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  #1  
Old 09-06-2022, 11:23 PM
alcladrv alcladrv is offline
 
Join Date: Oct 2006
Location: Southeast
Posts: 666
Default Alternator voltage?

Just completed a 3 hour cross-country flight. One hour into the flight at about sunset, the alternator output voltage dipped to 13.5 volts. It wavered there a bit then slowly climbed back up to 13.9-14.0 volts, where it was when I landed.

I knew the last 2 hours of the flight would be at night. So, I plotted my strategy of maybe landing somewhere while there was still some daylight, but I decided to continue on and watched the voltage like a hawk. I planned to divert at any time. It was about as unnerving as watching a gas gauge decrease and hoping you have enough to make it to a gas station.

Anyway, the alternator (NAPA Gold) has about 850 hours on it. I'm looking to proactively replace it rather than have it fail at some inopportune time/place. Of the 4 alternators I've had over the past 1800 hrs., this one has lasted the longest. 1) NipponDenso from Vans finishing kit (lasted 182 hrs.), 2) Had a local shop rebuild the unit from Vans (lasted 664 hrs.), 3) Purchased rebuilt NAPA Gold (lasted 100 hrs.) 4) The current NAPA Gold unit.

I seem to recall on these forums that a 14.5 volt output is considered good. The question is: Does a vendor consider an output voltage of 14.0 volts to be defective?
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  #2  
Old 09-07-2022, 06:50 AM
PilotjohnS PilotjohnS is offline
 
Join Date: Jan 2016
Location: Southwest, USA
Posts: 2,538
Default Killing it

Something seems to be killing your alternators. Your experience seems to be out of family to others.

Do you think the failure rate of alternators in your plane is in family with everyone else’s experience?

Here are some things to check:

Are there any heat shields on the exhaust, or does the alternator ( backside internal diodes and electronics) see the red hot glowing exhaust pipes?

Is there any air flow to the alternator especially to the backside?

Lastly, is there too much electrical load for the alternator?
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  #3  
Old 09-07-2022, 07:18 AM
BillL's Avatar
BillL BillL is offline
 
Join Date: Sep 2007
Location: Central IL
Posts: 6,850
Default 14.3-14.6 volts for AGM. Lower for EarthX. 13.8.

Actually that is a pretty good average for a commodity rebuilt in god-knows-where factory. I looked at OTS alternator vs PP vs B&C life from a 2016 thread and cost per hour. B&C was the lowest.

Your strategy of the OTS (off-the-shelf) looks pretty good. One thing to be comfortable and reduce failure possibility, is to use one for X hours and then just replace it before it fails. Pick a number for life, and use what they call "new" i.e. all new components (likely clones).

I have a PP w/250hrs and just ordered a backup alternator (weighs less than a 15 min TCW backup battery). Thinking about 14k, mountains, haze, light IFR, no nearby airport and late in the day was becoming less comfortable.

Based on your voltage wander description, replacement seems prudent but technically 13.8 is the age-old industry bottom voltage for PbA. I would say if the listed voltage was 14.5 and it has dropped to 14.0, then it is arguable that it is failing to the counter guy.

850 hrs!! I would be very happy. YHMV.
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Last edited by BillL : 09-07-2022 at 07:24 AM.
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  #4  
Old 09-07-2022, 07:36 AM
RV8Squaz's Avatar
RV8Squaz RV8Squaz is offline
 
Join Date: Feb 2006
Location: Senoia, Georgia
Posts: 976
Default

Quote:
Originally Posted by BillL View Post
Actually that is a pretty good average for a commodity rebuilt in god-knows-where factory. I looked at OTS alternator vs PP vs B&C life from a 2016 thread and cost per hour. B&C was the lowest.

Your strategy of the OTS (off-the-shelf) looks pretty good. One thing to be comfortable and reduce failure possibility, is to use one for X hours and then just replace it before it fails. Pick a number for life, and use what they call "new" i.e. all new components (likely clones).

I have a PP w/250hrs and just ordered a backup alternator (weighs less than a 15 min TCW backup battery). Thinking about 14k, mountains, haze, light IFR, no nearby airport and late in the day was becoming less comfortable.

Based on your voltage wander description, replacement seems prudent but technically 13.8 is the age-old industry bottom voltage for PbA. I would say if the listed voltage was 14.5 and it has dropped to 14.0, then it is arguable that it is failing to the counter guy.

850 hrs!! I would be very happy. YHMV.
13.8 ???

EarthX documentation specifies 13.9-14.6. https://earthxbatteries.com/wp-conte...oduct-Spec.pdf
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  #5  
Old 09-07-2022, 07:54 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
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Default

Quote:
Originally Posted by RV8Squaz View Post
13.8 ???

EarthX documentation specifies 13.9-14.6. https://earthxbatteries.com/wp-conte...oduct-Spec.pdf
Lithium is a different chemistry and runs at a higher steady state voltage than lead acid (~13.1 vs 12.8) and therefore likely a different float voltage range, so not a fair comparison. 13.8 is lower than I would like, but not that bad for lead acid. Autos used to run 13.8-14.0 range many decades ago and I think that is what the other poster was referring to.
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Last edited by lr172 : 09-07-2022 at 07:58 AM.
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  #6  
Old 09-07-2022, 08:01 AM
lr172 lr172 is offline
 
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 7,754
Default

While there is a good chance it is the alternator, it is not necessarily so. Intermittent connection issues in the wiring can also cause symptoms like this. I would go through all the wiring before condemning the Alt. My ND rebuild has gone 750 trouble free hours, but I use an externally regulated version- greater longevity, as the VR sees lower temps than tucked inside the back of the Alt case.

That said, if it is only putting out a max of 14 volts, something is going on and needs to be addressed. While a 14V float is acceptable, it is a sign of something wrong and likely to get worse or fail completely in the near future. Worth looking at that Battery as well, as some flaws in there can pull the voltage down, like intermitent internal open circuits between cells. They expand when hot and this can open a path between cells.
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Last edited by lr172 : 09-07-2022 at 08:13 AM.
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  #7  
Old 09-07-2022, 08:17 AM
DennisRhodes DennisRhodes is offline
 
Join Date: Jul 2007
Location: Taylorsville, Ga
Posts: 942
Default

Check the crimp or solder connection to the ALT. I've had a problem either where that lug or crimp loosened up and overheated. It got a new NAPA alternator but found the burned connection when I changed it out.
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  #8  
Old 09-07-2022, 08:59 AM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 1,372
Default Alternator Longevity -- Care & Feeding...

The following has been gleaned from numerous threads and first hand experience:

1. Make sure the belt is not TOO tight -- the pulleys in the system will expand with heat and increase the tension on the belt. Check in & around the starter nose, the intake snorkel, etc. for black dust. Dust will indicate that the belt is a bit too loose and is slipping.

2. Heat & Cooling -- Remember how a toaster converts bread into toast --radiant heat. The exhaust pipes are glowing red (or very nearly so), anything that "sees" that will absorb that infrared energy and become hot.
Apply shielding where necessary. Also, the alternator should have a blast tube aimed at the regulator & rectifier packs. 5/8" - 3/4" tube is sufficient.

3. Connections -- For whatever reason, Hartzell/PlanePower do not include the 3 rubber vibration/weather seals on the wire ends in the connector. Source and install them or apply some sensor safe RTV (aka. silicon rubber) to the cavity on the plug to "anchor" the wires.

4. Output levels -- 13.8V is on the low side, 14.6V is a bit on the high side, 14.47253V is just about perfect If you have an external regulator, adjust accordingly - try to match your ships battery chemistry. If yours is internally regulated, live with it...

5. If you have the "Big A$$ Breaker" on your panel (40A, 60A etc.) that is connected to the alternator "B" lead, don't pull it when the alternator is energized. This will create a "load dump" and blow up the diodes.

B
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  #9  
Old 09-07-2022, 09:41 AM
alcladrv alcladrv is offline
 
Join Date: Oct 2006
Location: Southeast
Posts: 666
Default

Quote:
Originally Posted by PilotjohnS View Post
Are there any heat shields on the exhaust, or does the alternator ( backside internal diodes and electronics) see the red hot glowing exhaust pipes?

Is there any air flow to the alternator especially to the backside?

Lastly, is there too much electrical load for the alternator?
Thanks for all of your input.

To answer the questions above:
) The alternator is in the usual place on the O-360 in my -7A which is several inches from the crossover exhaust.
) I have a 5/8" blast tube pointed directly at the rear of the unit.
) All of my exterior lights are LEDs. I kept the 2 screen G3X system running, but turned off the 2nd comm radio.

I should have added that the voltage output had been rock steady at 14.3 volts for several hundred hours, which is why I noticed the 14.0 volt and lower output voltages last night.

I left the 60A panel mounted alternator untouched. As it is, it doesn't look like I could purposely pull it out. It was supplied by Vans with their electrical kit when I built the plane in 2005.

Last edited by alcladrv : 09-18-2022 at 10:36 PM.
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  #10  
Old 09-07-2022, 03:14 PM
abuura abuura is offline
 
Join Date: Jan 2006
Posts: 140
Default

I've had a B&C L-60 paired with their LR3C-14 for 15 years/1420 hours. I went to an EarthX ETX680 three years ago after 12 years of using Odyssey PC680s (I think I used a total of three in 12 years). Since first flight, my voltage reads 13.5 volts, sometimes 13.6 a few minutes. B&C told me what you read depends on where you pick up, and that if everything works well and the battery charges ok, not to worry. Both the Odysseys and EarthX start the engine on one or two blades, IFR panel has always worked without a hiccup.
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