Big stereo = electrical problems HELP

[Nick Read]

FAO auto electricians / ICE experts...

Ive just finished putting a big stereo into my Scirocco - a JBL 80.4 four channel amp running the fronts and rears, with a JBL 300.1 monobloc running the sub. All up, puts out around 300W rms. Peak current draw is around 70 A

Got a brand new battery in there just to be on the safe side, dont know the Ah rating, but its 620 Cold Cranking Amps and 110 minute reserve capacity at 25 amps draw. So about as hefty a battery as I can fit in.

Problem is that after giving it a full charge, it only took half an hour of running the stereo fairly loud to run the battery down do badly that the wipers would barely move, and this was with the engine running as well.

Over the last couple of days Ive been charging the battery up overnight with a 4A slow charger, then putting the battery back in, running the stereo not that loud and every night I get home from work and the batterys wrecked again, the alternator light flickering on and off struggling to keep it idling.

So this is what I need help with: I think the alternator is a 90A model, does that mean it should be putting out a 90A current all the time its running? The most obvious answer to my battery emptying out after 20 minutes of loudish music is that the alternators not charging enough. Ive been to a local auto electrician but dont want to get stitched up so thats why Im asking here. What they found was that just having the blower, rear demister and headlights on sucks up 37A just for starters and the alternator is struggling to make much more than that.

Am I right in thinking its time I got the alternator overhauled or totally replaced or is it something else?

 

[Bryan]

defo the alternator

IMHO best to replace it

 

[JAMESSRICH]

get the alternator uprated!

 

[Fred@BTM]

bloody essex boys with their mobile discos!!!!!!

 

[Bryan]

Quote: Originally posted by Fred2001Dynamic on 27 January 2005
bloody essex boys with their mobile discos!!!!!!

is he not a norfolk boy now

 

[derv]

you can take the boy out of essex...........

 

[Dink]

are you just having the car idling when the music is playing??

it may be the alt but id may sure first

 

[Djw John]

If its a new battery then it must be the alternator I wouldve thought, especialy with the light flicking on and off!

 

[Nick Read]

LOL Im a Suffolk boy now, although I have to get the passport out to cross the Norfolk border twice a day.

Another thing its been doing recently is when you start it up, the red charging light stays on until you rev the engine. If you just leave it idling on the choke, the light stays on.

Anyone got any advice on best course of action now then, assuming it IS the alternator? Either take it to my local auto electricians and get it rewound/overhauled for 50 or 60 quid, or get a recon one from somewhere - obviously not Halfords as their stuff costs a fortune. What are GSF or LSUK like for recon alternators?

 

[Fred@BTM]

mate pm the details of you mobile disco (engine and year) and ill get you a price off GSF (my mate works there, so no VAT)

 

[Guilbert]

Quote: Originally posted by Nick Read on 28 January 2005


LOL Im a Suffolk boy now, although I have to get the passport out to cross the Norfolk border twice a day.





Yeah thats cause us Norfolk people know that you suffolk lot will steal anything thats not bolted down! So we like to know who is coming across the border so we can send the police round!

 

[Nick Read]

Ive just got the alternator out and its a Bosch, I think a 90A model but cant be sure. Anyway, Im just looking at it and there are raised letters on the back - W, W, B+ and D+. The Ws dont seem to have any terminals associated with them. THe B+ is the main positive output, a threaded post that was connected up to the starter and from there onwards to the battery + terminal. The D+ is the thing thats mystifying me, it has a little female spade connection and was hooked up to a thin bit of wire, almost bell wire, which makes me think its a low voltage signal wire.

So is this D+ terminal part of the circuit for the charging problem red light on the dashboard? I want to run the voltage regulators sensing from the battery + directly, rather than from the alternator output, so that I get a better charge when the things under full load. Is it this D+ wire that I want or does it come from somewhere inside the voltage regulator? When I took the regulator out (two screws) there were two brushes (?) that were spring loaded and a sprung strip of metal that the regulator tightened down onto, no wiring of any kind that I could see.

Any help or explanation appreciated. Im going to strip out all the existing wiring in the charging circuit and replace it before everything goes back btw, including running a cable across to link the B+ of the alternator with the + of the battery directly, instead of through the starter motor.

 

[Dink]

the small wire is used to create the magnetic field inside the alt. this would mean if the batt was low the field wouldnt be as strong so not producing much current.

this is linked to the light on the dash but cant remember how

did the brushed look alright? (no chuncks missing or look well worn?)

 

[Nick Read]

So the D+ is the input for the field current rather than an output? When I looked at the two brushes (dont know what else to call them, they were like carbon blocks), one of them was worn down to 6mm long, the other was about 10mm. Both had been worn so that the end wasnt squared off but had a circular profile where they had been swept away. According to Haynes the minimum length is 5mm but I dont know whether that is for the ones that Im talking about, or something else right inside the alternator body..

 

[Dink]

yeah if they are made of carbon then they are the brushes.

i would change them if the are different lengths. the springs holding them on the rotor dont hold them in place when they start to wear

yeah its the input rather than an output. as i said its linked to the dash light some how but cant remember

 

[Rorrie]

so your total fuse rating is 70amps? and you have a 90 amp alt. well, you not really going to be drawing 70 amps for more than a seocnd, unless this is what you have mesured it to be rather than fused.

have you upgraded the big three?

http://www.talkaudio.co.uk/vbb/showthread.php?t=34836http://www.talkaudio.co.uk/vbb/showthread.php?t=34836 , might be usefull

im mine, my amps have total fuse rating of 150 amps, i have the standard alternator, and i dont have too many problems, although i am going to upgrad it in the near future



Rorrie



PS - on a new clio, 1.2, whats the alt does it have?