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Discussion Starter #1
Hi all have looked hi and low for volkswagon t4 1994 alternator upgrade and couldn't find any above 90a which isn't any good for what i need and didn't want to got down the two batteries route and put strain on the alternator,
So am going down the route of making a bmw 180a alternator fit in next few days should be fun lol
Will post updates when can on how it went
 

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Wrong thinking....
A 90A alternator will quite happily support 2 batteries! (Or 3...85Ah starter and 2x 110 leisure...like I have)
The alternator is a "fixed voltage, variable current" device....so it will "try" to get to 14.4 volts, at the most current it can supply.
"Normal" charging (NOT after a 1st start of the engine), it will probably only be putting 10-20 amps into the battery.
Lights/heaters/etc on, will take another 20 amp MAX....so you are left with over 50 amps to charge a 2nd battery!

MANY years ago, I had an American Motor-home...with 5 batteries, and a 50 amp alternator....YEAH, FIFTY amps!!!
OK, you have to drive a few hours to charge the 500+ A/H capacity....but it never failed me.

If you want to be stupid, and fit a 180A unit, remember that ALL associated wiring will have to be upgraded, and you may go through belts faster than Trump goes through lies!
You'll need a big "poly-V" belt or at least 2x V belts with the correct pulley spacing.
Also, the tension required will be WAY over what the bearings are rated at on an OLD T4.
 

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Discussion Starter #3
With running 2 amps drawing over 120amps of power will need to run bigger alternator not enough to run them on stock alternator dont see wy it would go through belts and need to be under any more tension than normal obviously need to uprate wiring
 

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Basic physics...
180 amps, 14 volts, is over 2500 watts.
That equates to around 4 horsepower.....a "normal" V belt will struggle at up to 1Hp.
A Multi V belt, at the correct tension, will just about handle it.
I had a 120 amp alternator on my boat, double V belts....they lasted about 200 hours running time before shredding (feeding 6 x 120A/H batteries!)
Poly V pulleys cost me an arm and a leg to have machined, and still wouldn't last a whole season of cruising.

Also, remember, you won't get 180 amps out of it unless IT rotates at around 12,000 rpm...so make sure the pulley ratios are correct. (That's why the alternator pulley is always a lot smaller than the one driving it.)

I suggest you get a clamp-on meter and actually MEASURE the current your amps are taking!
You're looking at having to dissipate over 1Kw of HEAT from those amps (assuming the std, very poor, efficiency of car amps....AND the fact that they NEVER, EVER give the power that they claim!.)
I have a 1500W Mono Block for my subs...."quality" make, and tested under PROPER HiFi test procedures, it manages a max of 55 watts RMS before clipping...LOLOL

ACTUAL fact (look it up)... "ONE WATT OF SOUND, IN ONE CUBIC METRE, WILL RENDER A HUMAN DEAF FOR LIFE"!!!!!

Sorry, but you've joined the many ranks of people lead astray by manufacturers numbers.
 

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Discussion Starter #5
Have a 90a alternator on my van at the moment and is struggling with powering my small kenwood amp with 100watt speakers
 

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Have a 90a alternator on my van at the moment and is struggling with powering my small kenwood amp with 100watt speakers
Is the alternator working correctly?

90A not at idle maybe only 10A, but off idle 90A is pushing out 1kW should be enough to melt the amp, I take it the battery is going flat 100W is that RMS rating or peak, think you need to check input Amps or Watts to the amp.

How many speakers at 100W are you deaf yet!

There was 120A alternator available for the T4
 

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wheres the amp, what cable are you using & how long is the earth cable?

^^ common issues when connecting audio extras....

Rich.
 

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Is the alternator working correctly?

90A not at idle maybe only 10A, but off idle 90A is pushing out 1kW should be enough to melt the amp, I take it the battery is going flat 100W is that RMS rating or peak, think you need to check input Amps or Watts to the amp.

There was 120A alternator available for the T4
Reverse thinking there!
The alternator "tries" to provide a fixed 14.4 VOLTS.
The current it supplies depends upon the demand there is on it.
Voltage controlled, variable current device.

There is NO WAY that you are getting 100W RMS.....just a numbers game the manufacturers use to con you.
"Maybe", you'll get a 100W PEAK, for a fraction of a second, like when a drummer hits the edge of a snare drum with the stick.
Also the "100W" speakers....I bet you my van against yours that if you actually put 100 watts of power into them, they would either just die, or burst into flames!
A "genuine" 100W speaker would have a magnet around 10" diameter and a voice coil at least 3".....even then they usually have cooling fins on them.
Just look at professional speaker units used for broadcasting/PA work.

Think about your headlamp bulbs....
They are 55Watts....try touching one after using it for 10 seconds...LOLOL
 
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