100 AMP Transformer design help

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aurangzebhaque

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Hi,

I am trying to design a battery charger for charging 12 volt automotive battery of 1000 AH capacity from 230 VAC mains. I would like to be able to charge the battery at a max rate of 100 Amps. Charging current would be controlled using microcontroller based PWM system. My question is:

What should be the transformer secondary voltage for such a charger.

TIA

Aurangzeb
 

Since the battery voltage is 12volt,and you are using pwm method your voltage at the secondary voltage can be 14volt.
 

The answer depends on the exact topology you are using for your power circuit and how well the transformer is designed for low leakage etc - there is no straightforward exact answer to your question - to maintain 100A into your batteries you will need an output voltage able to reach 16.5VDC - especially if you will be using Pb-Calcium - acid batteries which are quite common now - they need a high voltage overcharge to stir the electrolyte (wet cells) and avoid stratification, Regards, Orson Cart.
 

Orson Kabiru,

I already have the battery selected. It is lead acid chemistry and is an automotive type battery modified for use in inverters/UPS. It is nominally rated at 150 AH. I plan to use 7 units in parallel to make a 1000 AH battery.

Theoretically 16 VDC is fine. However assume a resistance of 1 Ohm in the path. This would include Transformer secondary resistance, Rectifier Diode resistance, PWM FET resistance plus some connection resistance. Will this not create a problem

Aurangzeb
 

the assumption of 1 ohm gives losses = 100^2 x 1 = 10,000 watts - a bit high don't you think?

also 1 ohm at 100 amp would require 100V to overcome - a bit higher than your transformer output.

typically an SCR/diode has 1V @ 100amp = 100watts losses there, transformer losses should be in the order of 5-10watts secondary and 3-5 watts primary

This just leaves your FET PWM control - which should dissipate less than 20W at full power including switching losses with a good gate driver...

Regards, Orson Cart.
 
Last edited:

NEVER charge batteries connected in parallel. Fireworks in prospect
Click to expand...
what makes you say this? they need to be the same volts before you connect them in parallel - but after that charging in parallel has no obvious safety issues?
 

i wonder why zasto said that batter can'nt be charged when connected in parallel?
 

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