how to run dc motor - Page 1
Forum section: electronics / beginners

author: vishuarora
author_rank: Newbie
timestamp: February 02, 2013, 06:58:34 am
content: Hello,I am trying to run DC motor which can run at 3 - 6 volts and 4 amps with no load. I have power supply which can produce different voltages up to 5 amps. When i connect motor directly to power supply it stalls, when i use breadboard in middle it run fine. But what a breadboard is doing so motor don't stall? I tried using cap of 100uf but dose not help. I don't want to use breadboard all the time as i put load on motor and it draw more amps breadboard get too hot and melt.So what should i do?http://www.jaycar.com.au/productView.asp?ID=YM2772&form=CAT2&SUBCATID=983#1

author: houdini
author_rank: Regular Contributor
timestamp: February 02, 2013, 08:18:50 pm
content: 5amps is not a voltage. Try hooking it to a lantern battery (6v)

author: smackaay
author_rank: Regular Contributor
timestamp: February 02, 2013, 08:50:19 pm
content: When you hook it up to the motor directly, is there a voltage on the pins? I've had the issue where just by me having my wires in a certain position, they would conduct because either the wire was broken inside or the wire was sitting funny on the terminals.

author: vishuarora
author_rank: Newbie
timestamp: February 02, 2013, 10:02:38 pm
content: Quote from: houdini on February 02, 2013, 08:18:50 pmI meant different voltages @ max 5 amps.

author: IanB
author_rank: Super Contributor
timestamp: February 02, 2013, 10:12:03 pm
content: It seems like you have a wiring problem. Check your wiring and connections.

author: vishuarora
author_rank: Newbie
timestamp: February 02, 2013, 10:16:00 pm
content: I check with multimeter when i connect directly voltage is in mV that why it stalls and when i use breadboard it run fine with voltage 3.9 to 4.02 volts. But if i keep it running long i can smell burning plastic.

author: IanB
author_rank: Super Contributor
timestamp: February 02, 2013, 10:23:18 pm
content: If you have only mV at the motor terminals that would suggest bad connections or broken wiring. What voltage do you see on the power supply output terminals during this test?

author: G7PSK
author_rank: Super Contributor
timestamp: February 02, 2013, 10:55:47 pm
content: An electric motor can take many times the running current at start up, sounds to me like the breadboard contacts are acting as a resistance, hence the burning you mentioned, try a resistor in series with the motor fitted with a bypass switch, say half ohm at 3 watt, you wont need a larger size as it will be bypassed as soon as the motor starts. Other wise get a ten amp power supply. It states in the spec sheet that at stall it draws 67 amps and a static motor on start up is stalled for a fraction of a second, long enough to trip your power supplies protection circuit.

author: vishuarora
author_rank: Newbie
timestamp: February 03, 2013, 02:00:13 am
content: Quote from: G7PSK on February 02, 2013, 10:55:47 pmHi thanks for reply, can you please explain circuit in more details as am new to electronics. Also by stall i mean motor run - off - run - off its a loop.

author: vishuarora
author_rank: Newbie
timestamp: February 03, 2013, 02:03:59 am
content: Quote from: IanB on February 02, 2013, 10:23:18 pmI am using same wiring with and without breadboard so i dont think is the wiring issue. for eg Motor=wires=breadboard=wires=supply or Motor=wires=wires=supply.

author: IanB
author_rank: Super Contributor
timestamp: February 03, 2013, 02:36:40 am
content: Quote from: vishuarora on February 03, 2013, 02:03:59 amRight, but consider what G7PSK said. If you have only mV at the motor terminals it won't turn as it needs 3-6 V to turn. If you have only mV at the motor terminals, what do you have at the power supply output terminals? If you have only mV there also, it indicates that the power supply has tripped and shut down its output.It could be that your motor is too big for the power supply you have. When you first connect the motor it looks like a short circuit and trips the power supply. Including a resistor in series with the motor could reduce the startup current and avoid tripping the supply. Once the motor has started turning the power supply might cope.

author: w2aew
author_rank: Super Contributor
timestamp: February 03, 2013, 02:52:05 am
content: Quote from: vishuarora on February 02, 2013, 10:16:00 pmThe burning plastic smell is probably from the breadboard. A couple of amps is WAY too much current for the breadboard connections. The likely scenario is that breadboard I'd providing enough resistance to keep your power supply from shutting down, thus giving enough time for the motor to speed up and generate enough back EMF to bring the current down. But, even the running current causes too much power dissipation the the breadboard contacts causing overheating.

author: G7PSK
author_rank: Super Contributor
timestamp: February 03, 2013, 11:49:34 am
content: I have done a quick drawing in Dave cad for you, the data sheet gives the stall current as 67 amps this will also be the initial draw on first switch on so you have to put a resistance into the circuit as you do not have a big enough power supply 5 amps wont start the motor with a DOL (Direct on Line) starting system. The switch is to bypass or short out the resistor. I have just taken another look at the data sheet and note that the full load current is 13.5 amps the 4 amp rating is for no load full speed only, so you may find that the power supply will trip out any way.

author: codeboy2k
author_rank: Super Contributor
timestamp: February 03, 2013, 02:35:13 pm
content: and here's something similar in LTSpice.The motor is Rrun, the limiting resistor is Rlimit, and the P Channel MOSFET is the switchthat shorts the resistor after a time delay. In this case it's about 20msThe numbers don't match your motor, and a resistor is not a motor model, but it shows the current limiting and time-delayed un-limiting.You'll notice that Irun is limited to about 3A for 20ms, and then switches to the full 6A. This gets the motor up to speed and doesn't stress the PSU.However, as G7PSK says, that motor you have loads up to 13A and will probably still trip your PSU.

author: vishuarora
author_rank: Newbie
timestamp: February 04, 2013, 12:01:27 pm
content: Thank you everybody for the replies, I will try out your suggestions.