1 Thing to Know When An Alternator Problem Rears Its Ugly Head

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Robe de mariage À smocks At A.E.R.O. we run into pilots and mechanics that are having alternator issues. Before replacing the alternator, consider another option. Jumping to conclusions and replacing an alternator repeatedly won’t get you anywhere.

For the purpose of this article, we will be referring to gear driven alternators and alternator clutches used on Continental 360, 520, and 550 engines.

Evolution of Avionics

An alternator has a small current (1-4 amps) fed through the field terminal and then it multiplies this current. Once this happens, electrical power up to the alternator rating is available at the output terminal.

With modern day avionics being abundantly found in modern aircraft, an alternator producing full rated output at low engine RPMs is a great benefit. Without this evolution, avionics would not be as efficiently utilized as they are today.

A magnetic field is created inside of alternators, and this strength is regulated by an excitement power from the voltage regulator. If the alternator-charged system has a healthy battery and no resistance exists amongst the connections, the voltage regulator will properly vary the excitement current flow to maintain a charging system voltage.

What happens when this doesn’t work properly though?

Avionics can signal an overload by releasing smoke before they completely shut down. This is a costly signal that you never want to see. Once you see the smoke, they will need to be replaced.


The One Area You Overlooked

Typically we receive calls of customers needing new alternators, yet they’ve overlooked one major area.

This area we advise them to take a look at is the condition of the alternator clutch. The clutch is often the weak link causing issues, not the alternator.

The clutch slips when the rubber seal between the gears is deteriorated. Then, the gears begin to spin causing the alternator not to work. This could be caused by the alternator completely seizing up or a clutch failure.


When you replace your alternator, you should be replacing your clutch as well. This is a good habit to get into in order to prevent major issues, such as the one previously mentioned. Overlooking the clutch could be as simple as the new alternator not working or as catastrophic as an engine failure.

Should You Overhaul Your Alternator Clutch to Save Money?

If you are considering overhauling your alternator clutch to “save some money”, consider this first.

Sometimes when using overhauled alternator clutches, you can end up having bigger troubles than you started with. How is that possible?

By spending the money on an overhaul for your alternator clutch you are receiving a unit with the same gears and just a new rubber insert. If your old core has any issues then you will be charged core charge-back fees, adding on to the total of the overhaul. These charges can add up to more than actually purchasing an entirely new alternator clutch.

For this reason, A.E.R.O. offers a no core charge-back guarantee.

Installation Tips

Continental service bulletin 11-3 has numerous tips that should be taken into account when installing an alternator.

Earlier couplings equipped with a drive spring assembly are superseded with P/N 646655 which now has an elastomer section to help absorb torsional vibrations and provide a “shear” section.

This elastomer coupling can continue in service if a torque slippage check is completed. The torque required to slip the coupling elastomer when new must be at least 180 in. lbs. measured after 45 degrees of revolution at a rate of 1 to 2 degrees per second.

When installing the drive coupling assembly on alternators, you must remove the shipping washer. This could cause interference with the face gear on the crankshaft and result in damage to the engine and alternator.

Also, on the 520 and 550 engines, you must use the specific washer and cotter pin that is designed for these engines. If you don’t they may hit the alternator face gear and cause irreparable damage to your engine.


Tips like these are what can help keep pilots flying safely as well as helping you not waste money when you don’t have to.

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  1. November 5, 2015    

    I really like how you said, “Jumping to conclusions and replacing an alternator repeatedly won’t get you anywhere.” I think anytime an alternator issues arises it’s worth looking into fixing it. My brother had problems with his and at first he thought he would simply replace the whole thing. He found out there was only a minor detail that needed to be fixed and it saved him a lot of money and time. So I definitely agree with you about not jumping to conclusions. Thanks for the great read.

    • November 5, 2015    

      We’re glad you agree. There’s no reason in spending more than necessary! Thanks for reading.

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