SobeUK

What voltage should the alternator be puttng out to chage the battery?

Currently mine is outputting 13.7v. On the weekend had an issue after driving for a few hours in traffic. Called into services and after a break could not start. Turned over once then just clicked. Got a jump start and continued on journey with the ABS light on.

Today had battery tested and is 12.8v and he alternator is outputting 13.7v. The mechanis said that it needs to be over 14v to charge the battery.

Does anyone have the figures regarding this?

Cheers

nycgps

iTrader: (1)

Your mechanic is right. stock should be 14.4.

SobeUK

Thanks for the info. Just took it up to Mazda and theytested it. The Alternator voltage i a bit lo both on idle and under load. So looks like a new alternator will be on the cards. :-(

SobeUK

One new alternator later and £515 (a grand for you in the states) lighter I thought it would be all sorted. Ah but I was fooled. When I tried to start it from work to come home it turned over and didn't start first time. Second and subsequent attempts resulted in the clicking sound again.

I left it a few minutes and started to call roadside rescue. While on hold tried it again and wow it turned over and started.

So what could this be???

Could this be the starter motor fault that caused the recalls? I checked with the garage and apparently this car has now had all the recall work.

Any thoughts?

Cheers

ken-x8

Didn't see your post on this sub-forum...your first post here has a little more info...which merits a little more background. And I think you got hosed on the new alternator.

Just measuring the battery voltage does not tell if the battery is good. Batteries fail in two ways. One is that one cell dies completely, in which case you'll measure 10.something instead of 12.something. The other way is that it just deteriorates and has a fraction of its original capacity. It will still measure 12.something, but won't start your car.

Battery condition really has to be tested under load. A good garage will have the proper gear for that. If not, you should charge it, then turn the headlights on for 20 minutes (engine off) before measuring the voltage. That will tell you something. Even a bad battery is likely to measure full voltage if you check it as soon as you turn the engine off.

So if the guy who "tested" your battery just measured your battery voltage when you rolled in, he didn't really test it.

13.7 volts is a little on the low side, but it's within spec. Shop manual says 13 to 15 volts. So he didn't have a shop manual, either.

(I'm a little surprised by that 13 to 15 range. I like to see 13.5 to 14.5. IMHO, 15 will overcharge and eventually kill the battery.)

And the car starting after it sat for a few minutes isn't unusual. The battery would have recovered a bit during the wait.

Ken