Shunt with MGL equipment

[cjensen]

This question may be answered by anyone, but I put MGL in the title to get Rainier's attention (or any of you MGL users out there)...

I have my shunt mounted...

I plan to route things similar to this picture...

I'm using the MGL I/O Extender to get an ammeter in the EFIS, and the shunt is wired to it here-

Now, I know there is no polarity in the shunt, so I'm wondering if anyone (Rainier???) can enlighten me on the positive/negative connections on the Extender. The only thing I can think of, is that the + could be for the "high" side of the shunt, and - could be for the "low" side of the shunt.

Thoughts???

 

[AMURRAY]

If I am not mistaken the positive lead of th IO Extender is connected to the side of the shunt that goes to the alternator. The ammeter is reading the voltage drop across the shunt which is proportional to the current.

 

[breister]

You are correct, either polarity will work - BUT...

The "correct" orientation depends on your use.

Some put the shunt in between the battery and the bus. In this configuration you want the Amps to read Positive if the battery is charging, and negative if the battery is supplying power to the ship.

Some put the shunt between the Alternator and the bus, to determine total system load (systems + battery charge).

So hook it up either, and then decide if it is giving you useful info...

 

[cjensen]

If I am not mistaken the positive lead of th IO Extender is connected to the side of the shunt that goes to the alternator. The ammeter is reading the voltage drop across the shunt which is proportional to the current.

So...in finishing this thought...the negative side of the IO would go to the ANL limiter-to battery side of the shunt?

 

[cjensen]

You are correct, either polarity will work - BUT...

The "correct" orientation depends on your use.

Some put the shunt in between the battery and the bus. In this configuration you want the Amps to read Positive if the battery is charging, and negative if the battery is supplying power to the ship.

Some put the shunt between the Alternator and the bus, to determine total system load (systems + battery charge).

So hook it up either, and then decide if it is giving you useful info...

Yeah...still a bit torn about this. I think I want total system load info...still thinking about it though. In the second pic I posted, that would a total system load setup, correct?

 

[Rainier Lamers]

This question may be answered by anyone, but I put MGL in the title to get Rainier's attention (or any of you MGL users out there)...

OK, it worked. You got my attention...

Adding to the posts allready here is difficult as the question is answered.

Basically, the normal way to do things would be to measure whatever goes into or out of your battery. The polarity of the shunt does not really matter - it depends on how you view the reported positive and negative measurement result.
You would wire it such that the shunt would would effectively show battery charge/discharge - that is the important part.
You don't want the shunt to see total charge + power draw (of course you might want to anyway...).

Rainier
CEO MGL Avionics

 

[breister]

OK, it worked. You got my attention...

Adding to the posts allready here is difficult as the question is answered.

Basically, the normal way to do things would be to measure whatever goes into or out of your battery. The polarity of the shunt does not really matter - it depends on how you view the reported positive and negative measurement result.
You would wire it such that the shunt would would effectively show battery charge/discharge - that is the important part.
You don't want the shunt to see total charge + power draw (of course you might want to anyway...).

Rainier
CEO MGL Avionics

Hehe - and this is why I said it is a "preference." In my book, total alternator load is the only "useful" piece of information - by default, any time it reads zero in my plane is a "Problem" and there is nothing else I need to know about it - while knowing how much drain on my system is created based on what systems are turned on can help me diagnose any situation where the load is higher than "normal" (which you only know after you have flown your plane for a while daytime/night/IFR). If I suddenly started seeing 50 amps in daytime flight more than a few minutes after engine start, I know darned well something is wrong even if no other indication is present.

To me, knowing exactly how many amps are going into/out of the battery is pretty much useless because 95% of the time it will be approximately zero.

Opinions differ...

 

[cjensen]

Thanks all! Will be wiring it tonight!