disabling the alternator for better mpg

[Brock_from_WI]

I know I know this sounds like a crazy idea. But I got to thinking (my first problem). As I was scrolling though vag-com I noticed loading on the alternator was at about 25%. So I thought about somehow disabling the alternator on my trips to and from work (25 miles round trip).

So how easy is this to do? Is it advisable or would I be likely to damage the alternator in the process? I know a LOT about batteries and could even add 2 or 4 Trojan T-105's in the back to charge the main battery via an inverter and iota 55amp charger (or just parallel them). It might be an option to just set the charger for bulk (14.4v) and the alternator might not run anyway? The disadvantage here is the extra weight of the batteries, inverter and charger.

Anyone have an idea of what the car pulls in normal running once warmed up? 10 amps would be my WAG. I could put a shunt in line to read it, but with the alternator on it won’t be correct. If 10 amps were the case I should make it easy to and from work and charge at home (via solar). If that worked I would likely swap out the starting battery for a nice deep cycle.

My real question is how hard is it to disable the alternator and will it hurt the alternator? Pulling a fuse would be great and I could even show my wife where it was in case she had to use it to run somewhere.

And yes it is a goofy way to try to gain maybe 1, 2 or maybe 0 mpg, more of a test then a practical thing.

 

[GoFaster]

You want to charge the battery at home from a wall outlet so you can avoid using the alternator?

Sounds awkward, and the energy has to come from somewhere, so whatever tiny amount you end up not paying at the diesel pump you'll end up paying at your household electrical bill.

The car probably uses more than 10 amps. The two headlights alone are about 10 amps. Add in other lighting, radio, HVAC, instruments, whatever it takes to run the fuel injection, and all the electronics, and it's probably somewhere near 20 amps. The 25% alternator loading probably isn't at the alternator's maximum speed, and there is probably something in there for charging the battery after the last start-up and the last period where the car was not in use.

But ... 20 amps at 12 volts = 240 watts = 1/3 of a horsepower (roughly). Say 1/2 horsepower to allow for alternator inefficiency. Rolling down the highway uses 15 - 20 horsepower. The amount that the alternator uses is kinda diddly squat ...

What might be more productive is a way to cut off the alternator during acceleration / cruise and re-enable it during coast / braking, so that the alternator power comes from power that would have otherwise gone to the brakes, but on level terrain for long periods that's not going to work ...

 

[GoFaster]

Also, I have a feeling that whatever tiny amount of energy this strategy saves, it will cost back multiple times over via shortened battery life ...

 

[Mike_04GolfTDI]

Get a high capacity deep-cycle battery, and then cover the top of your car with solar panels. The battery will be charged all day long whether you're driving or not. Then, you'll likely have enough reserve in the battery to drive for a few hours without an alternator. You could also add a charger to the car so you can plug it in to top up if you need to.

In about 20 years your fuel savings might cover the cost of the solar panels....but it would sure be nifty!

 

[Brock_from_WI]

I have solar panels at home that I can recharge the battery so that’s not an issue. I guess I won't know until I somehow disable the alt and as long as I stay under 20% discharge on the battery it should last quite a while, not the original starting battery, but a true deep cycle.

I guess this is more of a test to see what the car actually uses electrically while running. I am also wondering if the ECU sees the battery voltage at likely 12.6 while running if it will assume something is wrong since it's not seeing 13.6-14.4 ish it usually sees. Only one way to find out...

Again my biggest concern with this test is if I might damage the alt somehow or if there was some other reason this would be a bad idea.

 

[Brock_from_WI]

I pulled the large wire on the left fused at 150 amps and that is indeed the alt. I drove down the street and the battery light came on, the engine was warm since I just got home from work, the voltage was 11.8 the load on the battery was only 8 amps, right after I stated it I had a reading of 23 amp. The 8 amp reading was engine idling and nothing on, DRL's off right now. I couldn't check the battery loading while moving but the voltage was pretty steady at 11.8 via scangauge. I checked for codes, but didn't have any in my short 1/2 trip. The headlights were noticeably dimmer.

When I got home I reconnected the alt wire and restarted the engine to see the voltage come back up quickly to 14.3 and was charging at a nice 35 amps.

 

[DrewD]

I disabled the injector pump to improvee my fuel economy

 

[troyg54]

What a great idea! I'll have to add it too my list. Who needs a water pump or an injector pump anyway.

 

[Brock_from_WI]

I know, I know, I am goofy crazy. It is just an experiment to see if it makes any difference or not. Although it might be like using a good wax to reduce wind drag or taking out the spare tire

 

[JRod]

Brock-

Don't let them bring you down for your efforts in the name of science. You are planning on disabling your power steering pump right? I am only slightly kidding, my brother has a beater A2 where the power steering pump started leaking so he just drained the system and disable it. It isn't too bad, but the car has smaller wheels. Maybe if he got a school bus steering wheel. It seems to get a little better mileage, but he is never that particular to say for sure.

 

[vwestlife]

my brother has a beater A2 where the power steering pump started leaking so he just drained the system and disable it. It isn't too bad, but the car has smaller wheels.

That's exactly what I've done with my '91 gasser Golf... I got tired of topping off the PS fluid every week or two, so I just let it run down and left it that way. The resulting steering effort at parking lot speeds is heavier than true manual steering would be, but it's bearable, at least with lightweight 13" alloy wheels.

And as for disabling the alternator, you could do that on an older diesel with a mechanical injection pump, but TDIs are too electronic-ized to make that practical. In fact, on old W123/W126-series Mercedes diesels, the engine consumes no electrical power once it's started -- so with the lights, HVAC, and radio turned off, the only electrical consumers are the clock and the fuel and temperature gauges.

 

[40X40]

The new a5 has electric power steering. (for better fuel economy)

Don't disable the alternator, most all the high tech safety systems
are electric. Want to bet your passengers lives that the battery has
enough charge to run the abs, air bags, etc.
I don't want to argue about how many watts, etc. the various safety
systems need, that info is nice to know. Its just that some things are
"a suckers bet" Your battery is just to get the car started and provide
extra energy (momentary) when demand exceeds the alternators capacity. The alternator only produces what the regulator calls for,
therefor if the battery has been recharged , it only has to produce the presently needed amount of current.
To recap,
Even well made and modern curcuits behave strangely when starved of the needed voltage. Your life and others depend on your car working
correctly. Oh yeah, the alternator out put can kill you. be careful.
Good luck, and keep on trying! (just something else, or on a non-airbag car)
Bill

 

[Brock_from_WI]

Yup I drove to work today with it disabled, normally at that same speed and outside temp I averaged 89 mpg (7 trips matched this one). Today I got 94. Of course this was only one trip. The voltage after the initial start slowly sank to 11.7 then suddenly jumped to 12.1 after about 4 minutes and slowly rose to 12.3 during the rest of the trip. I can’t think of what it was, it was only 41 outside so I doubt it was glow plugs that long. But it was a quick jump like something shut off.

Bill I think you are correct, right before I got to work the ESP light came on, still no codes but I suspect it was due to the lower operating voltage. I think I will have to use the inverter and charger idea. I will try a single deep cycle feeding a 400w inverter and a 10 amp charger back to the main battery, this whole setup come in less than 50lbs. I already have 10-3 (fused at 60 amps) from the main battery running to the back for the inverter so I can just send power back the other way, fused appropriately of course.

When I drove to work I got that same feeling of running about 900 miles with the gauge on empty and the light fuel on, on a single tank.

 

[Brock_from_WI]

Oh and I would never disable this with anyone else in the car, bad enough with just me on my max 35 mph route to work.

And yes I believe the existing battery is just to even out the bumps and get the car started, the alt does all the real work and supply’s the real power.

 

[DOX]

Hi, Racelogic use to make "Alterpower", a performance device that disabled the alternator at full throttle and it was claimed to give 6-8 BHP. As an economy device the best set up would be for the alternator to charge when coasting (foot off the throttle). The alterpower had built in battery monitoring to ensure the battery had adequate charge and so only used one battery.

 

[wantabeTDI]

Did you ever consider using a dc motor to run you alternator this would keep your battery charged up, and free up the lost horse power that alternator suckes up. As far as the battery goes it supplies all the power to the vehical, the alternator keep the battery charged

 

[bugablue]

Did you ever consider using a dc motor to run you alternator this would keep your battery charged up, and free up the lost horse power that alternator suckes up. As far as the battery goes it supplies all the power to the vehical, the alternator keep the battery charged

Now we're playing with perpetual motion. I think we may have the next Nobel Prize winner here guys!

 

[Lug_Nut]

I daresay the weight of the Trojans and the inverter and wiring will increase the rolling resistance enough to negate any fuel saving. The weight will undoubtedly increase fuel consumption in accelerating that added mass up to steady-state speed, as well as consume brake linings at a faster rate.
Change the 120 Ampere alternator for an 80. The re-charge will take longer following starter motor operation, but will be less load during that time. Disconnect the coolant heaters (750 watts or nearly 1HP when they're operating). Change the adaptation of the engine glow plugs so the pre-glow and post-glow phases are shorter in duration.

 

[bhtooefr]

This thread makes me laugh.

If you want ultimate economy, here's what you do.

You get a Mk2. Preferably one that never had power steering in the first place. Or AC. Actually, the less options, the better. (Except for the alloy wheels, you want those. )

Why a Mk2? Simple. It's a lighter car, and it's only slightly less aerodynamic than a Mk4 Jetta, and more aerodynamic than a Mk4 Golf or New Beetle, or a Mk5 Jetta. (Note: I don't have info on the B4 or B5.5 Passat, or the A3 Jetta.)

You get a 1.4L VE-TDI out of an old Polo. You put it in that Mk2.

You take the seats, except for the driver's seat out. You take the dash out and have the cluster barely held in. You take what remains of the HVAC system out. You take all trim out. You shave off every ounce you possibly can.

Then, you drive really slowly.

You don't disable the alternator.

 

[KROUT]

This is just dumb to consider. Really how much saving can you get from this. By the time you get something rigged up to work how much did you spend and will it really help.? How much life are you removing from your batt? This is one of those things you just laugh at and shake your head at.

 

[Slave2school]

You guys crack me up, the author knows this isn't practical but it is an experiment. I'm sure glad some "idiot" out there frigged around with mold long enough to discover the first of our practical antibiotics...let see what we can learn at someone else' expense.

 

[bhtooefr]

Wait a minute, so the chemical reaction caused by the batteries being run too far down will cure cancer or something?

 

[Slave2school]

No, but this is all good confirmation of what a person can do in a pinch if the serpentine belt happens to break in the middle of no where...at the very least.

 

[bhtooefr]

And this is well known already.

Heck, my car's manual lists belt sizes. By the size of whatever belt drives the waterpump for that particular engine configuration, there's an asterisk. The manual says that that belt is essential to engine operation and it is suggested that a spare be carried.

However, they didn't say that for the one that drives the alternator, at least on AC-equipped cars (those run the alternator off of a second belt that runs off of the AC compressor. However, the waterpump belt IS the AC belt.)

 

[uberdiesel]

So how easy is this to do? Is it advisable or would I be likely to damage the alternator in the process? I know a LOT about batteries and could even add 2 or 4 Trojan T-105's in the back to charge the main battery via an inverter and iota 55amp charger (or just parallel them). It might be an option to just set the charger for bulk (14.4v) and the alternator might not run anyway? The disadvantage here is the extra weight of the batteries, inverter and charger.

Anyone have an idea of what the car pulls in normal running once warmed up? 10 amps would be my WAG. I could put a shunt in line to read it, but with the alternator on it won’t be correct. If 10 amps were the case I should make it easy to and from work and charge at home (via solar). If that worked I would likely swap out the starting battery for a nice deep cycle.

Sounds like your attempting to bilt ze furst TDI hybrid!

 

[bhtooefr]

You can do that already

Just disable the clutch interlock, and put a fuel cutoff switch in the cabin. Then, crank the starter around town while holding the fuel cutoff.

 

[Slave2school]

I was fairly certain that if the serp belt breaks on the TDI you aren't going anywhere. Disconecting the wire as has been done here is the only way I thought you could carry on (and would be ok to do as the waterpump is on the TB, and I think you can live without a/c in an emergency situation). I for one didn't know that it really could be done because I've had no reason to try, or heard of anyone else trying.

 

[vwestlife]

the waterpump is on the TB

That is true for the Mk4 series TDIs and newer, and the old 5-cylinder Audi diesel, but not for 1Z & AHU TDIs and all older 4-cylinder diesels.

The one benefit of having the WP on a V-belt is that if the WP siezes, it won't ruin your engine.

 

[bhtooefr]

And, conversely, the one benefit of having the WP on the TB is that if the V-belts get thrown, it won't partially ruin your engine

*ahem*

(I speak as an owner of a 1.6NA that now needs rings due to an overheat because of the V-belts being thrown... )

 

[schwechel]

I think some people are missing the point of this and not reading the whole thread. I saw the title of this thread a few times and never thought to look at it because it didn't make much sense. I don't know much about cars, but I don't think that disabling the alternator is a smart idea, not to mention all of the risks that disabling it might come up with. Brock knows this too, and he has even stated (multiple times) that he is not doing this because he wants the ultimate in MPGs, or even to gain mpgs. He said that he is doing this as a test. I think it's awesome that people like Brock take risks with their cars and try different experiments. Where would we be if people didn't monkey around with their cars and try new things? Ernie wouldn't have is wing, david wouldn't have shown people how to do a .681 5th gear, etc. I agree that some ideas show more promise than others when they start out, but that doesn't mean that they shouldn't be explored or tried. I remember thinking that disabling the DRLs was silly because the slight increase in mileage that you might get might not be worth the risk that your car is less visible. Other people thought this as well, but it's now a common thing and widely accepted. All great inventors are thought of as crazy when they first start out with an idea so Brock apparently you are on the right track for something so I say keep going and I applaud you for having the guts and ambition to try this. Anyone who says you are crazy or that this is a dumb idea needs to open their eyes and look beyond what you are doing to the potential that it has.