Speed Control for Small DC Motors - Page 1
Forum section: electronics / projects

author: calzap
author_rank: Frequent Contributor
timestamp: March 25, 2014, 02:44:41 am
content: Curious about opinions on speed control on small (12 W or less) 12 VDC motors: voltage level vs PWM vs a combo. Would it make any difference for the low vs high end of the power range of a particular motor? My applications are low starting load and low power (moving fan blades and milk stirring paddles). Motors are geared down to 30-200 RPM full speed on the output shaft. Accurate speed control is not needed; it will be determined by the user observing the action. I've tried both PWM and voltage control, and it doesn't seem to make much difference except power consumption at half speed was a little less with voltage control. Years ago, I was using similar motors where there was a high starting load and fine control at low speed was needed. PWM was definitely superior to voltage control in that application.Mike in California

author: Rudolfo
author_rank: Contributor
timestamp: March 25, 2014, 08:24:12 am
content: Hi Mike,Using analog voltage control is quite simple, but digital control has a reduce power consumption. Here is a paper looking at analog and digital control of a DC-motor and might be helpful:http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.134.6191&rep=rep1&type=pdf.Enjoy your design work!

author: Harvs
author_rank: Super Contributor
timestamp: March 25, 2014, 01:42:43 pm
content: Unless you've got some specific requirement that precludes it, it's generally a no-brainer to just use a H-bridge and micro to do PWM control.Something like L289, on a PCB with heatsink runs at about $3 delivered, and that'll drive two motors. They're easy to use, and all the ones I've used off ebay have been just fine (albeit I haven't pushed them to the limit.)Add a uC for $1-5 depending on choice and a few lines of code and your done. Or if you really want grab something like a TL494 and do it old school in analog.If you want to do closed loop speed control, just put on some sort of tacho and do it in software.

author: calzap
author_rank: Frequent Contributor
timestamp: March 25, 2014, 03:55:26 pm
content: Quote from: Rudolfo on March 25, 2014, 08:24:12 amHi Rudolfo,Thanks for the reference, but neither FireFox nor IE can open the URL. Perhaps it's incomplete? If you could post the title and authors, I could look it up.Mike in California

author: Zero999
author_rank: Super Contributor
timestamp: March 25, 2014, 08:11:29 pm
content: Quote from: calzap on March 25, 2014, 03:55:26 pm

author: fcb
author_rank: Super Contributor
timestamp: March 25, 2014, 08:27:34 pm
content: It depends how complex you want to get.It could be a simple as a 317T variable voltage regulator, to as complex as a microcontroller based PWM I/R control.Is cost and/or development time an issue?

author: calzap
author_rank: Frequent Contributor
timestamp: March 26, 2014, 04:01:23 am
content: Cost and development time are not an issue. Controllers will be "off the shelf". There are so many inexpensive voltage controllers or PWM controllers available that there is no sense in a ground-up design for these uses. Only real work will be putting them in the right boxes and attaching the right connectors.Mike in California

author: calzap
author_rank: Frequent Contributor
timestamp: March 26, 2014, 04:05:41 am
content: Quote from: Hero999 on March 25, 2014, 08:11:29 pmTried again multiple times a few hours later and finally got it. Thanks.Mike in California