Alternator v. no alternator - 10% gain @ 70 km/h

[GasSavers_Brock]

DRW there really isn't much of a penalty for a larger battery beside weight. Well a typical lead acid uses about 1% of its rated power a day to stay topped off. So you could say a typical 440CCA battery, about a 60AH battery uses about .6 amps a day. A battery twice the size would use 1.2 amps a day to stay topped off. Not much in the grand scheme of things, but something.

Rh77, while it’s true that diesels don’t need much power once warmed up they require a LOT to get up to temperature. Even in the middle of summer my car will run its coolant glow plugs (60 amps or about 800watts) until the coolant hits 120F. I believe it does this to warm the engine quicker to help with emissions. In winter the car will run the regular glow plugs (80 amps or just over 1000w) for about 10 seconds before cranking and about 20 seconds after cranking depending on the outside temp. The two sets of plugs never run at the same time though.

[rh77]

Originally Posted by Brock

Rh77, while it?s true that diesels don?t need much power once warmed up they require a LOT to get up to temperature. Even in the middle of summer my car will run its coolant glow plugs (60 amps or about 800watts) until the coolant hits 120F. I believe it does this to warm the engine quicker to help with emissions. In winter the car will run the regular glow plugs (80 amps or just over 1000w) for about 10 seconds before cranking and about 20 seconds after cranking depending on the outside temp. The two sets of plugs never run at the same time though.

Ahh...didn't know that. From my Diesel ambulance days, (mid-90's Ford E350 Diesels) I don't believe the plugs were warmed at all unless called upon at startup. We ran a unit's batteries down to 0-volts on a long trip back to the station one stormy day when the alternator cable busted loose. It ran fine until we turned it off. Dunno about the emissions...

And yes, I was freezing cold most of the time in the Winter unless we drove a distance and kept it running all day.

RH77

[red91sit]

Originally Posted by JanGeo

Another thing to consider is the injector response is changed slightly when the battery voltage is reduced - think about it - it gets a pulse of a certain voltage which may be the full battery voltage through the ECU. Lower that voltage and the valve may open a little slower and end up leaning the air/fuel mixture - anyone ever trim the supply voltage to extend the mixture range? If anything it could affect performance at higher RPM.

I know on Ford ECU's (since 1986) they've had injector pulse -vs- voltage talbes (in case any one was wondierng)

[MetroMPG]

I wonder how it compensates. I'd guess that probably injector performance gets sluggish as voltage drops, so it lengthens the pulses to ensure enough fuel gets in.

[red91sit]

Originally Posted by MetroMPG

I wonder how it compensates. I'd guess that probably injector performance gets sluggish as voltage drops, so it lengthens the pulses to ensure enough fuel gets in.

I'm still tryign to figure out exactly what this does, but it clearly has something to do with voltage and injectors.

[DRW]

On the Mitsu ECU it uses something called 'deadtime' to adjust injector pulsewidth as system volts varies. Deadtime is a set ammount of pulsewidth added to the calculated injector open time. In effect, injectors need a certain ammount of time to open/close, during which they don't flow the full ammount of fuel. If volts are low, the injector opens slower. Once open it doesn't matter what the volts are. The Mitsu ecu has a table of deadtime values that can be changed, and they often need to, since swapping to larger injectors of higher or lesser quality is common in the DSM world. The stock deadtime values follow a similar curve to what red91sit posted.

[DRW]

Oh, one more thing. The Mitsu ECU stops trying to run the car at around 9 volts. There may be a similar cutoff point on other cars. YMMV

[JanGeo]

Originally Posted by red91sit

I'm still tryign to figure out exactly what this does, but it clearly has something to do with voltage and injectors.

As the voltage on the bottom of the graph is lowered (left) the intersection in the curve indicates the amount of added pulse width time - they may stay open a little longer depending upon the magnetic field strength and how quickly it decays which is a function of how hard it was energized.

[BuffaloChips]

Part of the reason for the mileage improvement is, of course, you took away the horsepower drain of the alternator. Sadly, the only thing is, you now are running solely on the battery(ies).

[MetroMPG]

The topic of generating electricity with thermocouples always seems to come up in the alternator-less threads.