Sarac

Firstly, i want to salute all members of this forum.
i am new at this forum ( registered today ) and would like to receive your help.

i am trying to design 1000 Watt UPS, but i am not quite sure how to charge 2x12Volt 60Ah Car Battery connected in series. The charger must go off when the battery voltage reached to 28-29 volts.

The charger will be used as a part of My UPS Project.

Any Help PLEASEEEE

bogdanfirst

well normally, a car batery is charged at a current about 10% of its capacity(in your case 60Ah===>6A current).

you want that the charger to disconnect when the battery voltge reaches a value, when the battery is charged.

what i think is that you should recharge the batts in paralel, and have a circuit for disconecting when it is charged for each batt

Sarac

thanks for the reply.
yes, i knew that i need at least 6A current to charge the batteries properly.

what my problem is how am i going to supply this 6 Amperes to charge two batteries in serries. I have a circuits diagram for 6A charging but it was designed for 12 Volts. How should i modify it to work under 24 volts.

if you could help, i can send the schematic to you by mail then you can direct me for modification.

Charging batteries in parrallel is out of question for me since in that case i will need 12A then the UPS will not be fully automatic. :wink:

thanks again

Sebi

Send me Your circuit diagram for correct replay.

Sarac

Sebi, I have attached the diagram for your study. the circuits charge the battery at 6 A till the battery voltage reach 14.4 Volt then it starts to charge the battery at trickle mode, battery voltage limited at 16.4 Volt max.

Can it be modified to charge two batteries in serries and keep the voltage roughly at 30-32 Volts

The original circuits published by Elektor 301 Circuits Book

regards,

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Sebi

Not simply...
First You need a new transformer with 36V 7A secondary. In this case the buffer condensator voltage about 55V. The opamp 741 max supply voltage is only 30V! High voltage types of opamps very expensive. I think,this circuit for 28...30V You can rebuild only with discrete transistors.

Sarac

Sebi,
Thanks for your time and suggestion.

bogdanfirst

you will need a 36 V transformer and a 60V capacitor, maybe use 2 2200uF capacitors in paralel, becausa a 4700V one would be very large.
now for the op amp. here is how i think it will do. instead of conecting the + and - terminals to the circuits power, connect them via 2 5.1V zenner dioddes ar maybe a smaller or a larger value acording to the voltage you mesure on the capacitor with no load on the circuit
here is what i think

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kinjalgp

So according to you what are these zener diodes going to do?

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bogdanfirst

well im not sure it will work, but you would have a voltage drop on them so the opamp voltage will not be so high as the suply voltage. and the output woltage of the amp would be at the same value as if you would power the amp directly to the suply(considering that it wouldn burn).
why i think it is better to use 2 zenner diodes and not one is that this way the output voltage of the amp will be about the same value and the power disipation on the diodes wouldnt be so high

herbymcduff

Actually, I think those zeners would do nothing to the circuit. They are used as voltage regulators usually in parellel with circuit. So if your trying to use them for a supply of 5.1v to the op amp, it won't work.

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Sebi

The opamp can work with these zeners, but in circuit the serial transistors PNP. If the opamp supply 1.4V lower that PNP serial transistor emitter,the output voltage practically equal to input.(The opamp out can`t go higher as + pin voltage.)