Test: Alternator vs. no alternator = 10% MPG gain @ 70 km/h

[orange4boy]

Going alternator-less may be an effective efficiency mod, but it's definitely not a money saving mod unless you have a source of free or cheap batteries.

I have to disagree. A good deep cycle battery can last over 5 years if you don't go below 50% discharged often.
On a metro it would take longer to pay for itself but on mine, (25mpg average) It paid for itself within a year. I picked up an excellent automatic charger for $36 and my batteries at Costco for $50 each x 2

Excellent article though, as always.

I wish I knew how to set up exel spreadsheets. It would be helpful to be able to figure out the possible savings vs costs per vehicle based on current draw, battery costs and gas savings.

[Nerys]

I think this one is better

158W Thermoelectric Cooler Peltier Plate | Virtual Village - US

its about half the watts but its 1/3 the cost at $8

I have a feeling the 320w or 158 watts is what they consume and won't even be CLOSE to what they "generate"

if they generate even HALF those watts (doubtful) it will be interesting though. what is the max temp they can take?

if I am reading correctly it says 180c that can't be right. I would think those little wires would melt at 180c

or is that what the PLATE can generate? does any part of our exhaust hit 180c?

how do you measure the amps something puts out? usually you need LOAD to measure amps. for $8 it might be fun to get one and play with it. I have a 5 pound copper heat sink lying around too :-)

[Daox]

This idea has been brought up many times. Feel free to try it out though!

[Nerys]

I am waiting for someone who has already tried it to post some numbers :-) its a bit expensive a gamble as I don't have a real use for the things if it don't work out :-)

[Daox]

AFAIK nobody has actually done it yet.

[Nerys]

well the one critter ordered a pair of them so we shall see what results he gets :-)

[JackMcCornack]

I've put a switch in my mini diesel sports car that disconnects the alternator whenever I'm at full throttle. I drive with headlights on, and I figure I'm paying about a horsepower in alternator load, so a full throttle alternator cutoff is giving me about a 3% horsepower boost when I most need it. All well and good, but I have a further step in mind: is there any way to increase the load on an alternator when the brakes are on? I don't use brakes very much and I strongly doubt I have to worry about overcharging, it seems like it would be a slick way to get some braking energy back in the system.

[MetroMPG]

Sure, you could hack the field circuit of the alternator to increase its output.

But if the battery is already fully charged when you temporarily increase alternator output, you're not really gaining any efficiency.

Several automakers are incorporating this kind of "mild" 12v nominal regen in their vehicles - BMW comes to mind with 12v regen on engine over-run and when braking. But they're also intentionally drawing battery voltage/state of charge down in between regen events for the efficiency gain. (IE. not just under full throttle conditions.) All computer controlled, of course: if the SOC starts to get too low and the driver isn't providing any "regen events", normal alternator function resumes to protect the battery.

[Bearleener]

BMW has been experimenting with Peltier elements on the exhaust, I think. Also with exhaust-powered steam turbine generators.

So how much electric power do we need to cruise?
Going back to MetroMPG's original figures: alternator delete improved FE from about 70.68 to 78.08 MPG at 70 km/h.
Converting to metric (sorry, it's much easier for me):
Fuel consumption reduced from to 3.32 to 3.01 l/100km (wow, that's darn good!), i.e. a savings of 0.315 l/100km.
At a speed of 70 km/h we have 0.315*(70/100)= 0.22 l/h
Gasoline has an energy density of about 8.9 kWh/l, so that's 0.22 l/h * 8.9 kWh/l = 1.96 kW. That's how much power the engine is using.
Assuming an alternator efficiency of 55%, an engine efficiency of 29%, the electric power consumption is 1.96 kW * 0.55 * 0.29 = 313 W.
Sounds reasonable (somewhere here I'd seen that keeping the engine running (ECU, spark plugs, fuel pump etc.) takes about 150 to 200 W, so at cruising engine speed it's probably somewhat higher.

So we need to produce that much plus whatever accessories, lights, etc. we've got on.

How about starting the engine? The starter uses about 1 kW, say we crank it for 3 seconds (pretty long), that's 3000 Ws, so if we were to replenish the battery at only 300 W it would only take about 10 seconds (plus a bit for battery losses, probably about 10%). Not a big issue.

[Nerys]

I doubt its anywhere near 313watts. seems awful high. 29% is about 30times too high. car engines are less than 2% efficient IIRC. they are 29% efficient at extracting motion out of the heat of combustion but that heat of combustion is only a fraction of the total energy available in gasoline. or is that 29% how much COMBUSTION energy we get from gasoline? I had assumed when people say that they mean 29% of the atomic energy in the structure of gasoline IE half of what comes out of a matter antimatter reaction so to speak.