Re: Bigger alternator - is there more to it? (for ICE purposes)
Posted: Sat Sep 19, 2009 11:57 am
I fitted a 90 amp alternator on my Storm back in Feb, I have had no problems, fires or fuses blow!
Right
A battery is a battery - it has similarities to an alt in the sense that you can draw power from both but a battery doesn't need to be running - you connect it up and it ill deliver power. Its not sitting their with all the power pent up, just the power needed when you demand it. An alternator needs to be spinning (magnets inside a coil generate current) but in a similar way it gives power when drawn and it only gives off what is asked of it
No - wrong way round. I said that the alt can deliver all its power but will not unless asked or fooled (spike). Most of the time a spinning alt will deliver 13+ volts but at the ampage required
Think like this - voltage is the flow rate - so a litre a minute say, ampage is the pressure, so if the 'hose' is a meter wide its going to trickle out, if its a mm wide the flow will slice you in half. Thats the premise of a water cutter.
You could draw direct from the alt but you won't like it - alt will give noise (mechanical and eletrical which is that horrendous whining) whereas a battery has no moving parts.
As the alt is charging the battery, by running the stereo from the battery you are getting a reltively constant supply. But all items actaully draw straight from the battery so the load drawn from the battery is replenished by the load drawn from the amp.
So yes the battery provides a reserve of power if the alt cannot cope hence i suspect when upgrading the alt ampage its best to follow suit with the battery. if 65amps from the alt is not enough then a 45amp back up won't be enough or it will but for not long enough.
Yes because the battery has a higher ampage rating (pressure) it can demand a higher ampage(pressure) from the alt to recharge or merely to pass on to the power demand. I think here if you have a 45amp battery and a 90amp alt then the flow rate can only ever be 45amps if the battery is in series. Some of this i'm working out as i go along with a combnation of logic/luck, a wet finger and a metal railing. Harder i hit the railing, the bigger the ampage
But a battery can also deliver cold cranking ampage for starting (or powering your stereo) so it will work and sound great at that level for a minute and the flatten the battery (unless the engine starts and spins the alt and charge is brought back on line)
Standard wiring is to have a power switch off the ignition. The idea is to stop the stereo playing when you are not in the car and draining the battery. It effectively is a switch. The head unit draws it usage power from the constant live
Your head unit is more likely to be 60w RMS * 4 and a real rating of 20w * 4
80w/13v = 6.12 amps - look at the stereo fuse. That will tell you the true wattage drawn
Best set up - is one big wire off the positive terminal with a 30 amp fuse in line near the terminal that runs to the amp. Splice off of that a thinner wire to the head unit
The head unit and the amp will have fuses in place onboard so we don't have to worry about getting the full 30 amps as they will protect should too much come down the line or too much be drawn. For the head unit as you are using the internal amps the currect switched live you have is fine. I would be tempted to put in a bigger earth and connect to the body somewhere inside the dash. Pop off the little plastic cover inside the glovebox - the bolt under there provides a perfectly decent earth
For the amp - a reasonably thick earth is required and one of the seatbelt mounting bolts is perfectly adequate. No need to run to the battery. Follow the main earth lead on your battery. It goes to 2 places. One the chassis leg where all the current going into the frame (from all over the car) comes back and to the block where all the earthed current from the motor comes out
So
1) run dirty big cable from positive with 30 amp fuse (or appropriate by finding out wattage rating of amp and headunit on serial number panels) and then applying calc as follows
Total max drawn watts divided by voltage gives ampage - = fuse rating
Do not use power output of the amps - it is a different measurement to power drawn and will be higher than drawn power because they are 'amplifiers' of the input signal
For example - 3 P1000w amps = 3000w/13 = 230 amps. You will get a weird look when you ask for a 230amp fuse.
2) splice into dirty big cable to give smaller constant feed to head
3) leave all fuses on head and amp in place
4) run larger earth from head unit - household cable more than adequate to fusebox rose or other appropriate part of the body
5) run bigger earth from amp -say1/3 to 1/4 of supply cable to appropriate earthing point on chassis
6) Put in bigger battery - 60amp should be fine but as big as you want
7) put in bigger alt
8) Fire up
9) Press play and if its all wied up correctly. Enjoy
Yes - more available energy gives you the ability to provide more energy to the speakers. As different fequencies require different power to provide the same volume a high power amp and supply gives the amp better control.
Speakers draw from the amp, not the other way round. Biggest mistake people make is to fit low power amps to big speakers. This is a recipe for blown cones.
If a speaker can handle say 200w pure (and that is a lot) and the amp can deliver 100w pure (still a lot) then when you turn it up the speaker will ask for a lot of power - this particularly the case for low frequencies which require a lot of air movement and thus a lot of power to get the cone moving the air - and once the amp is reaching its max it will start to clip (hence loss of sound quality, clarity) Turn it up more the clipping becomes audible distortion and eventually becuse the signal is so ragged the coil overheats and melts the speaker. The other way if a speaker is rated at 5w and the amp 1000w, then even at max power the speaker will only draw 5w max. You may getting the cone hitting the endstops due to sheer power but if it does go bang its not the same as distortion, its usually the cone splits under the massive movement - its a physical destruction as opposed to an electrical destruction. And easy to stop because on each beat the speaker makes an audible crack sound - turn it down if thats happening.
A smaller rated speaker with a big amp will deliver better quality than big speaker with a small amp
General rule of stereo is spend your money on the best source you can, then some good amps and then some decent matched speakers.
Fitting 10 subs, a 10w amp and Pye sereo will give you a crap sound and a lot of damaged woofers
Fitting a high end stereo (Becker, Naka, Blau, Alpine) a decent amp and poor speakers will give you a far better sounds and volume than the above
Remember the amp only amplifies (and colours the sound with its own internal noise) and speakers only intepret the signal (and colour it with their own characteristics)
Neither can make the quality of the signal higher, only a better signal from source will do that. With a set source different speakers and amps will give a different sound quality but that is against other speakers and amps, not the source.
Andy