Hi All,
I'm trying to control 3 motors(cheap 3V ones) using an arduino with PWMd speed control in one direction.
Everything was fine with 1 motor. I followed Grumpy_Mike's sites ( Motors 1 ). I used TIP121 and a 9V battery for power. Even then, my battery lasted only for a few minutes.
So for 3 motors with seperate control circuits, I used a 12V 500mA wall wart with common power for all 3. But even then when I slowly started a second motor while first one was rotating, the first one really slowed down. I'm unable to run 2 motors simultaneously, let alone 3. I looked around the net and found that these motors typically consume 200mA. Please advice whether it's a low current problem and whether a 6/12V 1A wall wart will fix my problem???
Although I'd prefer not, should I go for L293 chips?
and a 9V battery for power. Even then, my battery lasted only for a few minutes.
Well, now there's a surprise. The only people that encourage the use of 9V batteries are those that make them.
Get a real battery.
So for 3 motors with seperate control circuits, I used a 12V 500mA wall wart with common power for all 3.
I fail to see why you are supplying 12V to a 3V motor.
Wow! I looked up battery current capacity at Battery Capacity and boy was I surprised. I naturally assumed they are bigger so must deliver more current. Guess size isnt everything. XD
I read somewhere that TIP121 required large voltage because its a Darlington pair or something. Although I agree 12V is too much, I didnt have a 6V wall wart with me(thats why i used the 9V battery in the first place).
What do you recommend should be the voltage and current of my power source? I'm completely at loss here. 
I looked through almost all related posts on the net but most assume to be using 6V or bigger motors. Appreciate your help...
I read somewhere that TIP121 required large voltage because its a Darlington pair or something.
http://www.kpsec.freeuk.com/trancirc.htm
This suggests that the darlington pair needs sufficient voltage, but very low current, to turn on. It says nothing about there being a significant voltage drop across the output side.
The Arduino provides sufficient voltage to turn the transistor on, and sufficient current.
So, I would expect that you could power the motors with 3V. I'd try 2 D cells per motor.
Antzy:
Wow! I looked up battery current capacity at Battery Capacity and boy was I surprised. I naturally assumed they are bigger so must deliver more current. Guess size isnt everything.
A 9V battery is a "true" battery - that is, it is a device compose of multiple cells; what you buy at the store, commonly called "batteries" - aren't - they are "cells"; AAA, AA, C and D "batteries" are actually AAA, AA, C, and D "cells" - you need to connect multiple of these cells together to make a "battery" (likely, the terminology comes from the military, I bet - ie, gun "batteries" composed of multiple guns in a single emplacement).
Ok - so a 9V is a true battery (so are 6V and 12V lantern batteries - also car batteries are true batteries, as well as gel-cell batteries - do note, though, that at one time, it was possible to buy lead-acid cells in C and D sizes; not sure if this is still possible today, though); what kind of cells are inside?
AAAA - that's right - quad A - slightly smaller versions of the AAA cell. There exist a ton of other battery types (ever wonder why there isn't a B cell? Well, there is - or used to be - look it up), many designated by letters (N cells are interesting; there's also a certain cell out there that was for smoke alarms that supplied 22.5 volts and wasn't much larger than than a AA cell), others designated by numbers (or a combo, as is common with button cells).
I'd tell you go to wikipedia - but for the next 24 hours it is down (in the USA) due to protest against SOPA/PIPA (look those up too, if you care about the internet - and if you are in the USA especially)...
Darlingtons generally drop around 2V to 3V at modest current, so a 6v battery should be enough for a 3v motor. Mosfets are much better, you can get the voltage drop down to a fraction of a volt. IMO darlingtons are obsolete now that we have cheap mosfets.
PaulS:
So, I would expect that you could power the motors with 3V. I'd try 2 D cells per motor.
But thats what I dont want. I already have a battery for another component which I didnt want to run with motor power supply. So there are already 3AA cells, and adding 6 more D cells will make the project very bulky. And so many cells don't make much sense. I already tried providing seperate 9V battery for each motor but I didnt like the setup with so many batteries. Thats why I wanted to go for a wall wart. Just not sure about the voltage and amperage. I guess 6V 1.5A(or 3A?) should do the trick, right?
cr0sh:
I'd tell you go to wikipedia - but for the next 24 hours it is down (in the USA) due to protest against SOPA/PIPA (look those up too, if you care about the internet - and if you are in the USA especially)...
I can see these SOPA and PIPA protests all over the net. My favourite sites, apart from Wikipedia, like xkcd and questionablecontent are all staging the protest. Even arduino forums have got this STOP SOPA banner :D. Its surprising how this bill can even be considered!
please help me out here in selecting a suitable wall wart. I want to finish the project this weekend.
Determine the stall current of your motors, either from the datasheet or by measuring the resistance of one of them and dividing that into 3 volts. Then multiply by 3 because you have 3 motors. You need a 6v wall wart rated for at least that amount of current.