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 Vic 06-17-2014 03:47 PM

How many batteries do i need?

Im an electrical engineering student and im doing a summer research project regarding making a hybrid system with a turbine engine as the power source. This turbine puts out 480VAC 3 phase and has a maximum power output of 60KW. Im wondering what sort of battery(s) would be needed to handle that sort of input. Right now for viability purposes we are looking at using lead acid batteries (car batteries). Im wondering how many of these i would need to hook up in series/parallel so that they wouldnt get instantly fried. We have a rectifier to convert the VAC into DC, and a transformer, though im not intimately familiar with their specs yet. From what i understand batteries use the amperage-hour unit to determine their capacity, but i dont really understand the A-H unit. So hopefully there are some pretty knowledgeable people here in regards to the power side of things.

Edit: i just realized there is a battery subforum, maybe this needs to be moved there...

 Cobb 06-17-2014 05:24 PM

You will just vaporize the electrolyte. :eek:

Not enough information, we need to know voltage and amps. Assuming what you said is correct that will be 480 volts dc and 60kw or 125 amps an hour.

480/12 = 40 deepcycle group 27 batteries in serial. They are rated at like 115 amp hours, so to be safe, assuming full 60kw output do 2 strings or 80 batteries.

Quote:
 Originally Posted by Vic (Post 430249) Im wondering how many of these i would need to hook up in series/parallel so that they wouldnt get instantly fried.

 Vic 06-17-2014 08:00 PM

Actually i think i understand, the limitations are actually on how long wed like to run the motor. The 3 phase VAC can be rectified and transformed down to 14V (max charge voltage for a car battery). So the electric motor im looking at has a typical draw of 80A. To run this for 30 mins i would need 40 Ah, which is typical of one battery. Unfortunately this doesnt sound right. In addition if i am putting out say 30Kw from my powerplant and with the current planned setup i can run it for about 2 hrs, so for a whole tank i get about 60 kw, but i dont know the internal resistance of a car battery to figure out what that is in Ah.

 Cobb 06-17-2014 09:17 PM

If you are a real engineer student, you should go 170% over your needs for a good safety margin. Then when it comes to battery ratings of amp hours that assumed 100%, however if you go to 80% or more you will measure your lifetime in weeks vs years.

So in theory, assuming no resistance or losses, your 80 amp load will likely get 20 minutes from your 40 amp battery.

 vskid3 06-18-2014 12:28 AM

80A at 12v? That's not a very powerful motor compared to the generator and what would be required to move a decent size vehicle

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