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Battery Charging Help


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Smokey

Thu Aug 06 2009, 05:35AM

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I want to drive a big load. If u refer to the simple of a biasing a transistor with 0.95 Ohms of load at the emitter leg. I want that the maximum voltage drop at this load but not due to 2.2kOhms resistor(Simple voltage division rule).
Now I wana charge my battery and its internal resistance is 0.95 Ohms,I can’t charge it like this because of the problem and I can’t even use lm317 Voltage regulator to charge the battery.for example if lm317 is set to 9.5 volts and my 9V battery is discharged showing 8.6Volts. now if I connect LM317 to battery then LM317’s voltage drops to 8.6V and no charging(I observed for 2 hours for any change in Voltage).
So how can I get MAX VOLTS at 0.95 Ohms.

ExperimenterUK

Thu Aug 06 2009, 10:23AM

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Are you asking a question about the circuit shown or about charging a battery
with a similar circuit ?.

Batteries are very different to resistors, so we will need more information
about exactly what you want to do.

Smokey

Thu Aug 06 2009, 12:41PM

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[ Edited Thu Aug 06 2009, 12:53PM ]

Smokey

Thu Aug 06 2009, 12:43PM

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yes i tried this simple circuit and i calculated its internal resistance and it was 0.95 ohms. well if these are two different things then i have 2 questions then. how can i get max voltage across 0.95 ohms.
2nd i want to make battery charger with over charging protection circuitry. the circuitry i experimented was successful but it requires constant voltage to make decision. using LM358 (op amp) as comparator with Hysteresis,the hysteresis width(thats what i will call) is 0.6 v so circuitry will stop charging at 12.7V and start charging at 12.3V,V+ will give the hysteresis width in volts,use the formula when S1 is closed that is attached to the ground and the on it to have battery reference.so any change in voltage will disturb the hysteresis width so the voltage must be regulated.i cant use zener diodes as they are available in discrete values. ....sorry for posting 2 times.

[ Edited Thu Aug 06 2009, 12:51PM ]

sashijoseph

Sat Aug 08 2009, 09:53PM

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I can’t even use lm317 Voltage regulator to charge the battery.for example if lm317 is set to 9.5 volts and my 9V battery is discharged showing 8.6Volts. now if I connect LM317 to battery then LM317’s voltage drops to 8.6V and no charging(I observed for 2 hours for any change in Voltage).

the lm317 requires atleast 3v headroom for regulation...make sure the input is atleast 3v above the desired output.

As for the 2nd part(the comparator) I fail to understand how the ckt would ever work as you say...care to explain the working?
For eg when you start off by connecting S1 to gnd,the opamp output would fall to 0v. Now when you connect S1 to Vbatt(which say is at 12.3v) the output will swing to the +ve rail and as soon as this happens the voltage at V+ input of the opamp would drop below V- ,switching off the opamp output again.
Plz show all the voltages and resistor values in your ckt for a better understanding.

Regardless,you may try wiring the comparator with hysteresis in the more conventional manner.....like this

Let there be music........

sashijoseph

Sat Aug 08 2009, 10:03PM

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oops here it is..

And like ExpUK pointed out earlier,batteries are very different to resistors.
Designing a charging ckt based on the internal resistance of a battery is a bad way to start.
Hope you have spare batteries...