As far as solar cells, skewbe talked about that a bit when he first removed his alternator. For my 40 mile/day commuting I decided a 60 watt cell would probably be sufficient to charge me up while parked at work. A 150 watt or so cell would probably be more than enough to drive a blinker now and then and ignition coil without discharge.
Main issues in my opinion are the fact the 60 watter is about $300 and the 150 about $700+.
It takes a long time to recover those costs. Starter/alternator sounds like a good idea to me but then you have to deal with driveline losses. I always thought it'd be better to have a substaintially bigger motor on the driveshaft, it'd be used to accelerate up to 3-5 MPH and then popstart the ICE and also used to regen during braking (while engine could be completely off in neutral).
I have a question, is there a relay to kick in the alternator at full output?
I thought it was just one output (one pulley), when the engine spins faster it makes more current... ??
Or is there internal gearing in the alternator to tell it to give it little, medium, or a lot of resistance?
It has a lot to do with the sense wire, which goes directly to the alternator and gives input to the alternator's voltage regulator about the charge status of the battery - as much as it does alternator temperature and RPM.
When an alternator is stuck trying to charge a bad battery, it's pumping out full amps it can at a given RPM. When I load test them, it's easy to tell when I hook up the volt meter - 13.8-14.0 volts at the posts is about on par with a bad battery. In theory, if the sense wire was hooked to a volt source of under 10 volts it would give full output the whole time. The killer though, is that your battery will not like it and will die sooner. It is VERY easy to overcharge a battery and kill it's lifespan.
The alternator makes more amps the faster it spins (usually about 2 times the engine RPM) but it looses output the higher the temperature climbs. The graph below might make a bit more sense as it has RPM, temperature, and amp outputs on it.
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I wouldn't use such a relay personally, for the above mentioned issue of overcharging the battery, and because at higher RPMs the alternator could overload itself by producing way more voltage than normal (and hence way more charging current being pushed into the battery than normal)
Now, a relay that merely enabled or disabled normal charging depending on circumstances could be worthwhile. But in the grand scheme of things, the amount of energy the alternator is capable of receiving and shoving into a battery isn't much compared to what it takes to stop the car. You need a big beefy alternator and big beefy batteries capable of rapid recharging (read: weight or money, pick one)
Yeah, you'd really need a battery charger to regulate the power to charge them, not sure about lead acid, but you probably have to start a little low and then you can increase to full alternator power, but if this happens over a 5-10 sec period you're probably already don't braking.
The only other thing I can think of is a huge bank of capacitors to rapidly put major load on the alternator and then slowly feed the batteries. But that'd be money. Cheaply (and of course less efficiently but fun) you could remove cooling air to the brakes or use alternator as a brake to a sealed, resistor bank and throw a bunch of peltiers in there.
Horribly inefficient but peltiers aren't super pricey.
seems like a simple and effective solution. just wire the relay that you want to "full field" your alternator up to your brake light switch. it should draw more than 2 amps max. The only problem I see would be shutting it off automatically at idle so it doesn't draw power while you are sitting still.
You could make a small circuit that factors in information from the VSS. The VSS has a certain voltage depending on the speed, if you're going 0mph it will have a given voltage, at 20mph another voltage. So if it reaches or gets close to the threshold for 0mph, then the circuit will tell the alternator to shut off.