Charging a 9V rechargable battery using two 9V dc Motors

[FlipFlop1]

Hi,

I want to charge a 9V rechargable battery using two small 9V dc motors which are coupled front to front, one of the motors is being run by a power supply and the other one is generating a supply. I have tried but not much luck yet. Can anyone shed any light on this. I will be greatfull.

Thanks

FlipFlop

 

[audioguru2]

Hi FipFlop,
Having a DC electric motor drive a DC generator wastes a lot of power as heat in the motor and generator. What is the power supply and why can't it be used to charge the 9V battery though a current-limiting resistor?

 

[FlipFlop1]

Hi Audioguru,

Thanks for your reply and help. I know that I can use a power supply or a battery charger to charge the battery, but i want to use the motors instead, I have a regenerative plan in mind so I  would just like to know the most efficent way to charge battries using motors. Do I need some sort a regulation circuit or maybe something like a dc to dc converter. Please bare in mind that im not an electronics expert but just an active electronics hobbiest so I will be very greatfull for anyones help and ideas.

Thanks
FlipFlop

 

[audioguru2]

Hi FlipFlop,
Is your 9V battery a little "transistor radio" size, which is really 7.2V and is it a 120mA/hr Ni-Cad or a 150mA/hr Mi-MH?
Energizer recommends a max charging current of only 24mA and 30mA for them, so they will take up to about 6 hours to fully charge.

If your "generators" have variable speed then they will also have variable output voltage and current. To charge the battery each generator will need a series rectifier to prevent the battery from driving the motor when it is running too slow to be a generator. You also need in series a current limiting transistor circuit or just a resistor to limit the charging current to 24mA or 30mA.

It will be very difficult to determine when a partially discharged battery is fully charged. With higher-current AA cells my limit is 1.4V per cell for NiMH. With the low charging current of a 9V battery then its fully charged voltage will be less, maybe only 1.3V per cell or 7.8V for the battery. ;D

 

[FlipFlop1]

Hi Audioguru,

Thanks for your reply. I dont know what u mean by "transistor radio"size, but it is one of those rectangular ones, it is by Sony and on the front it says "9V Ni-MH 270mAh" but on the back it says "For 9V Applications (6F22) P-22H 270mAh 8.4V". I hope I have answred your questions.

Thanks

FlipFlop ???

 

[MP1]

oh, I have a transistor radio that is much bigger than that...  ;D

MP

 

[FlipFlop1]

Dear MP,

is that radio of yours AM or FM? because Im sure that will also make a lot of diffrence on how the 9 v battrey can be charged ;D

Thanks
FlipFlop

 

[audioguru2]

Your 8.4V Ni-MH battery will be about 9.8V when fully charged. I don't think a 9V motor that is used as a generator can supply 27mA for about 14 hours at 9.8V or more.

 

[FlipFlop1]

Then what shold i do? use biggers motors? I remember a circuit i saw on the net sometime back in which the author was recharging battries using a hand wound motor, right now I just cant recall the site i saw it on, but, but im looking for it. Thanks for your help.

thanks
FlipFlop

 

[audioguru2]

What is driving your motor/generators for 14 hours?
Do you have a big waterfall and are using a gearing system so that they operate at more than their max RPM?

Why do you want to use a DC motor as a generator? Just plug the battery into a charger in the evening and it will be fully charged by noon tomorrow. ;D

 

[MP1]

FlipFlop,
You will need more than 9 volts to charge a 9 volt battery to capacity. You will also want to regulate the charge so that you do not over charge the battey with your charge generator. This can be done by changing the speed of the rotor or by a regulation circuit. Are you sure the output of the motor is 9 volts? The specification of the motor is usually refering to what voltage the manufacturer recommends for powering the motor. Check out some of the wind power sites for help with this project as well. There is a lot of discussion on the web about alternate energy.
Hope it helps.

MP