[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]

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]

Monitor voltage ...

...
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!

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...

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?

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?

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?

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]

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]

look at Dynon's documentation

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]

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.

 

[mburch]

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...

I need to post an updated version of my schematic one of these days, now that it's more fleshed-out (although the basics remain the same).

A shunt and a Hall effect sensor are different electrically, but you're right that it should be no problem as long as your engine monitoring system supports it (mine does).

mcb

 

[w1curtis]

Also, a current sensor in battery lead mode allows you to "manage" your power budget should you have a failure of your charging system. Without the alternator, it will tell you how much current you are currently drawing from the battery. Draw less current, voltage stays higher, longer.

Even though I'm going with AFS EMS, I will be installing one of the below in battery lead mode and a switch to a shunt on each main electrical buss. The AFS would then show alternator output and this unit will show current usage.

 

[longranger]

Im a Nuckol-head myself, but not sure I agree here. ...erich

Same here. It may just be my 30+ years of Cessna experience, but personally, I'm a fan of the shunt in the battery feed to the bus as opposed to the alternator load meter. After master switch on, but before engine start, a small discharge indicates the meter is working. If the engine is running, needle in the center (0) or slightly to the right (charging) = good; needle to the left (discharging) = bad. Almost as good as an idiot light.

 

[sblack]

Same here. It may just be my 30+ years of Cessna experience, but personally, I'm a fan of the shunt in the battery feed to the bus as opposed to the alternator load meter. After master switch on, but before engine start, a small discharge indicates the meter is working. If the engine is running, needle in the center (0) or slightly to the right (charging) = good; needle to the left (discharging) = bad. Almost as good as an idiot light.

I get all that from my volt meter. When I put my master on I see 12.6v or so. After start it goes up a little bit and above 1500 rpm I see it go to 14.6V. if it doesn't jump up at that mid rpm I know my alternator is not working.

 

[BillL]

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

Yep - I did this too. The logic is - the voltage tells me the battery is charging or not. The shunt from battery to all loads tells me what the amperage draw is for the system, but missing the battery amps. If the voltage drops, then I can definitively manage the amp draw on the batt and know via voltage when it is going to die completely. I feel comfortable with this knowing exactly how I will use it. Every one thinks differently, so others configurations will work too.

Historically, the volt meters in cars were not very accurate, so a positive or negative meter worked for a car/tractor in the 40's, 50's and 60's. With digital voltmeters that are accurate, the picture changes.