoretically one generator could supply the entire aircraft if necessary) so I decided to incorporate a bus tie relay into my system. For engine start, the busses are connected via the diode as per normal and the bus tie switch is in START (relay open). After start when the alternator is doing its thing (and those ETX batteries are really thirsty), the busses are connected by placing the bus tie switch to NORM (which closes the relay by providing a ground to the coil) and allows the essential bus to see the full 14.2V from the alternator. The system is redundant because if the relay fails, power still goes via the diode but the essential bus will just see a reduced voltage. In normal operation, the essential bus battery is fully charged. In practice, after start, the bus tie switch goes to NORM and after a few minutes, both batteries are stabilised at 14.2 -14.3V and they stay that way. If the alternator fails and you wish to separate the busses, the bus tie switch goes back to START and the essential bus is isolated once again and powered by its own battery. The system has worked flawlessly from day one. I have attached a hand drawn pdf if you're interested. I suppose you could wire it so that power from the alternator closes the relay so it's all automatic but Bob Nuckolls always uses a ground to control a relay so that's good enough for me. I can remember to turn off a switch in an abnormal hopefully! The relay is the standard one from Steinair and my system when the EFII is going full power puts a max of about 12A through it - it's good for 40A I think. So, for my mental health, no criticism please - I'm just a dumb pilot. I read Bob's book, Dassault use it and it works perfectly in practice. Please feel free to adapt/use/ignore as required. Best of luck.

Good stuff. Seems like a simple solution. Thank you for the drawing. I’m going to study it.

 

[blaplante]

I like the automatic version Rolf described. When smoke starts escaping from wiring the brain may not remember the correct actions.
Rolf, what did you use to control the relay so that it would only close above 14.2 volts?

For those that say really unlikely to have electrical smoke, well there's the 2006 Cessna 182, virtually new, that made electrical smoke for my friends one night. Rare? Yes. So are engine failures.

 

[ariel_arielly]

I have an interesting problem here, looking for some advice on where to trouble shoot. RV10 with two earth X batteries. Electrical systems designed for two batteries, 1 main and 1 standby (which is continuously tied to the main under normal conditions when system voltage is above 12V and then automatically disconnects when voltage drops below 12V). The batteries power 1 main buss which in-turn powers 1 endurance buss. The main and endurance buss is connected with a diode (a four prong transformer rectifier) to allow main buss voltage to power the endurance buss but prevents the endurance buss from powering the main buss. Endurance buss is connected directly to standby battery via a direct feeder circuit to the standby battery and switched on/off in cockpit

So I hope I explained that well enough to understand the basic architecture.

So here is my problem, I’m experiencing voltage drop on the endurance buss during normal operation. I removed the standby battery to start my trouble shooting, so all voltage into the system is coming from one battery and it is is fully charged reading 13.28 volts under a small load, probably 3 amps. With the battery switch on, the main buss voltage is reading 13.25 volts, and the endurance buss is reading 12.48 volts. With the battery switch off and the endurance switch on, the endurance buss is reading 13.25.

So I’m getting a voltage drop of .75 volts between my two busses under normal operating conditions. The obvious suspect is something in the diode pack connecting the two busses is causing this but wanted to put it out there to see if anyone else has a suggestion.

Thanks

Robert
Replace the Bridge diode by Schottky diode such as SBR6030 (30V 60A) The voltage drop at 20 A is less then 0.4V (see attached graph).

Ariel Arielly
RV8A
S/N 8095
4X-OAA

 

[rolf]

I like the automatic version Rolf described. When smoke starts escaping from wiring the brain may not remember the correct actions.
Rolf, what did you use to control the relay so that it would only close above 14.2 volts?

For those that say really unlikely to have electrical smoke, well there's the 2006 Cessna 182, virtually new, that made electrical smoke for my friends one night. Rare? Yes. So are engine failures.

 

[rolf]

I like the automatic version Rolf described. When smoke starts escaping from wiring the brain may not remember the correct actions.
Rolf, what did you use to control the relay so that it would only close above 14.2 volts?

For those that say really unlikely to have electrical smoke, well there's the 2006 Cessna 182, virtually new, that made electrical smoke for my friends one night. Rare? Yes. So are engine failures.

All that data is, of course, at the Hangar! Sorry.
I will check next week, and if memory serves, it was a store bought product.

I found all the Data on the computer after a second search:
Installation and Operation Manual AEC9005 Series Low Voltage Warning and AuxiliaryBattery Management Modules
From the AEROelectric connection. Bob Nuckols website.

Rolf
N9EY