| Author |
Message |
Bill Glenn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 7:49 pm: | |
Okay Guys can I pick your brain for a while?
I need to generate high voltage D.C. in the range of between 54 to 600 volts.
I am looking at existing AC & DC alternators, and generators and have a couple of questions.
A.C. 1. What is the effect of spinning the AC alternator faster, or slower? Volts, hertz?
A.C. 2. How high can I adust the volts with the existing regulator? Can I install a different regulator to further increase the adustment, output range?
A.C. 3. What would the efficiency loss in rectifying the ac to dc?
A.C. 4. Any info, or links on how to do it?
D.C. 1. How high of a voltage can I get out of an readily available automotive style alternator?
D.C. 2. What would I have to do to increase the voltage?
D.C. 3. What are the volts limit of the existing diodes? I do not think the windings are the limiting factor. As the volts go up the amps go down.
Anyway you guys see where I am going. I need a unit between 1 and 5 Kw DC. and would prefer 240 volts.
Any pointers how I can economically convert, or purchase such an item.
I can adjust the R.P.M. to within the max speed of the unit.
Thanks
Bill Glenn |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 8:03 pm: | |
Buy a 5 KW genset with a 240 volt output and put a bridge rectifier on it. If you want cleaner DC get a 3 phase genset but the rectifier will be more expensive. |
David Hartley (Drdave)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 8:12 pm: | |
Well,
This is a deep subject with many answers..
You mention adjustable from 54 to 600 volts.
What amperage range do you need? ( or KW ? )
Mostly it involves something like a 12-lead alternator head with a separatly excited field so that you can adjust the output swing.
You do understand that as the voltage goes up the current falls off so a set of windings rated at a given current and maximum voltage will not have the same output current at lower output voltages due to the maximum design current of the windings.
( I know this sounds upside-down ) but you can't get more current than the wire diameter will carry.
So, If you need 100 amps @ 600 volts but you only excite the field to arrive at 54 volts you won't be able to exceed the 100 amp limit of the windings. In fact you probably won't get anywhere close to the 100 amps because your field current is reduced to bring the output voltage way down, less magnetic field means less output voltage and current.
I would say something like a Marathon 12-lead generator head wired for 600 a.c. volts and a bank of diode units and triacs or scr's to control the output voltage and current.
Electrically powered transit buses use 364 volts of batteries and an inverter to make the a.c. power, Then that is conditioned and switched and converted back to either 3-phase a.c. or d.c. to run a traction motor.
You could locate a 400hz military generating unit and step that up. then use rectifiers and triacs to control output. 400hz is much easier on diode packs and can be easier to switch with smaller components. |
Bob Wies (Ncbob)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 9:02 pm: | |
What'a ya gonna run..an electromagnet with enough power to pick up your bus?
Automotive alternators are basically three phase A/C
generators with the triode 93 phase bridge rectifier
which give them 160% of input (which is why they can charge at low RPM..contrasted to a DC generator).
You would need a B-I-G capacity DC generator with a carbon pile regulator to control the output for what ever in hell it is you want to do.
I'm gonna sit on the side and read...cause like the monkey said when he pe---d in the cash register..."this's running into money"!
NCbob |
niles steckbauer (Niles500)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 9:35 pm: | |
http://www.polarpowerinc.com/products/generators/index.htm
From what an EE friend says a 15 kw 120-240 AC generator can also produce DC with 2 Full wave rectifiers - HTH - Niles |
Gary Stadler (Boogiethecat)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 10:27 pm: | |
Bill,
I can probably give you a few good ideas, but the big question is, what's it for. Depending on your application, there are a lot of parameters that need to be paid attention to, and a lot you can ignore.
But without knowing what your end use is, there' really no way to give you a decent answer at this point.
Tesla coil? Cow killer? Giant hot dog cooker? |
niles steckbauer (Niles500)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, April 10, 2006 - 11:23 pm: | |
Sorry - Forgot to add - full wave rectifier should achieve 81% efficiency - FWIW |
Bill Glenn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 11, 2006 - 11:37 am: | |
The new solar inverters, and charge controllers run on high voltage. less amps, smaller wires, less loss.
With maximum power point tracking(MPPT)we can charge any lower voltage battery bank more efficiently, as well as multiple different volt battery banks.
Dave I do not need to vary the volts, available equipment can run in that range, I would rather have 240volt dc.
Thanks Niles
Thanks for the info folks.
Where is Richard, or Marc? I know you guys have experience.
Bill Glenn |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 11, 2006 - 12:07 pm: | |
I do not believe big DC generators with carbon pile regulators are still available.
I would recommend a three phase, 240 volt, 60 hertz, four pole (1800 rpm) or two pole (3600 rpm) alternator and a full wave three phase bridge rectifier.
Depending on what you are going to be using the DC for you may need some output filtering to reduce the AC ripple on the DC output.
Richard
A good electrical shop should be able to rewind an automotive alternator also to give you the output voltag you desire. |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 11, 2006 - 12:53 pm: | |
Bill: What did you see wrong with my suggestion? If you want 240 volts DC, that is the most reliable way to get it and everything is off the shelf. |
herman
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 11, 2006 - 2:27 pm: | |
As far as I know, all 'common' inverters that can handle DC voltages above 48V (nominal) are designed as grid tie units, and will not produce any AC power without first seeing an external AC waveform from a line having *very* low impedance, e.g. the grid. If you try to fake it out by using a low capacity (read: high impedance) inverter as an AC reference, the combined system will likely become wildly unstable as soon as the grid tie unit starts producing.
Regardless of whether you're planning on feeding an inverter or a charge controller, you may find that it does not enjoy seeing much DC ripple. For example, a charge controller's MPPT algorithm might be perturbed by it. To filter that down, you would probably need a large amount of capacitance; less if you also use series inductance.
You might want to see if there are any non-gridtied inverters that are designed to be fed by wind or hydro power; some such systems produce "wild" 3 phase AC, i.e. it is of variable frequency and power, depending on how strongly the wind/water is flowing at the moment. They would by nature be more tolerant of ripple.
But, what you really want is for the prime mover's speed and the alternator's field strength to be modulated according to demand, and an MPPT charge controller won't do that. In fact, it'll make it harder, because it will present to the source as a load that is 'optimal' for whatever operating point the source is currently at. You would instead have to look downstream at battery voltage and net current, and devise an additional controller.
For sure, you can't feed an inverter directly with your generated DC - how would you respond to a hefty load step, e.g. an A/C compressor starting up? You'd have to always be running the prime mover at an operating point that could cover the worst case demand; that loss in efficiency, added to the inverter losses, would put you below that of an ordinary genset. |
Richard Bowyer (Drivingmisslazy)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, April 11, 2006 - 3:19 pm: | |
It would be nice to know what the load parameters actually are.
Herman, inverters for Uninterruptible Power Supplies are commonly available up to several hundred kw.
I developed high voltage DC inverters for the luxury yacht market (mega-yachts). DC bus voltage was 600 volts.
I started with a PWM variable frequency motor drive and then filtered the PWM signal so that only the 60 hertz primary frequency remained.
The largest I ever manufactured was 250 kw each with two operating in parallel for a total of 500 kw. It was for the Sultan of Brunei's new yacht.
Richard |
Bill Glenn
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 15, 2006 - 2:29 am: | |
Nothing Wrong with your suggestion Stan, Thanks! Glad to have Richard agree.
Good points Herman, yes it needs some control circuits.
Thanks Doc the higher hz unit might be better.
Richard the loads will be whatever the max I can generate @ the variable rpm selected. Load the engine to the max fuel setting. I want ups thru the battery bank. How will the battery bank handle the ripple? Auto start @ low voltage, throttle down after bulk charge, shut off @ set voltage. No large loads over any significant length of time on the battery bank.
Thanks ALL
Bill |
Stan
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, April 15, 2006 - 8:22 am: | |
Batteries don't care about the ripple but if you are voltage sensing they only see the peaks of the sine wave which have very little energy.
You can eliminate the ripple entirely by using a three phase alternator. After rectification, a voltage regulator will clip off the ripple on the top of the DC. The same regulator could be used to control voltage into the load. Current control can also be used on the output. It depends on whether you want constant voltage or contstant current charging. Adjusting the charge rate with electronics is what the three stage regulators do and the same principal can be app;ied to your DC output.
All of this gets pricey when when you are talking KWs. |