Battery voltage on idle

[brassbones]

So, I went and put the charge pack on the wrong way round and moosed the battery and blew the 120A fuse (and main beam fuse oddly). Yes, I know, I'm a bellend.

 

My mobile mechanic sorted all the above but then told me the alternator isn't charging the battery but is providing charge to run the car while driving, based on the battery voltage being 12V not 14V on idle.

 

He claims I will gradually run the battery down with each successive start of the engine and this is probably why I was having to use the booster pack so much. I just put it down to not running the car for a couple of week. I have a fag lighter voltmeter and it clearly shows the battery voltage going up when I go faster so my questions are ...

 

1. What voltage do you guys read on idle? and

2. Is my mobile mechanic talking bollocks?

 

PW

[jagman]

The voltage is regulated - regardless of speed , it alters the current supplied depending on load - so if battery is low Volts the alternator provides more current , or if more load from heater, fans , rear window, stereo or whatever it also provides more current .

But if the alternator cannot provide enough current , slip rings worn , belt slipping , field coil high resistance or volts reg knackered it’s voltage drops .

Idle should be in the regulator range 13.6- 14.2 or so .

Toyota alternators seldom go past 100000 miles and the center slip rings /brushes are usually knackered - other people’s cars will depend on their battery condition but around 14 v

[brassbones]

Thanks once again Sir!!! So in summary, he's probably correct? I don't think my cock up has damaged the alternator though has it? It must of been the case prior to this "incident" as he stated?

[rider]

Last time I checked the alternator function it was 12.8V standing and 14.0V on idle.

[Tricky-Ricky]

Sounds like your mechanic is not to familiar with the way the charging system works, if its 12v or lower the alternator is not charging, as said the the current will vary with system load and battery condition, but the voltage when running will always be slightly higher than 12V, if the is current draw like headlights etc or the battery is discharged the voltage will be much nearer 14V, sounds like the regulator side or the alternator itself is not working.

[Al Massey]

Before you go out an try get a new alternator, try fitting a known good battery.

 

Your battery could just be goosed or on its way out hence why it needs jumping all the time.

 

I think the charge you see on idle is fine.

 

Do you own a multimeter?

[brassbones]

Al, my mobile guy swapped a brand new battery in.

 

It kind of makes sense that a 130k miles old alternator with very worn internals etc wont push out as much juice.

Having said that I'm not exactly flushed at the moment so could do with putting an alternator replacement off if I can.

 

I've done 3,500 in it this year as it is (assuming my balls up with the charge pack hasn't damaged the alternator, cf. my earlier query above).

 

Thanks for the feedback guys. Love this forum

 

Paul W

[djmakz]

Something I was advised myself - check with local companies that refurbish alternators. Paid £45 recently and few hours job and all works again. New alternator is pricey (£300-£500), even when you're looking for a refurbished one you have to send the old one back, so its still around £150.

[brassbones]

Thanks DJ. Keron wants £170 posted for a new one which is pretty good but £45 would be better!!! lol