Alternator v. no alternator - 10% gain @ 70 km/h - Page 6 - Fuelly Forums

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Old 10-11-2006, 02:31 PM   #51
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First you guys are great. I have a 2003 VW diesel TDI and have been messing with the alternator and most people over on the TDI forums think I am nuts. I have found I get about a 5-7% increase in mileage with the alternator disabled. I leave the alt in there and just pull the main fuse so it basically sees’s no load. I am sure if I removed the alt or belt it would help a bit but if my wife takes the car to work I can just pop the fuse back and everything is back to normal.

A couple of things I have found out. The car once warm pulls about 100w or 8 amps. Having a solar array on the house solar is not really an option.

The car will "throw codes" because it sees something is wrong. So I had to find a way to keep the main battery topped off.

When I start the car it runs glow plugs and then coolant plugs (even in summer) until the coolant temp hits 120F. These glow plugs and then coolant plugs use 80 amps and 60 amps respectively. So again I needed to keep the main battery charged.

So what I did was took some parts I had laying around, 6 6v deep cycle batteries (golf cart) put two of them in series behind the passenger seat. I ran that in turn to a 1500w inverter which in turn feeds an iota DLS 55 amp charger set at 14.4v. The voltage will slowly drop until the coolant heaters shut off then quickly come up to 13.8v. I haven’t thrown a code since I tried this setup.

I originally tried just paralleling the batteries but the voltage under those loads would just drop too far, usually about 12.4v and the car didn't like it.

But getting back to my testing. I ran a set route, 3 miles there and back 6 times, 3 each way. On my test runs I got 87 mpg with the alt on and 92 mpg (according to scangauge) with the alt fuse pulled about 5% better. I ran a whole tank last spring and saw about a 5% improvement on the entire tank as well.
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Old 10-11-2006, 02:51 PM   #52
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Nice work, man!

It's amazing to think that the fuel economy improvement from grid-charging the battery and not running the alternator offsets the FE hit of the added battery weight.

Just 10 minutes ago, I came in (from a de-belted alternator local mostly pulse & glide trip - 104 mpg), and thought to myself: "I need to add some extra batteries for longer trips."

Just out of curiousity, why did you have floodies laying about? You either have a cart, or you're an EV builder...
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Old 10-11-2006, 06:51 PM   #53
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LOL, close they are from my last battery bank from my solar PV system. My old battery bank had 8 Trojan T125's, my new bank is 8 AGMs for a total of 2000 A/H at 12v or 24kw total.

Oh no doubt the electricity is cheaper then the fuel burnt. Especially since I make some of it, and I charge off peak when my electricity rates are 1/2 the normal rate.
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Old 10-12-2006, 08:33 PM   #54
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Quote:
Originally Posted by Brock
First you guys are great. I have a 2003 VW diesel TDI and have been messing with the alternator and most people over on the TDI forums think I am nuts. I have found I get about a 5-7% increase in mileage with the alternator disabled. I leave the alt in there and just pull the main fuse so it basically sees?s no load. I am sure if I removed the alt or belt it would help a bit but if my wife takes the car to work I can just pop the fuse back and everything is back to normal.

A couple of things I have found out. The car once warm pulls about 100w or 8 amps. Having a solar array on the house solar is not really an option.

The car will "throw codes" because it sees something is wrong. So I had to find a way to keep the main battery topped off.

When I start the car it runs glow plugs and then coolant plugs (even in summer) until the coolant temp hits 120F. These glow plugs and then coolant plugs use 80 amps and 60 amps respectively. So again I needed to keep the main battery charged.

So what I did was took some parts I had laying around, 6 6v deep cycle batteries (golf cart) put them in series behind the passenger seat. I ran that in turn to a 1500w inverter which in turn feeds an iota DLS 55 amp charger set at 14.4v. The voltage will slowly drop until the coolant heaters shut off then quickly come up to 13.8v. I haven?t thrown a code since I tried this setup.

I originally tried just paralleling the batteries but the voltage under those loads would just drop too far, usually about 12.4v and the car didn't like it.

But getting back to my testing. I ran a set route, 3 miles there and back 6 times, 3 each way. On my test runs I got 87 mpg with the alt on and 92 mpg (according to scangauge) with the alt fuse pulled about 5% better. I ran a whole tank last spring and saw about a 5% improvement on the entire tank as well.

We have the makings a MPG beast here!
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Old 10-12-2006, 08:49 PM   #55
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Wow

Quote:
Originally Posted by Brock
LOL, close they are from my last battery bank from my solar PV system. My old battery bank had 8 Trojan T125's, my new bank is 8 AGMs for a total of 2000 A/H at 12v or 24kw total.
What a great idea!

So, did the added weight effect drivability and stress the rear suspension? Also, do you know the approximate weight and cost if someone where to set up something similar -- perhaps a write-up?

RH77
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Old 10-13-2006, 05:42 AM   #56
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Quote:
Originally Posted by theclencher
You guys basically made plug-in hybrids.
GM might say that, but I wouldn't. GM called its full-size pickups with autostop, an extra battery & an inverter for running power tools "hybrids". Silly marketing.

Doesn't a hybrid have to provide motive power from an electric motor to be a hybrid? Have to draw the line somewhere.

If you forget to push the clutch pedal in when you start a regular car and it moves via the starter, is that a hybrid?
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Old 10-13-2006, 05:58 AM   #57
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Quote:
Originally Posted by rh77
So, did the added weight effect drivability and stress the rear suspension? Also, do you know the approximate weight and cost if someone where to set up something similar -- perhaps a write-up?
The 6 batteries (even if 50 lbs each) would still have the car within its weight limits.
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Old 10-13-2006, 06:14 AM   #58
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Thoughts

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Originally Posted by MetroMPG
The 6 batteries (even if 50 lbs each) would still have the car within its weight limits .. If I'm saving 10% by running without the alt, then my fuel bill over the past year would have been reduced by roughly $34 over 8,700 km, or 0.39 cents/km. (And that's at higher CDN fuel prices.)
That's 300-pounds of extra weight, which I would say could account for a reduction in that 10% savings.

The question that next needs to be addressed is the range. Since the Diesel engine doesn't have a distributor, spark plugs, etc., then a battery isn't needed to run the engine. On a gasser, I'm thinking that the ignition system would drain the batts more quickly. I was also thinking about fewer batts for a short-trip commuter, but for a gasser, that might not be possible.

RH77
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Old 10-13-2006, 07:17 AM   #59
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The diesel may have a higher electrical overhead for the fuel pump, though, since they're high-pressure units. I don't really know for sure though. Just a guess.
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Old 10-13-2006, 07:32 AM   #60
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Frame of Reference

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Originally Posted by MetroMPG
The diesel may have a higher electrical overhead for the fuel pump, though, since they're high-pressure units. I don't really know for sure though. Just a guess.
The only frame of reference I have is a personal experience: driving an E-350 Diesel Ambulance back from a 100-mile round-trip transport. The charge cable to the battery busted loose (unknowingly at the time). Meanwhile, the digital electrical charge display was dropping like a rock. We were able to drive it for a ways, but it was storming and raining too hard to see (no wipers or headlights and tree limbs in the road), so we pulled into a gas station and had it towed back to base.

I think the alternator keeps things going -- in this case it was a heavy-duty alt.

RH77
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