Voltage Regulator

[ellisr]

Guys,

The attached image shows the issue I am having with my DA40. <24 Volts and +0 Amps.

The workshop believes it is the voltage regulator, was wondering if anyone had a similar experience and the diagnosis.

Got the low voltage annunciator but no Alternator Fail message.

Thanks in advance,

Russ

[Chris B]

Hi Russ -

It should be either the regulator, alternator, or battery. Or possibly some combination, or even a poor connection somewhere. Regulators are solid state, so they are generally very reliable unless damaged by another component. So I would rule out alternator and battery issues first.

Try turning off the ALT & BAT switches independently and note what happens to voltage & current. This will help diagnose the culprit(s). If possible, fully charge the battery before running this experiment.

Also, how old is your alternator, and have the brushes ever been replaced? How about the battery? Any issues starting the engine?

Chris

[Antoine]

What happens to your meter readings when you increase RPM?
The 0 amp makes me think it is not the battery - rather alternator or regulator or cabling.
As Chris said, regulators are usually robust.
How many hours on your alternator? Ever had brushes replaced?
If your brushes have failed, you may have noticed some erratic amp readings and alternator failure alerts previously. Did this happen?
If you have a mechanic nearby get them to check it - it should not take too long.
And if your alternator is dead, don't be sad: take the opportunity to treat yourself to a Plane Power alternator at this occasion, they are sooo much better.
(I have replaced mine despite it being fully functional).

[ellisr]

When you increase RPM the meters do not move.
Prior to the failure however the voltage meter and the amp meter would dance around for a minute or so the last couple of flights. Is that a symptom of brushes in the alternator? Having said that I never received the Alternator Failure msg.
Both the Alternator and Voltage Reg are original so have about 1100 hours TSN.

Russ

[Gary]

My alternator began to fail at around 1100 hours. Brushes wear and replacing them is relatively inexpensive. I got a new alternator and had the brushes replaced in the old one that I keep as a back up.

[Antoine]

When you increase RPM the meters do not move.
Prior to the failure however the voltage meter and the amp meter would dance around for a minute or so the last couple of flights. Is that a symptom of brushes in the alternator? Having said that I never received the Alternator Failure msg.
Both the Alternator and Voltage Reg are original so have about 1100 hours TSN.
Russ

This looks like an alternator failure to me (probably brushes with possible subsequent damage) but it could still be the regulator, I do not feel competent to judge though.

Mental note made: whenever my volt/amp readings are not as solid as normal, consider this as incipient failure, no excuses, no delaying, especially if intermittent. Just fly right away to a place where they can diagnose and intervene upon electrical issues.

[ellisr]

Thanks guys.

Antoine, agree with your mental note.

Anyone with an engineering background know a test process to difinitively check which of the two have failed? The plane is stuck in a remote site so I want to ensure I order and have the correct part replaced.

[Chromer]

The voltage regulator controls the field current to the rotor, the rotor builds a magnetic field, its this magnetic field which spins and creates your current in the stator to charge the battery. Chances are one of the brushes has lost contact with the slip rings on the rotor and the alternator can't build the field. If you know how to full field an alternator you bypass the voltage regulator, don't do this unless you know how to do it properly and then only for a short time.

[RC7]

I've experienced a similar failure. I never got an ALTERNATOR FAIL message, but did eventually get the LOW VOLTS caution message. It wound up being the alternator itself. Best of luck!

[Antoine]

If your mechanic cant come on site and you still have enough charge to start the engine I would get myself a backup solution for avionics (portable navigation) and fly the plane in day VFR (I insist 100% VFR) to the nearest mechanic.

You should power off every consumer that is not required for this flight to preserve whatever is left of your battery.
The plane will fly just fine without alternator but you would end up with no comms eventually.

The avionics draw about 8 Amps, so if you fly 15 minutes you would use 2 Ah which is probably less than the engine start...