Solar/plug-in 12V system, alternator optional

[MetroMPG]

hi all. my first post. i'm pretty impressed with the signal/noise on this site. good work.

here's an idea to mull over. pardon me while i think out loud...

i read recently about a guy who removed the alternator from his vw bus, installed pv solar panels on the roof and a couple of deep cycle (marine/RV) batteries on-board. The output of the panels and the extra storage capacity of the deep cycle cells kept the sytem working fine, even at night - he drove round trip from texas to seattle on this set up.

how much fuel would it save if an engine didn't have to turn the alternator? depends on how much power the alternator is supplying and the parasitic losses needed to supply it.

if i had to guess, i'd predict savings between 1 to 5% - but that guess is based on a series of assumptions so unfounded, i'm not even going to bother sharing them here. maybe someone else is more informed on this topic and can accurately predict (if so, please share).

other options...

<ul><li>leave the alternator on, but add a switch in the rotor field control wire, effectively giving YOU control over when the alternator is active (from an efficiency standpoint, it's best "ON" when you're decelerating or descending a grade - the same times regeneration is active in hybrids)<\li>


<li>same setup as above, but only use the alterator switch as a back-up for long range trips. for short-range use, re-charge the battery with a charger in the evening. (you can tell your neighbours you've got one of the first plug-in hybrids.) or recharge with solar when you're parked.</li>


<li>even more efficient: take the alternator belt completely off (there are still parasitic losses (bearing/pulley fan) in options 1 & 2). again, recharge when only when necessary via solar/dc charger. downside: less convenient when you need the alternator for long-range trips or "emergency" charging</li>


<li>buy 2 batteries and charge one (trickle/solar) at home during the day, then swap batteries each evening or as required</li></ul>

just a note: deep-cycle type batteries (RV/marine) would be a necessary part of this approach. a regular automotive battery will be damaged/degraded from a significant discharge.

anyone with a scangauge want to do a quick'n'dirty run to give an idea of potential savings? "normal" vs. belt on/alternator disconnected vs. belt completely off?

i've got a scangauge, and would do it, but don't have a heated garage. winter has truly arrived here in ontario, with the result that further efficiency mods are on hold until the spring!

darin

www.MetroMPG.com
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[DracoFelis]

Originally Posted by MetroMPG

i read recently about a guy who removed the alternator from his vw bus, installed pv solar panels on the roof and a couple of deep cycle (marine/RV) batteries on-board.

I've been thinking about alternator drag due to electrical use as well. The idea has merit, and it might save you more FE than you realize. However, the very first thing I would do (and did do in my CRX) is to convert many of the lights to LEDs, to greatly lower power usage. This will help (by allowing the alternator to work less hard, and thereby put less drag on the engine) even if you don't do anything fancy with the alternator setup.

See this thread for some ideas on LEDs:
http://www.gassavers.org/showthread.php?t=1558

Originally Posted by MetroMPG

how much fuel would it save if an engine didn't have to turn the alternator? depends on how much power the alternator is supplying and the parasitic losses needed to supply it.

if i had to guess, i'd predict savings between 1 to 5% - but that guess is based on a series of assumptions so unfounded, i'm not even going to bother sharing them here. maybe someone else is more informed on this topic and can accurately predict (if so, please share).

I think you are underestimating the loss due to the alternator. Follow the links in this thread for more info:
http://www.gassavers.org/showthread.php?t=1798

Originally Posted by MetroMPG

<ul><li>leave the alternator on, but add a switch in the rotor field control wire, effectively giving YOU control over when the alternator is active (from an efficiency standpoint, it's best "ON" when you're decelerating or descending a grade - the same times regeneration is active in hybrids)<\li>


<li>same setup as above, but only use the alterator switch as a back-up for long range trips. for short-range use, re-charge the battery with a charger in the evening. (you can tell your neighbours you've got one of the first plug-in hybrids.) or recharge with solar when you're parked.</li>

Yes, you would always be paying the price of the "no load" alternator drag with this setup.

However, it would be easy/trivial (even when driving down the road) to switch between "no load" alternator and full alternator drag. So it is "friendly" to the driver (especially when you find yourself on a long trip, and need that extra power)!

Some other thoughts:

1) If you want to get fancy, rig up an electronic relay setup, to engage the alternator when you want "regenerative breaking" (you could still have the "always on" override switch, for long trips). The easiest (but not quite the most useful) way to do this, is to have the alternator engage the same time the break lights come on (and the car is in gear, as it does no good to engage the alternator when the car is in neutral and/or the clutch is in). This will give you the extra "regenerative breaking" drag when you step on the brakes!

2) I'm not sure if you would need some voltage regulator to use them in a car setup, but you can get reasonably powerful solar panels designed for solar power in a home. And while they still cost a bit (about $80 for the cheapest ones, and closer to $300-$400 for a few amp unit), they are much cheaper per watt of power than many smaller panel setups. Even one of these panels could (on bright days) get you a few amps of power for your car. As just one example of what is out there, perhaps the panels sold by "Backwoods Solar" (a company catering to homeowners whose home is off the main power grid), could be easily adapted for use in a car:
http://www.backwoodssolar.com/Catalogpages2/solar2.htm

Originally Posted by MetroMPG

<li>even more efficient: take the alternator belt completely off (there are still parasitic losses (bearing/pulley fan) in options 1 & 2). again, recharge when only when necessary via solar/dc charger. downside: less convenient when you need the alternator for long-range trips or "emergency" charging</li>

Yes, that would avoid the drag of the alternator at no load. However, it is a PITA when you need the alternator power.

If you were going to take that approach, I would recommend wiring things in with the switch setup (discussed above), and then only remove the belt when you are reasonably certain you won't need the alternator for a while (and when you do remove the belt, keep it in the trunk). That way you can "easily" revert to the more flexible "switched setup" (when needed) by just popping the hood and putting the belt back on...

NOTE: With the belt off, you will not get the "no load" losses from the alternator. But you also will not have any option for "regenerative braking".

Originally Posted by MetroMPG

just a note: deep-cycle type batteries (RV/marine) would be a necessary part of this approach. a regular automotive battery will be damaged/degraded from a significant discharge.

Agreed. You would want to replace the normal car battery with something designed for "deep cycle" (and hopefully with more amp-hours than the normal car battery as well).

Originally Posted by MetroMPG

anyone with a scangauge want to do a quick'n'dirty run to give an idea of potential savings? "normal" vs. belt on/alternator disconnected vs. belt completely off?

Sorry, don't have a scanguage.

[JanGeo]

Aside from the belt load which may not return enough to bother with long term because you WILL need electric power at some point. The simplest solution that is non-invasive is to supply power to the electrical system from another power source i.e. solar panels and an additional power regulator from another battery. If the car battery is supplied current that keeps it about the 14.x voltage the alternator will stay "off" and not load the engine and the car battery stays fully charged and will not have it's life shortened by cycling. The additional battery will provide power until you want to regen down hill charge it from the alternator then you just load down the system and charge the extra battery or charge it from the solar and/or grid when you stop and park. This will also allow you to run accessories longer without the engine running like when you are coasting with the engine off while maintaining full system voltage for brighter headlights.