Voltage drop

[MP5_Joe]

So I noticed a little while ago that when revving the engine at a standstill the lights dim a little. I thought nothing of it at first, but now when my radio is where i usually listen to it my lights dim. So I decided to pull out the old trust Nexxtech (cuz I'm cheap like that) voltmeter. Here's what I found.

When idle voltage at the battery is roughly 13.9v.
Voltage when revving is in the 14's.

BUT, when idle and then revved a little (we'll say idle to 1500) the voltage takes a quick (probably less then a second) nose dive into the mid 12's.

From what I've been able to find online so far it sounds like I may have a diode problem in the alternator. So I figured I would check with you guys before I replaced it (or the car).

(and yes, I tested with the sub disconnected)
oh, and the belts are brand new as the alternator belt actually decided to give out on me... 2 hours away from home... at 9pm when nothing was open lol.

 

[jtlinna]

There has been a few problems people have that i know of.. One is that the voltage regulator in the ECU craps out or has trouble regulating voltage. So the alt wont charge at all or the voltage becomes erratic. Charging to high or low or just being slow to respond to a voltage demand, causing the motor to shake and shutter..
The other problem is the alt itself. It to can be slow or erratic with high and low charging numbers. With Identafix software we have a work people have had alot of both. Anyone with the alt problem itself could only fix it with a new alt from mazda.. Word on the street is they have a revised alternator.
On a side note the voltage system is not that awsome on our cars. Its not uncommon for things to dim when your operating headlights and windows and such.

JT

 

[MP5_Joe]

Ya, I understand it's not great. Alternators only like 60 amps? Pretty damn weak. Going to get a new battery soon to though as mines over 2 (unsure how old it really is).

I just find it weird the voltage drops when you rev it a little.

I am looking at getting a different car now though, this is my 6th car and has also been the biggest PITA.