ArVeeNiner

ArVeeNiner

Well Known Member
Hi all:

I've been scratching my head about this for a while. Just when I think I know what to do, I find another way to do it on the Internet.

I want my Dynon to read current flow into or out of the battery. This is position A as depicted in the Dynon manual. I know there are pros and cons to this location but this is what I want. I propose the following. Please let me know if this seems logical:

shuntsetupfg8.jpg
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Kelly Johnson
RV-9A
 
Based on what you want your ammeter to read (current into or out of the battery) your proposed location is where it needs to be placed. The only other location for the shunt would be between the battery and the master contactor but this would not be very practical as the shunt would need to be rated for the high current (100's of amps) that would flow through it when the starter is energized. The Dynon connection to the shunt should be such that current flow out of the battery is indicated as a negative current flow and current into the battery indicated as positive current flow.
 

There is a disconnect here with regard to what is essential information about the electric system in flight. Is it the battery load or the output and voltage of the alternator?

I could care less what the flow into or out of the battery is, what is important is the current load on the alternator and its voltage. If alt load drops to zero the message is "Houston, we have a problem". Alternator load and voltage tell much more about the health of the electric system than does battery load.

Battery load will show a "flow in" load after start as it recharges and then the load indication is essentially zero. The alternator carries the system load due to its higher voltage, the battery simply sits in reserve. Beyond starting the engine the battery has an easy life. A good check of its health is whether or not it started the engine. After start, an alternator load will show the battery being recharged and after a few minutes that load decreases to system load, also a very good bit of information as any abnormality within the system can show up as an unusual load. The battery is happy just sitting there in reserve. Its function after start recharge is essentially an electric sump and it serves that function well. The alternator always carries the system load when it is functioning properly.

I much prefer to look at alternator load and voltage in flight rather than battery load at zero. I suppose one could reprogram his mind to get the message of a failed alternator if the battery is suddenly loaded and its voltage has dropped to its residual voltage. My problem with that scenario is it is sort of like driving a car, not flying an airplane....:)











 
Ammeter charge/discharge?

This thread got me to thinking. I've got about 15 hours on my -7A now and I was under the impression that all electrics were working as advertised. But now I recall that after engine start my ammeter is indicating a bit LEFT of zero instead of RIGHT. Shouldn't it be reading to the RIGHT just after a major drain like starting the engine? After a few minutes it finds its way back to zero and remains there until the next start. Would swapping the two leads on the shunt that feed my ammeter correct the polarity so that it reads charge instead of discharge like it's supposed to? Thanx in advance.
 
Hawkeye7A said:
This thread got me to thinking. I've got about 15 hours on my -7A now and I was under the impression that all electrics were working as advertised. But now I recall that after engine start my ammeter is indicating a bit LEFT of zero instead of RIGHT. Shouldn't it be reading to the RIGHT just after a major drain like starting the engine? After a few minutes it finds its way back to zero and remains there until the next start. Would swapping the two leads on the shunt that feed my ammeter correct the polarity so that it reads charge instead of discharge like it's supposed to? Thanx in advance.
Click to expand...

Swapping the leads to the ammeter will move the needle in the opposite direction.
 
No reprogramming...

David-aviator said:

.......

I much prefer to look at alternator load and voltage in flight rather than battery load at zero. I suppose one could reprogram his mind to get the message of a failed alternator if the battery is suddenly loaded and its voltage has dropped to its residual voltage. My problem with that scenario is it is sort of like driving a car, not flying an airplane....:)
Click to expand...


...of minds needed if you have an EFIS/EMS installed.

Low battery voltage is a standard alarm on most (all?) of these units.

In this case, let the electronics think (well actually "monitor") for you...:)
 
One drawback to consider, depending on your design, is that if you have a back-up alternator e.g. an SD-20 feeding an e-bus, you may not know how it is handling the load if it is wired before the battery contactor.

Is there a drawback if the shunt is wired between the battery and ground? In other words, can a starter "blow" a 60 Amp shunt?
 
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