# Problem in deciding dc generator conecting to an inverter

1. Apr 23, 2010

### sai_rajdi

Hi,
Its great to see a forum like this thanks for your efforts and thinking that PF can help me a lot.
I Am ANANTH pursuing 3-2 B.TECH under J.N.T.U.H
i am working on a project of wind energy to electrical energy. but the problem is what type of dc generator(rating) should i use?
first i've decided about inverter and the rating of it goes here,
OUTPUT:-
3500 watts continuous power
7000 watts peak power
15.9 Amps
220 volt AC
50hz frequency.

but the INPUT at rating side is given as:-
12-15v dc

now the problem is at input side for 12v dc,for achieving output of dc generator as 12v dc, to get the desired output of inverter, what rating of dc generator should i use.how much amps should dc gen should it deliver to inverter and what should be the wattage rating of it.

2. Apr 24, 2010

### vk6kro

You are not given any information about the efficiency of the inverter, so, for a start, assume 100% efficiency.

3500 watts at 12 volts is how many amps?

7000 watts at 12 volts is how many amps?

Now you could make a guess at the efficiency and adjust these currents accordingly.
Maybe 75% ?

However, it would possibly be a good time to reconsider using 12 volts if this was a real life problem. These are enormous currents.

3. Apr 24, 2010

### sai_rajdi

Optimum efficiency of inverter is up to 90%.
at the input side of inverter they gave only for volts not for amps my problem is about the input current, how much should be given for achieving max output of inverter.actually the inverter should be connected to battery bank but i need to connect to a dc 12v generator what happens?

4. Apr 24, 2010

### vk6kro

The output power must come from the input power, so you can work out the input current from
Power = voltage * current
ie current = power / voltage.

If the Inverter is 90% efficient, then the input power = 100 / 90 times the output power.

DC from a generator is the same as from a battery bank.

5. Apr 25, 2010

### sai_rajdi

thanks vk6kro.
means if i connect a dc generator that delivers 12v, 16amps is sufficient?

6. Apr 25, 2010

### vk6kro

No.

3500 watts at 12 volts is 291.66 AMPS.

7000 watts at 12 volts is 583.33 AMPS.

These are very large currents, even from car batteries.

7. Apr 26, 2010

### sai_rajdi

okay fine now in the place of batteries i would like to connect an dc generator so can u please suggest how many watts of generator and what will be the size of the generator? but am expecting 3.5kw of power with huge size with heavy weight..........right// but the thing for my project is to reduce the size and weight of the generator so that i can directly couple to the wind turbine on top...........

8. Apr 26, 2010

### sai_rajdi

9. Apr 26, 2010

### vk6kro

The generator would have to supply the same power as batteries would, if you used it to drive the inverter directly.

You would have to research this to get a generator with the necessary power out.
This is a large and expensive project and you should get local advice before proceeding.

Since wind power is not usually constant, it is probably best to use the wind generator to charge up some batteries and use the batteries to supply power to your house or whatever you need it for.

10. Apr 26, 2010

### sai_rajdi

first i thought to use a alternator but due to speed variation there is a frequency variation but can use cycloconverter but it is not so efficient.
thinking a lot to make my project successfull!........

11. Apr 27, 2010

### sophiecentaur

I am not sure of your proposed setup.
Why did you want to use 12V in the system?
A turbine of that power would almost certainly be producing more than 12V - if only to avoid ££££ worth of cabling. If the project is supposed to be a realistic one then you should look at how this sort of installation is currently designed. It isn't necessary to use 12V just because it's DC.
Perhaps I've got hold of the wrong end of the stick, tho'.

12. Apr 27, 2010

### sai_rajdi

inverter which i am talking abt is of 12v input which is carried out through 12v batteries so to charge those batteries am connecting dc gen of 12 volts.......