hey Ross!
thanks for posting about our recent discussions. my proposed ideas brought out some great thinking and also helped to bring to light possible problems with using a 12 volt controler tied to one 12 volt batt in a series string of 12 volt batts.
story time now 
LOL
until now (approx 4 years) i have done without any form of battery charge controler. daily monitoring and manually turning loads on and off have been my normal way of keeping the batts at reasonable charge levels. talk about a pain in the butt!
most of what i do is for fun and seeing what i can make from a pile of salvaged junk. practically everything from my gennys and controls have come from salvaged dumpster goodies.
this winter i have been using my 7.5hp conversion to feed 3 phace AC to my heater bank i have installed in my oil fired furnace for additional heat. ballpark estimate, saved maybe 20% on fuel oil bills. largest problem i noticed was that very often the genny was running just under the 100 volt cut in and was basically loosing everything being produced under that. i used every conceivable heater configuration i could dream up including capacitors to bring the genny on line to small voltage sencing relays to control the load relays to the elements.
my solution, and i am sure gives me more captured energy in the long run, was to charge batteries and have them dump DC direct to the elements via a dump load controler.
a simple charge/dump controler that used to be available was the "mikes" charge/dump controler that was available as a build it yourself kit. it was basic, simple, adjustable cut in and cut out points, and was 100% better than no control at all.
so what i did was put the batteries i have ( a super mismatched set consisting of 2 6 volt trojans, a wallymart 12 volt starting-marine duty, and some desulphated car batts that seem to be working ok which i got from an auto repair facility). i totally agree with anyone that says that is a bad battery bank, and it is, but its what i got and it does work and does the job for now.
i did make 2 attempts in the past to build a mikes controler, but both did not work. the looks of them would even have scared Frankenstein. my electronic skills lack desire. the third one however does work.
so what i tried first was setting the batts up as a 48 volt bank. the genny is in a 1 star configuration but seemed to slightly stall under load unless wind was very strong. simple solution was to add another 12 volt battery and raise the cut in rpm, and it also brought up the kw rating of the element bank. all elements (6) are now connected paralell, and when the contoler dumps, i get a 32 amp input to the elements with about an average of 68 volts DC. almost a 2200 watt load.
the reason i tapped off of only 1 12 volt batt was because it was a simple soluton at the time, and does work extremely well for dumping. i have the trip points set at 14.6 volt and 12.6 volt. the dump mode often stays on quite a long time when i have good wind outside.
the controler does however not carry any of the dump load. the only load on the controler is a tiny 1 pole N/O-N/C 12 volt relay which is just used to control the coil in a 3 pole 40 amp contactor. the 3 poles of the contactor have been ganged together to be used as 1 pole. so far so good. DanB has suggested i find one of the old mercury displacement relays sometimes available on e-bay which would handle the dc voltage and current much better in the long run. i am sure i will eventually burn the contacts in the present one in use (but i got lots of them).
i daily take part in discussions on the irc chat line (i just go there to drive them all nuts 
and with the knowlege and expertise of many of them there, have helped to come up with some re-design strategy so that this simple controler can be made with additional parts, truely compatible with 12-24 and 48 volt battery banks. it will not have PWM or any fancy charge settings. it will be a basic charge/dump controler able to work on all 3 of the common voltage banks, and be fully adjustable for the charge and dump settings you determine.
i did some research locally and on e-bay, and found that the cheap controlers do not even have setable trip points (some locked at 13.8 and 11 volt) to the more elaborate (cadillac) of units and also cadillac pricing. price ranges seem to be from $23 to well over $500.
this is what has brought me to the idea that a revival with 12-24 and 48 volt capability of the original "Mike's controler may suit some of the needs by people out there who need a basic controler at a very affordable price. when all the bugs have been ironed out and i make another unit and test for sometime, i may consider having these units available for sale. personally at this time, a cadillac unit is beyond my budget and think many others are the same.
so far, the unit has been operating for almost 4 weeks without a glitch and does seem to work very well. that crappy battery bank of mine has seen all batts stay within .2 of a volt of each other after resting over night. to get an equalizing charge, i simply turn it off.
anyone with ideas, views, opinions good or bad, please spit it out. i would rather have possible problems brought to light now rather than later.
zubbly
