alternator charging issue

[dirtydubber]

Has anyone experienced this before? when i start the car and leave it idling the alternator does not seem to charge at full capacity, it is not until I rev the engine to 2.5k that it gets going properly. I only noticed this as I have a rather power hungry install, and at idle, it can drain the battery. I have tested the voltages at the battery and results are, at start with engine at idle 10.2 volts, but once engine has been revved, 14.2 volts at idle. The problem is that without the stereo on, it is quite possible for me to get to work and back without ever revving over 2.5k and hence not charging the battery correctly. No warning light comes on the dash.

 

[dainott2105]

only a guess but i think your battery is dying

 

[YerMother]

Is it 10.2 volts with all your install on? It is more likely to be the battery than the alternator. You should be seeing around 14.5 volts coming from the alternator.

See what the battery is giving out with the engine and ignition off! If it's below 12 then probably on it way out. just go to Halfords they'll do a free battery test for you.

 

[dirtydubber]

Voltage at the battery without engine running or system on is just over 12v. If i start the car (system off) and let it idle I get 10v produced by alternator. If i blip engine to 2.5k and then let it idle i get over14v and it then stays that way whether i have my system going or not, lights on or not. It is charging ok, but I was just wondering if having to blip the revs a bit first is normal behaviour.

Thanks for the replies by the way.

 

[YerMother]

Does sound like alternator then. Should be around 14v at all times when engine is on, whether at idle or the redline.

 

[dirtydubber]

Bummer. Not really what I needed just after christmas. oh well. Cheers guys.

 

[Adcupr]

i would get the battery professionally checked before you do anything else! chargeing systems are not what they used to be. faulty or low batteries can cause any number of strange problems. quite often the ecu controls the alternator according to battery condition, demand, and engine load... in many advanced applications the ecu can stop the alternator chargeing or cut out the a/c compressor under acceleration to give maximum engine performance without the power sapping accessories.
the new m3 does most of its chargeing under brakeing and on over run.

 

[dainott2105]

Yea get the battery checked first, but i had to buy a new alternator for my missus beetle (think its the same as the leoons as it goes but il have to check part numbers) and i paid £45 for it delivered (recon one) so no where near as much as i thought it would be (£195 form stealers, not that i would ever have paid that.
Go on find a part or breakers yard and leave the breakers email you. I had 5 replies in a day so plenty about. Good luck mate
PS if it is the alternator then can you put the part number on this thread when u get it for ref. for anyone who needs one in the future

 

[pwoiks20vt]

could be the voltage regulator on the alternator, ive just orderd a new one as mine is nakerd i think.

 

[1981whips]

it could be the bat as ive just had a free health check of seat and they sied my battery is ****ed but if i drive it daily should be ok for a while but i have seen all sorts goin on with me car an today struggled to start then esp light came on and it sounded like it was going to die any second turned it of and on again without stereo on and its been fine

 

[Adcupr]

like i said a faulty battery can cause all sorts of problems because the ecu relys on a good power supply, especially in top end vehicles like the lcr which use can-bus wiring... which basically means that a single wire does more than one job and the ecu sends signals to control things in the vehicle.

 

[dirtydubber]

Thanks for all the advice guy's. I think the battery is going to be my first port of call (probably the cheapest and easiest option anyway) I have been meaning to replace it for a while cos it has gone flat twice in the cold weather lately, but i put that down to the huge power drain from my stereo, and the fact that It takes less than 5 mins to drive to work so battery probably not getting a good charge by the time I get home. Once I get paid I will stump out for a decent heavy duty jobbie, and will let you all know what difference its made. (If any).
Thanks again.

 

[Romeoisgraham]

Could be battery, alternator, alternator belt not tensioned properly. Get a free battery check at kwik fit. they will tell you where your problem is.

 

[longman]

I believe that alternators generally would need to have gone over a certain rpm before they actually start deliverying charge to the battery.

I could be wrong but I think this is normal as 2.5K isn't too much to ask on any journey for the battery to start charging.

Anyone else with a Multimeter who could check theirs at idle pre and post blip!?

 

[Stan 24v]

The alternator "should" kick out 14.7vdc on startup, and at idle. It should also kick out the same value throughout the rev range, this is the purpose of the voltage regulator, to regulate the voltage. There should be no effect whatsoever from blipping the throttle, or even revving through the range.

You may have worn bushes on your alt, or you may even have a dodgy earth somewhere which is causing a drain of voltage.

As said above go to kwik fit for a test.