Driver to drive?

[John Popelish]

Jim Thompson wrote:

CdSe? I've heard of CdS, although I can recall, as a kid, dismantling
Selenium rectifiers and using a single plate as a photocell.

Cadmium selenide photocells are very similar to cadmium sulfide ones,
except that they have a larger infrared response. I can't remember if
they have a higher or lower frequency response.

This isn't a great reference, but it shows the spectral responses.
http://www.selcoproducts.com/CFM/photocells/photocell_PDF/Selco_PhotoCells_Construct.pdf
--
John Popelish

 

[Spehro Pefhany]

On 14 Jan 2005 08:10:39 -0800, the renowned "Andrew"
<xxragexx@gmail.com> wrote:

Hello,

I have a problem that I would like some assisstance with, if possible.

I am running two rather large brushed DC motors (Maxon RE40) in
parallel, using a Devantech MD03 motor driver. The problem that occurs
is that when run with a PWM signal, the motors become much hotter than
they should be. When viewing the current on an oscilloscope, it can be
seen that there are many harmonics. I believe it this osciallating
current (and harmonics) that is causing loss, which causes the motors
to heat more than necessary.

I want to add a DC motor choke to the system, in line between the motor
driver and motors. I think that a properly sized choke could help to
remove the harmonics in the current and provide a much cleaner signal,
which will hopefully decrease the loss (and temperature).

The terminal resistance of the Maxon motors is 0.312ohms, and the
terminal inductance is 80uH, which is pretty low. I am thinking
somewhere around a 400uH to 1.5mH inductor should be the right size
(about 470uH would be a great). The inductor needs to be capable of
handling a minimum of 12A continuous current (20A would be better).
The PWM signal is operating at 7.8kHz.

Are there any suggestions for inductors/components that would suit my
needs? Is this a common problem (the heat)?

Low inductance motors such as pancake motors have this problem. If you
don't get the frequency up or add an inductor you're going to be
getting tons of I^2R heating in the controller and the coils.

Size is of importance,
hopefully there is a solution that is not too large.

More than just being able to handle the current, you have to make sure
the inductor doesn't saturate at that current. That means volume of
core material.

Check data sheets, but it's not going to be an SMT part, and it's
probably going to require more than one screw to hold it down. ;-)
A Hammond 195C30 1mH 30A choke weighs 2.5kg.

Also, I realize that the 7.8kHz PWM signal is a bit low, but the ease
of use of this driver (I2C control, current sensing/limiting, automatic
temperature limiting) make it very appealing. I would prefer to
correct the problem some way other than a new driver! So, how bad is a
7.8kHz signal for a brushed DC motor?
Thank you for any help you can provide!

Sincerely,
Andrew

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Parse Tree]

Mark Jones wrote:

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Aunty Kreist wrote:

[computer-speak snipped]

This is alt.religion.wicca, not alt.nerdy.computer.geeks, so if
you don't mind, please remove us from your list of crossposts.



Haha. Don't ya just hate those nerdy computer geeks? But, not all
computer nerds are geeks... the same way that not all wiccans are
undercover Jahovah's Witnesses I suppose.

If there are any Wiccans that aren't undercover JW's then I've never met
them.

Blessed Butt.

 

[John Fields]

On Fri, 7 Jan 2005 22:08:49 -0600, "Rhyanon" <pissoff@uberbitch.com>
wrote:

Tough shit. Go cower in your killfile blankie with your equally balless
friends.

---
Hang it in your ass, you witless twat.
And don't top post.
--
John Fields

 

[Andrew]

I found this company: www.rencousa.com. It seems that their product
RL1256-8-470 (http://www.rencousa.com/RL-1256.pdf) is the proper item
for this purpose. It doesn't list weight, but it does list size (about
2.5" cube, actually cylinder).

I am trying to confirm that adding an inductor of this type would
correct my heating problem?
Is it normal that I am receiving this heating issue?

 

[Mark Jones]

Andrew wrote:

Hello,

I have a problem that I would like some assisstance with, if possible.

I am running two rather large brushed DC motors (Maxon RE40) in
parallel, using a Devantech MD03 motor driver. The problem that occurs
is that when run with a PWM signal, the motors become much hotter than
they should be. When viewing the current on an oscilloscope, it can be
seen that there are many harmonics. I believe it this osciallating
current (and harmonics) that is causing loss, which causes the motors
to heat more than necessary.

I want to add a DC motor choke to the system, in line between the motor
driver and motors. I think that a properly sized choke could help to
remove the harmonics in the current and provide a much cleaner signal,
which will hopefully decrease the loss (and temperature).

The terminal resistance of the Maxon motors is 0.312ohms, and the
terminal inductance is 80uH, which is pretty low. I am thinking
somewhere around a 400uH to 1.5mH inductor should be the right size
(about 470uH would be a great). The inductor needs to be capable of
handling a minimum of 12A continuous current (20A would be better).
The PWM signal is operating at 7.8kHz.

Are there any suggestions for inductors/components that would suit my
needs? Is this a common problem (the heat)? Size is of importance,
hopefully there is a solution that is not too large.

Also, I realize that the 7.8kHz PWM signal is a bit low, but the ease
of use of this driver (I2C control, current sensing/limiting, automatic
temperature limiting) make it very appealing. I would prefer to
correct the problem some way other than a new driver! So, how bad is a
7.8kHz signal for a brushed DC motor?
Thank you for any help you can provide!

Sincerely,
Andrew

This is just my two cents... but are the anti-parallel diodes across
the motor fast enough for your PWM signal? If they are not fast enough
to "catch" the reverse EMF, then....

 

[Rich Grise]

On Fri, 14 Jan 2005 11:16:05 -0600, John Fields wrote:

On Fri, 14 Jan 2005 08:15:44 -0600, "Rhyanon" <pissoff@uberbitch.com
wrote:

HA - ha!! And now you're even being a hypocrite! I wonder if this was a
record speed for dweeb - yanking?

---
Yawnnn....

It must have been the in vitro fertilization that made you sooooo
transparent, huh?

"No, Harvey, not in the box, in the dish!"

John, if you're going to play with these weenies, would you be so kind as
to take it to the weenie group? (that would be a.r.wicca).

I'm sorry I originally crossposted the joke - I had no idea that it would
turn into such a huge, inane, thread.

Thanks,
Rich

 

[Lady Chatterly]

In article <10ug0cr59gdvt8f@corp.supernews.com>
DeathWish <symphonic_nospam@gci.net> wrote:

You mean like you just did?

R2l2ZSB0aGVtIG91dCwgYW5kIGRvaW5nIHRoZSBKb2Igb2YgdHdvIHRvIHRo
cmVlIHBlb3BsZSwgd2hpY2ggc2VlbXMgdG8gZml0IHNvIG1hbnkgdGhpbmdz
IGFib3V0IEdvZCBpbnRvIEVuZ2xpc2ggYmVmb3JlIGNyb3NzIHBvc3Rpbmcg
dGhlbS4=

--
Lady Chatterly

"Still talking to the bot too. What a maroon!" -- Aratzio

 

[John Woodgate]

I read in sci.electronics.design that Rich Grise <richgrise@example.net>
wrote (in <pan.2005.01.10.05.29.08.540377@example.net&gt about 'windmill
being hoisted', on Mon, 10 Jan 2005:

On Sun, 09 Jan 2005 20:21:34 +0000, John Woodgate wrote:

I read in sci.electronics.design that ZZZPK <zzzpk_pkearn_class_a@multi_
band_cb_is_here.eircom.es.it.net> wrote (in <41e18032.101853584@news.iol
.ie&gt about 'windmill being hoisted', on Sun, 9 Jan 2005:

shades of a ''scraphead challenge'' here.

Freudian slip?

Y'know, actually, I think not.

We have the same sort of programme in UK, called 'Scraphea*P*
Challenge'.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Andrew]

Jamie, would a DC voltage in this fashion prevent the motor from
delivering its maximum torque at low speeds? I think driving the motor
with essentially a lower DC voltage will also lower its possible
torque, whereas using PWM will allow full torque, even at slow speeds.
Is this accurate?

Jamie wrote:

Andrew wrote:

All,

I am new to PWM signals and DC motor control, so I am bascially
learning as I go.

Mark, you mention anti-parallel diodes. Would these be located on
the
motor driver? I did not design the driver, so I have to assume
that
the company would have taken this into account since they chose a
fixed
PWM frequency output?

Larry, could you please provide me some further information on the
LC
filter? This sounds like a great alternative if it takes up less
space, and mainly, less weight. I am not familiar with designing
LC
filters for this application, so any information on this would be
great.

Also, Larry, you mention that you would predict the heat problem
based
on the eddy current induced. What exactly is eddy current? You
indicate that the frequency seems to be the cause of the high eddy
current, would a higher or lower PWM frequency help this, and do
you
suggest changing motor drivers rather than trying an LC filter or
choke? What frequency would be optimal for this configuration, and
why?

Thanks so much for bearing with me, and for your quick and helpful
responses! Keep em comin!

Sincerely,
Andrew Czop

eddy currents are the magnetic field that is polarized
in such a way so that when, you pass an object over its surface
a drag/pull will take place., just think of an alternator in a
car when a load is placed on it. you get a magnetic drag..
normally DC output is applied at analog levels because it
has to be rather constant with in reason.
PWM may not be such a good idea directly into the clutches or
brakes
due to wide PW at low freq's could cause mechanical chatter and ware,

but using a switching output
to keep the PW narrow into a high freq transformer then into a
bridge rectifier filtered with CAPS could work.
the idea is to generate a fixed pulse width but vary the number of
pulses/s
so in other words the duty cycle would look like 5% on the scope at
low output and at max it would be like 50% duty cycle.
something simply like a One Shot (narrow pulse time) being triggered
by a Astable 555 that varies its freq depending on the output
required.
this can give you a nice smooth DC out. and you don't have to worry
to
much about your drive components because they would be in saturation
and
thus less heating problems.

 

[Rich Grise]

On Fri, 14 Jan 2005 13:26:29 -0600, John Fields wrote:

Of all the people on this group, you're the _last_ one I'd have
expected to complain about off-topic posts,

Actually, I wasn't complaining about the off-topicicity at all - in fact,
I instigated that part.

I was only saying that you seem to be the only s.e.d denizen who seems to
enjoy participating in those folks's conversations, and _they_ are clearly
not going to quit crossposting, so I thought you could be the bigger man.

Sorry.

 

[Charles Schuler]

Many years ago when electronic cash registers were sort of new, I was in a
store and tried to pay my bill (in cash) and the cash register froze up.
The counter worker panicked. She said she could not calculate the sales
tax. I said to multiply the amount by 1.06 (6% tax) and then proceeded to
do that for her. She called the MANAGER over and explained the situation
and he haughtily told me that would not work! Yes, he was a college
graduate.

 

[Tim Wescott]

Charles Schuler wrote:

Many years ago when electronic cash registers were sort of new, I was in a
store and tried to pay my bill (in cash) and the cash register froze up.
The counter worker panicked. She said she could not calculate the sales
tax. I said to multiply the amount by 1.06 (6% tax) and then proceeded to
do that for her. She called the MANAGER over and explained the situation
and he haughtily told me that would not work! Yes, he was a college
graduate.


That's because _he_ was trained to use tables, published on paper by the

state. And if the tables had been in error it would have still been
truth to him.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

 

[Dirk Bruere at Neopax]

John Larkin wrote:

On Sat, 08 Jan 2005 21:46:26 GMT, Richard the Dreaded Liberal
eatmyshorts@doubleclick.net> wrote:


On Sat, 08 Jan 2005 09:06:03 -0800, John Larkin wrote:


On Sat, 08 Jan 2005 06:26:35 GMT, richard mullens
mullensdeletethis@ntlworld.com> wrote:



You are not evil, the American people are not evil, but your administration is. They have lied to you about the reasons for
going to war. It has happened in the UK too - to our eternal shame. I really don't think that the whole Iraq adventure was
conceived in order to bring freedom to Iraq. Sorry.

Personally, I believe it was done as a step toward bringing freedom to
the entire Arab world. Sorry.


And has anyone ever _asked_ the "entire Arab world" if they even _want_
the American brand of "freedom"?




But you see, the great thing about democracy is that, if the people
don't like it, they can always call an election and vote dictatorship
back into power.

Like in Iraq, later this month (assuming there is an election)

--
Dirk

The Consensus:-
The political party for the new millenium
http://www.theconsensus.org

 

[Clarence_A]

"John Larkin" <john@spamless.usa> wrote in message

Richard the Dreaded Liberal wrote:

<snip>

But you see, the great thing about democracy is that, if the
people
don't like it, they can always call an election and vote
dictatorship
back into power.

But, since we did NOT elect John Kerry, we're safe for another
four years.

 

[Mark Jones]

Aunty Kreist wrote:

"Randy McLaughlin" <randy@nospam.com> wrote in message
news:2q_Dd.1987$vM4.1828@bignews3.bellsouth.net...

"Aunty Kreist" <Aunty_Kreist@satanickittens.net> wrote in message
news:34ba4dF49du1mU1@individual.net...

"Mark Jones" <abuse@127.0.0.1> wrote in message
news:BOGdnXlJP_wwjn3cRVn-oQ@buckeye-express.com...

Aunty Kreist wrote:

"Mark Jones" <abuse@127.0.0.1> wrote in message
news:KfSdnYHDOtG4PELcRVn-ug@buckeye-express.com...


Aunty Kreist wrote:


[computer-speak snipped]

This is alt.religion.wicca, not alt.nerdy.computer.geeks, so if
you don't mind, please remove us from your list of crossposts.


Haha. Don't ya just hate those nerdy computer geeks? But, not all
computer nerds are geeks... the same way that not all wiccans are
undercover Jahovah's Witnesses I suppose.


I was just being silly. I have a nerd fetish.

Me <3's Clark Kent wannabees!


Aaaha, but Clark Kent is a superhero. I suppose guys feel the same
way about Buffy the Vampire Slayer? Hmm, yeah she's hot.

Kent isn't much of a nerd... really... is he?

(Oh crap, I might be a nerd!!)


It's the glasses.....

Hubba hubba!



Please stop all the cross posting.

Randy



I take it you don't have glasses then.

Could someone throw some Eye Of Newt (or maybe an isolation
transformer) at Randy?

Failing that, maybe he can chew on this for awhile:
http://3564020356.org/deserve.htm

 

[Randy McLaughlin]

"Parse Tree" <account@domain.extension> wrote in message
news:XV4Ed.446013$2W1.40576@news.easynews.com...

Charlie Gibbs wrote:
In article <+OW6VCIT4u3BFwhS@jmwa.demon.co.uk>,
jmw@jmwa.demon.contraspam.yuk (John Woodgate) writes:


I read in sci.electronics.design that Charlie Gibbs
cgibbs@kltpzyxm.invalid> wrote
(in <1107.868T1882T6245027@kltpzyxm.invalid>&gt
about 'OT: Safe Riddles', on Fri, 7 Jan 2005:


My .sig file does have the space, but my newsreader must be stripping
it off before it sends it out.

Microsoftware, in its ineffable wisdom, does that. I wish someone
would find a way of making it effable. (;-)


I'm posting this from my trusty old Amiga, though, which seems
to be ineffable in its own way.

WHOA! You win. I tip my hat to you, sir.

Please stop cross posting.

Randy

 

[Andy]

Robert Baer wrote:

Andy wrote:

Hello:

I am attempting to fix the quality of the video signal coming out of a
similar tuner (it's on a PC TV card). Currently, the brighness of the
picture is fluctuating on the high-brightness areas, in the rythm with
the sound; the tuner is powered from a LM7805-type regulator (which I
have already added to the card; intially there was none, and the
interference on the picture was terrible).

I suspect the power supply quality.

The datasheets for the FM1236 / FM1246 specify the "peak-to-peak ripple
voltage susceptibility" for the tuner section, but nothing for the IF
section.

On the IF section power pin, the voltage is fluctuating, depending on
the picture being received, with up to 6-8 mV pp over the TV frame, not
counting the overshoots.

Before I go further and swap the regulator (LM1117 looks a good
candidate, to improve the load regulation and overshoot) I would like to
know more on the required power supply quality.

Would anybody have any reference information about that? Details of a
reference design with these tuners? I had tested the Leadtek PVR2000
card and it seemed to have the same tuner as my card has, and it did not
have this problem. If somebody had the tuner powering details for that
card, that could help I think.

Thank you.

-- Andy


How about using a decent bypass cap (aluminum 'lytic)?

Yes, there is already a bypass on each of the two power pins: a couple
of ceramics + 100uF Panasonic FC series.

 

[Scott Miller]

Once you get the rectification process better under control, this will
get easier. You may want to parallel the resistive divider with a
similar capacitive divider (put a large, low voltage cap in series
with the ground end of the final supply storage capacitor). Your ADC
sample and hold will be better behaved.

Ok, I'll have to give that a try. I should have the high-speed diodes in a
few days - it'll be interesting to see how they affect the output.

A simple proportional control may be all you need. This would involve
having an output pulse duty cycle varied inversely with the ADC
measurement, with some max. pulse width to handle start up or overload
situations.

Pretty much what I was trying before...

You turn the proportionality constant up till the output starts to
wobble, and then cut it is half. You can temporarily use a second ADC
input with a pot across the supply as the gain adjustment. After you
decide what gain is appropriate, store it in the program, permanently.

That's a good idea, might save me a lot of reprogramming. Assuming I can
free up another ADC. I only used this particular part because I buy them by
the hundreds.

It ain't so bad. At such low current, it is quite functional if
wasteful of battery power. It also takes less understanding to get it
working.

Yeah, battery power is the main issue. This thing sucks a 9v alkaline dry
in no time. I know there are some designs that'll run for a month on one.
The MCU and LCD will add a few ma, but I want to be able to get at least 12
hours of runtime.

You can also make the MOV part of the voltage divider to the ADC to
increase the effective signal in the range of interest, though the
temperature coefficient will be higher.

I'd rather eliminate the MOVs completely if possible, but I'll keep
experimenting.

Thanks,

Scott

 

[Joerg]

Hi Spehro,

It's a very clever example of how something as boring as gift cards
can be extended in an unexpected direction- and effectively creating a
new form of currency, as Rich implies.

Now just imagine: Pa gives son a Home Depot gift card for Christmas. Son
hands Pa a present: A Home Depot gift card! This has actually happened.
Then there are the 'sinner's gift cards'. We can buy cards that hold
x-many pounds (pounds!) of bonbons and other candy from a certain local
brand. Yeah, it all tastes great but that really packs in the weight.

We only got one card ever. From neighbors whom we helped out of a
pickle. But there is a caveat: If you don't use it all up by this or
that date the restaurant takes a monthly 'maintenance fee' until
depleted. I never figured out what needs to be maintained on a gift
card. They never came out to polish the plastic or anything.

Now after that MP3 car radio story I feel really old. We live in the
stone age. No MP3, no DVD player, neither cable TV nor satellite. But,
we have a guitar, a piano, an old Hammond organ and a wood stove.

Regards, Joerg

http://www.analogconsultants.com