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Alternator Help Request

J

jtppalmer050390

Member
I have the nippondenso alternator and have been using it for 135 hours and it has worked perfect. Then all of a sudden my Dynon shows 11.8-12v when any draw is placed on the battery. I did some trouble shooting and determined the alternator was working but only putting out 12.1 volts. I took it to the auto parts store and they said it was working fine but I made hem replace it anyway since it had a lifetime warranty. I put the new alternator on the plane and it is doing the same thing!!!! Don't know what in the world could have caused this. The alternator wiring is simple. Two wires used. One to the B lead and one wire to the switched live post. Any advice would be helpful.
 
internal regulator. weird thing is it has worked perfect for a year and a half. nothing has changed other than I had to change the one amp inline fuse to the dynon that is on the shunt.
 
Have you checked your battery for corrosion on the terminals? What you're describing sounds like a poor conduction path.
 
Measure the output with a different meter, i.e. DVM. Whatever took out the shunt fuse may be degrading the Dynon measurement .

Dave
 
If the alternator is truly ok, and it should be if new, then assume it is making the correct voltage at the B+ post. Then think - that means it has a bad ground, or a bad connection for power to the system. You know your system, so go from there. If you know it well, then don't assume all your terminals are good cause they were when they were made, grab the wire and pull against the terminal. The pull test is over 100 lbs (for #8 AWG) , so don't worry that you will fail it in this test.

You may have to connect some smaller voltage sensing wires and run to cockpit so you can check some voltages safely when the engine is running. Like a shielded 24AWG.

Happy hunting.
 
If you can't find what is wrong (wiring is OK):

Take it to an Auto parts store to see if it is DOA or not. If it is DOA, it might only need a diode board replaced - not too expensive. If there is an alternator repair shop locally, you're in luck! I get 'em repaired locally for about $50.

If you want to change out the diode board yourself, it's not that difficult - I saw it done on a truck tailgate once. Un-bend and re-bend the 4 leads carefully. It ain't Rocket Science!

Check your wiring and terminals first, please.

Carry on!
Mark
 
Alternator is brand new. Current wiring has worked for 1.5 yrs and 135 hrs. Nothing has changed.

On the three pronged nippondenso alternator, do you guys only hook the IG to a switch? Do you hook the "S" lead to the battery?? For the last year, I had no "S" connection from the alternator to the battery. I see it both ways. The one on vans aircraft only shows a B lead and IG lead hooked up.
 
With all due respect, something HAS changed or you would not be here. If you do not have a dedicated ground from the engine/alternator to the battery (or equivalent), your alternator is using other wiring for a ground source.

If you have a the engine/airframe ground, make sure its resistance is .5 ohms or less. Cables can corrode internally and cause weird issues.
 
Ground !!

I agree with Ray. Make a temporary wire (#14 or so) and connect it from the alternator "ground" to the battery. The last thing you touched was the alternator so, the more likely it's a ground problem.
Also, there were many threads on that connector on the Denso as a fault
problem. John
 
jtppalmer050390 said:
Alternator is brand new. Current wiring has worked for 1.5 yrs and 135 hrs. Nothing has changed.

On the three pronged nippondenso alternator, do you guys only hook the IG to a switch? Do you hook the "S" lead to the battery?? For the last year, I had no "S" connection from the alternator to the battery. I see it both ways. The one on vans aircraft only shows a B lead and IG lead hooked up.
Click to expand...

It is broke, but nothing changed, what is wrong? Something.

I see you are in a medicine not engineering profession, so read the attached for basics. The alternator voltage is controlled by the voltage to the field. The regulator must sense an output voltage in order to control the output. The sense voltage wire S, might also be the field voltage supply. So, no voltage (from the system) to S, no field and no output. I take it you did not build this bird, so there is also a 5 amp fuse in that sense wire to the S post. You need to verify that the sense wire at the alternator is getting battery voltage when the switch is on even if the engine is not working. If you have voltage, then, it might be the terminal connector to the alternator - the reference Mike as posted below.

http://www.autoshop101.com/forms/alt_bwoh.pdf
 
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Check out the switch wire terminals (female) in the connector at the Alternator, they may have spread a bit with vibration - worth a look :)
 
BillL said:
It is broke, but nothing changed, what is wrong? Something.

I see you are in a medicine not engineering profession, so read the attached for basics. The alternator voltage is controlled by the voltage to the field. The regulator must sense an output voltage in order to control the output. The sense voltage wire S, might also be the field voltage supply. So, no voltage (from the system) to S, no field and no output. I take it you did not build this bird, so there is also a 5 amp fuse in that sense wire to the S post. You need to verify that the sense wire at the alternator is getting battery voltage when the switch is on even if the engine is not working. If you have voltage, then, it might be the terminal connector to the alternator - the reference Mike as posted below.

http://www.autoshop101.com/forms/alt_bwoh.pdf
Click to expand...


I'm betting Bill is right here! That is a great explanation of how the alternator works and how to troubleshoot it.
 
Just for reference a fully charged battery is 12.6 not 12.1. an AGM battery is around 13.0 so if you were at 12.1 your battery was 20-50% discharged.
 
jtppalmer050390 said:
Alternator is brand new. Current wiring has worked for 1.5 yrs and 135 hrs. Nothing has changed.

On the three pronged nippondenso alternator, do you guys only hook the IG to a switch? Do you hook the "S" lead to the battery?? For the last year, I had no "S" connection from the alternator to the battery. I see it both ways. The one on vans aircraft only shows a B lead and IG lead hooked up.
Click to expand...

I would argue that something HAS changed, you just haven't found it yet. You should run a temp wire directly to the B lead and measure voltage while running. If you are getting ~14 volts, then you need to find the reason that you are seeing 12V downstream. A bad connection adding resistance is the most likely culprit or even an open somewhere. You should also measure the resistance of the ground wire feeding the alternator.

Larry
 
BillL said:
It is broke, but nothing changed, what is wrong? Something.

I see you are in a medicine not engineering profession, so read the attached for basics. The alternator voltage is controlled by the voltage to the field. The regulator must sense an output voltage in order to control the output. The sense voltage wire S, might also be the field voltage supply. So, no voltage (from the system) to S, no field and no output. I take it you did not build this bird, so there is also a 5 amp fuse in that sense wire to the S post. You need to verify that the sense wire at the alternator is getting battery voltage when the switch is on even if the engine is not working. If you have voltage, then, it might be the terminal connector to the alternator - the reference Mike as posted below.

http://www.autoshop101.com/forms/alt_bwoh.pdf
Click to expand...

I don't know this alternator, but do believe that many alternators pull the sense voltage from the B lead, even if they have and S lead. You'll need to some research for your alternator.
 
Do you have the ability to turn on and off your alternator from possibly an alternator switch and or do you have a main breaker on the output of the alternator? Would probably be the " big" one. Might look for problems or bad connection in either of these devices. Would also be nice to set up the new alternator on a bench test and see its output up to at least 13.6 v . Also as mentioned in earlier, ground wire and terminals might be suspect. Good luck.
 
You need to check the single wire from your bus to the alternator. This is the "voltage sense" for the regulator. This tells the regulator what the system voltage, and or load is. When you turn your alternator field switch on, it sends the regulator bus voltage. The alternator will not charge if you have a problem with this supply voltage. Unplug the alternator and use a test light to verify that you have battery voltage. Don't use a high impedance meter. If it lights up the test light, then use a meter to test the voltage at the wire, then at the battery. The two voltages should be within .1V of each other. I'll bet there's nothing wrong with your alternator.
You should also refer to Van's service bulletin regarding improperly crimped terminal ends on Van's supplied cables. These are the pre-made cables. They weren't crimped with the proper die. I've seen one case where the oil and fuel pressure readings were erratic. This started several years after the plane was first flown. It was caused by an erratic ground potential due to a loose crimp. The engine would start fine but the ground potential would vary during flight. The cables were sold somewhere back around 2006? You can grab the cables and apply back and forth pressure. You'll be able to see movement of the wires inside the crimp. If you have these bad cables, remove all of them and have them recrimped. And yes, things can change all by themselves. This problem changes over time, varies with bus system load and will change with variations in operating temperature. This change in ground potential will cause variations in voltage on the "single wire".
 
Wanted to follow up with everyone. Thanks for the advice. I learned a lot about wiring!! Anyway, after everything, it turned out to be the Main B lead 60 amp fuse was blown and when I inspected it the first time I didn't notice it was blown. Very easy fix. Pain in the butt to find!!!
 
jtppalmer050390 said:
Wanted to follow up with everyone. Thanks for the advice. I learned a lot about wiring!! Anyway, after everything, it turned out to be the Main B lead 60 amp fuse was blown and when I inspected it the first time I didn't notice it was blown. Very easy fix. Pain in the butt to find!!!
Click to expand...

How did you blow a 60 amp fuse? Have you recently had a dead battery?
 
jtppalmer050390 said:
Wanted to follow up with everyone. Thanks for the advice. I learned a lot about wiring!! Anyway, after everything, it turned out to be the Main B lead 60 amp fuse was blown and when I inspected it the first time I didn't notice it was blown. Very easy fix. Pain in the butt to find!!!
Click to expand...

Glad you figured it out. I would be very interested to know what caused that to blow. This is not an insignificant event and a cause should be found sooner rather than later. It is possible that the old alternator caused it, but not likely given it's clean bill of health from testing. I recommend against "righting this off" to an unknown event. The risk here is not just losing power, but also potential electrical fires. As a previous poster mentioned, it could have come from a dead battery. What is the rating of your alternator? They often don't exceed their rated capacity.

Larry
 
I thought the primary purpose of the 60-amp fuse was to protect against a shorted alternator, rather than a run-away alternator?
 
It is a 60 AMP alternator. I am not 100% sure what caused the fuse to blow. It has been in service for a year and a half. The battery is still good. I have an off switch for the alternator. I always watch the Dynon amp meter and never have seen an output over 27 amps.

The only thing I did when I was trying different things is connect a wire from the G lead to the battery. I did this trying to determine why the Dynon was reading incorrectly. I am thinking somehow this blew the fuse. Not 100% sure. Everything is working fine now. If another fuse blows, I will readdress this issue in the forum!! Thanks for the input.
 
I see the real danger coming from the battery side of the fuse. If the cable shorts out before the fuse, you have 100's of AMPS to ground and the show would look more like a welding exercise. Even after the fuse, it would still be quite a show as the cable would need to stay in contact to blow a 70 amp fuse.

I guess I need the need for the fuse explainde to me.
 
I just went through this with my Plane Power alternator.

It turns out there was no problem with the alternator; however, my plane has 700 hours on it and the pullable breaker for the excite field had some minor corrosion on it. After cycling the breaker 20 or 30 times, the problem went away and has not returned.

Now, I make it a habit of pulling all the breakers and resetting them at least once a month.
 
gasman said:
I see the real danger coming from the battery side of the fuse. If the cable shorts out before the fuse, you have 100's of AMPS to ground and the show would look more like a welding exercise. Even after the fuse, it would still be quite a show as the cable would need to stay in contact to blow a 70 amp fuse.

I guess I need the need for the fuse explainde to me.
Click to expand...

Diode failure in the rectifier and/or short in the alternate circuit to ground. Protects that wire. It is possible this is a hold out from older technology alternators, i don't know. I wish we had B&C folks that could chime in.
It is generally accepted that the battery wiring to the main bus is not fused or limited. I guess battery failure or circuit shorts are rarer than alternator shorts, which seem pretty rare too.
 
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