MGL Avionics User Forum

i have a Sling 4 with a Rotax 914 with a backup alternator.

my ammeter always reads negative… usually -14A and goes down with more load. .
the battery charges so clearly the indication is incorrect.

any ideas? simple polarity issue? ie should i swap the leads around on the iBox?

Where is the ammeter installed? It almost seems like it's reading alternator output and not battery amperage...

Adam

interesting.
i’m not sure.
where should it be? should the reading be positive? i’m very confused

In most cases, it needs to be on the main battery cable that feeds the main bus so that it may show the differential of current drawn by the bus and charge replaced by the alternator/generator.

If the battery is charging, it should be at a positive number. If it's discharging, it should be a negative number. During normal flight, it should be a small positive number, or even at zero. TAF has a way of doing some...unique things though, so it won't be easy to say unless I know where the sensor is.

Thanks Adam.
It occurs to me that I have seen the charge sensor when I changed the battery.
I’ll simply flip it over so it reads positive……..

Hi Mike,

I have included a pic of the MGL Amp sensor I have on my plane, not sure if MGL has supplied other styles of amp sensor.

Where my amp sensor is attached to my electrical system at position 3 in the diagram below, it is on the main positive wiring to the planes master bus and switch, this suits my situation needing to know what my maximum amperage draw is from my aircraft's charging system, as it's limited to 17 amps continues and I like to keep a check on this current draw.

Yes your right if you are thinking, if I don't have another amp meter wired into position 2, you may not know when your charging system has failed unless you are very aware what your system's normal charging voltage is.



Placement of MGL or Other Amp Sensor


What Amps are you reading if you put an Amp Sensor in these wiring positions.







1. The Sensor placed at wiring position 1, will show the number of positive amps coming from the charging system going to either the Battery and/or the Instrument Panel System if turned on and should show no negative amps.

2. The Sensor placed at wiring position 2, will show the number of amps going to and from the Battery. This is the normal position for an amperage sensor. You will see both positive and negative amps flow to and from your battery.. Like when your aircraft system is charging your battery or you're on the ground pulling power from the battery.

3. The Sensor placed at wiring position 3, will show the total amps being drawn by your plane’s electrical system. Normally you should only see a negative amp flow at this position, if you see any positive amp flow, the most common reason is that the amp sensor's orientation is incorrect.

So as you can see depending on where your amp sensor is position in your electrical system, it will give you different amp reading for different things. So before you do anything, I would try to work out work what position your sensor is wired into your aircraft's electrical system.

From what you have said and that you feel your alternator is charging your battery, my guess your sensor is wired into your electrical system at position 3, so it's only showing your total amperage draw, if this is the case, it's working as it should for that position and will not show any positive amps.

I hope this has helped.

Cheers
JimJab

Hi JimJab.

Thank you so much - this is really interesting gen.

I need to have really close look at where it's wired. For me I want to know if the charge system fails - so I want to see pos amps going to the battery when at normal RPM. So it seems position 2 is the place for it to be.
I will have a good look on the weekend and see if I can figure the thing out..
Thanks again for the time to explain.
Mike

Hi Mike,

Something I did forget to say, with my type of MGL Amp sensors, it needs to be calibrated.

A simple thing to do from memory, once the senor is wired into the RADAC and before attaching it to the wire you want to sense the amps in, you need to calibrate the senor in the EFIS menu. It does explain it a MGL PDF file on the Amp sensor.

But do this calibration before you zip tie the sensor to the wire, otherwise you will have to pull it off again to calibrate it.

Cheers
JimJab