I'm trying to plan out my off-grid / post-SHTF power system.  I decided to have everything based off of 12 VDC for compatibility with BOVs and electronics designed to run off of 12 VDC.  Currently I have 150Ah of deep cycle batteries combined with a Xantrex Prosine 2.0 inverter/charger.  I also have an older 3200 watt 120/240 VAC generator my FIL gave me.

I really like the inverter, but not the generator.  The genset is loud, runs at 3600rpm all the time, and can't hold speed well enough to produce a reliable 60 Hz.  I would really like to seperate the 8 HP engine from the gen head and build a 12 VDC generator and produce the AC through the inverter to have clean AC like a Honda EU2000i. I see lots of home brewed 12 VDC gensets built with car alternators, but I would like something better.  I have internet searched for months but haven't found any quality DC genheads.

I'm looking for something that produces regulated 12-15 VDC, brushless, and around 200 amps continuous.  Has anyone seen anything like this?

Here is a what inspired me to build this:
DC generators

what you hhve found it about it. you can get a GM alt rewound at a shop for the 200 amps and run off a used push mower motor. 150Ah battery back isnt much since 2 6v batteries would give you 220Ah's. you will be very limited on how long you can run with that. the wife and i are working on buying our first house and my starting plan is 2 of the 6v batteries when we buy and buying 2 more come tax time so we would have 440Ah. my goal is to have all lights running off 12v direct and then the inverter to run the TV/SAT/DVD to keep the kids entertained. we will freeze 2L drink bottles in the chest freezer to help keep that and the fridge cold and will have temp monitors in both so we know when its time to fire up the genny to run each.

I agree, the battery bank is small right now.  I would like to get some 6V batts and give myself around 440-660Ah for a light duty system.

My reasons for staying away from alternators is because they are not design with longevity in mind.  You might get 1500 - 3000 hrs life out of one running at 25-40% load, but a 200 amp alt will not handle 200 amp continuous.  That is fine for a standby system or emergency battery charging, but that will not hold up if the gen head is coupled with a diesel engine especially a Lister with a life span potential of 100,000hrs

I understand it is a tall order, but I'm shooting for a no compromises solution.  I think to get a brushless gen head, I will have to have an AC unit and rectify it to DC.

your not going to find it. i can promise you, alt's can run for a LOOOOONG time. just look at how many miles and hours OTR truckers put on there rigs.

I don't accept that.  If I cannot find a gen head that will work. I will break down and buy one of the diesel generators in the above link in the first post.  If you read the specs on the generators, they are extremely long life and don't have many parts to fail.

You may be limited on run time by the amount of fuel you can store.

Go visit your local auto electric rebuilder,  ask if he (she?) will  build you up a 160 or 200 amp Leece-Neville 2800JB or Prestolite 110-555  for continuous duty  battery charging.
Either of these is capable of running  continuously at full rated output,   the prestolite will  need brushes after  5 or 6 thousand hours, they take 10 minutes to change.
 The leece-neville is a little harder to service, but will go 10,000 +  hours  before it needs  brushes and bearings.
 ...... Parts to build  are probably in stock  locally,  expect a couple days lead time, you might get lucky and pay  in the range of 300 to 400 bucks.
 If   you offer cash, arent real pushy , and  don't rush him, you may get a break.

Use an aviation or marine alternator instead of a car model....





 

You're going to need a REALLY big push mower...

Typically, it takes a 5 horsepower engine to get 60 amps out of an automotive alternator (yes, they're really that inefficient!). 200 amps would probably require close to 18 horsepower.

Using an AC generator to drive a switching-type battery charger is more efficient - and cheaper, too. As a bonus, the generator can be used to power other appliances when it's not charging batteries.

why does HP have any effect on the output of an alt? if the motor turns the correct speed the alt doesnt put that much, if any, strain on the motor.

No...



It's identical to the way a genset works - the more amps/watts, the more HP needed...





 

Because all of those motors have vastly more HP than is necessary to max out those alternators.   Car alternators are quite small, few can put out more than 1kW, and virtually none can put out more than 2kW.  That means that they would need 5-10 HP *MAX*, even with lots of inefficiencies and losses.  Cars don't take a whole lot of electricity.

In those cases, the limits are the magnetic fields in the alternator, the copper losses, and the ability of the alternator to cool itself.   As you increase the size of the generator and decrease the size of the motor, eventually the motor would be the limiting factor.   You generally don't want that to be a factor.

The more electrical power you want to generate, the more mechanical power you have to put into it.  Fundamental law of the universe.  If you can find a way around that, you will quite literally become  the wealthiest individual in the world.




It is only easy to spin when electrical load is light.  As demand increases, the mechanical forces needed to turn the alternator increase.  Sounds like magic, but again, it's a fundamental law of the Universe.  As Lenz first described it, it is called Lenz's law.  

Take a brushed DC motor, and spin it.  Nice and easy.  Now short the wires together, and spin it again.  You have just seen Lenz's law in action!

Id rather buy 4 new small engines and a dozen altenators for a home built with tons of spairs  then spend tons on some expensive alternator and small motor already put togather.

www.Northerntool.com is your friend.

with a 7-10HP motor you should be able to turn two 94 amp GM alts. its not 200amps but its close enough. you would need the correct mounts, pulleys, and belts but it could be done very cheap.

With a 7 HP motor, you'll be able to spin ONE 94 amp alternator at its rated output.

The off-the-grid community has been building small-engine DC battery chargers since the 1970's. The limitations of using car alternators are well-documented.

I don't know but I have personally seen a 3.5 hp briggs power a 67 amp chevy alt on several occasions. It was used to charge the battery in a drag car between rounds.

the epicenters setup for a 94 amp alt is a 5hp. they also run the 64's off a 3.5hp.