Alternator arching problem - Ideas?

[patterson]

I have a ND internally regulated alternator that has been on my RV-4 for 260+ hours now and has performed flawlessly so far. I recently noticed a bunch of pin holes, like something was trying to work itself out of the back of the alternators' thin cover on the back side of the unit. It is the little thin cover that protects the electronics, and it is pitted and slightly beaten out (from the inside!) Looks like somethnig was trying to work its way out of the case.

I removed the unit and took off the cover. I discovered that there has been some arching for the main shaft to the rear cover and that some of the metal is now fused to the rear of the shaft. The cover appears to have a thousand small smacks going outward and has actually altered the shape of the cover slightly.

My question is what the heck is causing this, and how can I resolve it? I don't like replacing something until I know what caused the problem in the first place.

thanks,
Ron

[Yukon]

If you buy a Plane Power alternator, I don't think you will have any regrets.

[gmcjetpilot]

Originally Posted by patterson

I have a ND internally regulated alternator that has been on my RV-4 for 260+ hours now and has performed flawlessly so far. thanks, Ron

First Yukon's suggestion is a good one. Second it's probably NOT a ND alternator, its a clone made from several companies, typically in China (which does make a difference, not all clones are alike and none are ND's).

Do you have a picture?

YOUR Description, weird and fascinating. You say it works still? Humm. It sounds like some kind of arcing between the brushes and metal cover and/or the two "slip rings". (The slip rings are the two surfaces on the shaft that the brushes ride on. See discription below.)

It's possible that the cover got pushed in too far and arcing occurred. The part where its now pushed out is weird. What force would push the cover out, I don't know?

Bottom line its not good and I would consider NOT flying this alternator till you get it inspected and fixed. At least replace brushes by the way; they can only last 300-900 hours depending on conditions, some go longer. Brushes are NOT FOREVER parts. They have two or three thing working against them that does not apply to automotive service:

You fly at high altitudes and the mosture is lower. The low mosture causes brushes to wear faster less dense air, cooling is less. (not sure if lower electrical resistance is a factor but arcing is more likely with less dense air.)

Second, the alternator gets cooked by the #1 pipe like crazy. In a car the alternator sits on top of a water cooled engine that sits behind a relatively LARGE grill has lot's of air, even when the car is not moving. A heat shield on the #1 pipe or alternator (with air blast tube) would be good). Actuall that metal cover is kind of a heat shield the ND has that other alternator don't have. However another shield would be goodness.

Last, vibrations are greater which can cause brush bounce.

Cheap solution:
You could go down to Auto-Parts R Us and get another alternator, off the shelf. It might be good quality. With out knowing what you have I guess you have the "Lester #14684". The part store should know what it is a:
SUZUKI, SAMURAI, 1.3L '95-'85 ALTERNATOR # 14684 The auto-store will give you a warranty as well. The trade in might be small so keep the old one.

Deluxe or Best solution:
Upgrade to a "Plane Power" unit.

Cheers George


**
Alternator basics
The brushes and slip rings transfer voltage to the "FIELD", the rotating electro-magnets on the shaft. The current however is only 5 amps, peak, so arcing is weird. All the "power" comes out of the stator, the windings around the case, the 50 amps for example. It's the rotating magnets or "field" spinning on the shaft, that induces power (current) in the stator, supplying the plane's electrical needs. The stator has three coils, producing alternating current, which gets rectified (bridge diodes) into DC. The voltage regulator, regulates the voltage going into the field (rotating part) so the voltage out of the stator is constant at the desired voltage (eg 14.3v). The more power sent to the field by the VR, the more juice the stator makes. The VR is a "control and feed back" device, which is inversely proportional. If output voltage (stator/rectifier) goes too high, it cuts voltage to the "field", vise verse. It contols the amount of power to the field with transistors and an internal voltage reference.

[cytoxin]

are all diodes installed per vans plans? 14.5 volts is not very likely to cause electricity to jump and air gap. regardless of current. could it be somehow when you switch off the master the collapsing field of the solenoid is finding this is the closet air gap to jump? i would be curious of painted grounds , missing diodes or something like that...how may hours on the plane? did you build it ?

[frankh]

Do it...Buy a Plane Power and forget about it..

Vans (as always) has the best price..the kit is complete with all brackets...Bolts right in there.

Frank