AC or DC?

[listerdiesel]

Peter is right on with his advice about wet (we call them flooded on this side of the pond) cells being best for serious use.  The only caution I would put in here is the normal one about "watch out for the AMPS".  You may only be using 12 volt configuration but if you have 200 amps reserve power or more you can weld with it.  It wouldn't be good for the batteries but you can see what a dead short in some part of your wiring would do!  Burn your house down in a real hurry. Appropriate sized wiring for DC is a must, look at the tables for that, it's bigger than AC wiring requirements.
Stan

All of our battery installations have safety fuses in both lines as a matter of course, if the customer won't fit them for any reason then we ask him/her to sign a liability release form, accepting the possible consequences.

110V DC at a few 1000 amps can cause a LOT of damage real quick!

The 620V 150A charger we did a year or so back had fuse and link in the pos and neg respectively (In the UK it is common to have a neutral link in a fuseholder so the circuit can be fully isolated by pulling both the fuse and the link out) and the customer had taken appropriate precautions on the battery, which was made up of 12 X 50V blocks. Not the sort of thing you'd want to pay for, these are Zebra batteries:

www.rolls-royce.com/marine/ downloads/submarine/zebra_fact.pdf

It is a Sodium Chloride/Nickel battery, read the tech sheet, it is quite an interesting piece of kit, although horribly expensive!

Peter

[cbr600]

That's why they recommend removing the NEGATIVE cable first from the battery before such operations. Now, ask me if I always follow such precautions! ;-(    (hint; no I don't)
Had a friend whose watch welded itself between the pos post and the shock tower - burned him right to the bone in a second! Not pretty at all!

Tim

I melted a 3/4" ring spanner one day on a 24V starter motor - was undoing the battery terminal and it swung around and touched the block - a small spark that welded it to the block, a yelp from me, and it began to glow. And glow and glow and glow, as two 12V b :oatteries with an available cranking current of about 1300amps discharged fairly quickly. By the time I figured out it was the battery isolator stuck on and had wopped it with a convenient sledgehammer that was nearby, all the battery wiring was a bit on the hot and slightly-melted side.

My spanner was banana-shaped after that.... which was actually pretty convenient at times.

[rcavictim]

That's why they recommend removing the NEGATIVE cable first from the battery before such operations. Now, ask me if I always follow such precautions! ;-(    (hint; no I don't)
Had a friend whose watch welded itself between the pos post and the shock tower - burned him right to the bone in a second! Not pretty at all!

Tim

I melted a 3/4" ring spanner one day on a 24V starter motor - was undoing the battery terminal and it swung around and touched the block - a small spark that welded it to the block, a yelp from me, and it began to glow. And glow and glow and glow, as two 12V b :oatteries with an available cranking current of about 1300amps discharged fairly quickly. By the time I figured out it was the battery isolator stuck on and had wopped it with a convenient sledgehammer that was nearby, all the battery wiring was a bit on the hot and slightly-melted side.

My spanner was banana-shaped after that.... which was actually pretty convenient at times.

I do not wear any rings or a wristwatch for this reason and possibly snagging on machine tools as well.  Haven`t worn a watch in perhaps 30 years.  Anyone know what time it is? 

[ZackaryMac]

I don't wear rings or watch either. I think most mechanics don't. Nothing worse than having your hand in a tight spot, touching something hot, reactively yanking your hand out, and either cutting yourself with the ring/watch from snagging on something, or NOT getting your hand out and burning it worse, then trying to "calmly" remove your hand. Fun.

[fattywagonman]

Well most of us know all rotative power starts out as AC... a brush type rectifies it with the commutator a brushless uses diodes... DC is easier to store than AC but AC can be stored in a flywheel / gen / motor I like the inverter generator concept with batteries in between... since batteries can be charged with solar or wind power if available...

[Doug]

I agree fully....

[fattywagonman]

Hi Doug,
I'm glad we're on the same page...
I'm surprised at how many off griders aren't using a DC / Inverter system... The Zantrez 5548 I use already has a starter / stop circuit for the generator so it's pretty easy ... using batteries also allows the use of wind or solar when it's available.. which IMO should be encouraged.. 

I'm also a huge fan of CHP ... IMO it should be used on every system..  not using CHP is like trowing away 2/3 of your fuel...

[Andre Blanchard]

Well most of us know all rotative power starts out as AC... a brush type rectifies it with the commutator a brushless uses diodes...

In practical use you could say "all" but in a absolute sense there is one generator that directly makes DC, no diodes or commutators just some slip rings.

The homopolar machine, low voltage, very high current.  One of their uses is teamed up with a flywheel storage system to provide short high current pulses to power things like rail guns.

[fattywagonman]

Hi Andre'
I didn't know that about homopolar generators.. how are they different?

These guys make a homopolar PMG

http://www.polarpowerinc.com/products/generators/index.htm

[Andre Blanchard]

Basically just a spinning metal disk with a brush at the rim and one at the center.  The magnetic field is aligned with the axis of rotation.

The over unity people have taken to using the word so when searching for info you need to separate out a bunch of useless junk.

[mobile_bob]

bobkrack:

10kwatt of dc is a buttload of power,, and to answer your question directly "i don't know"
it would depend i suppose on the answers to many questions, such as

1. 10kwatt at what voltage?

2. 10kwatt peak or continuous?

ok, i guess just two for now

the reasons are

1. 10kwatt at 12vdc is a horrendous amount of amperage, at 24 still a serious amount of amperage, at 120 manageable,

2. depending on voltage and the availability of equipment either alternator or generator


i cannot get my head around what you are trying to do, so that is why i ask
if you are charging batteries you are going to be in the insane catagory as far as bank size and dollars spent (not a jab at you personally)

to get you to that kind of power i would think definetely an alternator, perhaps a welding alternator
there are SD heads in the 10 kwatt range, that might stand up to 10kwatt output to a 48 volt string with a purpose built regulator
there are also 30 vdc at 400amp surplus generators available, that are relatively inexpensive from surpluscenter.com, that would get you close to
maybe 8kwatt at 24 volts, but would also need a purpose built regulator.

so i guess it really depends on what you need to do, and then decide how best to do it.

bob g

[Andre Blanchard]

I guess I did not ask the question correctly.

I wanna produce about 10KW electricty for a strictly DC usage.  Am I gonna be better off using an alternator or a generator?

Bob

That is up to you.

What is available?  Looking at new or surplus market.

Brushes can need more maintenance, but how many hours per year are you going to run it?

Brushes can take a lot more abuse from overloads and shorts any will likely give some warning before they fail, diodes just go pop.

Efficiency can go either way depending on system voltage and quality.

I tend to like an old generator just for the time period look.

[fattywagonman]

I guess I did not ask the question correctly.

I wanna produce about 10KW electricty for a strictly DC usage.  Am I gonna be better off using an alternator or a generator?

Bob

At what voltage?

10kW is a lot of DC...

Why 10kW?

If you really need 10kW I'd recommend having some batteries in the loop to absorb spike loads... this way you can get by with a much small and more efficient generator.
I've rectified 110 volt machines for 48 volt DC output and they work well... run some of the AC through a dimmer switch and then rectify the output to DC... send the DC back to the field to regulate the output voltage..

Or find an old brush type DC welding machine and use that as a DC generator... turn it to full and modulate the RPM's for the desired vlots / amps... if it has CV capability (a voltage regulator) you can just dial in and maintain the desired voltage...

[Andre Blanchard]

I am very impressed with all the knowledge displayed here but again ---- Generator or Alternator?

Bob

Should I paint my house red or brown?

[mobile_bob]

in the one kwatt range, i would go with a prestolite load handler or a leece neville 175 amp unit, both of which are available on ebay for cheap
remove the oem regulator, and go with a xantrex or balmar controller also available on ebay,
with the combo you have 3 step chargeing with temp compensation, soft start, equalization etc, with temp sensing of the alternator for its protection.
all parameters are programmable so you can dial it in to do just exactly what is needed, and the controller can tailor output based of input hp to match all parts
effecitively.

i know of no generator in the 1kwatt range that can be controlled so tightly, i would not consider a generator for your system.

bob g