Hello all, new member here, and thank you all for the hard work at such a great site. I am honored to be a part of this!
I know a little about alternative electricity, and wanted to share what I have discovered. Having lived off grid for 3 years, and working on a few systems, and having incorporated a few ideas like this into some vehicles, here are some thoughts to consider:
* IF you take the time to build good connections, use adequate/over-sized wires, use over-current protection, keep the batteries topped off(not too topped off... and don't use sealed batteries for your first system, especially if you are NOT electrically inclined), select a decent, well-ventilated inverter, take care of any neutral-ground-bond issues if you incorporate pass-thru AC(a DPDT relay works quite nicely), and last but not least- properly understand your vehicle's charging system and properly integrate your piggyback system into it, THEN i CANNOT EMPHASIZE ENOUGH how great this works!! I say this with all due respect to the aforementioned negative comments and concerns, (most of which can easily be mitigated with, well, dealing with my "if's" above.)
* When a vehicle is driving down the road, unless you have an EXTREMELY fuel efficient engine, there is already so much waste it isn't even funny. So to piggyback a system on the existing infrastructure is for the most part a free ride. I'm not claiming "free energy", just making the comparison to 'most' gensets to wit: once it's running, the electricity is pretty much free. I'm not talking about loading the genset clear down to 3/4 of it's rated load, nor am I talking about installing a huge battery bank in a late 70's Ford/Mopar pickup with a 'puny' 40 amp alternator. Quite the contrary, I have found a strategically implemented system will harvest LOTS of SUPER-CHEAP battery charging.
* Most of the negatives can be mitigated as follows:
1 Installing a vacuum switch to activate an isolation relay which only connects your auxiliary battery bank into the vehicle's charging system when you are decelerating(high vacuum). This is true regenerative braking, as close to free energy as you are gonna get. For those of you with a decent amount of hills to negotiate and you are able/willing to use your tranny more for braking, you can really cash in. (Of course a dash-mounted switch can manually connect the system full time as needed.)
2 Installing a higher amp alternator. You can't justify installing a smaller alternator pulley unless you intend/need to really work this system as your primary charging source, in which case it's still cheaper than running 'another' generator at home.
3 Place the batteries where extra weight will assist with traction (in the winter) if you can, and of course read previous posts for much discussion about hydrogen gas & crash dynamics. With a little care, most of you can find a 'neat' spot for the batteries. There is a point of diminishing returns as to how much battery to pack around. A full size rig can easily justify 2 golfcarts and more, whereas a Geo Metro might want to limit to 1 group 27 in the trunk(read up on safety/missiles/hydrogen gas/acid). They must be protected from the nasty salt spray in the winter, and should be protected from the weather if you can. I run some of mine inside and some outside the passenger compartment. The ones inside are sealed, and yes they will become missiles in a crash if my bracketry (quite hearty) yields to the cubed velocity forces at work. I am intimately aware of my batteries' states of charge, take felt temp readings regularly, and am taking the risk on the missiles. But should 'you' put your batteries inside- probably NOT.
4 Most of the rest is good connections, ventilation, fuses/breakers, big cables, GFI, keep it dry/don't cook it in the summer sun, etc. etc.
5 For FANTASTIC system performance, some of you can install a simple battery isolator (the ones with 3 or 4 threaded posts in the heat-sink-finned aluminum), and hook it up in an UNCONVENTIONAL and SIMPLE way as to get well over 15 volts delivered to the axillary battery bank out of your stock, unmodified alternator. As long as your alternator can remote sense voltage, this works. Really nice.
We had a full size rear wheel drive domestic car with a 65 amp plain Delco alternator with 400 lbs of battery in the trunk. Selectable switching on the dash to select no alt output(nice for cold starting), low volts (13.x to the main system and 14.x to the aux bank), and hi volts (14.x to the main system and 15.x volts to the aux bank). Batteries only in the trunk(seriously restrained) wired to a 7-wire RV plug at the rear bumper(8 gauge wires used on the ground and batt terminals of that pug believe it or not), and a 12VDC only cabin. When we got home, we parked in the same spot each time and plugged the cabin into the car. I cannot tell you how nicely this worked. 12VDC input on our only laptop at the time which mainly supplemented home schooling, 12V florescent and LED(ugly homebrew) lights, an 8 cell boombox for tunes, few other goodies and we were all set. When we went to town, we had over 3 hours of engine run time round trip. By managing the voltage select switch and looking at return amps, this old car worked out pretty nice. We even left a few lights on in the cabin when we left so when we got home in the dark and plugged the house in, voila- we could enter a lit home. I even ground the tab off the trailer plug that locks it in the receptacle so as not to destroy the harness should drive away with it plugged in, which I did once:)
It can be done! Look at your average drive/errand times, and I bet most of you would benefit from some version of this idea. Gotta get to working, more to follow. Hope this painted a good picture. No criticisms/questions too dumb- feel free!
