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how to test my alternator?

prkaye

Well Known Member
I just completed some panel work. When I started the plane up again after the work, my Alternator-out indicator light did not extinguish after starting the plane. I double-checked that the wires to the starter switch and the Alt/Batt switch had not become disconnected. When I pulled the indicator light out of the panel, I accidentally shorted the leads. Now the alternator-out light doesn't illuminate at all, even when it should (i.e. when BAT is on but ALT is off).
The Alternator Field circuit breaker did not trip, and I checked the relevant fuses.
When I start the plane, my voltage only shows 12.4 volts, and 0 amps.
So I don't know if I have a wiring problem somewhere, or if my alternator is fried.
I have a PlanePower alternator.
How should I test/diagnose this situation?
 
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Phil,
While you were wearing your Builders hat that internal voltage regulator alternator sure was nice because it's simplified wiring and building isn't it? However now that you're wearing your mechanics hat that internal voltage regulator makes things a bit more difficult. The fact of the matter is that doing on the plane testing will only help you determine that there's a problem somewhere in the system but it won't be able to isolate if the problem is in the alternator or in the wiring somewhere.
That would still require a fair amount of multimeter troubleshooting to determine the cause. Probably the easiest and simple solution is going to be remove the alternator from the plane and take it down to one of the Big Chain auto parts stores like Advance Auto or Pep Boys Etc. Have them bench test it for you.
Charlie
 
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plane power alternator failures seem pretty common, from my observation.
Best to first check the three wire connector. These are known to fail and the fix could be that simple. A search will show the details.

Larry

I just completed some panel work. When I started the plane up again after the work, my Alternator-out indicator light did not extinguish after starting the plane. I double-checked that the wires to the starter switch and the Alt/Batt switch had not become disconnected. When I pulled the indicator light out of the panel, I accidentally shorted the leads. Now the alternator-out light doesn't illuminate at all, even when it should (i.e. when BAT is on but ALT is off).
The Alternator Field circuit breaker did not trip, and I checked the relevant fuses.
When I start the plane, my voltage only shows 12.4 volts, and 0 amps.
So I don't know if I have a wiring problem somewhere, or if my alternator is fried.
I have a PlanePower alternator.
How should I test/diagnose this situation?
 
Let me sequence what I think you said:
- The alternator worked fine before you did the panel work.
- The alternator did not work at all after the panel work (as evidenced by the zero output and alt out light)
- To add confusion, your alt out light now does not work after you shorted the leads.

My thoughts:
- I suspect the alternator is just fine. Ring out the source power line going to the alternator (as in measure voltage to ground with the master on and the alt source breaker/switch/fuse on, engine off). I suspect you will not have any voltage and the reason why the alternator is not working.
- For the alternator light (the second connection in addition to the source voltage in the little alternator plug), the alternator does not provide power to this light, it does provide a ground when the alternator is not running (thus the light comes on). The +12vdc to the light comes from someplace else - as in a fuse or breaker. When you shorted the leads I suspect you popped this fuse or breaker.

Carl
 
Back to basics . . .

First, the alternator wire that has the jumper (the I terminal in the center) must be connected to the hot side of the battery (+12V). As Carl mentions, that should be your first stop with the volt meter. Without the engine running but master on, alt on, test that (center) terminal should yield battery voltage with the "-" probe grounded to the alternator.

IF you have 12 volts, equal to battery voltage, then you have just validated the field supply and a rough test of the ground. The field grounds through the alternator case back to the battery ground. It must be low resistance.

If you dont have 12 volts (battery voltage) then fix that first (see below). If you do, then install the connector (potted, right?) and the alternator will work, or it is bad (unlikely).

That's all for now, report back with results.

Edit - it seems you have been flying this plane for a while, maybe not the builder? There is a builder trick where the 5 amp fuse for the field is hidden in the wiring, like the "mayhem" guy in the TV commercials.
 
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Ok, this is weird. It magically started working again.
The issue with the lamp was a fuse. Fixed that. then I pulled the plane out and fired it up again, and the alternator worked normally. Good voltage, and the alt-out lamp extinguished as it should.
The Plane Power documentation says that in the event of an overvoltage condition the alternator disables itself. Could it be that there is some kind of timer that re-enables it after a period of time?
Another question - is it possible that my battery-saver trickle charger could affect the alternator if I turned the ALT switch on while the charge is connected to the battery?
 
Ok, this is weird. It magically started working again.
The issue with the lamp was a fuse. Fixed that. then I pulled the plane out and fired it up again, and the alternator worked normally. Good voltage, and the alt-out lamp extinguished as it should.
The Plane Power documentation says that in the event of an overvoltage condition the alternator disables itself. Could it be that there is some kind of timer that re-enables it after a period of time?
Another question - is it possible that my battery-saver trickle charger could affect the alternator if I turned the ALT switch on while the charge is connected to the battery?
Short answer - yes. Don?t use these chargers but if you really must anyway, never run anything in the plane with a charger connected.
Such chargers have killed more batteries than they are worth.

Carl
 
I'm an internet expert and know internally regulated alternators (read pet subject for which I have opinions, some of which are right).

First you have I assume a ND clone. Not slim clones or rebuilds are the same quality or even design as the original.
Second opinion by shorting the charge light you shorted out the voltage regulator and it's kaput.
Third and this a fine point internally regulated alternators do NOT havew a "Field Wire". The field is looped internally from the rectifier (B lead or output back through the VR).
Fourth the IGN wire is a way to make the alternator "sleep" and is an indirect control over the field.
Fifth turning the IGN wire off and on while its spinning and under load is a good way to blow the internal voltage regulator as is shorting CHRG LT.
Sixth not all counterfeit of counterfeit Taiwanese China cli6ne ND alternators and their internal Voltage regulator are the same. Genuine ND from Japan made in Japan is best but some of these are way out if production, especially the small light compact models. There are new ND's you can buy and high quality clones (and poor quality). You will pay more (way more) for NEW genuine ND. Those are far more likely to NOT die from a short or monkeying with IGN lead power (on/off) while running. Quality clones are out there.

I recommend (my opinion) not counting on ignition power to kill alternator in flight for say runaway voltage but put a manually trip in the B-lead, like a panel mounted CB or relay with OV protection. OV is very unlikely with a quality genuine ND or even quality clone (some clones are excellent but there is garbage out there with VR's filled with sawdust and rocks). With that said a day VFR airplane with modern Electronics with its own over-voltage protection you may not even want to worry about it. Internet expert switch off.
 
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I'm an internet expert and know all about internally regulated alternators (read pet subject for whicI have opinions, some of which is right).

First you have I assume a ND clone. Not slim clones or rebuilds are the same quality or even design as the original. Second opinion by shorting the charge light you shorted out the voltage regulator and it's kaput. Third and this a fine point internally regulated alternators do NOT havew a "Field Wire". The field is looped internally from the rectifier (B lead or output back through the VR). Fourth the IGN wire is a way to make the alternator "sleep" and is an indirect control over the field. Fifth turning the IGN wire off and on while is a good way to blow the internal voltage regulator as is shorting CHRG LT. Sixth not all counterfeit of counterfeit Taiwanese China cli6ne ND alternators and their internal Voltage regulator are the same. Genuine ND from Japan made in Japan is best but some of these are way out if production, especially the small light compact models. There are new ND's you can buy buy and high quality clones (and poor quality). You will pay more (way more) for NEW genuine ND. Those are far more likely to NOT die from a short or monkeying with IGN lead power on/off) while running.

I RECOMEND not counting on ignition power to kill alternator in flight for say runaway voltage but put a manually trip in the B-lead, like a panel mounted CB or relay with OV protection. OV is very unlikely with a quality genuine ND or even quality clone (some clones are excellent but there is garbage out there with VR's filled with sawdust and rocks). Internet expert switch off.

Dear Mr Internet Expert, the OP stated that the alternator is a PLANE POWER. ;)

It has a special brush holder with the tab that usually connects to the B buss severed and attached only to the "I" terminal in the connector. It is not an ND clone although it uses many components of the ND design. The regulator housing is like the ND, but the module (big chip) is custom. I suspect it contains the OVPM.

Edit - Oh - it is made by Unipoint, Taiwan.
 
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