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

[MetroMPG]

Originally Posted by darlo

How do I go about figuring out how much draw I have???

http://ecomodder.com/forum/showthrea...amps-9642.html

see also...

http://ecomodder.com/forum/showthrea...olts-8908.html

[darlo]

Any word on how large of guage wire I will need to use? Is 8 guage large enough for my two deep cycles? I only have a 50 amp alternator, so I will never be drawing more than that! LOL

[some_other_dave]

You really really do not want to go too small, so it's better to err on the side of too large.

The size of wire you need depends on the current it needs to pass, and on the length of the wire run. More current, more length == larger. You also need a ground path that is as large/capable as the + wire.

If the stock wires are 8 ga., I'd use 4 ga if the run is about the same length. If it's longer, I'd go with 2 or even 0.

-soD

[darlo]

50amps max at 12 feet max........

I think 4 will do!

[darlo]

Should I leave my starter battery in the mix, or disconnect it and save it from draining? Although if I keep it hooked up, all three batteries will drain less......hmmmmmmm

[byte312]

I really like this study that you have done. The same must be true of the power steering pump. I don't think I really need power steering once I get rolling. Could I run the steering pump off of a small electric motor that would turn on and off as needed? An ECU could do that based on speed.
The catalytic converter burns up the unburned hydrocarbons so why not replace it with a fuel cell? You would not need an alternator to produce electricity. I understand that I a talking about some big money to do all of this but you could also remove the other loads from the engine to test the gains.

[jasonck08]

A few things that people are forgetting.... I don't know about all cars, but I know my car 1989 Toyota Camry, does not like running without the alternator.

When the alternator is running the cars electrical system should be getting ~13.5-15v. With just a battery, the cars electrical system may only be getting 12-12.6v.

I know my headlights are dimmer, clock backlight is dimmer, sometimes acceleration feels strange some other glitches here and there, when voltage is lower.

Ideally, if you want to delete your alternator you should add a 7 cell lead acid battery (hard to come by). This would give you an extra 2v.

[Nerys]

12-12.6 volts is essentially a "dead" battery. once you get down to 12.5 or 12.6 volts you should STOP using that battery.

also remember you are running the car on a single "starter battery" which was never designed for that kind of load.

this is why we would use TWO deep cycle batteries.

also some of our cars are very simple "electrically"

I would for example never suggest doing this to a much more complex car. my pop's 96 town car is VERY ECU centric and uses a lot of power. it would NOT be wise to attempt to go alternator less in such a car :-)

your camry may be the same way.

[jasonck08]

Huh 12.5v-12.6v open circuit voltage is almost full for a car battery... Automotive battery - Wikipedia, the free encyclopedia

Starter batteries are designed for "that kind of load" they just are not designed to be fully discharged like a deep cycle SLA battery.

[Nerys]

I thought resting voltage full charged was 12.9 to 13.0 volts. Huh strange I see 12.6v all over the place so I am inclined to accept that value.

I have "know" for years 90% was 12.9volts. 12.5 volts would be 50%

I wonder where I got that from.....

while my assumptions appear to be wrong the value stands. at 12.6 volts you should not be using that battery. (12.5 resting volts is over 20% discharges 12.3 volts is 50% discharged)

unless you have a deep cycle battery than 12.3 volts regularly is "safe" without damage.

all resting voltage of course. so if you demand power is that high that you hit 12.3 volts pretty quickly you need to increase capacity IE second battery in parallel. 2x 12v deep cycle.