2 alternator on shunt

RVG8tor · #1 04-19-2011, 03:11 PM

Dynon only supports one ammeter. I have a main alternator and and a standby. The standby only produces power when its voltage regulator senses bus voltage below a certain point which is below where the main alternator would have the bus voltage at, the logic is with a good main alternator the standby stays asleep, so they both will not produce power at the same time.

What I want to do is take the B leads from each alternator to separate current limiters then attach both to one side of the shunt the out side of the shunt would take the power to the bus. The shunt is in a location after the alternators and would show the load going to the battery and main bus.

Is this OK? I am looking at the Z12 diagram which is what I am using from the AEC and the B leads both attach to the start contactor post, all I am suggesting is putting a single shunt in just before this connection and then feeding the "B" leads to the other side of the shunt.

Thanks for any help

jdeas · #2 04-19-2011, 05:16 PM

If the current limiters also have reverse current protection this should work fine. The only issue is how would you know when one of the alternators died?
Have you considered a second shunt and a toggle switch to see what each alternator is producing? You could leave the 'primary' shunt to the EFIS and when a failure hits, simply switch to the backup and know you got some repairs to do.

RVG8tor · #3 04-19-2011, 05:36 PM

Jdeas

Not sure what you mean by reverse current protection. The B lead off of each alternator is protected with a current limiter (replaces panel circuit breaker traditionally used). This is kind of like an in line fuse but it does not blow as easily.

As far as knowing when an alternator dies, the standby sits idle until the main goes out, when the standby kicks on there is a light to tell me it is running and with a hall effect sensor it will tell me if it is overloaded. I figure I can control my loads so I am not using the optional hall effect. So when the light some on I know I have a problem with the main alternator. With the main alternator off the ammeter would be reading only the voltage from the standby alternator. The way the standby alternator works is that its regulator keep is idle (no power to the B lead) until it sees voltage drop, this set point is below the voltage that the main alternator would keep the bus. So there should never be two alternators providing power to the bus, the standby even has its own over-voltage protection and will not be effected if the main alternator over-volts. The idea is that the main over-voltage has a chance to work and shut itself off then the standby would pick up the load.

So what do you mean by reverse current protection?

Quote:

Originally Posted by jdeas

If the current limiters also have reverse current protection this should work fine. The only issue is how would you know when one of the alternators died?
Have you considered a second shunt and a toggle switch to see what each alternator is producing? You could leave the 'primary' shunt to the EFIS and when a failure hits, simply switch to the backup and know you got some repairs to do.

jdeas · #4 04-19-2011, 08:58 PM

It was just a thought that one failure mode is a shorted alternator. The diode isolates the short from the second alternator. If you already have a sensor that tells you when the second alt is working then you already have a fault detector. As for the reverse diodes, it may already be built into the regulator/current limiter you have.
Not seeing your setup I was just posting items to consider in the design.
Using two shunts and three wires you could install dual shunts and a switch so the EFIS could give you more information that a light.

rzbill · #5 04-20-2011, 04:56 AM

If I understand the proposal of using single shunt, it creates a single point failure mode for the whole charging system. Your call obviously, but I would not.

I do not have Dynon, so I am curious about aux inputs that would read an analog voltage. Nothing available?

RVG8tor · #6 04-20-2011, 11:11 AM

The Dynon FlightDEK 180 only supports one ammeter, I can get bus voltage but the amp reading is what I can't double up on.

As far as single point failure, I guess you are correct but a shunt is a fairly robust piece of equipment, I think I am willing to take that risk, it is no more likely to fail than the wire carrying the current.

Quote:

Originally Posted by rzbill

If I understand the proposal of using single shunt, it creates a single point failure mode for the whole charging system. Your call obviously, but I would not.

I do not have Dynon, so I am curious about aux inputs that would read an analog voltage. Nothing available?