Oatley K25 PWM kit - feedback and questions - Page 2

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Re: Oatley K25 PWM kit - feedback and questions

"Franc Zabkar"
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** Why on earth does the PWM circuit run at 300Hz ??

This is far too low a frequency for good efficiency.

There will be large current pulses in the motor at almost any setting while
the brushes and motor windings will suffer from additional heating with no
benefit. Simply raise the frequency to say 3kHz and put a heatsink on that
Schottky diode and it will be far better job all round.

Using a higher frequency makes the current flowing in the motor become
nearer to steady DC at all duty cycles of the PWM.  The Schottky diode will
then pass more average current (and less peak) during the "off " times in
the PWM so will dissipate more heat.

A correctly operating PWM drive provides the same kind of speed control over
a permanent magnet motor as variable DC voltage control does  -  but with
the high efficiency essential for battery powered vehicles and the like.

I note the circuit provides no " braking " function and this could be an
issue for some vehicles. Braking means placing a short on the motor to bring
it to a rapid stop.


.... Phil



Re: Oatley K25 PWM kit - feedback and questions
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I pulled a border around the image - hit CTRL C

opened corel draw, and pasted it.  It was stretched, but could be
pulled back into shape and saved

Re: Oatley K25 PWM kit - feedback and questions

"kreed"

I pulled a border around the image - hit CTRL C


** Seems to all depend on the version of Acrobat being used.

  PDF files are impervious to any such coaxing on my PC.


....  Phil



Re: Oatley K25 PWM kit - feedback and questions
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Get PDF image extractor from:
http://www.somepdf.com/some-pdf-image-extract.html
Seems to work ok, they also have some utilities like text extractor and
more.

Tom

Re: Oatley K25 PWM kit - feedback and questions
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9.41



Re: Oatley K25 PWM kit - feedback and questions
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Ive found free image from PDF extractor, it worked. Gave up Acrobat quite a
while ago as its a huge to download, slow and sluggish.

Tom

Re: Oatley K25 PWM kit - feedback and questions
finger to keyboard and composed:

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while ago as its a huge to download, slow and sluggish.

I use both Foxit and Acrobat Reader. Some PDFs are handled better by
Acrobat, while some have "dictionary" errors and need to be handled by
Foxit. Therefore I have modified Windows Explorer's r-click menu to
give me a choice of "Open with Foxit" or "Open with Acrobat Reader".

I also speed up the launching of AR by disabling its unnecessary
plugins:
http://www.softpedia.com/get/Office-tools/PDF/Adobe-Reader-SpeedUp.shtml

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Oatley K25 PWM kit - feedback and questions
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inkscape can open and edit it, another approach is to use pdftops and
edit the ps file with a text editor to remove the lines that define the
undesired elelements.

--
⚂⚃ 100% natural


Re: Oatley K25 PWM kit - feedback and questions
Hi,
one thing to look for would be  - are you using a linear potentiometer for
your external control?

Greg


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Re: Oatley K25 PWM kit - feedback and questions

"gcd"
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** The OP's symptoms are far worse than that would explain.

He's make some kind of stuff-up with the construction -  like failing to
solder a few leads to their pads or bridging pads.




....  Phil





Re: Oatley K25 PWM kit - feedback and questions
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This suggests that the first stage (IC2:A) isn't oscillating.
check pins 1,2, and 3 of IC2 for shorts to their neighbours.



--
⚂⚃ 100% natural


Re: Oatley K25 PWM kit - feedback and questions

"Phil Allison"


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** Reason:

The heating of the motor windings is a function of the RMS value of the
current flowing whereas the torque and hence power output produced is in
proportion to the average current.

The ideal situation is having smooth DC current flow, where the RMS and
average values are the same.

Having discrete current pulses of current means the RMS amps value is higher
or even way higher than the average amps value.


...  Phil







Re: Oatley K25 PWM kit - feedback and questions

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Thank you for clarifying that point.

Grant.
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