Turn on a little Motor DC - Page 1
Forum section: electronics / projects

author: electronbean
author_rank: Contributor
timestamp: May 20, 2022, 10:17:03 pm
content: Hello fellows,What do you think about this circuit?https://ibb.co/8gvxgjSI intend create a circuit where I can activate this motor (https://datasheet.octopart.com/MOT1N-Velleman-datasheet-22075344.pdf) and regulate your rotation through this potentiometer (https://www.tme.eu/fr/details/ow20bu-10k-lin/potentiom-plastique-a-rotation-unique/omeg/ow20bu-10ka-bush-cp7mm-spindle-f2-l-16mm/).Firstly I think use four this batteries (https://data.energizer.com/pdfs/l91.pdf), theoretically will last 18 hours (6000mAh/320mA = 18Hours and 45 minutes). But to don't waste battery and harm de environment I am thinking use this power bank (https://www.mi.com/global/10000mAh-mi-18w-fast-charge-power-bank-3/specs). Where will she last around 17 hours (I am using parameter Rated Capacity: 5500mAh/320mA = 17 Hours).What do you think about this circuit? The goal is turn on the led, while the circuit is turn on and regulate the velocity this DC motor.Thanks

author: MarkF
author_rank: Super Contributor
timestamp: May 20, 2022, 10:40:45 pm
content: I think you're not going to have much slow speed control.A better solution would be to use PWM to control the speed.The minimum supply voltage for the 555 is 4.5V.You would need to add a couple series diodes with the motor to drop the voltage to 3V.Here is a circuit (Google 555 timer PWM):

author: electronbean
author_rank: Contributor
timestamp: May 20, 2022, 10:46:35 pm
content: Sorry, I didn't mention but this project will be use on a project school to my little daughter. For this I can't "complicate" very much the project. But thank you for your help.

author: MarkF
author_rank: Super Contributor
timestamp: May 20, 2022, 10:50:29 pm
content: Have you ever played with a HO model railroad?Remember how the locomotive does not start slow but jumps to a fast speed when turning up the throttle? PWM will allow the motor to run a slow speeds. A PWM frequency between 30Hz to 90Hz will work best. I use 80Hz on my model railroad.

author: ledtester
author_rank: Super Contributor
timestamp: May 20, 2022, 10:51:54 pm
content: I think you'll find that you have very little control over the motor with the potentiometer.This controller might work with a 3V motor:https://www.amazon.com/Voltage-1-8v-Motor-Speed-Controller/dp/B07MK1SKRTYou can probably find the same product on ebay or aliexpress.There are some youtube videos which show it in operation at higher voltages, e.g.:https://youtu.be.com/iQORBg3_YsUhttps://youtu.be/UG9jRdrviaI

author: ledtester
author_rank: Super Contributor
timestamp: May 21, 2022, 12:06:40 am
content: I tested this one transistor controller on a 3V DC motor I had lying around:The supply was 3V and the MOSFET was a 2n7000.It worked kinda sorta. Only the last 20% of the pot had any effect on the motor speed. A lot will depend on the motor you're using. There's another video which uses a jellybean NPN transistor:https://youtu.be/rXG5jkI6S9YCould be an option if you already have the parts on hand. Otherwise I'd go with ready-made solution which is likely to be a lot more energy efficient. These ad-hoc circuits waste a lot of power in the transistor.

author: eugene
author_rank: Frequent Contributor
timestamp: May 21, 2022, 10:41:07 pm
content: Quote from: electronbean on May 20, 2022, 10:46:35 pmWell, if you have specific requirements, then you need to spell those out for us. How old is your daughter? What is the actual assignment? (If it is written, then reproduce here in English.) If not written, then try to express as clearly as possible what your goal is.If you want to know what I think of that circuit, I think it's all wrong. But I don't know what you need, so I can't suggest something right.

author: electronbean
author_rank: Contributor
timestamp: May 24, 2022, 03:32:47 pm
content: Quote from: ledtester on May 21, 2022, 12:06:40 amI tried draw a schematic from the video did you share. I obtained this:https://ibb.co/MkfvG27What do you think?Thank all to yours advice

author: kevin original
author_rank: Contributor
timestamp: May 24, 2022, 09:21:15 pm
content: The motor's no-load current is about 350 mA and the BC557 transistor in your circuit has a maximum collector current of 100 mA. Pick a BJT with a higher collector current and power rating. Also, use an NPN if you are going to drive it on the low side of the motor.

author: Zero999
author_rank: Super Contributor
timestamp: May 24, 2022, 09:29:38 pm
content: If you don't have the skills to make a PWM motor controller, then buy one. There's not much to be learned from building one anyway, apart from a bit of soldering practice.Search for 3V PWM motor controller.https://www.amazon.co.uk/Adjustable-Motor-Speed-Controller-Switch/dp/B00Y2AV4G8https://www.fruugo.co.uk/dc-18v3v5v6v12v-2a-pwm-motor-speed-controller-low-voltage-motor-speed/p-51555124-103825843

author: electronbean
author_rank: Contributor
timestamp: May 24, 2022, 10:17:50 pm
content: Quote from: kevin original on May 24, 2022, 09:21:15 pmWhat do you think about this model? (I think which this model fit very well to feed my motor)https://www.onsemi.com/pdf/datasheet/p2n2222a-d.pdfMy schematic it is well designed?https://ibb.co/MkfvG27thanks to your help

author: ledtester
author_rank: Super Contributor
timestamp: May 24, 2022, 10:21:39 pm
content: Quote from: electronbean on May 20, 2022, 10:46:35 pmHere's another idea...Get a bunch of low ohm resistors... like a bunch of 1 ohm and 2 ohm resistors. Connect them in series like so:By connecting the battery/power source to various points in the resistor chain you alter the current through the motor.Finding out the range of resistance values you need to control the motor will be half of the fun.

author: electronbean
author_rank: Contributor
timestamp: May 24, 2022, 10:23:49 pm
content: Quote from: ledtester on May 24, 2022, 10:21:39 pmThis is a very good and didactic idea. Thanks

author: Zero999
author_rank: Super Contributor
timestamp: May 25, 2022, 11:17:33 am
content: Quote from: electronbean on May 20, 2022, 10:17:03 pmA few points.Here's a link to a better data sheet, which I've also attached to this post in case that site stops working.https://www.jprelec.co.uk/pdffiles/450-010.pdfWhat load is the motor driving?A motor behaves like a DC voltage source in series with a small resistance. The DC voltage (back EMF) opposes the supply voltage and is proportional to the shaft's speed. When stalled the current is determined by the resistance of the motor's winding. As the shaft spins faster, the voltage generated by the motor approaches the supply voltage and the current drops. When unloaded, the back EMF is near the supply voltage and the current is low. As a mechanical load slows the shaft down, the current increases. If the shaft is spun fasted by applying a rotational force in the same direction as the shaft is spinning, thus speeding it up, the current direction will reverse and the motor will act as a generator, charging the battery.The 300mA specified on the data sheet is when nothing is connected to the shaft. When stalled the motor current will be close to 4A, at 3V, which indicates its internal resistance is V/I = 3V/4A = 0.75R. The stall current is briefly drawn when the motor is started, but can't be sustained for long without damage. Try powering it up and measuring the current with your finger pushing against the shaft to slow it down. Obviously don't do this for too long, otherwise you can burn your finger, as well as the motor. According to the data sheet, the rated current is just over 1A, with a load of 14g·cm, at which point the speed will be 11k5 rpm. The motor might overheat if this load is exceeded for too long.A linear controller which dissipates the voltage difference between the supply and motor, gives off Vdifference*I Watts of heat. This applies regardless of whether the element dissipating the heat is a transistor, or plain old resistor. A PWM controller i.e. one where the transistor is either on, or off, does not have this issue, which is why this has been recommended, even though it's more complicated.If the motor voltage is reduced, the motor can't draw as much current, due to Ohm's law.If you're using linear method to drop the voltage, the maximum possible power dissipation in the resistor, or transistor will be a quarter of the motor's power consumption when stalled. Half the voltage will be dropped across the motor and half across the resistor or transistor and the current will be half of the rated stall current. P = VI = 1.5*/2A = 3W. Your resistor/transistor will need to be able to dissipate at least 3W for short periods of time. The continuous power rating of the resistor/transistor should be about half the motor's full power rating, so 3*1/2 = 1.5W.If you don't have time to read the above, make sure your resistor/transistor can safely dissipate 3W peak and 1.5W continuously.