6v motor speed control

[blowhard]

Hi All,
Firstly, please excuse my lack of expertise, I am just someone who likes tinkering and am more mechanical than electrical orientated.

I have a 6v motor currently connected to a 6v/9amp hour battery and would like to install some means of controlling the speed of the motor - variable control.

I have tried a couple of variable potentiometers (100k) recommended by the local electronics parts store, but one fried immediately and the other started smoking.

Is there some simple method of installing a variable control for the motor?

Do I need to get a lower amp hour battery? The motor specs are listed below.

I have limited space to install the control, which is why the potentiometer was chosen.

Any assistance would be appreciated.

thanks

AD


6V 9,000 RPM DC Electric Motor

- Torque 80g-cm
- 2.3mm driveshaft
- M2.6 threaded mounting
- Generously ventilated
- Solder tag terminals

Voltage: 6V
NO LOAD
Speed (RPM): 13500
Current (AMP): 0.5
AT STALL
Torque (G.CM): 191
Current (AMP): 5.25
AT MAX EFFICIENCY
Efficiency(%): 49.6
Power (W): 5.96
Speed (RPM): 9679
Torque (G.CM):60
Current (AMP): 2
AT MAX POWER
Output (W): 6.44
Speed (RPM): 7845
Torque (G.CM): 80
Current (AMP): 2.6

 

[MikeMl]

You need a Pulse Width Modulated Motor Driver, consisting of an large MOSFET transistor mounted on a heatsink, driven by a variable pulse width multivibrator (pulse generator), such as this one.

The MOSFET acts as a switch, which has a very low (0.1Ω) resistance when ON; and a very high (almost infinite) resistance when OFF. The 555 timer makes the variable OnTime/Off Time while keeping the pulse rate more or less constant, but at a rate so high that the motor responds to the average current through it, making a smooth speed control as the pot in the circuit is turned, and providing lots of torque when starting.

Trying to speed-control by putting a resistance (rehostat) in series with the motor is an extremely crude and wasteful way of doing it. At some settings, the rehostat will get stinking hot (wasting energy) from your battery. The speed regulation sucks; the slightest change in mechanical load on the motor will cause the speed to change; while with the PWM method, the motor speed will stay much more constant.

To crudely speed control your motor, it would take a huge 300W 10Ω wire-wound Rehostat with a 6A current rating, like the MP40 shown in this document. Unless you can find one surplus, you will find that the cost of this rheostat is much higher than the simple MOSFET speed control....

 

[blowhard]

Thanks I'll investigate your suggestion. AD

 

[Joe G]

I've used that same circuit (Dave's) on my pcb drill press for the feed motor which was driven from a 5.7 volt cell phone charger, and it will run the motor just about to a "crawl".

 

[Boncuk]

Hi blowhard,

if you don't have a PCB design yet here is one using SMD parts. I replaced the IRFD024 with an IRF7401, which can stand higher current (up to 7A).

Board size is 25.2413X19.8428mm (0.99375X0.78125").

The second design uses wired components and the MosFet transistor IRFD024 (Dave Johnson)

Board size is 33.3750X36.83mm (1.3125X1.4500").

If you're interested obtaining the Eagle files please PM your email address.

Regards

Boncuk