120 volt dc charging system
 

if you were to use 120 volt dc motor, with 10 , 12 volt batteries in series, how could you charge them using 120 ac outlet?

Well you'd first have to rectify the AC into DC, then you'd probably find you had ~110V DC and you need more like 13.5-14.5V/cell to get any juice into the batts, so you could realistically charge only 8 cells in series.

wouldn't 120vac rectified be closer to 170 or 180vdc? 120 is the rms value thus when rectified will give you a constant peak. with that you could use a 180 volt system running your dc motor. but I think your range would be limited using car batteries.

my ac-dc theory may be rusty, been 10 years since college.

Yep, it's 170, but remember it still goes from 0 to 170 constantly. Without an inductor in there, the peak current would be too high and the average current too low.

A variac and rectifier would work, but a charger would pay for itself by charging the batteries right and making them last longer. If you want a cheaper system, drop the voltage.

couldn't you use a capacitor bank like they do on DC motor drives to keep the voltage at 170 or near that? I understand that the current would be tremendous which could be a major problem.

may be better to charge them all together in parallel. possibly set up a switch matrix with contactors to change them from series to parallel for charging. those contactors could get expensive thoug. you could have a run state and a charge state for the system. maybe have the series (run) state using all normally closed contacts and the parallel (charge) state on all normally open contacts and use 120v coils on the contactors so that you have to plug it in to charge it. also have a set of normally opens that the charger has to go through just in case someone accidentally unplugged the system.

there is probably a much easier way and what I mentioned may be more complicated than I stated, not sure.

this is something I threw together really quick so it may not be completely accurate but it may give you an idea of what I am talking about.

the contactors are pretty crude but remember that there are usually 4 sets of contacts on a contactor. also remember to take note of current carrying capacity of any contactors that you use. I think this will work but if you try it, it is at your own risk. I don't mind blowing up my own stuff but I am not going to be responsible for what someone else blows up.

also I am going on vacation and will not be posting for the next week so good luck

A friend of mine got around this by using a charger which runs on 240 volts...