I am using one of the PWM on my K8055 to run a little 3v motor, and connected it like this
it works, and I can adjust the speed, the problem is just that it got absolutely no torque left. Everything under 200 is close to unusable.
I am supplying it with 5V from the usb port, and changing to an external power supply makes no change.
I also tried to add a small capacitor to remove some of the riddle from the PWM, and it helped a bit, but far from enough.
A larger might help more, but it is then running too long before starting to run slower.
Maybe the motor is not running well with low voltage.
PWM 128 corresponds 1.5V if you use 3V supply. Maybe you have use higher voltage supply.
Have you tested the motor separately with a 1.5V battery? Does it run well?
Does the PWM output go low enough when active? You need an oscilloscope to check this.
Motor runs perfect with two 1.5V batteries connected in serial. I am not 100% sure about my reading, but my multimeter said 45-60 mA on full load the C337 is hardly getting warm too.
If you adjust the PWM to 128 then the average voltage over the motor should be about 1.5V.
Does the motor work well with a single 1.5V battery?
[quote]it works, and I can adjust the speed, the problem is just that it got absolutely no torque left. Everything under 200 is close to unusable.[/quote]This indicates the transistor is OK.
It is not at all uncommon for small, low-voltage, DC motors to have narrow operating voltage ranges, in fact I just looked at Jameco’s catalog and the 3.0V “nominal” motors have typical operating voltage ranges of 1.5V to 4.5V, only 2 will run below that, one at 1.0V and one at 1.2V.
This is strange result if the average voltage over the motor really was 1.5V when connected to the K8055.
Maybe the motor do not like the PWM waveform…
[quote=“VEL255”]This is strange result if the average voltage over the motor really was 1.5V when connected to the K8055.
Maybe the motor do not like the PWM waveform…[/quote]
Ah no, it doesn’t, it could hardly run without the capacitor on. Maybe I have to connect a larger to make it smooth enough for it, that would just add some more delay on speed changes.
Adding a capacitor indeed smoothes the PWM signal to the motor.
If the capacitor is in parallel of the motor then the transistor charges it very quickly during ON state. The capacitor discharges to the motor when transistor is in OFF state.
If you use very big capacitor the discharge takes long time and the capacitor will be charged via the transistor before it is empty.
This causes the average voltage over the motor will increase.
Tried a bigger, and it just made it close to impossible to control the motor, plus it ran faster than planned, until it then suddenly drops and again looses speed until coming to a hold.
Maybe it’s just a bad motor to do that with. Will just be too difficult to change it. I was experimenting with a cheap fan with LEDs in one of the wings, and it was showing patterns in the air while spinning. By changing the speed, i could make even more patterns out of it, but the problem is just that it can’t turn itself while running on the pwm output.
Oh well… New ideas for the pwm channels then…
Are there any kit that can make it usable with a higher current and voltage? Thinking about something like a wiper motor from a car, running on 12V.
Might “just” be something with some more heavy duty transistors, controlled by the one on the K8055 board?
You may use an external transistor. For example TIP120 can handle collector current up to 5A.
Using this circuit the PWM setting is inverted. The setting 0 gives max speed and 255 stops the motor.
[quote=“VEL255”]You may use an external transistor. For example TIP120 can handle collector current up to 5A.
Using this circuit the PWM setting is inverted. The setting 0 gives max speed and 255 stops the motor. [/quote]
Looks nice and simple, and with the 5A sounds pretty close to perfect. If 5A is too little, is it then possible to put two TIP120 in parallel and then get 10A?
It may not be a good idea to connect transistors in parallel. The current may not be distributed equally between the transistors.
Better to use a 10A transistor e.g. TIP142T fairchildsemi.com/ds/TI/TIP142T.pdf
[quote=“VEL255”]It may not be a good idea to connect transistors in parallel. The current may not be distributed equally between the transistors.
Better to use a 10A transistor e.g. TIP142T fairchildsemi.com/ds/TI/TIP142T.pdf[/quote]
Yeah, looks better, then maybe with some active cooling on too easy to just use an old CPU cooler, and drill a hole in with a bolt through
will try and order the parts for this, plus a hand full of relays and such, and then make a nice little thing wit it
Used an old computer power supply, 12V runs perfect, 5V runs perfect, 3.3V starts up without any problem and sounds tired when getting some load on, but still finds it surprised that it can run on that low voltage!
I wish success.
BTW: The heat sinks look quite small.
If you drive 5A at 3V to the motor then the power dissipation is (12-3)V*5A = 45W !
In case you use 12V voltage source.
I suggest to use larger heat sinks…
Please note the collector of the transistor is connected to the “frame” of the transistor (I think).
[quote=“VEL255”]I wish success.
BTW: The heat sinks look quite small.
If you drive 5A at 3V to the motor then the power dissipation is (12-3)V*5A = 45W !
In case you use 12V voltage source.
I suggest to use larger heat sinks…
Please note the collector of the transistor is connected to the “frame” of the transistor (I think).[/quote]
Oh yes, sorry, you couldn’t know. Thoose small are only for some LM317 transistors.
This is the heat sink I am planning to use for the ones who drive the motor.
And only loosely held together, still need to fabricate some brackets to hold it to the print so it won’t hang in the transistors
Going to add another print under it with the power supply, and two K8067 on, one to monitor the heat sink, and the other just because there are two inputs on the K8055
