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2003 Outback wagon
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Discussion Starter · #1 ·
Hi everyone!

A couple weeks ago I noticed a terrible sound coming from my alternator. Upon opening the hood I could smell her burning up. Multimeter readouts were in the 11-11.5 volts at idle.

So I bought a used alternator on eBay that was supposedly tested. Upon installing that my voltage (no accessories on) at idle at the alternator and battery is around 13.7 volts. If I rev up the motor to 2000 rpm I can see the voltage fluctuate to 13.9, but never 14 or above.

I then tested with my multimeter at the alternator and battery and under load with such accessories such as my headlights and my ac fans running, the voltage at idle is 12.5-12.7 volts. If I rev it up with accessories on, the voltage will go to 13.4-13.7.

Never once with this used replacement alternator have I seen 14 volts or above.

Does the above situations and multimeter findings, seem normal or is the replacement used alternator not working up to capacity either?
 

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2020 Outback Premier 2.5i
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Unless things have changed, 13.8 to 14.2 @ 10 amps off idle was what I learned long ago. 11V does not explain the notion that it was "burning up". That sounds like something other than an electrical problem, such as friction.
 

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Discussion Starter · #3 ·
Unless things have changed, 13.8 to 14.2 @ 10 amps off idle was what I learned long ago. 11V does not explain the notion that it was "burning up". That sounds like something other than an electrical problem, such as friction.
So the fact that with loads such as ac and headlights, I'm only getting 13.8 volts max with the engine at 2000 rpm, that would indicate a charging issue?
 

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Doesn't sound like it but you'd have to know what that load is. We used to hook up to a load tester that had a carbon pile resistor and turn the dial to impose the 10A load. You'd need an ammeter to measure the load.
 

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Discussion Starter · #5 ·
Doesn't sound like it but you'd have to know what that load is. We used to hook up to a load tester that had a carbon pile resistor and turn the dial to impose the 10A load. You'd need an ammeter to measure the load.
Gave my multimeter a thorough checking because we'll, it's from harbor freight. Found that the positive tester cable on the multimeter was not making a good connection where the factory soldered it. Gave it a resolder and my voltage numbers look much better. Took a detailed video of various voltage readouts with and without load as well as under rev conditions.

 

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Discussion Starter · #6 · (Edited)
Today I drove the car about 160 miles in 90+ heat and 90% humidity and the alternator performed great. Charged at 13.8-14.1 volts consistently.

The one thing I have learned about OEM Mitsubishi alternators is they under powered at medium to high load when the car is in idling in park position (no transmission load). As soon as you go above idle and hit 1000+ rpm, the alternator even under heavy load charges at 13.8+ volts.

I performed the same test on a 2004 Accord and that alternator stayed steadily charging even under high load at 14+ volts. I've read other threads about idle alternator power on older Subaru's being underpowered.

I think the factory alternator is 90amps. Is there a possible upgrade I could put in?
 

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I was trying to watch your vid last night but couldn't get thru all the way as I have company staying. Looks to me like you don't have an issue with the alternator. Interesting that there was an issue with the meter though. Unless you intend to run a lot of power drawing lights, camping gear or the like I wouldn't even consider a larger unit. That's not going to raise your charging rate - that's controlled by whatever the regulator is (e.g. built into the alternator or perhaps controlled by computer module).
 

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Discussion Starter · #8 ·
I was trying to watch your vid last night but couldn't get thru all the way as I have company staying. Looks to me like you don't have an issue with the alternator. Interesting that there was an issue with the meter though. Unless you intend to run a lot of power drawing lights, camping gear or the like I wouldn't even consider a larger unit. That's not going to raise your charging rate - that's controlled by whatever the regulator is (e.g. built into the alternator or perhaps controlled by computer module).
Thanks Micron. Appreciate you taking the time to watch me ramble. Got a couple hundred miles on the alternator so far and the voltage has been good.

I do have to say the factory alternator in my opinion is underpowered at idle when a lot of accessories are on. I've played around a lot with load tests from a voltage standpoint and it's interesting the affects certain accessories have on the alternator voltage. My guess is the engineers didn't make it too big of an alternator for gas mileage purposes. I'm assuming the bigger the alternator the more drag it pulls on the motor.
 

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More rotating mass would take more power to move of course, but the biggest drag is when the alternator is putting out power, and the higher the capacity the more HP it takes to do that. Your battery is mostly for starting while the alt should be able to maintain the battery in a charged state as well as provide power for electrical systems in the car. Unless there is a problem doing that when most/all systems are drawing power there's really nothing to worry about unless that becomes a prolonged condition. Then the battery reserve starts to drop (all that assumes it can achieve a fully charged state). I wouldn't get hung up on the numbers too much as long as the battery's state of charge can be maintained with normal use.
 
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