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Running multiple 12v motors of one PWN controller (help required)

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finn5000

New Member
Hi there,

First off a bit of background, this is part of a university project where I want to control the flow of water from a reservoir into 12 small tanks (the flow going into each of the 12 tanks needs to be the same, roughly 30ml/min). My way of achieving this is to use 12 peristaltic dosing pumps which will all be hooked up to a single PWM controller, so I can vary the speed of all 12 pumps at the same time.

I am studying ecology (not an electrical engineer!) and my knowledge in this area is limited. I have a plan I just want someone to have a look at what I am planning on doing to see if it makes sense.

I have:
power supply 12v 10A
PWM controller 12v 8A https://www.jaycar.co.nz/12vdc-8a-dimmer-motor-speed-controller/p/MP3209
12x DC motors (pumps) 12v 300mA http://www.ebay.com/itm/12V-DC-DIY-...804987?hash=item43e622203b:g:PVsAAOSwZVhWTZd4

I will connect the power supply -->PWM controller --> 12x pumps (connected in parallel) (see attached diagram)
My understand is that since the 12 motors require 0.3A I need a total of 12 x 0.3 = 3.6A, therefore the 8A I have to play with is plenty.

Does this seem feasible, are there any other components that I need?

Any advice much appreciated.

Cheers,

Finn
 

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JimB

Super Moderator
Most Helpful Member
Your thinking so far seems OK.

There is however a bit BUT...
The motors, although nominally identical, are unlikely to run at exactly the same speed, and so the volume of water delivered in a given time will be different for each pump.

Will this be a problem for your project?

JimB
 

alec_t

Well-Known Member
Most Helpful Member
Welcome to ETO.
The start-up current of a DC motor is usually a lot more than its rated running current when up to speed. Can you measure the DC resistance of the motor? That would enable calculation of the maximum current your power supply would have to provide.
 

finn5000

New Member
Thanks for the quick reply.

It depends how much variability there will be, if it was less than 5% it would be OK, any more than that and I would have to look at other options. I was also thinking about hooking up each motor to a separate pwm controllers but then I would have to mess around calibrating them all to give them same flow, would that be the alternative option?

Cheers,
 

finn5000

New Member
Hi Alec,

Cheers. I will be able to (not right at this moment though), So I should measure the start up current and use that? e.g. 12 x start-up current = ? but as long as it is well below 8A I should be OK?
 

JimB

Super Moderator
Most Helpful Member
How much variability there will be between pumps I do not know.
I suggest that you do a little experiment with say 3 or 4 pumps, running from the same supply and measure the flowrate.
If the flowrate variation of the sample is within acceptable limits you will probably be OK with the full complement of 12 pumps.

One thing which may help to give a consistent flowrate between pumps, ensure that the tubing on the inlet side of each individual pump are all the same length, and similarly that the tubing on the outlet side of each individual pump are all the same length.

As regards the switch on surge current, if it turns out to be a problem, how often will the pumps be stopped and started?
Every few minutes?
or
Started and left running for days and weeks?
If the latter case, just have several switches and switch the power to two or three pumps at a time.

JimB
 

finn5000

New Member
Sounds good, I'll set-up a small scale version of the experiment and see what sort of variability I get in terms of flow.

The pumps will be started and left running, OK I'll get a few switches so I don't have to switch them all on at once.

Great, thank you for the advice, I am feeling much more confident about things now!

Cheers,

Finn
 

alec_t

Well-Known Member
Most Helpful Member
I'll set-up a small scale version of the experiment and see what sort of variability I get in terms of flow.
If variability is excessive you could use adjustable clamps on the tubes to even out the flow rates.
 
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