13.6V alt output?

kevinh · #1 12-09-2005, 07:05 PM

Hi ya'll,

Does anyone around here know anything about the failure mode of ND internal regulated 60 amp alternators? I can ask on AeroElectric, but thought I'd poke around here first.

My alternator has started putting out a mere 13.6V. If I recall correctly the normal output of an automotive alternator is supposed to be 14.8V ish? This voltage is high enough that the battery is not draining, but not high enough to charge an Odessey PC680.

I'm not used to this 'low voltage' failure mode - kinda surprising.

I've checked that the belt is tight, contacts good - anything else I should check before taking the alternator off and trading it in on it's lifetime warantee?

Kevin

bearair · #2 12-09-2005, 07:42 PM

Actually, the typical charging voltage of an automotive system is 13.5-14.0 volts. It should never be over 15 for any reason, and anything over 14.5 is considered too high if it lasts for more than a few minutes. A 12V (12.6 actually) battery should charge just fine at 13.6. The big question is the amperage output. You can use a clamp on style ammeter on the output, or remove it and have it tested.

I'd take a close look at the battery first. If your battery can't supply enough voltage and current to the field windings, it can look like a bad alternator. Just fixed one of those this evening before leaving work. Battery that was less than a year old with a cell failing making it look like the charging system wasn't working. Max charging voltage was only 12.8 but the battery failed on the tester even though it had 12.4V-12.5V with no load or charge to it. After putting a new battery in, the charge voltage was back up to 13.8-13.9 which is right on spec for the car it was in.

FYI. Most newer internally regulated alternators won't charge much over 14.0 volts due to the sensitivity of the computer components in newer cars. 15.0V is enough of a spike to write off a weak component. I've seen electronic climate controls, transmission control modules and engine control modules killed by a voltage spike when jump starting. If you own a computer controlled car, always make sure you turn a load on in the car (lights, fan) before starting the car with the good battery. This will prevent about 99% of jump starting related electronics failures!

dan · #3 12-09-2005, 08:06 PM

Check your engine ground strap(s). Probably not part of the problem, but rule it out first.

)_( Dan
RV-7 N714D (716 hours)
http://www.rvproject.com

sprucemoose · #4 12-10-2005, 01:29 AM

Quote:

Originally Posted by bearair

A 12V (12.6 actually) battery should charge just fine at 13.6.

This may be true for a sealed lead-acid or gel-cell, but an RG battery like the Odessey neads a higher voltage to charge. The Odessey for example requires at least 14.2V.

Ref: http://www.odysseybatteries.com/files/techbook.pdf

Most internally regulated automotive alternators don't put out enough voltage to properly charge sealed RG batteries like the Odessey, which is one more reason not to use them.

OK George, your turn

redbeardmark · #5 12-10-2005, 11:21 AM

Quote:

Originally Posted by kevinh

Hi ya'll,

Does anyone around here know anything about the failure mode of ND internal regulated 60 amp alternators? I can ask on AeroElectric, but thought I'd poke around here first.

My alternator has started putting out a mere 13.6V. If I recall correctly the normal output of an automotive alternator is supposed to be 14.8V ish? This voltage is high enough that the battery is not draining, but not high enough to charge an Odessey PC680.

I'm not used to this 'low voltage' failure mode - kinda surprising.

I've checked that the belt is tight, contacts good - anything else I should check before taking the alternator off and trading it in on it's lifetime warantee?

Kevin

Same problem this fall, except the voltage would wander from 12.2V to 13.3V. Checked the same items, no problems seen. Put in new alternator and life is good again at 14.3V.

Lifetime warantee? Ya mean I got a spare now?

Ironflight · #6 12-10-2005, 01:27 PM

Quote:

Originally Posted by sprucemoose

Most internally regulated automotive alternators don't put out enough voltage to properly charge sealed RG batteries like the Odessey, which is one more reason not to use them.

I guess I'll have to say then that the Oddyssey Battery is one incredible piece of equipment, since I have started my airplane with one at least 150 times in the past couple of months, and if my ND (internally regulated) alternator hasn't been charging it, that is one heck of a reserve capacity!

Hey, not trying to start a war or anything, but something doesn't sound right. Seriously, my ND alternator and Oddyssey battery system seem to be working great, and playing well together.

Paul

vlittle · #7 12-10-2005, 05:54 PM

Slightly off topic, but for those who use Vans's discrete voltage regulators and unregulated alternators, here's a tip that I'll pass along from George McNutt:

Mount the voltage regulator on the firewall, and drill a hole through the firewall to access the voltage adjustment screw from inside the cabin. I mounted a nut plate over this hole so that I can use a #8 screw to seal the hole.

Now, it's easy to adjust the charging voltage with the engine running with getting wacked in the behind with a Sensenich. Crawl under the panel, take out the screw, insert a small screwdriver and make the adjustment. Be sure to securely tie down the aircraft before you do this!

You can see the arrangement I used in the photos below. BTW, the bottom lug of the voltage regulator shares the mounting bolt for my main firewall ground. The top lug uses a nut plate mounted on the aft side of the firewall, and the visible nut plate is the one used for the adjustment screw. The adjustment potentiometer is recessed in the V.R., so the nut plate won't interfere with it.

Vern Little -9A. Panel in, planning first engine start next week.

sprucemoose · #8 12-10-2005, 08:22 PM

Quote:

Originally Posted by Ironflight

Seriously, my ND alternator and Oddyssey battery system seem to be working great, and playing well together.

What is the output voltage on your ND alternator?

Ironflight · #9 12-10-2005, 08:59 PM

Well, it is usually aout 14.2 - 14.3, of course - which is probably why I don't have any problems! So is your point that you shouldn't use internally regulated automotive alternators, or that you shouldn't use ones that don't put out at least 14.2 volts?

Sorry, I don't mean to be obtuse, I simply don't like absolutes. There are LOTS of airplanes flying around with these alternators that work great, and I really don't believe that they are accidents waiting to happen - any more than the old-fashioned, externally regulated Ford alternators in so many light planes. In the 23 years I owned my AA1B, I went through four of those alternators - two of them failed while I was IFR. Do I go around telling people not to buy them, or to throw them away if they have them? No - I tell them that no matter what you have, you should have a backup plan.

Of course, as you point out Jeff, we should probably wait for George's upcoming lengthy posting on the topic...

Paul

sprucemoose · #10 12-10-2005, 11:09 PM

The point I was making, in my own obtuse way, was that RG batteries like the Odessey require a higher charging voltage than other battery types. I was responding to the post which said that the battery would charge OK at 13.6 V, which is incorrect. Of course, I couldn't resist the chance to get in a shot at internally regulated alternators. Come on George, where are ya?

Perhaps we should take this discussion over to the Aeroelectric List and let Bob have his say?