Alternator issue?

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Rich
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Re: Alternator issue?

Post by Rich »

A diode bridge can be replaced. Typically it's a pair of circular parts separated by 6 diodes which convert 3-phase alternating voltage/current to a fairly flat direct output. If one or two of these diodes fails, the output becomes a wavy direct, rather than constant. I had this happen once. It was decades ago and the behavior was that peak output was reduced and with no radio noise. But everything else about the plane was far more primitive and likely less sensitive.

EDIT: BTW, the diode failure could be confirmed by physical inspection in the alternator. What happens is a lead breaks off and it's easy to see after opening up the alternator.
Last edited by Rich on Thu Mar 18, 2021 7:44 pm, edited 1 time in total.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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astaib
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Re: Alternator issue?

Post by astaib »

This is what we will do (visual inspection), but as the failure (noise in the radio) is not constant but only when the voltage is above 30v I hope that it will be visible anyway...

Today when I flew (test flight), I had no noise but the voltage was always in the 28.x. Sometimes 29.x. And occasionally 30v.

Really difficult to troubleshoot.

I’m desperate !
Arnaud
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Re: Alternator issue?

Post by astaib »

Hi all,

Just to give you some news, not really good as I sent my Voltage Regulator to Lamar and they tried it on a bench without finding any problems!

If I sum up:
-Voltage regulator is OK
-Wiring that comes out the VR are all ok
-Alternator is ok (brushes, diodes checked)

Honestly I don’t know what else to check and no mechanics has no idea of what to do!

I’m grounded without any idea of what to do, damned !
Arnaud
DA40 Star 180 / 40.026 / 2001
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Steve
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Re: Alternator issue?

Post by Steve »

Arnaud: Sorry to hear that. I can only offer some general electrical gremlin troubleshooting advice. Was any work done on the aircraft just prior to the problem first appearing? Often, something can get knocked loose by someone working on something else.

Often, electrical issues can be traced to bad ground connections. My recollection is that there are three ground connections to the alternator on my airplane. I would check them carefully if you haven’t already done so.

The other guiding principal in electronics troubleshooting is to measure voltages. So, you may need to make up some long test leads to check the voltages on all of your alternator terminals while the engine is running.

Good luck,

Steve
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Re: Alternator issue?

Post by astaib »

Hi Steve,

Thank you for the time you’ve spent to answer me.

There was no maintenance just before the problems appears.

3 grounds? I only have one that is made by the body of the alternator itself because he is bolted to a bracket in contact with the engine. The other connection are field, aux, F1 and F2.

I think that you are right and that I will have to make some voltage measurements while the engine is running.
Another option is to send both the alternator and the voltage regulator to a shop that will test them together.

This is my real first big issue with my plane.

Arnaud.
Arnaud
DA40 Star 180 / 40.026 / 2001
Wingtip, landing and taxing LED (Whelen)
Skitube
GNS430 NON-WAAS
Steam gauges
Non certified ADS-b
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Rich
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Re: Alternator issue?

Post by Rich »

astaib wrote: Fri Mar 26, 2021 9:37 pm Hi Steve,

Thank you for the time you’ve spent to answer me.

There was no maintenance just before the problems appears.

3 grounds? I only have one that is made by the body of the alternator itself because he is bolted to a bracket in contact with the engine. The other connection are field, aux, F1 and F2.

I think that you are right and that I will have to make some voltage measurements while the engine is running.
Another option is to send both the alternator and the voltage regulator to a shop that will test them together.

This is my real first big issue with my plane.

Arnaud.
According to the wiring diagram, F2 should be grounded, though the physical site of this grounding is not clear.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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astaib
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Re: Alternator issue?

Post by astaib »

You are right, I cannot remember if I checked this point precisely
Arnaud
DA40 Star 180 / 40.026 / 2001
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Skitube
GNS430 NON-WAAS
Steam gauges
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astaib
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Re: Alternator issue?

Post by astaib »

Rich wrote: Fri Mar 26, 2021 9:45 pm
astaib wrote: Fri Mar 26, 2021 9:37 pm Hi Steve,

Thank you for the time you’ve spent to answer me.

There was no maintenance just before the problems appears.

3 grounds? I only have one that is made by the body of the alternator itself because he is bolted to a bracket in contact with the engine. The other connection are field, aux, F1 and F2.

I think that you are right and that I will have to make some voltage measurements while the engine is running.
Another option is to send both the alternator and the voltage regulator to a shop that will test them together.

This is my real first big issue with my plane.

Arnaud.
According to the wiring diagram, F2 should be grounded, though the physical site of this grounding is not clear.
From this schematic the alternator is grounded in 3 points as Steve was saying: the body of the alternator, F2, and also the + (does it make sense to have the + grounded?)

Btw do you know what “18 awg” means?

Arnaud.
Arnaud
DA40 Star 180 / 40.026 / 2001
Wingtip, landing and taxing LED (Whelen)
Skitube
GNS430 NON-WAAS
Steam gauges
Non certified ADS-b
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Rich
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Re: Alternator issue?

Post by Rich »

This isn't exactly the same thing, but here's a relevant experience I had in 1984:

Driving a Chevette at night, I noticed the headlights starting to get dimmer, along with the instrument lights. And the car seemed to be losing power. I opened up the hood/bonnet with the engine idling and noticed there was a ground strap from the alternator to one of the studs holding on the valve cover that had broken from vibration and was disconnected. The car was sitting there idling. I touched this strap to the bolt and the engine bogged down and the headlights got brighter. I managed to get the strap snugged down beneath the nut for that stud and drove on home. It turns out that that particular model actually had the VR built directly into the alternator. So it was happily regulating voltage completely independent from the car as a whole AND with no way to deliver charging current to the battery. The car was running solely on the battery.

Note that F2 should be connected to the ground lead from the VR and the shield for the main current delivery to the main bus, and the three grounded somehow, probably near the alternator. Also check the ground strap from the battery to the engine block. On mine there is an intermediate terminal on the engine mount. Watch for any sign of corrosion on any of these terminals.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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Rich
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Re: Alternator issue?

Post by Rich »

18 AWG means #18 American Wire Gauge. The diameter of the conductor. + is not grounded. It's the shield of that wire.
2002 DA40-180: MT, PowerFlow, 530W/430W, KAP140, ext. baggage, 1090 ES out, 2646 MTOW, 40gal., Surefly, Flightstream 210, Orion 600 LED, XeVision, Aspen E5
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