troubleshooting electrical issue - Dynon EMS readings don’t add up

[dominikos]

I have been trying to troubleshoot an electrical issue which resulted from a short caused by the landing light. Before the short, Dynon showed properly both charging voltage and amperage. After the short, I get this reading from Dynon - it basically shows battery voltage and discharging.

It would almost made sense but the battery is not discharging. Did a run today - 30 mins and the battery voltage was still 12V. The Amps readings do change depending on the load - fuel pump, GPS Nav on/off.

I will take plane for service next week - at this point trying to pin point the issue. Has anybody seen a similar behavior? Any other suggestions for troubleshooting?

more details: plane: Mooney M20J, engine: Lycoming IO360, alternator: Hartzel ALY -2520R. The amps is configured as Ammeter Shunt.

 

[Carl_Froehlich]

Is the shunt located on the alternator output (reads amps out of the alternator) on the battery output (reads amps out of the battery)?

Regardless, the low voltage says you are not charging the battery. I suggest you first verify the voltage reading to be correct.

Perhaps more detail on your landing light short?

Carl

 

[maartenversteeg]

The shunt is connected via two wires to the EMS, these wires normally include a fuse in each wire, it might be that your short blew one of these fuses

 

[dominikos]

I will check the fuses.

@Carl_Froehlich, the short didn’t trip the fuse and as a result created heat that melted one of the wires around alternator. the wire has been replaced. I checked the voltage on the batter after running plane for 30 minutes and the voltage was 12V+ and consistent with Dynon reading

 

[Danerazz]

I checked the voltage on the batter after running plane for 30 minutes and the voltage was 12V+ and consistent with Dynon reading

What the voltage shows AFTER shutdown is not relevant.

If you wish to check your electrical system vs. your indications, or your electrical system at all, with any accuracy, you need to use a multimeter with a probe attached to ground and a bus bar WHILE THE ENGINE IS RUNNING. That will immediately tell you what the system voltage is.

If it is only 12v running, then your alternator is not working. It should be about 14.2v. Your statement is the Dynon was correct after shutdown, which means it is likely correct while the engine is running. A short somewhere could have affected your voltage regulator or the alternator itself.

Depending on the battery, they don’t always have a linear discharge. It might read a surprisingly high voltage but be in quite a low state of charge.

Troubleshooting can proceed from there.

 

[dominikos]

To close the discussion, it turned out to be the alternator. Got it swapped on Friday and readings went back to normal. Put 5 hours since then

 

[Rhino]

Thanks for coming back and letting us know.