Alternator going bad?

[speed5]

I get a battery light in the dash flashing on sometimes during hard acceleration. On a recent trip to PA, the battery light would stay on if I cruise above 70mph.
Autozone ran a test, and said my battery (2010) is good, alternator good, rectifier bad.
I brought my 5 to dealer and they said battery bad, alternator good, and offered to sell me an identical undersized group 26 Mazda battery for $160. No thanks!
I picked up a bigger group 35 Optima Red Top for $150 and swapped the battery.
Guess what? Problem is still there.
So I checked online. I can get a new rectifier for $30 but then I would have to open up the alternator to swap the rectifier. Then what if there was something else wrong with the alternator. I dont think I want to go thru that trouble. So I found a new OEM-fit replacement alternator for $95. But also considering a high output alternator. Has anyone here replaced a Mazda5 alternator? any DIY tips? Any comment on aftermarket new alternator? or high output alternator? I heard the stock Mitsubishi ones are junk, and the Denso is the best. But Denso stock 90amp costs as much as high output aftermarket one.

 

[jmcglynn]

Unless you know someone who rebuilds alternators, or have a lot of time on your hands, I wouldn't recommend trying to change the rectifier... Much easier to just replace the whole alternator and take the core return rebate. As far as going with the high-output unit... I'd say it all depends on your load. If you're running a higher than normal load (because of things like trailer lighting, accessories, blow-out sound system) then it's worth it to go with the high-output... but if you're running basically a normal load, then I'd say the high-output is overkill, and go with the Denso stock. I would also check your main wires pretty thoroughly... If there's any hint of damage or wear, I'd swap those out for a better set too. I didn't do that once with an alternator change on my old VW Rabbit Convertible... turns out the old alternator had toasted one of the wires, causing a short, that in turn toasted my new alternator. A pricy lesson learned...

 

[Robotazky]

I'm no charging system expert, but when I hear someone say they have a battery light at high rpms I think belts. The battery and alternator, from my experience, really show their problems at idle. Again, that's just my observation and I could be totally wrong. I've had some kind of belt issue on my 5 since it was brand new, so maybe I'm just jaded.

 

[thaxman]

I'm no charging system expert, but when I hear someone say they have a battery light at high rpms I think belts. The battery and alternator, from my experience, really show their problems at idle. Again, that's just my observation and I could be totally wrong. I've had some kind of belt issue on my 5 since it was brand new, so maybe I'm just jaded.

Battery probs are at idle, since the alt isn't turning enough to sustain the power demand. At speed, the battery is receiving a charge from tha alt & is not supplying any power. If the sys thinks there is insufficient power at speed, then its either the alt not creating the correct charge or there is a problem with voltage regulation somewhere else in the system. IDK what the rectifier is, but it sounds like an in-alternator voltage regulator.

 

[speed5]

thanks all. it was a Saturday, and i didnt want to wait a week for the $95 alternator. so i went out and got a brand new Duralast Gold from Autozone which has a lifetime warranty. I did the swap the same day, took me a couple hours. All is good now. 13+ volts consistently whether at idle or speed.