Previous in Forum: Power Transmission   Next in Forum: Earth Pit Calculation
Close
Close
Close
19 comments
Power-User

Join Date: Feb 2010
Posts: 190
Good Answers: 2

Generator vs Alternator

05/19/2010 8:01 PM

In designing a turbine driven electric generating system, would you use a generator or an alternator for the electric generation.? If it was for home use wouldn't the alternator be easier as you would not have to convert the DC to AC current as you would for the generator? Or are there other trade offs?

__________________
The time has come the Walrus said to speak of many things, of shoes and ships and sealing wax, of cabbages and kings.
Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
2
Guru

Join Date: Oct 2008
Location: Deepest Darkest Rutherford Oz
Posts: 951
Good Answers: 145
#1

Re: generator vs alternator

05/19/2010 8:56 PM

Depending on the scale of the installation and the requirement for COTS.

Also to consider is whether you want to produce just DC or AC/DC

For a given physical size an automotive alternator will provide superior current/voltage over a similar sized generator.

Ergo, a 12v generator from a VW beetle will if your lucky produce 30Amps at a engine speed of 3600rpm, on a good day, down hill with a tail wind. Though it won't produce any viable current at under 1200rpm.

The optional 12V Alternator will produce 55Amps at 2600 rpm and the voltage output will be well regulated within 0.5volts. At idle it will still produce a reasonable amount of current.

Considering that Automotive alternators are now available which are self exciting, and provide their rated output at modest rotational speeds. That would be the way I'd go.

Now by turbine driven are you referring to wind or water?

If your near a handy stream, then that might provide you with a valuable energy source.

Wind becomes challenging due to the deciding what method of capturing the wind your going to use. Balanced with what wind (on average) you have to work with.

For my druthers, I'd be using three energy sources, wind driven alternator, Diesel Generator and a solar panel array to charge a bank of batteries and then use a synchronous inverter to convert that to my household AC, main reason being that most modern day appliances are fussy about what frequency they operate at. Using an inverter ensures the supply is at the right frequency. Having the three sources ensures I have the ability to maintain my household needs.

__________________
There are two reasons for a man to do a thing, One that sounds good, and the real one...
Register to Reply Good Answer (Score 2)
Power-User

Join Date: Feb 2010
Posts: 190
Good Answers: 2
#3
In reply to #1

Re: generator vs alternator

05/20/2010 7:16 AM

I should have been more specific, sorry. I am working on a solar powered turbine generator set for off grid home use. I am using a working fluid instead of water because of the high btu requirements of superheated steam. The turbine would then turn the (generator/alternator) to produce power. I am looking for a system that generates 8-10 Kw at peak. I have been unable to locate any information as pertains to the power requirement necessary to start and keep running an 8-10 Kw generator or alternator. Any help would be appreciated. I have also been unable to find a source for generators from any manufacturer. They all seem to put them into their own standby generators. I can by as an after market product from their parts inventory but that would be pricey.

__________________
The time has come the Walrus said to speak of many things, of shoes and ships and sealing wax, of cabbages and kings.
Register to Reply
Anonymous Poster
#4
In reply to #3

Re: generator vs alternator

05/20/2010 8:35 AM

Can you please tell what will be the RPM of the turbine? and will it be controlled ?

AC Generators - Alternators (may be with Permanent magnet for efficiency but separate field control will give you much more control over the outlet voltage)

Induction generators is another lucrative option. You may try for off grid Induction generators, the search may give you a few papers (and best part is it may be converted form normal Squirrel cage Induction motors)

DC generator I do not personally prefer (the control systems remain similar, however the maintenance may be a bit higher)

Register to Reply
Power-User

Join Date: Feb 2010
Posts: 190
Good Answers: 2
#15
In reply to #4

Re: generator vs alternator

05/21/2010 7:30 PM

For our Guest: As far as the rpm's of the turbine, you can figure on at least 1800 rpm because it is the rpm's of the generator that is important. As I understand it, most generators require 1800 rpm to generate electricity. Tobugrynbak: Because this is totally for home use I will be generating AC only. I will have need of 240 however as well as 110. Thank you Energygod for you valuable input. This has been quite an undertaking and I could fill a text book with what I have learned. I am going to document every step of the way. I feel confident that I am on the right course and have garnered the assistance of a corporate engineering group to help me. The threat of the government taking over my power in my home just keeps me going longer and stronger on this project. Laughing Jaguar can you offer any more information on those jet engine starter generators? Fishpipes: As far a a collector is concerned, I am leaning to either a parabolic concentrating collector or cylindrical collector. It all depends on whether I decide to store the unused heat or not. If I decide to store the heat for later use, I will use the parabolic collector. If I do that I will probably use salt as my principal fluid that will vaporize a hydrocarbon working fluid. The turbine will be a condensing style that will recapture the hydrocarbon for use again. Designed as such I can avoid the EPA rules and regs as much as possible. In other words, no escaping gas and no EPA.

__________________
The time has come the Walrus said to speak of many things, of shoes and ships and sealing wax, of cabbages and kings.
Register to Reply
Guru

Join Date: Apr 2006
Location: Cincinnati, Ohio, USA
Posts: 662
Good Answers: 48
#16
In reply to #15

Re: generator vs alternator

05/22/2010 12:18 AM

Michael-

Regarding collector style- Your best choice is to use a flat plate solar collector and a light weight oil for the heat transfer medium.

Flat plate can easily generate 180-200F fluid and will collect solar energy on both clear and cloudy days. Concentrating collectors- evac tube or parabolic- essentially need direct sunlight for effect and more or less fall down on cloudy days.

If you use R-410 refrigerant (it is one of the new GOOD GUYS) you can produce over 650 PSIG gas with less than 160F refrigerant. It condenses at 100F (allowing air-cooled condensing) at about 225 PSIG so you can get over 400 PSIG operating differential.

If you want to make your system a Solar CoGeneration system, use about 270 PSIG terminal pressure and use 40F domestic water to condense with a 105F leaving domestic hot water output to produce all the domestic hot water you need and water hot enough to use in a fan-coil for heating your home or to keep your pool warm.

That is why I suggested the over-sized collector surface and storage tanks for 24/7 solar power.

__________________
NO MATTER HOW WELL YOU HAVE DONE SO FAR, ALWAYS TRY TO BE BETTER TOMORROW.
Register to Reply
Power-User

Join Date: Feb 2010
Posts: 190
Good Answers: 2
#18
In reply to #16

Re: generator vs alternator

05/22/2010 6:58 AM

The R-410 refrigerant you refer to has issues, not the least of which is the special handling and certification that is required. I like the high psig and wish that the hydroflouroether I am looking at had the same potential. There must be another product that is less regulated that also had a decent PSIG. The more the better: up to a point.

HFE's are also expensive, unlike R-410. I need one that is inexpensive, has a high psig and is unregulated by the FDA.

If you have any suggestions, they would be welcomed.

__________________
The time has come the Walrus said to speak of many things, of shoes and ships and sealing wax, of cabbages and kings.
Register to Reply
Guru

Join Date: Apr 2006
Location: Cincinnati, Ohio, USA
Posts: 662
Good Answers: 48
#19
In reply to #18

Re: generator vs alternator

05/22/2010 12:43 PM

Michael-

You can check out virtually all of the available products, including pressure vs temp at Dupont.com in the refrigerants section.

__________________
NO MATTER HOW WELL YOU HAVE DONE SO FAR, ALWAYS TRY TO BE BETTER TOMORROW.
Register to Reply
5
Guru

Join Date: Apr 2006
Location: Cincinnati, Ohio, USA
Posts: 662
Good Answers: 48
#6
In reply to #3

Re: generator vs alternator

05/21/2010 12:48 AM

Regarding operating drive power-

At 100% conversion efficiency, the drive will need to make essentially 1.35 HP for each kW to be produced, based on 1 HP = 746 watts, so 1000 watts (1 kW) requires 1000/746 or 1.340 HP.

However, you will have drive losses and other frictional factors, plus you should allow for some conversion losses as well. Assuming 50% drive losses and 20% reserve factor, you should allow for a drive system having (1 + 50%) X 120% X 1.35 HP = 2.43 HP per kW. Based on your upper limit of 10 kW, you will need about a 25 HP drive.

If your system is "better" than that, it will only need to produce whatever HP is required but you will have adequate power available if needed.

If you can afford the installation, I recommend that you install at least twice as much flat plate collector than you need to operate your system and run lightweight oil through the collectors. Store whatever hot oil that you do not need for daytime operation in a well-insulated tank so that you can drive your solar system 24/7 on solar power.

You might also look at using a "small" battery bank as a buffer between your generator system (regardless of type) and feeding an inverter plus UPS with voltage regulation prior to your building. You could use the inverter alone for "major" loads like range or clothes dryer and just use the UPS for more critical loads like the main building distribution system.

Since you are planning for solar power, your input energy costs (not including amortized capital costs) will only be to cover maintenance costs. Assuming an average output of 4 kW, and service every 6 months at, say, $150, your maintenance costs will be ($150 / (8760 hours / year X 0.5) or $0.0343 per kWh, (which is still about 33% of most residential electric utility bills). Obviously, as maintenance costs increase, so does your net power cost.

Regarding amortized capital costs, allowing for some tax credits (which will actually offset your loan interest costs) and assuming an installed cost of, say, $12,500 with an expected life span of 20 years- your amortized installation costs will be $12,500 / (20 years X 8760 hours/year X 4 avg. kW) = $0.0178 per kWh. Added to the $0.0343 yields a total electric cost of $0.0521 per kWh, still only about 60% of "normal" costs.

Good luck- and go save the world.

__________________
NO MATTER HOW WELL YOU HAVE DONE SO FAR, ALWAYS TRY TO BE BETTER TOMORROW.
Register to Reply Good Answer (Score 5)
Guru
Hobbies - Musician - New Member Australia - Member - Torn and breading Engineering Fields - Nanoengineering - New Member APIX Pilot Plant Design Project - Member - New Member

Join Date: Jun 2006
Location: Magnetic Island, Queensland, Australia
Posts: 3721
Good Answers: 74
#7
In reply to #6

Re: generator vs alternator

05/21/2010 1:26 AM

Reading is believing. GA from me.

__________________
The Twain Has Met
Register to Reply
Power-User
Belgium - Member - New Member

Join Date: May 2007
Location: Flanders (Belgium)
Posts: 343
Good Answers: 21
#9
In reply to #6

Re: generator vs alternator

05/21/2010 5:09 AM

Well done, GA from me.

Register to Reply
Guru

Join Date: Apr 2006
Location: Cincinnati, Ohio, USA
Posts: 662
Good Answers: 48
#11
In reply to #6

Re: generator vs alternator

05/21/2010 10:00 AM

It was late and I typed faster than I was thinking.

The ACTUAL maintenance calculation should have been 150 / (8760 X 0.5 X 4 kW) which equals $0.0086 per kWh (not $0.0343). I should have caught this because maintenance costs are usually in the tenths of a cent range.

Therefore, the likely total cost of the solar system will be $0.0086 + $0.0178 or $0.0264 which is 25% to 30% of normal residential costs.

Sorry for the mix-up.

__________________
NO MATTER HOW WELL YOU HAVE DONE SO FAR, ALWAYS TRY TO BE BETTER TOMORROW.
Register to Reply
Guru

Join Date: Sep 2008
Posts: 692
Good Answers: 28
#10
In reply to #3

Re: generator vs alternator

05/21/2010 9:44 AM

If you are talking a small turbine unit that would drive an automobile alternator which produces only 12-13 volts then you are also going to need a step up transformer of about a 10:1 turn ratio in order to produce 120 volts. If your alternator can produce 50 amps at 12 volts then your output will only be 5 amps at the 120 volt output.

I really don't believe that an auto alternator is deigned for continuous operation either. I would rather believe that the auto designers only utilize design criteria for some limited number of hours equivalent to some number of miles/km.So you may want to procure a couple of units and swap them out at predetermined times and have them rebuilt and put back as a spare. Otherwise it would probably be your least expensive route.

__________________
Spinco
Register to Reply
Power-User
Belgium - Member - New Member

Join Date: May 2007
Location: Flanders (Belgium)
Posts: 343
Good Answers: 21
#12
In reply to #10

Re: generator vs alternator

05/21/2010 10:05 AM

Keep in mind that a automobile alternator gives out DC, this can not be steped up by a transformer.

You have to open the alternator and step up the voltage before the rectifing diode brige. But than the frequency of the voltage will be +/- 400 Hz, depending from the speed. So probably you need a special transformer...

Register to Reply
Guru

Join Date: Sep 2008
Posts: 692
Good Answers: 28
#13
In reply to #12

Re: generator vs alternator

05/21/2010 10:25 AM

Actually the alternator produces a/c but has diodes take that a/c output and convert it to d/c. So you are right in that one would have to remove the diodes in order to get a/c and run the a/c output from the point just before the diodes. Should be doable.

__________________
Spinco
Register to Reply
Participant

Join Date: May 2010
Location: Jakarta
Posts: 1
#2

Re: Generator vs Alternator

05/20/2010 3:42 AM

Dear Micahael,

it is the same meaning between alternator and generator. Generator and Alternator is generate electricity, both are generate alternating current. if you mean is DC generator, it will be said as DC generator, not generator.

For generator that driven by turbine engine, usually it is a big enough power to generate, and the effecience will be lower than convensional machine (rule of thumb Gas driven is only 25-35 effeciency in full load).

Please Think again if you use for home using.

Regards

Ongs

Register to Reply
Guru

Join Date: Jul 2008
Posts: 927
Good Answers: 55
#5

Re: Generator vs Alternator

05/20/2010 11:41 PM

Jet engine manufacturers use starter-generators for a number of reasons but mostly to save weight. By throwing a switch after it gets the engine running, the DC starter is now a generator. I do not know their output but they quite generous I am told

This ability to be both starter and generator may be of some value.

L.J.

__________________
"Both the revolutionary and the creative individual are perpetual juveniles. The revolutionary does not grow up because he cannot grow, while the creative individual cannot grow up because he keeps growing." Eric Hoffer
Register to Reply
Anonymous Poster
#8

Re: Generator vs Alternator

05/21/2010 4:34 AM

try a search for "mecc alte spa" we fit gen/alterators 110/240 6kw up to 20kw under vehicles powered from vehicle engine. they supply just the gen/alt unit and make a very large range and like for like are the most cost effective we have found. hope this helps.

regards

Rob.

Register to Reply
Power-User

Join Date: Feb 2007
Location: Nebraska
Posts: 104
Good Answers: 2
#14

Re: Generator vs Alternator

05/21/2010 5:38 PM

What type of collector are you planning on using? I've been looking at he Evacuated Tube collectors. It is amazing how much heat they will generate. They are also not very expensive. I've looked into building my own evacuated tubes but there is just no way I can build them for what I can buy them. I've bought a little experimentor tube off of ebay for 25 dollars. But if you look you can buy 30 72" tubes for 700 dollars. I've been reading that there has been some experimentation with using freon as the heat transfer medium. I keep thinking that there must be a way to get cooling out of these things, but the heat transfer is in the wrong direction so I don't think it is possible, but it would be cool if you could. Good luck with your project. I'd like to hear more about what your doing as I'm wanting to do the same thing.

Register to Reply
Commentator

Join Date: Sep 2006
Location: Circe,9 Majadahonda 28220. SPAIN
Posts: 94
Good Answers: 2
#17

Re: Generator vs Alternator

05/22/2010 5:47 AM

I have a semantical doubt:

What is the difference between alternator and generator?

Thanks for a complete explanation.

Arturo

__________________
QUIMERA
Register to Reply
Register to Reply 19 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be Good Answers:

These comments received enough positive ratings to make them "good answers".
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); ARTURO (1); energygod (4); fishpipes (1); ky (1); Laughing Jaguar (1); Michael Rock (3); ongkek (1); rudy.leurs (2); Spinco (2); Tobugrynbak (1)

Previous in Forum: Power Transmission   Next in Forum: Earth Pit Calculation

Advertisement