100 AMP Transformer design help

[aurangzebhaque]

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

 

[kabiru]

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

 

[Orson Cart]

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.

 

[aurangzebhaque]

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

 

[Orson Cart]

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.

 

[sahu]

Can u post sch ?

 

[ZASto]

NEVER charge batteries connected in parallel. Fireworks in prospect :lol:

 

[Orson Cart]

NEVER charge batteries connected in parallel. Fireworks in prospect

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?

 

[kabiru]

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