Hi, iv just bought an '04 Impreza and im just wondering if anyone out there can help???

Bout a week ago i left on the interior lite on all nite, it started fine the next mornin wen i went to work, i tried to move it later on butthe battery was dead, i jumped started it got it home and for th next couple days gave no probs. On Sat i used the car as normal but it wouldn't start again wen i went to use thta nite, i charged it up Sun and it was fine. It did the same thing Mon mornin so i tested the voltage thta the battery was gettin and put i t down to the battery bein faulty and not haoldin charge. i put on a new battery tested the charge and got a readin of 12.8 volts. I foned up a Scooby dealer and was told it shuld be chargin at at least 14v.

I bought a new alternator on that basis which has arrived but iv been told by parts supplier that the system only charges wen it needs to. Iv just teasted it again, no point changin the alt if i don't need to and found thta wen at idle speed it only puts out 12.8 volts but ween u load up the system it then charges 14.4 odd volts. Should this happen an is it a normal thing or shoul;d i change the alt too???? Any advise greatley recieved,

 

13.8 to 14.2 is normal charging voltage
12.6v is normal charged battery voltage

at idle, if its slow, then the alternator may not give full voltage, but from 1500rpm onwards it SHOULD
...Ive heard this thing about alternators only giving charge when needed: dont understand it - alternators are/were dumb and charged as soon as they rotated at speed.
an ammeter would be helpful - but nobody seems to fit them any more

I suggest a long trip to charge the battery (ort an overnight charge off mains) then check voltage at battery with engine off and with engine running
if it doesnt start after an overnight charge then it has to be the battery

 

Have read that some MY's have a so called 'smart alternator'. This type of alternator only charges when it senses a drain on the system, the advise is to drive with at least side lights on at all times.
Turn on the side lights with engine running and test the charge to the battery, you will then prob find the alt is giving 14.?volts
If the search was working i would post previous threads but.........

 

Hi thanks Scoobian and b13bat for your help on this problem,

Yeah still kinda confused bout the whole thing tbh. I haven't changed the alternator looks like il b sendin it back!!! lol It's ben ok since i tested it on the 19th, starts first time everytime so i think it's chargin as it should. I haven't heard of any other systems like this except for apparently late Fords. Im gona give the place where i ordered the new alt and pick their brains over the idea but i think ur both rite in the fact that it only charges wen needed. Thanks again

 

Yep, i had exactly the same problem on my 04 WRX, always drive with your sidelights on or blowers on two or above, otherwise it doesn't charge properly.

Someone mentioned to me at the time that Subaru actually recommend driving with the side lights on to counteract this problem.

 

Is there any truth to the above smart alternator? As mine struggling to start recently and checked battery and pulling normal load when engine off and only pulling 12.5 volts with engine running!
I'll try checking again with side lights on.
But surely if this was the case they would be wired permanently on like Volvos????????????

Mine is a 2003 sti type uk if this makes any odds.


Obviously don't want to spend out on alternators if its meant to be a smart version

Thanks in advance for any advice

Adam

 

yes they charge variably as and when required, i think they were fitted to late bug eyes on to current models.

 

Thanks for the response, but how do you go about charging your battery then! As never seen other Scoobies driving around with side lights on?

Odd design or what???????????????????????

Cheers

 

not really,it charges when it needs it,on demand,not that odd to me m8,its rare to drive with nothing on in this wheather anyhow,i seem to have rear screen heater on all the time and the fan clearing screen in the cold so just use more ellectrics so it charges and should be fine,also take it for a good drive at weekends to get it topped up.

 

I wonder why all manufactuers aren't like this? Most cars are either charging or not! I may look at the battery, incase incorrect one fitted at garage, as i'm sure an sti uses a stronger battery than a wrx for example would?

Cheers

 

The battery fitted on my sti type uk is a varta D47 60ah.12v.

Is this the correct battery for this car?