Electrical Guru's -
 

Lets say I have a 120 volt AC generator.

And, Lets say I have a set of 4 lead acid batteries - each 12.6 volt nominal all in series.

Can I "rectify" or whatever the AC generator and make it a battery charger????

Yep, simple diode bridge. Add a capacitor to smooth it.
If the amps are low, its under $5.
Bad part is the 160+ VDC will charge the batts REAL fast and blow them apart. It would only work if you had more batts in a series to get closer, say 12 of them.

A basic charger would be much safer :)

Not my drawing :

https://lh5.googleusercontent.com/-K...ow_charger.JPG

Wish I could take credit for it

yes you would have to rectify it. but your looking to charge a battery pack of 48 - 50vdc? to get that voltage that you need its not that easy.

you will need at about 58-60vdc and between 20-30 amps.

I would leave it 120 and install a battery charger

I know in my job i work with battery chargers. I know sens makes a 120vac input 24vdc @10 amp output charger thats a reasonable price. or Charles is another company.

I have 4 batteries in series. I want to charge them at once with 120 volts.
Seems to me 12.6 times 4 equals 50.4

Seems to me alternators normally charge batteries at 14 volts. So, it seems to me if I charged at 60 volts DC, I would be pretty close to perfect.

So if I take 120 volts, and stick a diode in it the right direction, I'm gonna kill one leg of the AC current, and have 60 volts peak charging my batteries.

Obviously it is not this simple, so what am I missing?

where do I find a 50 amp, 60 volt charger cheap?

is that your output? what type of input are you needing?

my input is an 8 horsepower briggs and stratten engine.

120VAC (RMS) has a peak voltage about 170VAC.
No matter how it's rectified, you still have 170VDC peak. Even if it's pulsed, your batteries won't like that.

If you run the 120VAC through a suitable step down transformer, then rectify it, that'll work, but it'll probably cost you near the same as a "proper" battery charger anyway.

You could use a varriable AC transformer (varrac) and charge at what ever voltage you want. They can be had on ebay for cheap I bought my 300v 5kw varrac for $180, smaller can be had for a lot less.

I am sure you can pick up a small varrac for a lot less than a 48v DC charger.

Also you could automaticly control the charge time with cheap lamp timer or light switch (or heat lamp) timer from lowes.

1: the batts will need something to reduce the amp draw to them. Even if you hooked a 60A rectified xfmr to them, the batts will try to draw as if they were a near short. Heavy charging will hurt them quickly.

2: charging at a higher pulsed voltage will not kill your batts, but you need to use a timer as oilpan4 stated. I've charged 36V and 48V golf carts/ scrubbers/ pickers with this circuit. I watched it, but about 4hrs oon a timer would be good.

3: Alternatively, you could use a xfmr to drop to around 39VAC then rectify that to DC and have a trickle charger.

hmmmm......
Ok then.

How about this. I have 4 batteries in series. Can I build a non grounded alternator, and a switching mechanism to charge one battery after another?

So, I'd charge the first battery with the alternator for 2 seconds, switch to the next, etc.

I'm thinking about using a set of 4 or 5 lead acid batteries in series to run a golfcart motor (cheap).
Then use a small onboard gas engine with alternator/generator to extend the range.

How large of a battery pack do you have that you want to charge it at 50 amps?

You can buy a 45amp 48v charger for electric fork lift batteries for about $1,000 used 250CII by HOBART BROTHERS CO - Buy or Repair at PLCCenter - PLCCenter.com
And they weigh around 150 pounds.
I always figured that charging my batteries was something that I wanted to do carefully because my pack in my car cost $900 and I want to get as many years out of it as I can.

If you want a proper cheap 48v charger, check out golf cart chargers, they come in either 36v or 48v.

My varrac weighs under 10lb and I bet you could find one used on ebay for less than $100. Also you could use it to charge any voltage stack of batteries up to about 170 or so.

Automotive alternators put out higher voltage if you remove their voltage regulator, at that point the voltage either needs to be regulated by how fast it is spinning or by a modified voltage regulator and I'm pretty sure that there are people selling modified voltage regulators for the home built "wind turbines".

If you want to use a golf cart motor you either need the rest of the drive axle's differential to support the drive end of the motor or you need to build a new face plate for the motor and get a splined shaft to fit in to the drive end of the motor, if you or anyone else has a project that they need a splined shaft like that for, send me a message because if all goes well I'm hoping to get a price quote on having some made at a local shop that does CNC machining, I already have a hand full of them that have the other end fit in to the drive shaft of a Honda CX500 or Honda Goldwing and I have the CNC file to make them, but I don't have a price yet nor do I have solid ideas on variations that other people might want.

120 vac, or your "normal" house current, only has "1 leg". If you look at the sine wave, it goes up to 120v+ and then down to 120v-. A diode cuts out the negative side of the wave and you end up with only peaks of 120v+, not 60v.