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MetroMPG 11-28-2007 09:49 AM

Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h
(Note: this thread originally written October 2006.)

Preliminary results

Speed 70 km/h / 43.5 mph

A: alternator belt ON - 71.16 mpg (US) - avg of 3 bi-dir runs (6 one-way runs)

B: alternator belt OFF - 78.08 mpg (US) - avg of 3 bi-dir runs

A: alternator belt ON - 70.2 mpg (US) - avg of 2 bi-dir runs

Or about a 10% improvement, sans alternator

MetroMPG 11-28-2007 09:50 AM

When people read about this, one of the first questions that inevitably comes up is: "can you just use a solar panel?"

Short answer: not really (for reasons of cost & potential aerodynamic penalties).

If you drive a normal amount, it will cost you a lot of money to get enough panels to keep your battery topped up, and you'll probably destroy your car's aerodynamics mounting them on top

The only reason I can get away with solar recharging is because I don't use my car very much (less than 200 miles in May). It could easily take a couple of days for my panel to replace the electricity I use from the battery in half an hour of driving.

The panel I have is equivalent to a 1 amp trickle charger, and it cost $160 CDN (I got it to keep a boat battery charged):

A typical electric battery charger "trickle" setting is 2 A (twice the power of my panel), and they cost a fraction of what solar panels cost.

MetroMPG 11-28-2007 09:52 AM

I've updated with an article on this topic, summarized and describing my experiment in more detail:

Thanks to Brock for corroborating the results with his Jetta.

MetroMPG 11-28-2007 09:58 AM

For this approach to make sense financially, you would neither either (or both) of:

1) fuel that is much more expensive than it is now;

2) a supply of free or cheap batteries.

Fortunately, I've found (2).

Today, with two 6v "junk" batteries (from the forklift company) in series to make 12v, then in parallel with the existing 12v starting battery, I did a 46 mile / 74 km alternator-less round trip.

Starting voltage: 12.68
Ending voltage: 12.40 (batteries resting for 1 hour)

11.7v is "empty", so I used 26% pack capacity in that trip, with light accessory load: wipers occasionally; heater fan occasionally; lights; occasionally; plus engine overhead, turn signals & brake lights.

Assuming similar electrical loads, my total range to 100% depth of discharge is about 177 miles / 285 km.

MetroMPG 07-29-2008 10:21 AM


My home-made water pump belts were enough of a pain in the butt that I hadn't been doing much alternator-less driving since last summer (2007). The belts would work for several hundred km, and then fly off or fray and wear out (and then fly off).

I once missed hearing the belt fly off, and pegged the temp gauge. So I was looking for a way to electrically shut off the alt, and leave the reliable OEM belt on to drive the water pump.

But because the Metro uses a "1 wire" alternator (senses battery voltage and feeds current through a single fat wire), there's no easy external way to tinker with the "control" wiring to shut down the field.

So I took the plunge yesterday and simply cut the output wire. Put two golf cart batts into the back of the car, and headed to Ottawa for the EVCO meeting. (I'll add a switch in the wire later.)

Predictably nice results - and one of those super rare situations where I had a tail wind on both directions (moderate on the first leg, light on the return)!

78 mpg (US) on the way there, strictly DWL with an avg speed of 36 mph, (that speed includes city driving at both ends, and passing through one town in the middle). My "target" highway speed was around 45 mph.

84.5 mpg (US) on the return trip, DWL again with an avg speed of 37 mph, max of 57.

Compare that return leg to a previous winter trip on the exact same route where I got 75 mpg (US), with an average speed of 28 mph, using 3rd gear pulse and glide the entire way. The winter differences being: alternator on, no Kammback, no tail wind, wet/slushy roads, and it was 2 C instead of 19 C.

Daox 07-29-2008 11:44 AM

You crazy 1L drivers...

Very nice though.

Formula413 07-29-2008 10:14 PM

Great info.

MetroMPG 07-29-2008 11:01 PM

Recharged (mostly) the batts today via an 80w solar panel.

I have another couple of short-ish trips tomorrow. Will post back on the MPGoodness of them as well.

Now I just need to go find myself either a beefy switch or male/female connector so I can reconnect the alternator wire next time I need the dino-powered electricity.

MetroMPG 07-30-2008 04:29 PM

62 km round trip (about 38 miles).

90% on secondary highways, 10% sub/urban, light crosswind, 22 C.

First leg: 78.8 mpg (US), 39 mph avg speed, 60 mph max speed, strictly DWL except EOC to stops in the sub/urban stuff on each end.

Return leg: 86.4 mpg (US), 37 mph avg speed, 53 max, mostly DWL with about 10 P&G cycles thrown in for good measure around hills.

Batteries are recharging via solar...

RacerX 07-30-2008 11:09 PM

That's Ironic that you started this thread up. I've been reading your tests and have been thinking about it for a while now. Just this past Sunday this is what I did. I'm doing this in preparation for some wild ideas I have.....Anyway. I cut that battery cable going to the altenator. My plan was to use a plain old bosch relay and throw a toggle in on the dash. But when I flipped the fuse cover and saw that massive 70amp fuse in there I instantly decided to use a Continous Duty Solenoid. Like a Ford starter solenoid. Well I wired it up and it works great. It makes a big difference at idle. I can't really tell at 55 mph....I don't see a difference on the vacuum gauge or tach. If I get a chance this weekend I'll post some pics on this thread.

Question: What do you think the % gain mpg wise would be If the Altenator was to be driven off of the right rear wheel?

Has anyone ever made an altenator spin just from air/wind speed?

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