mrrbearxd

Hello,
I have a 1991 Ls400 and recently my alternator went out.
As i was about to purchase a new alternator, i was heading for a higher amp output alternator.
Assuming stock alternator is 100-120amp and there is a stock 120amp ATL fuse, but the one i want is 140-165 amps for the alternator.
My question is,
1. if i purchase a higher amp alternator lets say 165amp, do i need to get 165 amp fuse as well?
2. If i get a 165 amp ATL, can i use a 170-180amp fuse, or do i have to get the exact 165amp fuse?

im sure these are inexperience & common sense question, but i want to be sure if i were to overestimate things a little, i surely do not want to burn any wires because of this.

any suggestions or input would greatly help. thanks.

LScowboyLS

as I recall, your factory alternator is 100 amp in that model year, not 120 amp, and I am going to wait on Yamae's answer on the rest of this question, as he is the world renown electrical engineer at Club Lexus, and far more qualified to give the definite answer than anyone else here.

sam12345

iTrader: (1)

Isn't there a point I which you're wiring limits the amperage regardless of the fuse?

Yamae

It's up to the the current. If you want to draw 165A from the alternator, you definitely need to replace both the fuse and wires. But there is a solution which is to add an additional draw line with a fuse.

If you are planning to add some extra high power equipments such as big amplifiers, extra big lights or etc, add an extra draw line to the terminal B of the new alternator preparing a suitable wire and a fuse. You need to insert an extra fuse to the line and supply the current to additional loads.

If your equipments are not changed nor added and you don't consume that much of current regularly, you just can replace the alternator expecting the margins of the original fuse and wires. But don't expect too much. Those might be up to 20% or less and also the time of the excess current should be not the order of seconds.

The job needs some knowledge and the skill of electricity. Without doing calculations and the confirmations, you might have some problems. You also have to think of the situation of the accident. I have seen a car burning caused by the poor wirings by an amateur.

LScowboyLS

see, I told you his answer would be worth the wait!

Gene01

You may also want to check that the power steering system is not leaking fluid onto the alternator.
If it is, you will get to repeat the alternator replacement experience sooner than later.

LScowboyLS

Yes! This.

mrrbearxd

That was the problem to begin with LOL, yeah i am currently working on that now before i make a purchase for the alternator. Thanks.