Oatley K25 PWM kit - feedback and questions

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Folks,

Has anyone assembled this kit and used it?

It went together well, but had a few issues when connecting wires
(basically the 2.5mm2 wire) fitted into the terminals, but once I
tightened up the terminals, and mounted the board on a heatsink, the
rigidity of the cables snapped the terminal away from the PCB pin.

All fixed now, but the 5K external pot is basically giving me 0 speed
for the first 15 degrees of rotation, then full speed as a sudden step -
and all around to the remainder of the pot's rotation.

I figure it will have something to do with the opamp circuits and their
voltages, but  with only a DMM at home, I'm kinda stumped to find the
cause - will presevere, but looking for some experienced guys to point
me in the right direction.

Thanks,
Des





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Re: Oatley K25 PWM kit - feedback and questions
: Folks,
:
: Has anyone assembled this kit and used it?
:
: It went together well, but had a few issues when connecting wires
: (basically the 2.5mm2 wire) fitted into the terminals, but once I
: tightened up the terminals, and mounted the board on a heatsink, the
: rigidity of the cables snapped the terminal away from the PCB pin.
:
: All fixed now, but the 5K external pot is basically giving me 0 speed
: for the first 15 degrees of rotation, then full speed as a sudden step -
: and all around to the remainder of the pot's rotation.
:
: I figure it will have something to do with the opamp circuits and their
: voltages, but  with only a DMM at home, I'm kinda stumped to find the
: cause - will presevere, but looking for some experienced guys to point
: me in the right direction.
:
: Thanks,
: Des
______________________________________

Mine worked OK, and is still working. What are you driving with it?

Colin



Re: Oatley K25 PWM kit - feedback and questions
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  Will be driving a 350W scooter motor - tried with just a multimeter
across the output - volts ranged from 0.6VDC at the low end, then up to
23.5 - 24.0 VDC at the "fast" end. ("End" is relative to the step at the
10degree travel mark.)

With the motor connected, the motor is stationary at the low end, and
flat out at the higher end.

I did have a 6800uF electro cap across the output for smoothing, but it
made no difference (connected or not)



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Re: Oatley K25 PWM kit - feedback and questions

"Des Bromilow"
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** It's never a good idea to connect a large value cap across the output of
a PWM motor drive circuit.  Such circuits need to see a resistive or
inductive load  -  in the latter case the current can then approximate
smooth DC.

A large value cap spoils the whole operation of the circuit and likely cause
excess peak current to flow in the switching mosfet.

The fact your 6800uF electro made no difference tells me that the PWM
oscillator is simply not running.


.....  Phil








Re: Oatley K25 PWM kit - feedback and questions
Hello Phil,
OK - didn't know that about PWM - so used to plonking in caps with other
PSU type things - will pull it out.

I do agree that it's looking like the oscillator isn't running - am basically
going to pull the circuit apart on paper and trace each pad/ trace and component
to ensure no errors, then  replace the op-amp chip in case it cooked off.
only issue I found on the first pass over the cct was the terminal for V+
had cracked when I tightened on the 2.5mm2 cable - so it wasn't making a
reliable contact. - I ended up removing the the terminals for the supply
and motor and drilled appropriate sized holes in the PCB and attached short
lengths of 2.5mm2 cable going off to chocolate block terminal strip for a
more robust connection.

either way this cct is coming out of the application and being replaced with
one which doesn't have the 5s "soft start" option - the application here
is a lather and it's disconcerting for the user to press the "start button"
and then not have something happen within a second or so.

the embarassing bit is that I used to be reasonably good at the hardware
side of things, but too many years in programming, it've fallen out of touch
- this was/ is my foray into trying to regain some familiarity - and it's
fallen into a heap.

thanks all, i'll be in  touch once I get this fixed (along with the PC which
died, and sort out some other issues...) too many jobs, not enough time.
Thanks again for the pointers,
Des



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Re: Oatley K25 PWM kit - feedback and questions

"Des Bromilow"
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** OK.

Simple PWM motor drives are something I've spent a lot of hours on  -  using
both BJTs and MOSFETS installed in a couple of  RC model boats packed with
lotsa sub C Ni-Cds. Their smooth, wide range speed control of simple
permanent magnet motors combined with high efficiency is close to magical.

My first ever published article ( in the CDI pages of EA ) described my
earliest effort.


....  Phil





Re: Oatley K25 PWM kit - feedback and questions
On Sat, 12 Mar 2011 07:58:57 +0000 (UTC), Des Bromilow

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AFAICS, reducing the value of C3 (100uF) should reduce the soft start
time. I believe a value of 22uF should give you a 1 second delay.

- Franc Zabkar
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Re: Oatley K25 PWM kit - feedback and questions
On Sat, 05 Mar 2011 22:16:21 +0800, Des Bromilow

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I'd start by measuring the voltage at the wiper of the pot, at both
ends of travel, and at the centre. Is it linear or log?

The LM358 op-amp supply (pin #8) should measure 8.0V.

Pin #6 should be ...

8.0 x 47K / (47K + 39K) = 4.4V

BTW, here are the notes for the kit:
http://secure.oatleyelectronics.com/files/K252notes.pdf

To view the redacted circuit diagram, drag a border around the image
(Tools -> Basic -> Select Image), copy it to the clipboard (Ctrl-C or
Edit -> Copy), and then paste it into your favourite image viewer.

- Franc Zabkar
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Re: Oatley K25 PWM kit - feedback and questions
On Wed, 09 Mar 2011 16:18:25 +1100, Franc Zabkar

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Actually, dragging a border is not necessary. Just single-click on the
image to highlight it. You can see the circuit in the Clipboard Viewer
(Window -> Clipboard Viewer), but it is mirrored and rotated.

- Franc Zabkar
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Re: Oatley K25 PWM kit - feedback and questions
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Is that using Adobe Acrobat? I'm using Foxit Reader and it doesn't work,
obviously the complete image is still present in the pdf file.
Tom
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Re: Oatley K25 PWM kit - feedback and questions
finger to keyboard and composed:

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Yes, my instructions were for Acrobat Reader. BTW, you can also
r-click the highlighted image and select Copy Image to Clipboard.

- Franc Zabkar
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Re: Oatley K25 PWM kit - feedback and questions

"Franc Zabkar"

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** None of them work at all using XP.

 PDF files are not internally compatible with Windows.



....  Phil





Re: Oatley K25 PWM kit - feedback and questions

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Seems ok for me with XP Home SP3 + Adobe Reader 9. Copies image from adobe &
pastes into MS Paint. Image aspect is screwy but easily stretched back.

I guess Oately will change their "protection" now Francs exposed the
loophole.



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

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I first became aware of this security flaw when Mohammed Haneef's
barrister uploaded the transcripts of his AFP interview to the world.
I have a slow machine and on this particular day it was running even
slower than usual. I could see the original transcript contents being
rendered, then followed by the blacked out redactions. The stupid
barrister had exposed Haneef's private phone numbers, email addresses,
and home addresses, both in Australia and in India.

Worse still, an Italian schoolboy likewise exposed the redacted
information in publicly released US military documents.

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

Re: Oatley K25 PWM kit - feedback and questions
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I thought that Oatley were above these methods of doing things.

All this does is hurt their business and particularly support
reputation.
Their kits are normally so reasonably priced that the majority
wouldn't go to the trouble of trying to "roll their own".

Re: Oatley K25 PWM kit - feedback and questions

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The redactions are soft (the electronic equivalent of a label with
backed with gum arabic - a little steam and it comes off),

they could have easily corrupted the yucky bitmap image that comprises
the schematic if they wanted to really keep it secret.

--
⚂⚃ 100% natural


Re: Oatley K25 PWM kit - feedback and questions
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Strange, they've published another kit a few months ago in Silicon Chip
that contain this schematic with addition of couple of relays to change
motor direction yet they keep this one secret...

Tom

Re: Oatley K25 PWM kit - feedback and questions

"Tom"
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** Hmmmm  .....

So Oatley have just about caught up with my design of circa 1980 for a RC
model boat.

A simple PWM controller using a 555 ( running at 5kHz) and TO3 Darlington
PNP output stage with hefty Schottky diode for freewheeling. A 10kohm WW
pot, modified so it had only 110 degrees of  rotation, was directly coupled
to a RC servo for speed control. The same servo also did two more jobs:

1. At the extreme CCW ( stop) position  - it operated a push on / push off
switch.

2. At in the extreme CW position -  it closed a hefty microswitch.

Job 1 energised or de-energised a 10 amp DPDT relay for motor reversing.

Job 2 bypassed the Darlington output stage for "overdrive".

Power came from 12 sub-C Ni-Cds and drove a 5 pole geared motor - a German
made " Decaperm".

http://www.cornwallmodelboats.co.uk/acatalog/decaperm_vlrg.jpg




......  Phil



Re: Oatley K25 PWM kit - feedback and questions
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I'm impressed.  (usually am by clever use of electromechanics)

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

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High-Power Reversible DC Motor Speed Controller:
http://www.siliconchip.com.au/cms/A_112070/article.html

http://us1.webpublications.com.au/static/images/articles/i1120/112070_4mg.jpg
http://us1.webpublications.com.au/static/images/articles/i1120/112070_5mg.jpg

- Franc Zabkar
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