how to turn off alternator

[Stealer Of Souls]

With track day looming, I'm looking at anything that'll liberate a few kWs. So what's the best way to shut off the alternator? What wire should I disconnect? My battery should easily last the 8-10 laps per run, and I'll just reconnect the wire in the pits to recharge the battery between runs.
So what wire? Power? Ground? Sense? A different wire?

[pervert]

Not sure, but maybe you could take the belt off??? Or is that a stupid idea?

If electrical, I would recommend the earth wire be disconnected.

[deaf_rattle]

yeah i would agree with pervert.
take the belt off or its not worth doin.

as you are putting power into turning that pulley.

[kingcorolla]

if this is for your 4age, you cant take the belt off, otherwise your waterpump wont get drive.

if you disconnect the main power lead, (not the plug), it should shut-off charge. but IMO it is a waste of time with the engine still driving the pulley.

but meh, go for it.

[AceSniper]

lol as been said.... Taking a wire off just means ur batt dosnt get the power.... It dosnt have a clutch in the pully to stop the alt turning.

just pull ya a/c powersteering belt (if u dun want powersteering ) bit less drag.

make sure the belt on the alt is'nt to tight... just tight enough so it dosnt sqeal(slip)... some are done up to tight an drag the engine

[matt dunn]

if this is for your 4age, you cant take the belt off, otherwise your waterpump wont get drive.

Correct.

if you disconnect the main power lead, (not the plug), it should shut-off charge.

And will quite probably root the alternator as it will still try to charge the battery and the power will have nowhere to go so it will cookm itself.

Assuming that it has the tree pin plug on the rear, you can unplug it and run safely,

but,

With our race cars we have run we find without the alt going you will get 12.0 to 12.2 volts if you lucky withe everything running as opposed to 14.2 or more and that after only 2 laps of Levels the car started to miss as there was not enough voltage to the coil and we got weak spark at high loads.

But you can try it if you want.

Matt

[Stealer Of Souls]

if this is for your 4age, you cant take the belt off, otherwise your waterpump wont get drive.

Electric water pump.... so I don't need to drive it anyway...

as you are putting power into turning that pulley.

Okay in theory without power to engergise the rotor coil then there will be no output from the stator windings. It is this inductive connection that puts load on the drive shaft.
While you are putting power into the shaft to drive the pulley, it is the lesser amount of energy when compared to the energy required to turn the inductively coupled rotor/stator setup.
Also without the rotor field there should be no output from the stator as there is no rotating magnetic field.
That's motor/generator theory in a super nutshell (inaccuracies a plenty I'm sure).
Please correct me if a car alternator does not run the same way. I don't want to cook my alternator.



I'm running a spiral wound type battery. I think I should be able to sustain 12V for at least a few laps. When my alternator died I had the car running okay on only 11-11.5V, but I wasn't running high RPM. So maybe the same will happen here.
Try this at home kids. Disconnect the power lead from the alternator and listen to the engine... it will give you an idea as to the amount of load a alternator presents. (Hot4s dyno tested up to 6kW at high rpm from a modern alternator).

[kingcorolla]

if this is for your 4age, you cant take the belt off, otherwise your waterpump wont get drive.

Electric water pump.... so I don't need to drive it anyway...

ok so take the belt off then..

[ee904age]

Having an electric waterpump is probably worse, if you disconnect your alt, your battery will drain even quicker.

[NZ_AE86]

If you undo the 3 pin plug on the back you will be safe and not damage the Alt. but if you disconnect the main +ve terminal you will cook the Alt within seconds! As Matt said you will be lucky to get one lap before you start to have problems as your fuel pressure will be lower and your spark will be smaller. Try it if you want but I assure you that your Alt. will not draw more then 1-1.5HP!!!

[Twolitre]

Stealer Of Souls,
Was that the article whereby they were doing a few runs and on the last run they decided to take off the belts to see how much power could be gained? From memory the waterpump wasn't being run either so they could only do a quick run before the engine would overheat?
Personally I don't think removing the alternator belt is a good idea, but perhaps power steering might be a better alternative if your car is such equipped?

[sopachrga]

You will loose more power than you gain. The current that the battery will be able to put out will not be enough to provide a decent spark.

It will still run and you will still have +12volts, but there will be so little current that the sparkplugs will be less effective.

In all honesty I think you will be wasiting your time by doing this, also a battery will take about 30mins to fully recharge at driving revs, not idleing.

Allthough if you still want to go ahead with this, take the belt off, not the leads, you may find that some of the cars electrics will not work while the alterntor is disconnected.

[Dr-X]

Most of the drag from the alternator is caused by the inductance, not the moving assembly itself, therefore if you cut power to it, it will reduce drag.

Removing the belt is very simple, you just need a shorter belt. A lot of people here dont seem to think about little things like that.

edit: aaarg, sopachrga beat me to my next point. That's what happens when you open a thread in a new window then get up for a beer.

Someone tell me if this theory stacks up:
As has been said, when you run without an alternator, you're looking at about 12 - 12.5 v, as opposed to 14 - 15v. I would have thought that the extra power you get from running an alternator would give you that much better a spark, that removing it is likely to be detrimental to performance, if anything.

[ee904age]

Removing the belt is very simple, you just need a shorter belt. A lot of people here dont seem to think about little things like that.

Did you think about the little things like how the hell do you adjust/tighten the smaller belt without the alternator???

Although your posts are getting more productive Dr X, they still need more thought behind them.

[Dr-X]

I'm not familiar with these particular vehicles, but a lot of cars ahve nore than one point from which to tighten it. Can the waterpump not be moved on a bracket? Even if not, the alt could easily be replaced with a bracket and a pulley, which could be adjusted.

All I'm saying is dont dismiss these things because it's a little out of your perspective. Most problems like these have simple solutions if you just give it some thought.

[Drifter4ag]

waterpump is fixed.
No shorter belt can be used nunless you use the idler from another engine bolted on where a ze one would normally be on PS bracket or alt bracket from ZE
Removing the alt is not a great idea and net gains will be marginal when everyone laughs at you for running out of power coming through the s's and spluttering to a stop ..
while this sounds like a good idea in theory it would only be useful for a drag run .. not any serious / or even pretend racing.
Get inventive .. theres gotta be something else you can do .. you would be better of running race fuel and 25+deg advance

[blitza]

I recon you run 6-8 laps without it plugged in, then the same with it charging and see the result yourself, all the reasoning in the world don't proove shit. didn't do anything in matt's case, maybee it will in yours.

[RedMist]

I read an article once, forgot where it was, about 1/4 mile drag cars running alternators as the battery degraded to the point they didn't spark at full intensity. They were getting quicker 1/4 mile times with the alternator reinstalled.

But don't take my word for it... try it!
You could clutch the alternator, or remove it an put an idler there. I wouldn't just unplug it. There is an off road racer that breaks his exciter circuit with the kill switch. Every time the Kill switch goes off, the alternator is fried!

[Stealer Of Souls]

Twolitre:
The article in question was one where they purposefully disconnected the alternator to see what would happen. They disconnected one wire and that caused the alternator to shut off.
The result was a repeatable 5kW on a skyline and 3kW on a 1200 datto ute on the dyno. This is more than 1-1.5 hp.
The said they got about 4-6 full power runs on the dyno before everything started to give up.


Sopachrga:
I've had the car with no alternator on it before. Runs fine. Just a little scary when you watch the voltmeter dip violently every time you push the brake pedal... But that battery was very unhealthy.
I've also made a 20minute journey at night, with my headlights on, with that same sick battery...


blitza:
I will try this. But to be honest I'm not planning to try and break any records. So the results I come back with could be a little tainted.


Drifter4AG:
Gotta agree with the probably only useful for drags. But frankly I can't be bothered rigging up something that lets me cut the alternator just for the back straight... Which is my real desire...
Race fuel and 25+ advance will cost money...
Turning off the alternator --> free... 3kW for nothing... or pay for temporary performance...


ee904age:
Yeah. Waterpump will cause increased drain rate (it draws 7A at full load). But my battery is rated at 40Ah (120min reserve) so to kill the battery in 10 minutes means I'd have to draw 240A per hour.... In theory.


To the current/spark thingy --> Transformer theory.
12kV @1.5mA secondary would be 12V @ 1.5A primary.
so even if it was...
12kV@10mA sec --> 12V@10A primary
My battery can provide
780CCA or 780A for 10 secs at zero deg C...
or around 1100MCA --> 1100A for 10secs at 25 deg C...


And Dr-X sounds like he might have done some motor generator theory...

Anyways... I'm gonna try the run one session with alt, and one session with and make up my own mind. Guess I'll have to unplug the whole thing. Sounds like the safest easiest route. Although I have had the +ve supply to the alternator disconnected before (unknowingly), and the alternator is fine (it was off for about 2 minutes).
If I get more than one lap before I have problems I'm gonna come back and gloat...

[matt dunn]

Yeah. Waterpump will cause increased drain rate (it draws 7A at full load). But my battery is rated at 40Ah (120min reserve) so to kill the battery in 10 minutes means I'd have to draw 240A per hour.... In theory.

Yes but the AH rate is to dead flat. Your car will not be too good below 10V.


To the current/spark thingy --> Transformer theory.
12kV @1.5mA secondary would be 12V @ 1.5A primary.
so even if it was...
12kV@10mA sec --> 12V@10A primary
My battery can provide
780CCA or 780A for 10 secs at zero deg C...
or around 1100MCA --> 1100A for 10secs at 25 deg C...


Resistance of a Elec Ign coil can be down to 0.8ohms which at 14v is 17.5 amps thorough coil primary. This is to charge it up at a fast enough rate.



If I get more than one lap before I have problems I'm gonna come back and gloat

You may get a few laps, but depending on the spec on condition of your car you may not too.

Matt