couple questions on battery voltage with sound soundsystems

[Phil_beeza]

The starting performance has been 'iffy' for a bit, suspecting the alternator might not be charging the batt properly. Pretty sure the battery is known good. The 90 amp alternator is 8+ years, has a slight high pitch ball bearing noise if thats relevant, altho the timing belt has been replaced recently.

After long (1 hour+) trips, and then leaving the car sitting for a couple of days, its been flat/low more than once (britannia rescue job). Starting th car up daily and going for short trips, its been fine (including thro the snow)

After getting a low battery jump start from britannia rescue after 3 days, the batt was recharging at 12.75 volts.


(possibly related question)

After starting the car a few times the radio has 'gone off' when waiting at idle. I'd previously thought this was a loose connection on the fascia plate. I just had it now when i was driving along, at the moment I switched the headlights on. I'm wondering if anyone knows if the radio has a low voltage threshold, that I'm guessing the battery is going below, and its a symptom of a low alternator charging voltage. Could make sense.

Just got myself an incar voltage display

the boot amp head unit remote switch on wires are all set up ok.

After a short good journey just now at idle the charging read 13.2v approx

i'm happy to replace the alternator with an uprated one, just wondered if anyone had any ideas on this, thanks.

I've got less than 1000w rms in the boot, the only one of the big i havent done is alternator mount-> chassis ground. i do get lights dimming at loud bass hits, I've done long journeys with light dimming behaviour. poss not a great idea.

 

[Phil_beeza]

just wondering if anyone knew what the alternator size options are

had a quote for a 120A alternator, £236 fitted

 

[wayne n]

Charge voltage seems low to me should be about 14.4, you will find diesel models have the bigger alts.

If you run the standard 90a alt and just up grade the battery to a 90a unit you should have no issues running 1000wrms.. as a rule of thumb you need 100a for every 1000wrms.

 

[Slimy]

What is the voltage above idle? Most cars I've worked on don't charge the battery at idle, it takes at least 1500-2000 revs to give you the 14.4 volts that you should be seeing.

To me it suggests the battery is a bit poorly rather than the alternator, and as the cheaper option I would replace that first.

 

[adelelzomor]

hi, a quick question.should i change my 50amps battery to the same 50amps or can i get a 70amps ?
i am writing this cause i am having a dimming lights in my car and the new battery is my suspect.
thnx

 

[wayne n]

I would go for the biggest you can fit. You can never have too much power.

 

[Nautilus]

Stronger current alternators usually need good cooling.

The 120A alternator from the 1.9TDI/150 and 1.8Ts fits in the place of the smaller engines' 90A alternator. Yet the way it cools itself is obviously not optimal: the air flows straight through the grill into the engine bay, yet the alternator draws air from the side and exhausts it forwards, against the air flow from the grill.

In summer and even in winter if the car is slowly driven, the alternator approaches the temperature of the engine block on which it is bolted.

Tried to make a cooling duct from a corrugated 60mm aluminum hose. It started in the front grill, above the plastic flap which directs air to the radiator, and wound around the intake hose to bring air to the alternator near its pulley, that is the place where the inside fan draws.

During city driving, the temperature of the alternator case was only slightly cooler.

Yet after a highway run (not very fast, maybe 70-80kph/43-50mph at its best), the alternator case was stone cold, as cold as the outer panels of the bodywork, despite being bolted to 90°C engine block.

So it works

For the minimal cost of a corrugated hose and 3-4 plastic ties, it makes a great difference.

~Nautilus

 

[adelelzomor]

thanks