Technical Alternator kill switch question

[Buurin]

I'm looking at my car's charging circuit diagram and it says there's 4 wires going to my alternator:

1. A big wire - must be the output
2. A white wire going back to battery through a ALT-S fuse. I guess this is for voltage sensing.
3. A red/blue wire fed by GAUGE fuse. Terminal is marked IG so it gets battery voltage when ignition is on.
4. A yellow wire. It connects to bottom leg of charge warning light and DRL module, puts out charging voltage when turning.

So if I am to install a alternator kill switch, should I tap into the white or red/blue wire?

[Daox]

What I did on mine was start disconnecting the smaller wires one by one. You'll know when you disconnect the right one.

[Buurin]

Just to bring closure to a (not so) old, (not quite answered) question.

I did an experiment today and the answer is IG wire. Disconnect that and the alternator puts out nothing.

That's good news, because that means I don't need to build a circuit to fool it into believing the battery is fully charged.

[TTercel]

Why are you doing this?

[Buurin]

Bump an old thread? To conclude it.

Install an alternator kill switch? To effect some sort of regenerative braking and save some gas.

[RningOnFumes]

When you say "regen Braking"... wouldn't this be a really round about way? Where are you send this energy when you're braking? Or am I looking at this wrong?


The plus side to this is that the alternator doesn't drag on the engine to charge the battery. Think reason for detaching the power steering-- less load. In this case, more for fuel economy than for power to the wheels.

[Buurin]

Originally Posted by RningOnFumes

When you say "regen Braking"... wouldn't this be a really round about way? Where are you send this energy when you're braking? Or am I looking at this wrong?


The plus side to this is that the alternator doesn't drag on the engine to charge the battery. Think reason for detaching the power steering-- less load. In this case, more for fuel economy than for power to the wheels.

Yes, roundabout as in mild to the point of undetectability. My idea is I'll let the alternator drag on the engine when I slow down. That would work better with a high output alternator = bigger drag until battery is full.

I installed this switch and a FAS switch this past weekend. I need to mosey over to cleanmpg or ecomodder for hints on using them. Next is to wire in the circuit to have alternator engage when I tap the brake.

At least my idle fuel rate is down by about 0.2L/hr with alternator disengaged.

[Stevo_Echohb05]

Originally Posted by Buurin

My idea is I'll let the alternator drag on the engine when I slow down. That would work better with a high output alternator = bigger drag until battery is full.

I don't think I understand quite what you're trying to do.

If you disconnect your alternator while the car is running all you're doing is taking power from the battery, there isn't any more or less drag caused by your alternator.

[Daox]

Yes, the alternator does put a load on the engine Stevo. The electricity it produces isn't free.

[Buurin]

Update

Brake trigger circuit wired up. Ran my battery once beyond drained and put in a Optima Yellow Top. Next is a voltmeter.

The gains, if any, is almost undetectable.

[Pineapple]

^What ever saving you had is spent on new battery. But its a good experiment.
How about make a switch to work with battery voltage? Turn off alternator when battery is above a certain voltage and turn it on when battery is below a certain voltage?

[Stevo_Echohb05]

Originally Posted by Daox

Yes, the alternator does put a load on the engine Stevo. The electricity it produces isn't free.

O.K. I agree energy isn't free, you are taking power produced by the engine to produce electricity.

I am curious though, if you took the belt off the car and spun the alternator how much torque you would need and then the the key on put a load on the battery and spun the alternator. How much more force is necessary? Enough to have an effect on fuel economy?
Also if you are running off your battery and the alt is off then you only have 12.~V in the best situations not the 14.~V that you get with the alternator running which might affect your spark

[Daox]

A guy on ecomodder did before and after testing by removing the belt for the alternator. His testing showed a 10% increase in fuel economy without the alternator.

http://ecomodder.com/forum/showthrea...g-gain-98.html

It is quite possible that the lower voltage effects spark. I haven't seen any valid testing showing the effects though.

[Stevo_Echohb05]

Originally Posted by Daox

A guy on ecomodder did before and after testing by removing the belt for the alternator. His testing showed a 10% increase in fuel economy without the alternator.

The test he did involves removing the belt, which, depending on what else that belt drives ie; water pump, power steering pump, idler pulley, a/c. would not be putting load on the car. Also his testing method cannot be that accurate,what were the driving conditions, how far did he drive? There are so many variables to consider ie; throttle position, how fast he accelerates, wind speed, direction........ it goes on and on.
I would expect this result on any car, he didn't turn off his alternator, he removed it completely.

The easiest test
1. remove belt, spin alternator
2. turn on key, turn on all accessories, spin alternator

If it becomes harder to turn the alternator while it is charging then it confirms your theory, if it is the same then you will not see any better fuel mileage.

[Daox]

I would agree with you and would likewise be skeptical of any testing, but I know the individual and I know how he tested.

So, I know his car doesn't have power steering or A/C. The only thing on the belt is the alternator.

He used a level strip of road 1 mile long, made multiple passes in both directions with cruise control and averaged them. He ensured there was next to no wind.

So, he pretty much did everything within his power to make it as ideal as possible. There of course still are variables, but they are minimized. He also wouldn't post info that showed that the gain was less than the inconsistency between runs.

I agree that removing the belt would show greater benefits than electrical disconnection, but I doubt its that much.