Partial Alternator Elimination

[gascort]

Before I begin, this is a modified version of AndrewJ's and several other people's ideas...
I like the idea of eliminating the alternator, but I don't like the possible FE consequences of sensors and ecu operating at battery voltage and not alternator voltage. I also don't want to lug around heavy batteries. My solution: Alternator runs the Ecu and fuel pump only, attached to a small lawn tractor battery. Everything else runs from original battery, still in original location (just with the alternator not plugged in to it), with a (probably a relay) charge switch that connects the two battery circuits.

Here's a schematic of my plan. It allows for a cheap lawn mower battery to be used as a capacitor in the alternator - ecu circuit, and a source of power as the ecu needs to be on before the engine is turned over.
The regular car battery remains in its current state, wired to everything else on the car. I'll install a heavy gauge wire and a heavy duty "charge switch" between the two systems so I have the option of using the alternator as it's typically used. I think I'll try to use it when decelerating at offramps and down hills as well. The reason I want it to be capable of 50-60A is so if the big battery is drained down past the point where it'll turn the starter, I can use the lawn mower battery to do the job (infrequently, for sure, but a nice emergency jump-starter).
I will need to get a volt-meter to monitor my big battery's charge so I can charge it before it goes dead. For now, I'll probably wire my Digital MultiMeter (DMM) in to watch it.
I'm going to use a trickle-charger to charge the big battery nightly, and somewhere down the road I might try out some solar charging like Andrew did.
Any thoughts????

[FastPlastic]

Sounds like a good alternative to completely removing the alternator from the equation. Doesn't add a whole lot of extra weight/still has plenty of power for the parts the need it. Sounds good to me

[metromizer]

I like your approach, but my gut tells me you'll be replacing batteries much more often. Maybe often enough to reverse any economic gain from a small increase in FE...

my racecar has a 'total loss' electrical systems, meaning no alternators at all. We'd only charge the racecar battery before race day, then at the track after a few rounds. I'd trickle charge it every 6 weeks or so, during the off season. When battery voltage drops below 11.2v or so, the MSD ignition box delivers an intermitent signal, the engine misfires as a result, so having a battery in great condition was always very important. Sounds like you have that covered with two batteryies.

The standard lead-acid automotive grade car batteries I used would only last 2 years tops, but I'd replace them after one season (10-12 races when we were hitting it hard), relagating last years battery to trailer duty, where I was usually able to get another season out of it.

[MazdaMatt]

You may want to research the idea of connecting up a fully charged battery to a near empty one. This could result in a massive current spike from one to the other.

[gascort]

Originally Posted by MazdaMatt

You may want to research the idea of connecting up a fully charged battery to a near empty one. This could result in a massive current spike from one to the other.

Good point; would be the same as jump starting another car. I don't imagine it's recommended to jump start others very often... I may have to think about how often I'll need to connect the two. My hope was that I'd only do it in the instance of a freak - dead battery and on long road trips. On road trips, hopefully I'd have the big battery charged before leaving.
If I kill it, maybe the parts store will allow me to upgrade to a deep cycle battery with part of the return cost.