Battery

[paparts]

I have a problem with the 9v battery. I measured the battery's voltage directly to the multi tester the measurement says its 9v but when I supply it to the circuit and measure the voltage the battery gives 4v what do you think is the problem?

 

[Nigel Goodwin]

The battery is flat! - or (less likely) you're drawing far too much current from it.

 

[simrantogether]

See...

See...

a very simple concept... the true voltage of a current sourcing device is that you measure when it is not connected with any circuit...

Am i right...

Regards,

Simran..

 

[paparts]

does the battery voltage chang whn you supply it to a circuit?

 

[dknguyen]

does the battery voltage chang whn you supply it to a circuit?

Yes, it does. It changes depending on the current level being drawn as well as the current charge left in the battery.

 

[simrantogether]

Well...

does the battery voltage chang whn you supply it to a circuit?

Battery's internal voltage remains same... but that same voltage is not visible on multimeter because the circuit is eating a lot of current and potential...

Regards,

Simran..

 

[Hero999]

What are you powering with the 9V battery?

 

[paparts]

im powering a mobot. I am using a 7805 to supply for the microcontroller and for an ic(LM339), and 5 ir's. LM317 for an adjustable output for the motor driver.

 

[Krumlink]

I would not use a regulator for a motor (unless its a servo) and I would not use a 9V. Use AA, etc just not a 9v for all your apps.

 

[paparts]

Why? There is no place for 4 AA bateries. I need the adjustable output to control the speed

 

[bananasiong]

9 V battery has very low capacity. AAs last much longer. For controlling the speed, use PWM.

 

[simrantogether]

9 V battery has very low capacity. AAs last much longer. For controlling the speed, use PWM.

Ya...

for controlling the speed use pwm than going for reducing voltage...

Regards,

Simran..

 

[Hero999]

im powering a mobot. I am using a 7805 to supply for the microcontroller and for an ic(LM339), and 5 ir's. LM317 for an adjustable output for the motor driver.

9V batteries drop to below 8V very quickly so the regulator will loose regulation.

What current does the motor draw, bear in mind the starting current will be much higher?

What's the maximum voltage you want the motor to run at?

No wonder you're having problems.

 

[paparts]

I want to create a high speed mobot would pwm help? I am using the motor friver found @ bobblick.com and it does give the speed. thanks for the info on 9v batteries. Can I ask for circuit diagrams for pwm's working on a 7.2V(6 1.2 batteries) battery

 

[bananasiong]

What circuit do you want? Just use a transistor to drive the motor. The signal comes from the microcontroller.

 

[paparts]

can I ask for a circuit of a proximity sensor?

 

[weegee]

using pwm will make your robot faster than by varying the voltage. using pwm you are supplying the motor with full voltage, and the ability to draw full current that it demands, there for your motor will be developing maximum torque at any given speed.

You are just varying the time that the motor has power applied, but except at very low speeds, you will not see any jerkiness - and when you want it to speed up, it will accellerate much faster than it does just now, as it has much more available torque.

 

[paparts]

will it be still effective using the motor driver found at bobblick.com?

 

[weegee]

if this is the one - http://bobblick.com/techref/projects/hbridge/hbridge.html

then yes, as thats how the author has tested his was with pwm, on a basic stamp2 processor.