Bigger alternator - is there more to it? (for ICE purposes)

[Junglist]

Gonna fit a 90 amp to my GTII replacing my 45 amp one or whatever it is. It's off a passat. What effect will this have? Will the battery recharge quicker? Will the running voltage increase? Will I need a different battery? Can it damage my battery? Can it cause problems? How much will it improve things and in what way(s)?

My reasoning for fitting it is my high-current-draw head-unit is not always getting full power when it needs it, so the RMS wattage isn't what it could be and I don't get full bass output sometimes. I'm hoping it'll keep the batteries at their fullest so the power's always available when needed.

Seems a cheaper option than getting a capacitor and all that nonsense. I can get good prices on batteries too if that's what I'll need to get the benefit of the bigger alternator. Will I need a bigger battery?

Cheers y'all!

[Mr Funk]

I've been thinking of doing the same over the winter so will be interested in what is said.
Got myself a big silver top bosch battery which was good. Although saying that I left the car for a week and the bloody thing wouldn't start so need to investigate

[scalainj]

Right - i'm not claiming to be an electrical expert at all but here goes

My 65 amp alt pushes 13.54v at idle, 13.04v with everthing on. An amp without worn bearings will push a little more
You really do not wish to drop below 13v when everythings going as your not going to recharge the battery from the starting power loss very quickly especially if your using a lot of power.
When the car is running the alt drives all the electrics. You could in theory take the battery out of the circuit.
I have a 60 amp battery as i find the bigger batteries are far better for quicker starting as they will turn the starter in astronger manner for longer hence the engine will turn over more readily - its the cold cranking power your looking at - thats what it puts out when starting from cold.
Years ago i took a full cranking shock by accident. Its worse than a HT shock let me tell you.

With a bigger alt pushing larger alt the voltage will be the same/similar but it should charge a higher amp battery quicker than a small amp alt.
The effect on a small amp battery i don't know but i've always had recommendations to up the battery amp as you up the alt amp.

Improvements - more ampage

Downsides - it will take more power from the motor driving a bigger amp as turning the alt with a larger ampage will reqiure more torque. Is it much - no

I assume that your head unit lights are pulsating to the beat?

Andy

[Junglist]

Not that I've noticed actually. What I have noticed is that at higher volume, the sound clarity drops a lot. In other words, the more power it's pulling, the more blurry the sound. I'm not talking distortion here - I never have the volume high enough to cause distortion. I'm simply talking overall crispness of the music. It becomes less clear when loud. I understand that a lack of available power causes this and capacitors are the usual choice to combat it, but I want a cheaper method with the same result.

[scalainj]

Back in the day when i had sound the upgrade to 65amp alt & 60 amp battery was more than adequate to cover amps woofer plus 6 speakers

I had the flickering head unit lights when it was turned up loud prior to going for a bigger alt.

Andy

[Junglist]

I think I've got a very cheap 90 amp one coming, otherwise I wouldn't have gone so big. I'm trying to figure out if it can cause any damage by being too big.

[Mr Funk]

Amps are fitted with fuses for that very reason I'd guess. Worst case you replace all your fuses!
Reckon I might follow your lead and go for a big passat alernator

[Junglist]

Right, I'll find myself a big fat battery then. Or would I be better sticking with the two battery arrangement I'm rocking at the moment? Got my second one strapped behind the off side headlights on the ledge in front of the alternator. Cracking little space that seems almost made for it.

[scalainj]

Stereo will only draw what it needs. Because an alt can deliver 90amps doesn't mean it giving all of that all the time. Fuse is there to stop whatever is behind it drawing more than it should because of a short drawing it all because it going straight to earth or to stop spikes so if for some reason 90amps did come the line it goes bang (i can't think of what causes spikes though other than shorts) What 90 amps being available for a battery of 45amps could do i don't know. Personally i'd go one big battery as i don't know how series or parrallel running of batteries affects the amp rating. Certainly doesn't increase the voltage

There is a calc you can make with volts, amps and watts that means you can work this out.

Watts = Amps * Volts

Amps = Watts/Volts

You should be able to test your electrics to find out the draw with the car running and everthing except the stereo on. You can do it with stereo at full tilt but neighbours never seem to appreciate it.

Then find out the watts rating of the amps - its usually on the serial number plate

So watt rating of 300 divided by 13v is 23ish amps. Don't use RMS, thats the output of the incoming signal voltage amplified (with other calculations for resistance and distortion) and then i think they add 00000s

Andy

[Mr Funk]

You seem to know what you're on abpout when it comes to the devils power.
Good. I till have that ashtray here. When I hand it over you can answer a few questions I have!

[Nate]

one thing to remember. it's all very well putting in a big alternator and a larger battery, but if you're head unit is connected with the same spindley bit of magic string as when it left the factory, it won't make much difference. you'll also need to re-wire the head unit supply (+ve constant, +ve switched and -ve) with larger magic string.

think of it as pipe with water running thru it. small pipe only lets a small amount of water through, larger pipe = more water

[millsy20]

Have you thought of putting a capaciter in the circuit for ICE. Its supposed to be better because it stores the charge. And they are cheaper than a new alternater and battery. A 1 farad capaciter is plenty.

rich

[Junglist]

Head unit came with big chunky wires for the power (Alpine 60w x 4) - never seen such big wires on a head unit. I ran thick wire off the pos but not the neg. I'll upgrade it.

As for fitting a capacitor, it would be cheaper normally, but I have got hold of an alternator for next to nothing and can get batteries for wholesale prices direct from factory, so it works out much cheaper this way. If someone tells me a capacitor's better for the job though, I'll probably get one. I thought it was the cheaper means to an end and this option was better, but correct me if I'm wrong.

[scalainj]

When i did mine i usea big chunky wire straight off the positive terminal with a 30 amp fuse and behing that i had 2 amps - i big one driving the woofer and a smaller one driving the other 6 speakers. I spliced the wire as it came through the dash and took the constant positive from there but because my head unit was a pre only i used the ignition live that came with the car plus a piece of mains wire as the negative. If you are using the amps in the head unit you need to find a an ignition feed on the fusebox and run a bigger wire wire their for ignition live lus a good sizeable earth. Again the usebox has the earthing 'rose'

For the amps i used a reasonable size piece of wire for the negative and earthed it in the boot.

A capacitor will store for sure, think of it as a water tank constantly be recharged by the battery. Sometimes however you can draw more than its re-supply

Andy

[Junglist]

Sometimes however you can draw more than its re-supply

Andy

That's what led me to think my idea of bigger battery and alternator was better option. So a big battery is essentially a hardcore alternator with much better staying power? Or am I misunderstanding this?

One of your earlier posts states that the power is all being drawn from the alternator when the car's running, but if I power the head unit by running a wire from the battery (like you have), I presume that's where it will take it's power instead. Therefore the reserve "juice" will be plentiful as long as I install a big battery, yes? Assuming the alternator's recharging it quick enough, which I think a higher amp one will do - is that right? So the power comes direct from the battery and the feed to switch the unit on is a farty little wire running off the horn fuse (since that's only powered when ignition's on). It's like this now so it won't drain the battery with the engine off. Standard wiring-up for a head unit I suppose.

I guess I should also power the amp this way, but with the switch feed coming from the head unit, obviously, as there's a wire specifically for that purpose.

So my head unit is powering each of my 4 speakers from it's own 4x60w(more like 20wRMS) amp and the sub is driven from it's own amp (bridged 2x100w). I've always preferred this set-up. It seems a good balance.

So in summary, and correct anything I've missed or misunderstood or is just plain wrong:

1. Upgrade all power wires, pos and neg, to head unit and amp (so 4 wires in total - pos&neg head, pos&neg amp)
2. Run power direct from battery (I guess running neg back TO battery can only be a good thing too)
3. Fit large capacity battery
4. Fit 90amp alternator

So as a result, my system will be able to draw a chunk more power when needed through it's new big wires, but the big alternator will be able to keep the battery full so there won't be an issue of it running out of supply. A constant abundance of power will then result in constant sound clarity at high volume. HAVE I GOT ALL THAT RIGHT???

So what size fuse do I fit on the power leads because I don't want the fuse to restrict how much the system can draw as that will defeat the object, but nor do I want an electrical fire!

The questions never end...! ha ha.

By the way all this advice is ace - I really appreciate it. Thank you. Keep it coming! We're nearly there!