Attention! Alternatorless modders. Get your voltage up

[RobertSmalls]

Originally Posted by gascort

If my logic is correct, my Optima Yellow Top D34/78 has 55AH of capacity. It has been fine to get me to and from work. Since this new battery I'm adding in series is 4V out of the total 16, it will only be providing 1/4 of the amps to the circuit, so its 9AH * 4 = 36 effective amp hours relative to what the optima was providing.

Nope.

If you have the batteries in series, the current flowing through each will be the same. To use a plumbing analogy, voltage is like pressure, and current is like flow rate (how many electrons pass a point per second, if you like). So if you draw 18A while driving, your 55Ah battery will last 3 hours, and your 9Ah battery will last 0.5 hours. The best case scenario is that your 16V will slowly droop as the batteries discharge, and after 0.5hr, the 4V battery will be at 0V and the system will be at 12V. The worst case scenario involves internal resistance rising in the 4V battery.

If your starter draws 200A, the terminals on your 4V battery need to be rated for 200A as well.

Hmm, that leads to an interesting idea. Why not just place a 2.3V NiMH battery in line with the fuse that goes to the ECU, or whichever system you're trying to fool? You won't blow out headlights or anything. If all you need to fool is the alternator warning light bulb, the battery would probably go weeks between recharging.

[hyperyaris]

Do alternatorless cars use magnetos? I am honestly intrigued, never heard of this.

[Daox]

Going alternatorless is a mod we do here on EM. No cars come without alternators.

[MetroMPG]

No cars... except certain hybrids. :P

[orange4boy]

Arrgh! I just blew my inverter by hooking it up in reverse.

I am going to take it apart because the manual says it has internal fuses. Hopefully that's all that's wrong.

I'm going back to the 3-6 volt trojans for now.

It looks like I'm headed for a very good tank. I found some info while searching for 16V batteries that racers run higher voltage to get a hotter spark for higher HP.

Mpguino is still not working. Must be a bad solder.

[Daox]

Did you ever actually confirm that higher voltage returns higher mileage?

[orange4boy]

Just posted my latest fuel log and for this tank, a mix of hilly bowen, hilly city and some highway, I'm getting 24.36 combined. My usual average is 22.5 mpg. That's about 8% better. This is very encouraging because I did about double the Bowen driving to city/highway ratio. My last tank I kept voltage up only half the time but it shows an improvement as well.

This is the first tank where I managed to have the voltage up 90% of the time. I kept it at 14-14.5 but I think 18 volts will give even more gains. I found some info on racing sites where they were running 18v for more HP.

I keep hoping someone with a more consistent driving routine will test the high-low voltage issue. I rarely have the chance to do any benchmark A-B-A stuff here.

This really is important for alternatorless driving because all the results on this site are for going from 14.5 to 12V or less and the gains were about 10% so if there is another 8% to gain from alternatorless by keeping the voltage up then we have a much better ecomod here than previously thought.

Any takers?

[Daox]

When I posted my alternator disable on cmpg, a user there suggested running a DC to DC converter just for the ignition coil to get the voltage for the spark up. I doubt the rest of the system cares about voltage as much. Would be interesting to test it.

[orange4boy]

The DC-DC converter is the way to go. I plan to do it as soon as the budget allows and if I can find a 12-18V or 12-14.5 DC-DC converter. The wiring would be a pain but worth it for the savings and simplicity.

I think the fuel pump could use a boost as well. At least keeping it at 14.5. I'm sure fuel vaporization is much better if it can keep a high pressure. (another thing to test)

[Daox]

I'm pretty sure pressure regulation is all mechanical.