Measuring Current

[Noah]

Planning a two alternator (Primary/Standby), single battery configuration and trying to determine where to locate current sensors (shunts). All of the spam cans I have flown have a single "current meter" which shows the battery charging or discharging. In this instance, I believe that the shunt is located at the battery ground cable. Fast forward to "the modern age". Several recent schematics from present day builders show current sensors on both alternator B leads. Although this tells you the current being put out by each alternator, I don't think it will tell you whether the battery is charging or discharging. Additionally, it does not give you a complete picture of the ship's loads, I don't think.

Just trying to get a handle on why measuring current at the alternator B leads is "better" than a single location at the battery.

At present, I am planning an SB1B regulator for the standby alternator, which has a light that flashes if you are overloading the standby alternator. So that already has a current sensing feature - granted, pretty coarse - either ">20A" or "<20A".

Any idea why sensing current at the alternator B leads is preferred over the battery?

[mburch]

You can very easily tell whether or not the battery is charging, just by looking at the voltage. Below about 13V, it's discharging.

On a related note, I'm using Hall effect current sensors instead of shunts on my airplane. Smaller and easier to install (IMHO).

mcb

[w1curtis]

Originally Posted by Noah

Any idea why sensing current at the alternator B leads is preferred over the battery?

The preference is that of the manufacturer. Some prefer alternator lead (Piper, et al) while others prefer battery lead (Cessna, et al) mode. Each configuration has it's pro's and cons. Also, while many EMS vendors allow configuration in either mode, some only allow one mode or the other. AFS for example only offers alternator lead mode with their EMS.

In a nutshell, alternator lead mode will show how much power is being generated by the alternator. Indication are typically 0-60 amps or capacity of alternator. It will indicate zero when the engine or master is off or the alternator is dead.

Battery lead mode will show the charging (or discharging) state of the battery. Indications are typically -60 0 +60 and will indicate a + indication (battery is getting slightly more power that is being consumed from it) under normal conditions. When alternator is off line, it will indicate a discharge.

[AltonD]

Here is what I did.
I have a primary Plane power alternator and a B&C B/U SD-20.
The B&C in the backup configuration has a current sensor that flashes the warn light when it is over loaded. That said, I do not need a current read out for the B&C.
I am using a AFS-3500 with two current indications.
#1 is on my main bus, Hal effect. This tells me how much I am consuming.
#2 is the traditional primary alternator indication.

I have not flown yet, but I think I will be satisfied with this setup.

[L.Adamson]

This is another one of those divided camp threads..

My preference is still the Van's method which immediately shows the status of the battery charge/discharge..........along with a volt meter, which I also feel as being essential.

L.Adamson --- RV6A

[DGlaeser]

Originally Posted by Noah

...
Any idea why sensing current at the alternator B leads is preferred over the battery?

AeroElectric Bob Nuckolls would tell you that current sensors don't really provide any useful in flight purpose, so put them wherever you want. Monitoring voltage, with immediate notification of low voltage is the important thing to do. Ammeters are good for trouble shooting on the ground.

[Noah]

Thanks for the enlightening responses, guys!

Originally Posted by mburch

You can very easily tell whether or not the battery is charging, just by looking at the voltage. Below about 13V, it's discharging.mcb

Good points Matt, I have studied your schematic on several occasions, BTW, since I am planning something similar. Are the signal outputs for a shunt and a hall effect identical? Probably not, but if your EMS accepts the hall effect...

Originally Posted by w1curtis

The preference is that of the manufacturer. AFS for example only offers alternator lead mode with their EMS.

Thanks Bill, I always figured you could install the sensor anywhere you want and it would show current flowing. Maybe you mean that the EMS vendor does not support the display of a NEGATIVE (discharging) current flow and that is why you can only put the sensor on the B-Lead for an AFS install?

Originally Posted by AltonD

Here is what I did.
I have a primary Plane power alternator and a B&C B/U SD-20.
The B&C in the backup configuration has a current sensor that flashes the warn light when it is over loaded. That said, I do not need a current read out for the B&C.
I am using a AFS-3500 with two current indications.
#1 is on my main bus, Hal effect. This tells me how much I am consuming.
#2 is the traditional primary alternator indication.

I have not flown yet, but I think I will be satisfied with this setup.

Interesting... I will have to think about this some more - my planned setup is identical. I assume you are using a Z-12 like architecture?

Originally Posted by L.Adamson

This is another one of those divided camp threads..
L.Adamson --- RV6A

Whoops, maybe should have put this in the never ending debates section, just below primers and above tipup vs. slider?

Originally Posted by DGlaeser

AeroElectric Bob Nuckolls would tell you that current sensors don't really provide any useful in flight purpose, so put them wherever you want. Monitoring voltage, with immediate notification of low voltage is the important thing to do. Ammeters are good for trouble shooting on the ground.

Interesting, I just re-read AEC last weekend, must have missed that. I suppose that if you are planning an endurance mode, that would be one place to monitor current usage, but otherwise I would tend to agree.

[erich weaver]

Originally Posted by DGlaeser

AeroElectric Bob Nuckolls would tell you that current sensors don't really provide any useful in flight purpose, so put them wherever you want. Monitoring voltage, with immediate notification of low voltage is the important thing to do. Ammeters are good for trouble shooting on the ground.

Im a Nuckol-head myself, but not sure I agree here. The current sensor certainly gives you a very good idea about whether something is actually functioning or not. If I turn on my boost pump or landing lights or whatever and see my amps bump up by what the manual and experience has told me is the correct amount, Im feeling pretty confident that its working as advertised. For me, thats useful.

erich

[DBone]

Dynon has a very useful diagram in their D180 install manual (page 3-12) that I used to plan my location. It's the best simple explanation/diagram I've seen regarding this subject.

You can see it HERE

[Noah]

Originally Posted by DBone

Dynon has a very useful diagram in their D180 install manual (page 3-12) that I used to plan my location. It's the best simple explanation/diagram I've seen regarding this subject.

You can see it HERE

Great reference, explains a lot. Thanks for posting.