555 timer motor control

I have a small dc motor and a 9 volt battery. When I start the motor going I need to have a fair amount of torque which i know means small voltage, big amps. but as time increases I want voltage to increase and current to decrease.

The idea i have is to use a 555 timer on a voltage regulator, any ideas on where i can find this schematic?

I suggest you study electronics and electrics a little more, nothing you say makes any sense.

that's really not very helpful. but i don't see what doesn't make sense. P=VI which therefore means as V increases, I decreases and vise-versa. If your confused about the torque think of it like a car. start off in low gear speed is low but torque is high. but at higher speeds you need very little torque. still confused?

Aiden1015 said:

that's really not very helpful. but i don't see what doesn't make sense. P=VI which therefore means as V increases, I decreases and vise-versa. If your confused about the torque think of it like a car. start off in low gear speed is low but torque is high. but at higher speeds you need very little torque. still confused?

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I'm not the one who's confused

Low voltage/high current doesn't mean high torque, and doesn't even happen.

Gearboxes give high torque at low speeds because of the mechanical advantage they give, this doesn't apply to an electric motor (unless you add a gearbox to it).

Current is directly proportional to voltage (simple ohms law), the higher the voltage the more current a motor takes, and the more power it produces. Low voltage gives low current, and the lowest torque.

Your P=VI is correct, except power doesn't stay constant, as voltage increases so does current, and power by the product of the two.

I have seen the rule on motors, but what about arc welding? they use a very high current (140 amp) but a voltage of 1.5 volt I guess, so high current lo voltage is possible.

To Aiden1015, under no load the electric motor eats more current while it starts, later the current consumption is lower.

Otherwise, the current consumption will increase proportionaly with the load that your motor is driving. So make sure your batteries provide enough current to meet the requeriments under maximum load.

You don't have anything else to do with the motor current

Instead use an adecuate way to control the given voltage to the motor, to select the desired operating speed

Correct me if I'm wrong, but the torque of an electric engine remains constant at any RPM, opposite to internal-combustion engines - att: discovery channel

Menticol said:

but what about arc welding? they use a very high current (140 amp) but a voltage of 1.5 volt I guess, so high current lo voltage is possible.

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Yes, because R is reduced here: The internal resistance of a welding power supply is very low, say 10milliohms using your values.

Menticol said:

Correct me if I'm wrong, but the torque of an electric engine remains constant at any RPM

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Nope.

Each type of electric motor has its own torque vs. speed curve. In simple DC PM motors, the relationship is linear, where torque is a function of current, and speed a function of applied voltage.

That's true you connect a constant voltage source and you get a near-constant speed motor and if you connect a constant current souce you get a near-constant torque motor.

If you have a simple DC motor the current will be proportional to the torque delivered by the motor, and the voltage will be proportional to the RPM.

Lets say the motor is unloaded and the 9V voltage is applied to the motor. Then the motor will reach high RPM (dependent on the motor) and the back EMF at that RPM will be 9V, and there you have the highest RPM that can be achieved with a 9V voltage source. The current can at this stage be approximated to zero.

But when you put some kind of load on the motor the RPM will go down, because the current will go up proportionally to the torque on the motor. So if there is 9V on the motor the RPM will go down a little when little torque is applied, and more when more torque is applied. Then finally when to much torque is applied the motor will come to a stand still. There will be no back EMF and the stall current will now only be dependent on the internal resistance in the motor, meaning that the current will be high.

So to be able to answer your question regarding your needs of a PWM signal to the motor, you need to provide us with more information of how your application is assumed to work.