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Relay x16 Board and PWM for motors


#1

I need to control six 12VDC motors and trying to figure if the Relay x16 board is the best way to do this. The motors run peristaltic pumps and two will be simply on/off for short durations (e.g. on full speed [30 rpm] for 1 sec, off for 1 hour), but for the rest of them i want to be able to set the speed and slow them down to a crawl. Quick reaction is not necessary. The motors are small, the ammeter says 0.18 amps when running at 12VDC. So are relays necessary or are there transistors these days that handle that power? Can the relays on the x16 board handle pwm for controlling motors in this simple way?


#2

Do you need to make one or volume?
What fez do you have?


#3

In the past I used an optocoupler with triac output that could directly drive motors of that size. Search for phototriac or take a look here: http://www.vishay.com/docs/49828/vmnsg21.pdf


#4

Just concerned about one right now, Gus. Maybe more down the road. I’m using a PandaII.


#5

For just one, I would go the easy way. First, use an hbridge circuit to control the motor. Those are extremely common. You can also do it chaper using a FET since you do not need reverse current.

Once you have one, you can make 10 more easily.

You can use relays for on and off but can’t control speed.


#6

So, keeping it really simple for me, the 16x Relay board won’t work with PWM, right? I wouldi need some kind of pwm motor controller for the subset of motors where i want to control the speed and, as i don’t need to reverse the motors, an FET based controller is enough. The Vishay phototriac that Wouster mentions might work and then it might be overkill for this app (it says it is made to control AC circuits so not sure why i would use it for a DC motor?).

So there are probably commercially available affordable FET-based controllers out there that would work with my Panda II’s pwm, but, of course I would appreciate any reference to a particular one that works for this size motor. To clarify quantity: Initially, I need to control 1 set of 6 motors, four of which i could use speed control on. Later i will need to control additional sets of six.

Back to the 16x relay board sold by GHI. I assumed the relays are solid state. True? What type of relays are these? Since, in my very limited understanding, pwm is simply very fast relaying. My application can probably live with just relays and no speed control at all by simply running the pumps intermittently at full speed, which is really just very slow pwm. I mean, a period of a minute or 10 seconds or 1 second rather than milliseconds works for me. So what is the maximum frequency that works for the 16x board relays? Can they switch at 1 Hz? 1/10Hz? 10Hz? Perhaps not a hard number as they may work at a frequency for a while and eventually break down.


#7

Like I said in last post,
Relay = on/off
PWM connected to a FET = control of speed + on/off
PWM connected to hbridge = control of speed + direction + on/off

example of FET http://www.sparkfun.com/products/10256
example of hbridge http://www.seeedstudio.com/depot/l298-dual-hbridge-motor-driver-p-284.html?cPath=170_173

If you only need to control 2 motors then it is easier to just use this http://www.ghielectronics.com/catalog/product/177

The 16x relay is not solid-state and you do not need solid-state, too expensive, a $0.10 FET will do just fine


#8

Thanks for the links to the example MOSFET and H-bridge drivers, Gus. Currently looking at a Logos 6 channel driver from Seeed (http://www.seeedstudio.com/depot/6ch-high-current-driver-1x3-kit-v1-p-792.html?cPath=170_173). Will look around for others as well.


#9

A rather timely article…