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



"Des Bromilow"

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

** 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
Click to expand...
 
"Des Bromilow"
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,
Click to expand...

** 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
 
On 2011-03-09, Tom <tom@no.spam.invalid> wrote:
On 9/03/2011 3:46 PM, Franc Zabkar wrote:
On Wed, 09 Mar 2011 16:18:25 +1100, Franc Zabkar
fzabkar@iinternode.on.net> put finger to keyboard and composed:

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.

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.

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
Click to expand...
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

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On 2011-03-10, kreed <kenreed1999@gmail.com> wrote:

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".
Click to expand...
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

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On 2011-03-05, Des Bromilow <desbromilow@yahoo.comV2> wrote:
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.
Click to expand...
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

--- news://freenews.netfront.net/ - complaints: news@netfront.net ---
 
On Sat, 12 Mar 2011 07:58:57 +0000 (UTC), Des Bromilow
<desbromilow@yahoo.comV2> put finger to keyboard and composed:

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.
Click to expand...
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
--
Please remove one 'i' from my address when replying by email.
 
On 10/03/2011 12:31 PM, kreed wrote:
On Mar 9, 10:29 pm, "Dennis"<blub...@blibber.com> wrote:
"Phil Allison"<phi...@tpg.com.au> wrote in message

news:8tp3cmF7i5U1@mid.individual.net...





"Franc Zabkar"

Is that using Adobe Acrobat? I'm using Foxit Reader and it doesn't work

Yes, my instructions were for Acrobat Reader.

** None of them work at all using XP.

PDF files are not internally compatible with Windows.

.... Phil

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.


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".
Click to expand...
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
 
"Tom"
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...
Click to expand...
** 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
 
On Mon, 14 Mar 2011 09:26:41 +1000, Tom <tom@no.spam.invalid> put
finger to keyboard and composed:

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...
Click to expand...
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
--
Please remove one 'i' from my address when replying by email.
 
"Franc Zabkar"
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
Click to expand...
** 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
 
"Phil Allison"


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.
Click to expand...
** 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
 
On Mar 14, 9:51 am, "Phil Allison" <phi...@tpg.com.au> wrote:
"Tom"



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...

** 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
Click to expand...
I'm impressed. (usually am by clever use of electromechanics)
 
On Tue, 15 Mar 2011 14:19:37 +1100, "Phil Allison" <phil_a@tpg.com.au> wrote:

"Phil Allison"


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.

** 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.
Click to expand...
Thank you for clarifying that point.

Grant.
... Phil
Click to expand...
 
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