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Topic: Wire ratings, specs and interpretation (Vibration Motor) (Read 792 times) previous topic - next topic

simonB2013

Feb 19, 2013, 01:18 pm Last Edit: Feb 19, 2013, 01:21 pm by simonB2013 Reason: 1
Hi,

Well, I am looking at operating several of these :
Product: https://catalog.precisionmicrodrives.com/order-parts/product/307-100-9mm-vibration-motor-25mm-type
Data Sheet: https://catalog.precisionmicrodrives.com/order-parts/datasheet/307-100-9mm-vibration-motor-25mm-type

On the face of it, the wire gauge required is simple.
Typical Op Current : 130mA
Max Operating Current: 160m
Max.Start Current 430mA
And the manufacturer has already attached some lead wires:
Lead Wire Gauge: 32AWG

.. and if I look up the rating for 32AWG, I see 2 values:
1 for 'chassis wiring' and 1 for 'power transmission'.
For 32AWG they are 0.53A and 0.091A respectively.
http://www.powerstream.com/Wire_Size.htm

I did google these two terms (chassis vs power), but "Unfortunately the ship is not a simple one, it depends on a number of factors... "
and seems each individual application is , well , individual !

I did grasp that a lot of it comes down to wire length. .. the longer the wire, the more 'strict' one had to be in adhering to rules.
Given that the supplied lead wires are only 46mm, this how we get away with 32AWG ?

But I will need wires <=1 meter.
I will also not be in control of how frequently the motors will be switched on/off.
Theoretically they will be absolutely hammered, starting & stopping from standstill all the time.
(When 'on', they will be controlled via PWM, but I believe this will induce less than Start Current, as there is already momentum in the unit)

What's worrying me, is that if I need a higher AWG wire, I am going to have to open the motor unit to access the existing lead wire solder points :(
Or possibly I could use 22AWG (0.9A Power) for 1 meter and simply connect the 46mm leads to the ends ... though seems messy/untidy.

Would anyone be able & willing to advise me on how to approach this problem/calculation ?

I have emailed the manufacturer, but I would appreciate an 'outside' persepective as well ... also might be interesting reading for others on the forums.

Many Thanks
Simon


Other notes:
These motors will be mouted on or close to human skin, hence I am quite keen to build in the most sensible margin of error when it comes to safety :)

michinyon

The issues you are concerned with involve two interelated issues.

The ability of the wire to transmit the current with a feasible voltage drop,   and the ability
of the wire to transmit the current without overheating.

Assuming they are copper wires,  it is easy to find the resistance per metre of the wire.

If you assume a current of 200 mA  (  or any other figure you care to use ),   you can figure
out the voltage drop in the wire over the length you are going to use.    You can also figure
out the voltage drop.   If the motor needs, say, 12 V,   and you put 12 volts in at the supply end
but only get 9 volts at the motor end because of the losses in the wires,  the motor may struggle
and draw even more current.

Once you know the resistance of the wires,  you can also consider how much they will heat up
under sustained operation.  Worst case would be almost continuous operation but with frequent
short interruptions,  so you get the inrush current again right after each interruption.   You can
then figure out the heat loss through the wire insulation,  and consider the ventilation,  to determine
the temperature the wire might reach.

Not simple, but not rocket science either.

There is no need to try to reconnect new wires inside the device.  There is nothing stopping you
connecting thicker wires to the existing leads,  just outside the device.


michinyon

For your 32 gauge wire,  the resistance is about 0.54 ohms per metre.

Pushing 200 mA through that will cause a voltage drop of 0.1 V ( per direction ),
which is probably acceptable,    and a heat dissipation of 21 mW,    which is not going
to set anything on fire.

simonB2013

Thanks Michinyon,

So it's just basic Ohms law stuff then !?
..the wire was just any other resistor in a cirucuit.

I just did the calcs and matched your results, which is reassuring, so thanks :)

Power & Heat are things that still interest me.
I know this is a puny project as far as power goes, but I am trying to do things 'right' because it'll be a good habit to get into before I progress onto more sizeable challenges.

I've seen heat dissipation ratings on elecronic component data sheets, yet very rarely on wire/cable specifications.
In my case, I was considering ribbon cable to power several motors .. and have just found an interesting article which might be of interest to anyone else with my 'problem':
http://www.mosaic-industries.com/embedded-systems/electronic-instrument-design-new-product-development/cables/ribbon-cable-current-rating

Many Thanks again
:)

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