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# lead acid battery charger design help

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#### giorgia

##### Junior Member level 3
battery charger design

Hi friends,
Anybody can help me to design an automatic battery charger system for lead acid battery 24 Vdc 660 A/h
in fact i need a big current around 66 A @ 27 Vdc
Wich is the best method:switch mode regulator, linear regulator or ferromagnetic regulator?
any one have a sample project?
Any help will be very appreciate!

uc3906n float charge schematics

Hi Giorgia

Your asking for some big currents there. i got some questions for you
A brief description how a chager works. When the batteries are 80% discharged (if teh charger is caple of charging at 65amps) starting current will be 65amps it will take approx 10hrs to get to 80% charged (which is known has gassing stage) 2.4VPC (volts per cell) X12 (24V) = 28.8 the batteries start gassing this starts the timer off which can be set for 3/4hrs by this time the charge rate will have droped ( the batteries take control to limit the current) and has the batteris reach fully charge 2.6VPC = 31.2 and the SG reading in teh battery should be 1250-1280 because if the batteries dont reach then the capacity will be reduced and if teh SG is over 1300 tehn this means teh batteries have come to the end of there useful (I.E wont hold charge) then after 3 or 4hrs the charger should switch off to prevent over charging them. after gassing stage you can control the current and keep the battery voltage at 27.6V (this is known has floating ) the current can be 5% of the of the max ouptut current

Can you give us more information about the battery. Is a heavy duty type car battery or are they sinlge cells (2Volts each) a 660AH battery is quite a big battery pack.

Q1. what's the time spam that you want to recharge the batteries in beacuse i work it out to be 660/8=82.5 Amps to recharge the batteries in 12-14hrs from 80% discharged. and to charge. them in 8hrs you would need a 132Amp charger.
Q2. If these are heavy duty 12V batteries is it the AH your reading or craning capacity ?

you would need a transfomer cable of supplying 70-75Amps so you dont over work the transformer and a output voltage of 33-35V. you would have to use a bridge Rectifier (85amp type with 4 75Amp diodes and a big heat sink ) a mians contactor to switch it on/off and a timer card to be able to dectect the battery voltage.
So basicly i think you are looking for an industrial type of chager. it all depands on the batteries you are using.
I've only give a brief description has i can go on on (thats ten years in the battery and charger game does to you)

hope this helps you

wizpic

### giorgia

Points: 2

Hi Wizpic,
Thanks a lot for you help, and sorry for the late in my reply

the battery are heavy duty car type 4x 12 v 330 A/h each one
and i need to recharge it in about 10 /12 hours.
I'm looking for a schematics, ideas and documentation on how build an automatic battery charger.

Thanks in advance, any help will be very appreciate!

### giorgia

Points: 2
designe switching battery charger

Hi,

h**p://www.vicr.com/documents/design_articles/pb_battery-charger.pdf

h**p://www.panasonic.com/industrial/battery/oem/images/pdf/Panasonic_VRLA_ChargingMethods.pdf

h**p://wwww.ges.cz/sheet/u/uc3906n.pdf

My problem now is to build AC(230Vac)-DC(40Vdc) (100W) converter (maybe switch mode for high efficiency)?

NeuralC

Points: 2