Alternator off when landing

Hallo.

I've been flying with my -9A since 2011 with 0 problems.
My electrical system is the Bob Nuckoll's Z-11 with a Bandc L-60 alternator and a L3C voltage regulator, mounted on the engine side of the firewall.

After 4 years of flight alternator breaker sometimes pops when running the engine after say a month (hangar cold and humid). After a few minutes, maybe wire contacts dries and alternator goes on again. Bandc told me to perform the regulator troubleshooting but I didn't do it, yet.

Now, in the last flights, in different days, the alternator goes off in the middle of the approach, just before landing. I bought a new battery, but still haven't installed. The installed PC680 has 6 years. It is still capable to turn the engine, even if I suspect it is getting old.

Before changing the battery (behind the baggage bulkhead, so 1 hour of work), I am wondering if the problem is the battery or not (i.e.: regulator). Is reasonable for a cranking battery to die when asked for a huge load (i.e.: all lights on, engine at minimum and so alternator not producing power)? Is possibile that the alternator breaker goes off because the battery voltage drops under 10 volts? Or the problem is located in the regulator?

Thanks.
Camillo

Replace the field wire and it's connector at the alternator and call it a day.

I have some ideas, but need a bit more clarity. Which breaker pops? Is that the field or the alt output? You say the alternator stops. Please elaborate.

I would aboslutely replace the battery. Batteries can hold enough charge to crank an engine and still hold a low voltage /refusing to increase drawing large current, over-driving your alternator.

Even if it is not the cause, your battery has passed it's usefull service life and is almost as likely to hurt than help you at this point.

Larry

I agree that we need to know which breaker pops. I have seen several planes with 60A alternators and 35A alternator breakers. The breaker doesn't pop after start normally because the alternator cannot put out more than 35A at idle, and by the time the power I crashes, the battery is mostly charged back up. If it pops on landing, maybe it is because of turning on landing lights and so on, exceeding the 35A capacity.

In short, we need more information to be able to make recommendations.

Replace the 6 year old battery anyway... it's done it's duty...

az_gila said:

Replace the 6 year old battery anyway... it's done it's duty...

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Why not do a capacity test on the battery before throwing it away? I can't see a good reason to trash a battery if it passes a capacity test.

1001001 said:

Why not do a capacity test on the battery before throwing it away? I can't see a good reason to trash a battery if it passes a capacity test.

Click to expand...

A good reason to replace a 6 year old battery is that it is WAY more likely to fail or cause problems than a new battery. Murphy tells us that the problem is most likely to occur at a time we're least prepared to deal with it. I normally agree with your logic, but not with wearable components as finnicky as batteries. This is especially true if the user is not familiar with the failure modes and the symptoms they can cause.

Larry

60 amp alternators get a 70 amp output breaker. That and a good battery.

Carl

I've never actually seen a 70Amp breaker, but I always install 60Amp breakers on the alternator and have never seen them pop. The breaker, of course, is to prevent the wire from failing.

From the B&C Website: "They are typically sized 1:1 against the alternator?s rated output (i.e. a 40 Amp alternator would require a 40 Amp current limiter)."

Carl Froehlich said:

60 amp alternators get a 70 amp output breaker. That and a good battery.

Carl

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As it has been said, breakers protect wires, so if you install a 70amp breaker then the wires had better be sized for 70 amps. If you have a 60 amp alternator use a 60 amp breaker abs size the wires for 60 amps CONTINOUS load.

Bob burns
Rv-4 n82rb

n82rb said:

As it has been said, breakers protect wires, so if you install a 70amp breaker then the wires had better be sized for 70 amps. If you have a 60 amp alternator use a 60 amp breaker abs size the wires for 60 amps CONTINOUS load.

Bob burns
Rv-4 n82rb

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I'll have to disagree.

Don't look at a 60 amp alternator as a device that will only put out 60 amps. They will and do exceed 60 amps depending on circumstances and the tolerances of the alternator itself.

I have had a 60 amp breaker pop on a 60 amp alternator - two different airplanes. The 70 amp breaker is the correct selection for this application.

Here is one place to get one: http://www.aircraftspruce.com/catalog/elpages/70amp.php

Carl

Alt breaker

I have a 60amp alternator and breaker. My breaker has popped off occasionally when I take off with hallogen landing lights on. I think it's related to a depleted battery charge, high electrical demand and high engine revs resulting in max alternator output. John

Thinking of trying a 60A ANL current limiter for the alternator B lead protection myself, rather than a circuit breaker.

Yes, get a new battery.

az_gila said:

Replace the 6 year old battery anyway... it's done it's duty...

Click to expand...

Absolutely. B&C recommends changing them every two-three years whether they need it or not. That seems like overkill to me, but I changed my last BC-100-1 at 3 years. It's one less thing to worry about. The charging voltage on these is supposed to be 14.6 +/- 0.2 VDC.

In my opinion, the battery itself part should be the very last thing to check in B-lead CB-trip troubleshooting.

Hint: Somebody find the B-lead CB or fuse in their car, and we can talk.

Charlie

edit:
OK, just re-read the OP's description, scrolled through all the responses, and realized that he didn't specify if it's a B-lead CB that's tripping; he just says that 'the breaker' is tripping and alternator is going off-line. He also says that it's wired using Aeroelectric Z-11. Z-11 (correctly) doesn't use a B-lead CB. So if it's wired to Z-11, then it's the field CB that's tripping. That's likely why B&C told him to run the regulator checklist. The field CB could trip due to the CB itself being bad, or due to an overvoltage condition, which the L3C monitors (which means that it's policing itself).

So, Camillo:
A weak battery could easily have enough power to *start* the engine (typically takes about 5% of the total *energy* in a healthy battery), but not have enough *energy* to run all the loads for many minutes. If that's happening, the alternator may be asked to supply everything it's got to keep bus voltage at the regulator set point. BUT. That will *not* cause the field CB to trip.

Now, if you actually have a B-lead CB, instead of the ANL link recommended in Z-11, and the CB has the same rating as the alternator, then it *could* be tripping due to overload, as others have mentioned.

Charlie

rv7charlie said:

the alternator may be asked to supply everything it's got to keep bus voltage at the regulator set point. BUT. That will *not* cause the field CB to trip.
Charlie

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That is not correct. It maybe correct in your installation, but not universally. The field current increases with the output of the alternator. More accurately, the amount of current fed through the field determines the current output of the alternator. This field current must be sourced from the input power to the VR, which is ypically protected by the field CB.

I have a 45 amp alternator. I once took off after not recharging a drained battery. This caused my alternator to run up to 50 amps, where after 10 seconds the 5 amp field CB would pop. Turns out my alternators requires over 5 amps of field current to drive 50 amps of output. A 7.5 amp CB eliminated the issue.

Larry

So, did it pop the *properly sized* field CB?

rv7charlie said:

So, did it pop the *properly sized* field CB?

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Define "properly sized." I followed the research I did on this site when choosing the 5 amp. Clearly it wasn't right for my alternator. I can blame only myself, but had no access to the specs for my alternator. The only way to know the proper CB size is to know the max current draw on the field from the manufacturer of the alternator. Do you know the specified max current draw on the field for the OP's PP 60 amp alternator? Do you know the rating of the CB on the OP's plane?

Larry

Thank-you very VERY much for your input.

I have an ANL60 current limiter, as per Bob diagram, and a 5 amp alternator field CB. This CB is the one who pop's.

By the way, I have both landing and taxi halogen lights off (don't know if burnt or the wiring; CB do not pop). This may be connected to the alternator/regulator issue.

Yes, I will change my battery on saturday and perform the LR3C troubleshooting check.

Before and during flight I have the same stuff on as per landing (alternator field, all radios and DME, strobe and position lights, for say a 18 amperes load: no landing and taxi...). So, problem rises when I take off power. Regulator speaks to field CB and tells him: high current? Boh.

Maybe I should try to try incremental solutions. I.e.: regulator troubleshooting first.

Thanks.
Camillo

rv7charlie said:

...Hint: Somebody find the B-lead CB or fuse in their car, and we can talk. :-...

Click to expand...

Its very common for cars to have a fusible link right at the alternator. Thats what I use on my airplanes. I carry a spare link and crimp in my toolbag in case my setup "trips" while out and about.

What size is my alternator?

I have a Prestolite alternator out of an R22 helicopter. I have searched high and low for info on how to tell its input and can't find any.

Would anyone here know how I might find out?

Your battery has done its duty I would change it before doing much of anything else.

Mike,

It's been a long time since I've needed to actually find the link in a car; they may well be mounted near the alt in current cars. But that's not the place they're actually needed. Follow the logic of system design. You need the B lead to be large enough to: A. carry the full output of the alt without excessive voltage drop due to resistance (which will render the next point moot), and B. remain cool enough at full alt output that the insulation isn't at risk of melting or burning. Any wire size smaller than that means you're carrying unnecessary alt weight, since you can't get the power to your systems. And if it's sized correctly, the alt can't damage the wire. (Reason follows.)

One of the characteristics of field wound alternators is that they can put out what they can put out. They can't be damaged by overload; the output voltage just starts dropping when they reach their limit (which means that the field voltage is also limited, to the battery voltage and/or the alternator output voltage.

So, if the B lead wire can handle the max output of the alt, what's being protected? Answer: the wire should be protected *from the battery*. The battery can supply hundreds of amps. If the alt fails shorted to ground, the battery can easily supply enough current to melt the insulation; perhaps even start a fire. The car mfgrs may be working with the assumption that their wire loom routing and installation make it virtually impossible to have a B lead get chafed and shorted to ground somewhere along its run, so they place the fusible link near the alt to make it more accessible (or easy to manufacture). However, most of the stuff we're doing as homebuilders, especially with 'systems' installations, is much closer to 'one-off' prototyping than proven in millions of installations. We are at much higher risk of mis-routing a wire to avoid damage. It follows that the B lead protection should be on the end facing the battery.

Charlie

Camillo said:

Thank-you very VERY much for your input.

I have an ANL60 current limiter, as per Bob diagram, and a 5 amp alternator field CB. This CB is the one who pop's.

By the way, I have both landing and taxi halogen lights off (don't know if burnt or the wiring; CB do not pop). This may be connected to the alternator/regulator issue.

Yes, I will change my battery on saturday and perform the LR3C troubleshooting check.

Before and during flight I have the same stuff on as per landing (alternator field, all radios and DME, strobe and position lights, for say a 18 amperes load: no landing and taxi...). So, problem rises when I take off power. Regulator speaks to field CB and tells him: high current? Boh.

Maybe I should try to try incremental solutions. I.e.: regulator troubleshooting first.

Thanks.
Camillo

Click to expand...

I'd definitely start with B&C's regulator troubleshooting guide. If the 5A field CB is tripping while running the engine at near max rpm, The 1st thing I'd think of would be overvoltage due to the regulator not doing its job. Do you have any kind of data logging in your plane? Some engine monitors record various parameters, including bus voltage. That would tell you if bus voltage is rising above the overvoltage protection threshold (B&C's install guide says that's 16.0volts).

If you don't have data logging, you can monitor your volt meter during operation to see if system voltage is going too high. If you can borrow a 'peak-hold' volt meter, it will be much easier to tell if voltage is going too high.

If it's not going too high, then that points to either a bad CB (tripping at too low a current), or a defective overvoltage protection circuit in the L3C regulator.

If voltage *is* going too high, that indicates a problem with the L3C's regulator circuit. It's set point might have drifted too high, or it might just be defective.

Hope that helps,

Charlie

Camillo said:

Thank-you very VERY much for your input.

I have an ANL60 current limiter, as per Bob diagram, and a 5 amp alternator field CB. This CB is the one who pop's.

By the way, I have both landing and taxi halogen lights off (don't know if burnt or the wiring; CB do not pop). This may be connected to the alternator/regulator issue.

Yes, I will change my battery on saturday and perform the LR3C troubleshooting check.

Before and during flight I have the same stuff on as per landing (alternator field, all radios and DME, strobe and position lights, for say a 18 amperes load: no landing and taxi...). So, problem rises when I take off power. Regulator speaks to field CB and tells him: high current? Boh.

Maybe I should try to try incremental solutions. I.e.: regulator troubleshooting first.

Thanks.
Camillo

Click to expand...

When you pull the power to idle with an 18 amp load, this likely falls below the current produced by the alternator at idle RPM. THis causes the volts to drop and the VR calls for more power by upping the field current. However, the alternator will only draw a field current level somewhat consistent with it's output level (should be well below 5 amps at an 18 amp output). The fact that your field CB is popping is most likely related to the VR. Could be a bad VR, bad ground to the VR or a poor connection on one of the wires to the VR (internal or external). Bill may be able to expand upon this, but a problem with the commutator or brushes could possibly cause an uncontrolled draw on the field, leading to a tripped breaker. All of this points to an alternator issue, given the VR is built into alternator.

It is suspicious that you only pop the breaker at idle at the end of your flight and not at idle at the beginning of your flight. is anything different in these to phases of flight, related to your electrical system or load? It's worth considering that heat is a factor. The VR is an electronic device and it is quite common for modern electronics to fail hot but not cold. Most CB's used are thermal based and will take many seconds to trip when only marginally above their rated current. Something to think about in your troubleshooting.

If you have some type of overvoltage protection circuit ii would be a suspect. They react to overvoltage by running up the current on the field to force the CB to pop. This circuit could be failing or it could accurately be detecting an over-voltage condition.

Larry

lr172 said:

Define "properly sized." I followed the research I did on this site when choosing the 5 amp. Clearly it wasn't right for my alternator. I can blame only myself, but had no access to the specs for my alternator. The only way to know the proper CB size is to know the max current draw on the field from the manufacturer of the alternator. Do you know the specified max current draw on the field for the OP's PP 60 amp alternator? Do you know the rating of the CB on the OP's plane?

Larry

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I feel like we're having a Struther Martin moment. You're telling me I'm wrong in my statement, because you couldn't find good documentation on proper sizing of your CB.

;-)

rv7charlie said:

I feel like we're having a Struther Martin moment. You're telling me I'm wrong in my statement, because you couldn't find good documentation on proper sizing of your CB.

;-)

Click to expand...

Actually I was saying your were wrong because you stated that something universally couldn't happen and I was providing evidence that your claim was inaccurate and is instead based upon the unique requirements of the alternator.

I don't desire to be argumentative here, just want to be sure we leave good data points for those that will use this in the future. more detail means more contextual knowledge. This level of detail would have helped me when I first searched this issue. Instead, I found universal statements that 5 amps is what's needed and clearly that wasn't the case in my setup.

Larry

lr172 said:

When you pull the power to idle with an 18 amp load, this likely falls below the current produced by the alternator at idle RPM. THis causes the volts to drop and the VR calls for more power by upping the field current. However, the alternator will only draw a field current level somewhat consistent with it's output level (should be well below 5 amps at an 18 amp output). The fact that your field CB is popping is most likely related to the VR. Could be a bad VR, bad ground to the VR or a poor connection on one of the wires to the VR (internal or external). Bill may be able to expand upon this, but a problem with the commutator or brushes could possibly cause an uncontrolled draw on the field, leading to a tripped breaker. All of this points to an alternator issue, given the VR is built into alternator.

It is suspicious that you only pop the breaker at idle at the end of your flight and not at idle at the beginning of your flight. is anything different in these to phases of flight, related to your electrical system or load? It's worth considering that heat is a factor. The VR is an electronic device and it is quite common for modern electronics to fail hot but not cold. Most CB's used are thermal based and will take many seconds to trip when only marginally above their rated current. Something to think about in your troubleshooting.

If you have some type of overvoltage protection circuit ii would be a suspect. They react to overvoltage by running up the current on the field to force the CB to pop. This circuit could be failing or it could accurately be detecting an over-voltage condition.

Larry

Click to expand...

Larry, when I start the alternator, all stuff are shut off and the engine is 1.000 rpm. Then, I switch on avionic master, strobe and position and before take-off also landing, taxi and pump.

I have to add that some time ago alternator field breaker popped just after engine has started. Finally, after a lot of investigation I founded there was water inside the regulator (this is because I mounted it in the upper part of the engine FF side and when rains water maybe enters between the cabin skin and the cowl skin and enters the regulator, too, even if it has a rubber cover on top; friend of mine told me that a regulator should be mounted upside-down; I plan to do this and move it inside the cabin, at the next annual inspection). Maybe it has ruined from then.

However, the strange thing is that the battery cranks the engine, the alternator works will all the stuff on during all the flight, expect from the last landing segment. That is why I wrote, because it seems to me that this is connected to the lower alternator output AND battery wear AND, maybe, poor regulator management control. Or every combination of those.

Thanks.
Camillo

Finally, I changed airplane battery with a fresh new Odyssey PC680 equivalent one. Meanwhile, I discovered that the LR3C regulator was not working well. During the test, I read 0 volts where I should have read at least 9 volts.
I am sure it was ruined after getting water inside.
New unit now arrives with a "place inside che cabin" and "do not let water to reach the unit" label, which I am almost sure was not present in 2010, when I bought it.

I made some proofs, today, on some aborted take-offs (could not go in air for legal reasons), and all is working well. Engine starts quickly and alternator goes on and doesn't go off.

Edit: problem solved