Still trying to figure out battery discharge

[Alan Maurer]

Hello Mooney People

If I want test backup alternator in Ovation, will it work to switch off alternator field and turn on emergency bus? Will that operate the backup alternator?

Thanks

Alan

 

[carusoam]

Alan,

you probably have two separate alternator switches, controlling two separate voltage regulators… operating two separate field wires… that go to the two separate alternators…

If you have two separate alternator switches… you have the ability to turn off each alternator and test them independently before departing…

Power supply, is probably independent of the busses being selected…

PP thoughts only, my O didn’t get the E-Bus or second alternator… yet.

 

Standby for somebody with actual knowledge of the system…

Best regards,

-a-

 

[MatthiasArnold]

For my O2 GX 2006 I do the ground check procedure as follows:

• monitor BAT AMPS being in the positive range (+2 .. higher)
• increase Prop RPM > 2000
• ALT switch off -> BAT AMPS negative -10..-16 (depending on load)
• EMERG BUS switch on -> BAT AMPS rise to values in the range -2..0 (the standby alternator delivers electrical power)
  • Optional: further increase Prop RPM to check whether standby alternator is able to serve all loads (BAT AMPS in the postive range, POH mentions to go up to 2500 RPM), decrease PROP RPM back to 2000
• EMERG BUS switch off
• ALT switch on
• check BAT AMPS in the positive range again
• decrease PROP RPM to idle

@carusoam: not claiming to have any knowledge of the system

Best,

Matthias

[GeeBee]

I would add to the above procedure. When you turn the alternator off, check the annunciator for "Low Voltage" on the annunciator and verify RED "Alt Low Volts" flashes . When you turn on the emergency bus switch verify amber "Emerg Bus" illuminates and red "Alt Low Volts" light extinguishes.

The procedure is in your POH. 

[N231BN]

You may need to check the supplements if it's not in the normal/emergency procedures.

[Pinecone]

On my 252, there are two Alt switches.  And a gauge with 3 needles, one for total % load, and one each for the two alternators % load.

So part of pre-takeoff checklist is to turn off the main alternator and see that the load transfers to the 2nd alternator, then turn it on and the 2nd alt off, to see if the load transfers back.  And checking the voltage on each alternator as you cycle the load to it.

[Alan Maurer]

Hello Everyone...Thanks for the information. I do not have two alternator switches. Just one field switch. I will try going back and forth between the 

main bus and the emergency bus to see if the backup alternator picks up the work. This all became a question because using both Battery One 

or Battery two for a flight...both show -2 amps and both show 28 volts. So on both battery sides there is a lack of charging....

thought about a problem with main alternator or ? slipping drive?

Cheers

Alan

Ovation 2 GX from 2008

[Guest]

From the Maintenance manual 

[carusoam]

So…. If both alternators can be selected… and a couple of amps are missing…

Keep in mind the different sizes of the alternators…

As doc’s page above indicates the 20Amp alternator2 is bit small…. Hence the reason for the the E-bus and power shedding…
 

Things to check the health of…

Alternators and their couplings…

Unless your alternator2 is belt driven… it probably has a coupling… if it is belt driven… belt tightness will have a measurable spec.

Some IO550s use an alt2 mounted on the vac pump pad…

 

We have discussed some coupling issues around here before… mostly starter couplings… when the fail, it is a fix now kind of issue… parts can migrate into the oil flow…

 

Either way… it sounds like Alternator1 isn’t keeping up with the load… or the amp meter needs to be calibrated/checked/tested…

Might be a good time to check the amp meter since both alternators were showing the same problem… while both batteries seemed to be staying charged…???

PP discussion points only, not a mechanic…

Best regards,

-a-

[GeeBee]

14 hours ago, Alan Maurer said:

Hello Everyone...Thanks for the information. I do not have two alternator switches. Just one field switch. I will try going back and forth between the 

main bus and the emergency bus to see if the backup alternator picks up the work. This all became a question because using both Battery One 

or Battery two for a flight...both show -2 amps and both show 28 volts. So on both battery sides there is a lack of charging....

thought about a problem with main alternator or ? slipping drive?

Cheers

Alan

Ovation 2 GX from 2008

With the main alternator ON and the Emergency Bus switch OFF you should have positive to zero amps at or above 1000 RPM. If you don't check your main alternator and its coupling.

With the main alternator OFF and the Emergency Bus switch ON, you should see near 28 volts and a slight discharge -1 to -3 amps at 2000 RPM. Increase RPM to 2500 RPM to fully check that it will create a 0 amp condition. If it does not, check first that your batteries are not weak with a capacity check. If good batteries,  check the diode in the field wire and then the coupling.

Remember if you have weak batteries the standby alternator will not generate enough current ever to charge them during the check. In fact, if you read your emergency procedures you will note if your main alternator fails and activate the standby alternator via the Emergency Bus switch you are required to pull the Battery CB to isolate the battery from the system until it is needed to extend gear and flaps. This is because the standby alternator is only powerful enough to supply the Emergency Bus items, not charge the battery which is also why it is a self exciting alternator unlike your main alternator which requires a connected battery to operate.