Charging a 12v battery bank w/alternator

[tcmtech]

That's where spending the extra money for a larger case size commercial applications unit pays off.

Especially when you are buying a stock automotive 80 amp unit with a at best 50% duty cycle for $80 - $100 Vs a commercial unit that can do 120+ amps continuous duty for $30 - $50 more.

It's a no brainer when dealing with larger battery systems.

Here's the ones I put on our tractors and they have no problems with keeping up with a nearly 800 watt load plus charging two 120 ah 12 volt batteries at the same time at just over idle!.

**broken link removed**

~ $140 at available at most any Napa store with a 1 year or better warranty.

 

[mendoAu]

What do you think your "4kW generator is"?

......a wonderful piece of modern technology.....a bit more complex than my simple mind can fathom, however, that is why I am in awe of the internet and sites like this one to ask questions and acquire knowledge. I remember back many moons ago the only cars me and my buddy's could afford were old and had generators, not alternators so please forgive me for my lack of proper terminology. But I have done my best to explain what I'd like to achieve and with helpful posts I'm zeroing in to a solution, which appears not to involve four alternators, HA!

 

[mendoAu]

Thanks tcmtech...I bookmarked that Napa site. I also checked the power output of the generator/AC alternator and it reads 119.7 +/- a speck so.......
And "at just over idle!. " is very interesting. I've read a couple places where some require like 3000 RPM or more to achieve efficent output.

 

[mendoAu]

To many good football games today to deal with that old air compressor to check out the electric motor but probably will yank it out tomorrow to check out the rpm and power draw.

 

[tcmtech]

And "at just over idle!. " is very interesting. I've read a couple places where some require like 3000 RPM or more to achieve efficent output.

Well idle on the engine is only about 600 RPM so given a roughly 4:1 pulley ratio the alternators are putting out at least 800watts at around 2400 RPM give or take.

I think the specs sheets that came with the last two I bought said they were at full rated output at 3600 RPM but have a few tens of amps more capacity at RPM's further above that.

 

[mendoAu]

Nothing happens fast out here (except flash floods) so will return to post info on the project in a few days. Gotta figure out how to weld my frame and size out a pulley system. Got a feeling that getting a few pulleys might save a couple trips to town. PS: Got about a pennyweight ($50.00+/-) of gold in a couple of hours this afternoon so a little more dredging and I'll have a new Delco....

 

[tcmtech]

If you are planning on using an electric motor to run one of those bigger alternators you will need upwards of 4 - 5 HP to drive it which will likely be beyond your 4000 watt generators ability to start and run reliably.

Given that I would highly recomend using a separate dedicated 5 HP engine for the charger unit. In the end you aren't going to burn any more fuel using a second engine than you will be by trying to run a large electric motor off your gen set to drive the alternator. On top of that it will keep you from killing your gen set trying to start and run an oversized load as well.