on/off switch for alternator? (Looking for directions / help / how-to)
 

Hey everyone,

just wondering how i would go about adding an on/off switch to deactivate my alternator to achieve higher mpg! ... if anyone could send me in the right direction that would be great

i'm driving a 2003 toyota echo

thanks

I did this to my Paseo (which has the 1.5L engine that came just before yours). It works extremely well as long as you don't need to go on long trips. You'll also need a deep cycle battery to replace your normal starting battery. You can see my mod done here:

Daox's 1997 Paseo Build Thread - alternator disable switch

easy stuff...

do you know where i'll find that "alternator field wire"... is it a tiny wire that runs of the alternator into the cabin?

My alternator has a connector with three smaller wires coming off of it. I unplugged each of them individually until I found the one that made the difference. It was noticeable. Unless you have a wiring diagram, thats the only way I know how to identify it.

Hey

ok .. i think i go it ... I saw the 3 wire plug off my alternator ... red/blu/yellow...

i'll mess around with it on the weekend.

thanks for your help! :)

Might even be the same alternator. Mine was the middle one, it was blue.

could you find the positive lead and connect a SPST toggle On-Off ?

Connecting and disconnecting the positive lead on a working alternator may harm the voltage regulator (or something else). If your alternator is self-excitingand doesn't have a field wire (not to be mistaken for the dash light wire), then you're more or less screwed. Someone here tried re-soldering ther electronics of a self-exciting alt, but I'm not sure if it worked.

I think your gains would really depend on a number of factors too - lot of people pull their alternator entirely (mostly for racing) because the engine still has to drive the alternator even if its not being used and puts drag on the engine.

I played with going alternator-less but I couldnt find a belt that would work and I didnt want to put a pulley in place of the alternator because I wanted to be able to re-belt for long drives (pretty simple matter with the Ford escort if you have a breaker bar - takes about 5 mins)

So..I gave up.

This is a bad idea, too many undesirable side effects (other than the obvious dead battery risk) for negligible gains.

Negligible gains? AutoMc - you may want to read up on this one a bit more.

Of all the mods I've done, going alternatorless offered one of the single largest MPG gains (10% boost at 70 km/h). It's right up there with the full boattail (15% @ 90 km/h). Almost all the other mods I've done are in the 2% improvement range. Others can provide similar alternator success stories.

But the operator has to know when/how to use this mod to get significant gains. Simply turning it on/off at various times while driving won't net much (could actually make MPG worse.)

Fuel economy gains will only come from depleting the battery while driving, then recharging from the grid (or other source) at the end of the trip.

Side-effects can be managed. It's not without problems, but it can provide big returns.

If you've reduced all other losses to the extent that you're seeing over 80mpg, then yes it becomes a larger % of the losses. I'm sure that the measured 288W while running @ 14.4V was way less than 200W @ 11.5V. Perhaps null point if that loss is being taken out of the equation but you can reduce this loss while retaining functionality.

Spinning an unloaded alternator by hand is easy, that belt is not very significant. What is would be reducing the loads. The best method is explained in that article, switching the regulator voltage. Think about what happened there.
-You cut the voltage going to the spark plugs (possibly reducing MPG). Ideally you would want to keep this one up there as a weaker spark is less effective as plugs wear.
-slowed down the fuel pump. Unless it's mechanical pump or a fancy PWM controlled one instead of the old on/off+FPR setup. It's possible that downsizing this could help.
-cut the lights and resistive losses drastically. Do you think if those were all LED's you would have seen nearly 10% difference?

To be honest I am shocked to see that chopping 1/2HP would yield such a result in that test. That would mean the motor is only operating at 5HP?? Not very inclusive of a typical drive if the gains are totally swamped by a single acceleration.

Sorry to be so dismissive about this but I feel that it's a pretty important part to keep on there. From the perspective of running at a loss to recharge at home I can see the benefit, but outside of that it seems like you'd be putting yourself in a position to constantly fret about reliability in range and restarting.

You could install a dual load alternator like Honda uses, which voltage output changes according to load .

Also what about switch to high output phase when you hit brakes , that might help and not hinder mpg .

Make sure you label the switch for your wife. I've gotten 2 really nasty calls from my wife when she has taken the truck and couldn't get it started to drive home.
I use mine as a poor mans power boost. Making a left at a light or accelerating uphill, merging etc... I turn off the field wires (and A/C if its running). I have a small solar panel on the dash so on the way to the airport I turn off the alternator and then recharge the battery while truck sits at the airport for a couple of days.

And under those conditions, I have consistently seen a significant, measurable improvement in fuel consumption in real world driving (vs. that as-controlled-as-possible steady speed testing).

AKA range anxiety. Once you understand how much energy is available, and learn to monitor consumption (voltage, simply), it can be managed.

I also drive an EV. I understand this. It doesn't cause me to fret.

I'll be the first to say disabling the alternator is a complicated and not particularly user-friendly mod. I don't usually recommend it to people who aren't willing to put in the effort required to reap the gains. It's definitely not a "set it and forget it" situation.

EDIT: Also, you need to do the math. If your goal is financial savings, it could be a wash, since you'll be burning through and replacing batteries at a faster rate. (I have a source of cheap/free used batteries - not an issue to me.)