Looking for someone to test my power supply. 99% of parts, pieces,& assembly
were as per Ben's book.  Just need something to compare to see if everything is
up to snuff.

corrected email..
gmfoster@...
Sorry

On Thu, Dec 10, 2009 at 11:03 AM, Garry Foster <garry.foster1@...> wrote:
> I have an older book that may be of some interest to some of you.
>
> It is a Book on building a metal cutting lathe from old truck pistons and
> Angle iron.
>
> It was Ramah machines and is based on using templates for locating all holes
> ect. The templetes have never been removed from the book and I would say the
> book is in very good shape. It has been read and reread. I learned a ton
> from this book even though I never built the lathe. Believe it or not it was
> my introduction to witness marks that I still use all the time today.
>
>
> It was often compared to the lathe Dave Gingerly made from Cast Alum.
>
> I am cleaning house and would sell the book for 5.00 postage paid to
> anywhere in the US. Other parts of the world would be 5.00 plus actual
> postage.
>
> Shoot me an email if interested..
> gmfostera@...
>
> Ben if you consider this spam feel free to delete it..I am offering it here
> first because I thought one of the EDM readers may want to see what you were
> up to in the past. Always being very creative.....
>
> If you are not the same Ben I apoligise.
> Garry
>
> I do have your� current book and have studied it cover to cover as well.
>

Should be perfectly safe and better than an underrated transformer.

The current rating of a power transformer is the maximum current it can safely
deliver.  All circuitry attached to the transformer should draw a total current
less than the transformer's capacity.

The voltage rating of a power transformer is the voltage that it will deliver
with the primary attached to its specified source.

HTH,
Donald.

----- Original Message -----
From: "skullworks" <skullworks@...>
To: EDMHomeBuilders@yahoogroups.com
Sent: Thursday, December 10, 2009 2:40:56 AM GMT -05:00 US/Canada Eastern
Subject: [EDMHomeBuilders] Transformers

Hi group;

I have my Ben's PCB completed for now - may add items required for the meter,
but still undecided.

My question is - I have a pair of 24V 4A tranformers (12-0-12 CT) is there any
benefit/detriment of using these higher current rated tranies ?

All the rectifiers used were "beefier" than what was spec'd mainly cause they
were all ready on hand.

Thanks;

Greg



------------------------------------

Yahoo! Groups Links

Hi group;

I have my Ben's PCB completed for now - may add items required for the meter,
but still undecided.

My question is - I have a pair of 24V 4A tranformers (12-0-12 CT) is there any
benefit/detriment of using these higher current rated tranies ?

All the rectifiers used were "beefier" than what was spec'd mainly cause they
were all ready on hand.

Thanks;

Greg

Yes hydraulic cylinders do work well. I have build EDM using BENs design before
with hydraulic ram and it works well. Now it's a pulse edm and it still works
like a charm. Luckily these were surplus EDMs (with existing hydraulic systems)
and came very cheap at a junk price but it's not an everyday find.

I intended to use pneumatic since I would like to build more of these EDMs for
my friend but a smaller setup. Using a brand new hydraulic system kit would cost
me at least 1,800$ including pump+valves+cylinder and this is a bit expensive.

My Reasons is:
1. Less load on the driver circuit. 1 Amp proportional solenoid.
2. Cheaper than hydraulic little bit more expensive than DC motor.
3. Easy to fix and maintain rather than rewinding a new motor.
4. Small application.
5. Air supply is available.
6. Feed rate is easily adjusted via air regulator rather than messing with the
circuits.

Since the head ram is small and not heavy this would be of no problem at all. Of
course for my existing EDM pneumatic or motor driven is out of the question I
reckon 20kg is my ram. But on my next project I intend to make the Ram no
heavier than 1kg.

I have the same setup as Bens except that my transformer is rated at 80 Amps and
more shunted watt resistors. The electrodes I use are heavy copper electrodes
weighing about 1kg~1.5kg.

I use these for making "key ways" slots for big drive shafts that require a
perfect edge. Naturally wire edm is the way to go but they are difficult to fit
in most common machinery. This is why I rebuild these edms to have a bigger
tank.

But for the newer light version I intend to use pneumatic drive.

--- In EDMHomeBuilders@yahoogroups.com, Roland Jollivet <Roland.Jollivet@...>
wrote:
>
> rambling....
>
> But why would you want to use pneumatic if hydraulic works well?
>
> A hydraulic mechanism sounds good, and I've often thought it would be a good
> idea for a CNC sheet metal punch.
> The principle is that you have a low mass work cylinder on your EDM or punch
> press.
> The beauty is that you can have all manner of motors and valves sitting in a
> box on the floor, instead of trying to sit all that mass atop the Z axis.
> You can have a short fat cylinder on the Z, and a long thin cylinder on the
> floor. The ratio gives you an increase in linear resolution. Here, the floor
> drive cylinder is driven by a leadscrew or eccentric cam. Obviously you need
> a feedback mechanism.
>
> With hydraulic EDM, one could also have a power stroke cylinder to do the
> lift motion, and a small cylinder tee'd in for fine control.
>
> Proportional solenoids are in common usage for liquid and air, but are
> expensive, and I think a bit difficult to make oneself.
>
> Roland
>
>
>
> 2009/12/9 franz_schluter <franz.schluter@...>
>
> >
> >
> > Topic:
> >
> > Is this feasible? Since we make hobby edms maybe it is possible to drive
> > the ram with a pneumatic system. I have been making these rams (now rebuilt
> > 2 edms sinkers) with hydraulic rams. I'm trying to come up with something
> > new since I am loving the hydraulic design (No high loads for my up/down
> > driver). Has anyone attempt using pneumatics? I know it isn't accurate but
> > perhaps it just might do when using very low air pressure (very slow
> > movement).
> >
> > I'm thinking about making it spring loaded btw. Such that the return is
> > retracted through a spring.
> >
> > Side related topic:
> > I've seen engine fuel injected system and they have this Idle intake air
> > valve that's PWM regulated. It opens or closes in a specific way to regulate
> > how much air is being fed into the system. I think there are similar systems
> > that could be applied for the edm ram pneumatic. I guess nobody used a
> > pneumatic ram since it is too weak for industrial applications. But maybe
> > for the DIY builders this might work. A simple 12V air compressor to be used
> > (The one we use for inflating our car tires)
> >
> >
> >
>

Topic:

Is this feasible? Since we make hobby edms maybe it is possible to drive the ram
with a pneumatic system. I have been making these rams (now rebuilt 2 edms
sinkers) with hydraulic rams. I'm trying to come up with something new since I
am loving the hydraulic design (No high loads for my up/down driver). Has anyone
attempt using pneumatics? I know it isn't accurate but perhaps it just might do
when using very low air pressure (very slow movement).


I'm thinking about making it spring loaded btw. Such that the return is
retracted through a spring.


Side related topic:
I've seen engine fuel injected system and they have this Idle intake air valve
that's PWM regulated. It opens or closes in a specific way to regulate how much
air is being fed into the system. I think there are similar systems that could
be applied for the edm ram pneumatic. I guess nobody used a pneumatic ram since
it is too weak for industrial applications. But maybe for the DIY builders this
might work. A simple 12V air compressor to be used (The one we use for inflating
our car tires)

Cary several changes have been made in follow up printings of the book (current
printing is #4) many are along the lines you suggest.

I would agree that the control transformer is a little on the small size
(current wise) but the rating you cite are max for each component and seldom if
ever are they all operating at max current.
With some of the changes made in later printings of the book the motor driver
output current (to the motor) is off more than it is on, this alone helps reduce
the heat dissipated in the motor driver chip.

In the original design I attempted to use Radio Shack ( in hine site not
necessary the best choice for various reason) as the main parts source to avoid
some of the complaints recently aired on this list, mainly the high cost of
shipping. If you are not careful the cost of shipping cost from online sources
can outweigh the cost of the items purchased. My thinking was If most of the
parts were available from a ready available one stop source (US) then the
shipping cost could be reduced. I chose the largest size (small) control
transformer that Radio Shack offered at the time which was the 45ma.  Even using
a transformer of marginal current capability I have yet to hear one person (not
to say there isn't) complain of blowing the control transformer, so I don't
think this is a serious issue.

Yes the LM7812 should have had bypass capacitors on the input and output side as
suggested. Newer printing of the book have more than doubled the size of the
smoothing cap. In printings of the book after the first edition (and on the PCB)
bypass capacitors have been installed on all the chips.VCC2 can be 12 volts or
as I chose to use the raw 17VDC (aprox) to feed to the motor in order to have a
higher motor voltage. The (suggested) motor I used was rated for 19VDC so a
higher voltage was needed/desired. Motors do not need super smooth voltage to
perform their duties, it really gets chopped up going through the motor brushes
anyway. If a 12VDC motor is used then VCC2 could pick the 12VDC off the power
supply after the smoothing cap.  BTW In printing after #! I also hang a
capacitor across the motor to help with spikes, more caps maybe better but
looking at it on my O-scope I could not tell much difference.

Pins 4,5,12& 13 on the motor driver chip are tied to ground and on the PCBoard
there is some heat sinking via the copper trace on the bottom side of the board.

  The spec sheets for both the motor driver and comparator indicate a wide supply
voltage range up to 36VDC for both chips.  Yes the motor driver spec sheet
recommends VCC1 to be 5.5VDC but in the absolute maximum rating it say it can be
-0.5V to 36VDC, this suggest to me there are many options available, 12 VDC is
along way from a max of 36VDC. Yes  a 5VDC regulator could be used as suggested
and maybe the better choice.

As stated in the front of the book I am not an electrical/electronic engineer
though I do have some electrical/electronic background. Lots of people have
build and operated the design very successful and with no problems, Others have
had problems and most of the problems exist around the motor driver chip. Can it
be improved, sure, most things can be improved, after all, how many version of
windows do we have? Not only that but we are constantly getting up dates to it
as well as most anything related to computers. Ford GM Honda etc etc are always
having recalls to fix things that are not quite right. I have never said this is
the perfect EDM  it is not a perfect world,  there are many ways to skin the
cat.



Ben


--- In EDMHomeBuilders@yahoogroups.com, "packrat0_15" <c.hhestand@...> wrote:
>
> First off I'm NOT trying to start a flame war.  As each new group of people
build the machine there always seems to be problems with the driver chip.  I did
some research and came up with some causes and some cures.  I have not tried
these, but, I'll try to explain what they are and why they should be changed. 
I'm also posting a partial schematic in the files section with the changes made
in it.
>
> These are not just things I made up but "common electronics procedures".  All
of these are based on the schematic in the copy of the book that I have, the
first printing.  maybe some have been changed in newer printings.
>
> 1.  The control transformer is too small.  If you go to all the data sheets on
all the components and add up the current ratings that they use, it comes to
around 1.9A.  The transformer RS#273-1365 has a output of 45mA.  About a 1/4 of
whats needed.  That causes everything to be current starved and to overheat!
>
> 2.  The smoothing capacitor on the control power supply is too small.  The
"rule of thumb" on power supply is 3000uF per Amp of current.  The reason for
this is to lower the 'ripple voltage.'  Higher ripple voltage causes more heat
in the components.
>
> 3.  The LM7812 regulator has no by pass capacitors.  The data sheet calls for
a .33uF on the output and a .1uF on the input of the regulator.
>
> 4. The SN754410NE chip is switched by 12VDC, and has no bypass capacitors on
VCC1 and VCC2.  The data sheet and the application schematics show it to have
VCC1 and the switching and enable pins at 5VDC.
>
> 5. The VCC2 supply to the SN754410NE is taken from before the power supply
smoothing capacitor.   Doing that puts too much ripple on the power and in the
chip, causing more heat.
>
> 6.  Added a LM7805 to give 5VDC to the parts that need it.
>
>
> Again Not trying to start a war, just trying to improve the design.
>
> Cary
>

I found this;   http://www.kronosrobotics.com/an142/GAN142.shtml

He was blowing chips until he put capacitors on the motor. Maybe it would help
you guys out too.

Also if you look at the data sheet (front page) it calls the ground pins #4, 5,
12, 13  GROUND and HEAT SINK. Maybe you could come up with a way to tie these
four pins together with a piece of metal as a heat sink.

Cary

--- In EDMHomeBuilders@yahoogroups.com, Benjamin Nathan Fleming <bnf@...> wrote:
>
>
> Cary I would be interested in seeing your data.
>
> Thanks
>
> Ben
>


Ben, have you had a chance to look at the comparator data I posted?

What is your conclusion to what I showed?  I'm interested in your thoughts on
it.

Cary

First off I'm NOT trying to start a flame war.  As each new group of people
build the machine there always seems to be problems with the driver chip.  I did
some research and came up with some causes and some cures.  I have not tried
these, but, I'll try to explain what they are and why they should be changed. 
I'm also posting a partial schematic in the files section with the changes made
in it.

These are not just things I made up but "common electronics procedures".  All of
these are based on the schematic in the copy of the book that I have, the first
printing.  maybe some have been changed in newer printings.

1.  The control transformer is too small.  If you go to all the data sheets on
all the components and add up the current ratings that they use, it comes to
around 1.9A.  The transformer RS#273-1365 has a output of 45mA.  About a 1/4 of
whats needed.  That causes everything to be current starved and to overheat!

2.  The smoothing capacitor on the control power supply is too small.  The "rule
of thumb" on power supply is 3000uF per Amp of current.  The reason for this is
to lower the 'ripple voltage.'  Higher ripple voltage causes more heat in the
components.

3.  The LM7812 regulator has no by pass capacitors.  The data sheet calls for a
.33uF on the output and a .1uF on the input of the regulator.

4. The SN754410NE chip is switched by 12VDC, and has no bypass capacitors on
VCC1 and VCC2.  The data sheet and the application schematics show it to have
VCC1 and the switching and enable pins at 5VDC.

5. The VCC2 supply to the SN754410NE is taken from before the power supply
smoothing capacitor.   Doing that puts too much ripple on the power and in the
chip, causing more heat.

6.  Added a LM7805 to give 5VDC to the parts that need it.


Again Not trying to start a war, just trying to improve the design.

Cary

My unit is almost complete but I've been pondering some of the suggested
improvements before I proceed any further. Has anyone tried the circuit with the
suggested 5 volt regulator instead of the 12 volt regulator? Has anyone tried
the revised comparator circuit suggestions? Has anyone cut the circuit traces
where suggested? So far those ideas seem to me that they might have some
validity but I'm not a designer. Granted the circuit works as designed, those
changes would be easy to implement and sound like they may possibly help the
chip life expectancy.

--- In EDMHomeBuilders@yahoogroups.com, "arush404" <arush404@...> wrote:
>
> I am almost finished with my generator and am going through the "final"
testing. The resistor on the Servo LED burned up and then I measured 77VDC at
the plug. I know this isn't right but have racked my brain trying to find the
problem. Anyone else have this problem? Thanks in advance.
>

That sounds like your power output lines have been applied to the servo. 
Measure at your banana plugs and see if you have 12-18V (don't remember off the
top of my head) there.  If so, you have electrode power and servo power swapped.

GsT

I am almost finished with my generator and am going through the "final" testing.
The resistor on the Servo LED burned up and then I measured 77VDC at the plug. I
know this isn't right but have racked my brain trying to find the problem.
Anyone else have this problem? Thanks in advance.

We don't have a problem most of the time with the way
people post on this list, in part I think this is because we
do not have a high traffic level of emails. But to avoid any
future problem might I suggest the follow guidelines.
Most of the guidelines are basic email courtesy, to
make the reading of the postings and in particular the
digests versions of the list easier for everyone to follow.

1. Please Trim your replies.
This in my opinion is perhaps the worst offense that
happens here. Many times we will see a post
in response to another one that quotes the entire
other message, or the entire thread with multiple
replies going back several days or longer. We only
need to see the portion of the preceding message
or thread that applies directly to your response, but
be sure to include enough of the previous message
so that people will know what you are talking about.


2. Bottom Quoting is usually preferred by most readers
i.e. the sentence or two that your quote to give context
to your reply should be above your answer, not below it.
  This allows the reader to get the context before reading
your reply. Replies are often hard to understand if they
are read without context.

3. Subject Titles. I think this is the second worst offense
Subject titles should be relevant the topic being
discussed in the post. If the subject line on your reply
no longer reflects the content of the post, the subject
line should be changed when you reply.


4. Please turn OFF the HTML on the email you send to
  the list. Many mail readers don't convert it so that people
wind up with a bunch of code on their screen and
whatever message you were trying to send gets lost in
the code.

Many of our non US members pay for their email
by the KB, and this type of code costs them money to
download something they can't read.

Please be considerate
and just send your messages in plain text.

If we all examine our posting habits and make these
small adjustments, it will make reading the postings
and digests far more "user friendly" for everyone.

From our family to your Wishing everybody a very
Merry Christmas 2009 and a successful and prospers 2010

Thank you

Ben Fleming

Yes the comparator can be viewed as correct. But has room for improvement. I
know what you mean and it gave me a headache as well. This is why I used a cheap
PLC instead of the circuit.

Nope vibration is 80% diminished since I use a different approach. I let the
built in PID of the PLC handle the speed approaching the spark gap. Then this
speed is maintained and adjusted by the PLC and advances in a very slow manner,
so slow it doesn't need to reverse. It'll only vibrate in the very first mili
seconds after it senses the current and then will stabilize. This is a different
approach from a comparator. In the essence it is the same but different since
the feed rate is adjusted via PWM through the PLCs motor driver.

Wear out has also greatly diminished in my case. And I am able to use tungsten
copper with my setup with very little wear out. But I believe this is due to my
pulse gen setup.

I have tried building this circuit using discreet logic devices but only gave me
major headaches. The PID function is the hardest to make and was very
unsuccessful. In pulse EDM comparator circuit is different because there is an
OFF and ON time.


Yup the edge finder in my setup is like a simple switch. When in contact to the
workpiece the hydraulic down movement is disabled and only the upper movement is
enabled. Only low voltage and ampere is present during measure mode.

--- In EDMHomeBuilders@yahoogroups.com, cary heestand <c.hhestand@...> wrote:
>
> Franz,   a couple of years ago I posted a link for a schematic to make a
"edge finder"  for EDM.  And a few posts later answered someone on how to use
it. If you search the site here  for Edge Finder it should still be in the
archives.
>  
>  
>  
> What you are saying about the "window" is correct. But you'll never, as far as
I've seen, eliminate the slight up/down vibration of the ram. Just the nature of
the beast. Especially with a hydraulic ram.
>  
> I've come up with a comparator that uses a single potentiometer that has a set
voltage gap in it, that stays the same amount as you vary the voltage. The fix
is only one extra part, but really wrecked my brain trying to come up with it!
>  
> Cary
>
> --- On Fri, 11/27/09, franz_schluter <franz.schluter@...> wrote:
>
>
> From: franz_schluter <franz.schluter@...>
> Subject: [EDMHomeBuilders] Re: circuit problems
> To: EDMHomeBuilders@yahoogroups.com
> Date: Friday, November 27, 2009, 2:29 AM
>
>
>  
>
>
>
>
                                        \
    < SNIP >
>
> 2. Measure mode. (Sinking the electrode to the workpiece without damaging or
scratching the workpiece for measurement purposes only since I found it hard
using eyesight method). It's basically a circuit that puts 12V in the electrode
just to use it as a feeler. So when electrode touches workpiece it'll just be
unable to move further down. It's a nice function for people with bad eyes such
as me.
>
>
                                        \
                < SNIP >
>
> 2. Window. I think there should be 3 windows. reversing (when too much shorted
or too high current) ,forward (Open) and (optimum spark gap "desired value or
spark gap"). The desired spark gap should move along with all the windows so
they don't overlap to each other.
>
>
                                        \
             < SNIP>
>
> My ram almost never reverses but just pushes forward in a very very slow pace.
>

OK Cary redesign Bens circuit to use a stepper and while your at it find a
long thin stepper not a short fat one like most are.
Brian.



cary heestand wrote:
>
> No one including ME has ever said that Ben's design doesn't work!!!
> Can it be better?  Yes.
> The design uses a brushed gear motor for the ram, easy to do.  But
> there is a reason that ALL the other EDM plans for the home shop use a
> stepper motor, even if it's harder.
> Have you ever looked into a electric drill at the brushes when you
> reverse it with out coming to a stop first?
> If not try it.  You'll see a large burst of sparks from the brushes.
> This is what is happening every time your ram reverses direction.  And
> it reverses constantly.  What do you think that burst of sparks is
> doing to the brushes and commutator of the motor?
> A stepper is made to reverse instantly.  Thats one of the reasons they
> were developed.
> As far as the comparator in the circuit having a over lap.  That is
> the reason that Ben's design works as good as it does.  When the
> comparator is over lapped, it puts the motor into dynamic braking.
> That stops the motor from coasting to a stop.
> Stop and really think about that gear head motor.  It's got a 80RPM
> according to the plans.
> But the actual motor is running at around 12000RPM. that can't stop
> instantly, it moves past where it needs to be.
> A stepper can move a very small fraction of a turn, depending on the
> driver. stops exactly where it's supposed to.  Can reverse instantly
> without coasting.  Just what is needed for a EDM ram.
> In short does Ben's design work? Yes.    Can it be made better? Yes.
> Does anyone want a want a improved machine?  Thats up to the
> individual.   I'm just trying to help those that might want a better
> machine.
> After all thats one of the missions stated on the site guide lines.
> If you are satisfied with yours, why stop the others that might want
> to do better?
> Cary
> --- On *Thu, 11/26/09, Brian Fairey /<bfairey@...>/* wrote:
>
>
>     From: Brian Fairey <bfairey@...>
>     Subject: [EDMHomeBuilders] circuit problems
>     To: EDMHomeBuilders@yahoogroups.com
>     Date: Thursday, November 26, 2009, 4:44 PM
>
>     Ben, are these guys trying to say that your circuit is wrong?
>     or is it a case of "you do the spade work" and I will nitt pick it?
>     I'm happy with what I built and that I blew something up that was
>     my fault.
>     Brian.
>
>

I would hardly say wrong - it seems to work for many people, which is the final
test.  I would try to make improvements to eliminate some of the reported
issues.

Donald.
----- Original Message -----
From: "Brian Fairey" <bfairey@...>
To: EDMHomeBuilders@yahoogroups.com
Sent: Thursday, November 26, 2009 4:44:45 PM GMT -05:00 US/Canada Eastern
Subject: [EDMHomeBuilders] circuit problems

Ben,  are these guys trying to say that your circuit is wrong?
or is it a case of "you do the spade work" and I will nitt pick it?
I'm happy with what I built and that I blew something up that was my fault.
Brian.

--- In EDMHomeBuilders@yahoogroups.com, Brian Fairey <bfairey@...> wrote:
>
> Ben,  are these guys trying to say that your circuit is wrong?
> or is it a case of "you do the spade work" and I will nitt pick it?
> I'm happy with what I built and that I blew something up that was my fault.
> Brian.
>

Nope it is not wrong. In fact it does work. Though a few people here would like
to further improve this circuit and make something more efficient which isn't
bad IMO. I have build this circuit before on my machine and it gave me a very
good understanding on how to approach in building my dream machine and how to
further improve it.

I have a similar circuit already. I have finished building mines 4 months ago
with pulse generator. It works like a conventional edm even better than it was
originally (1967 RC EDM). I find it a bit difficult to upload everything since I
have a bunch of relays for the automatic operation and the schematic is too big
to fit. Everything is hand drawn.

Options I included was:

1. Automatic stop and drain. (edm ram goes up and removes edm fluid and triggers
a mechanical bell after lower limit switch triggered)

2. Measure mode. (Sinking the electrode to the workpiece without damaging or
scratching the workpiece for measurement purposes only since I found it hard
using eyesight method). It's basically a circuit that puts 12V in the electrode
just to use it as a feeler. So when electrode touches workpiece it'll just be
unable to move further down. It's a nice function for people with bad eyes such
as me.

3. Flush Interval. (Can be set from 1min~10min the flush intervals whereas the
ram goes up for a few seconds and flushes by a secondary flusher that is
triggered via solenoid valve. It will resume operation after flushing.

4. Emergency Stop Button. (When pressed voltage goes off and ram retracts to
upper limit switch).

5. Auto Burn. (Experimental, I have a long code for this but in general this is
a set of algorithm that constantly adjusts the spark gap to optimum distance so
that it will burn as fast as it can depending on how fast it is actually
burning). This function tends to not work as how I expect it to be... It seems
to override my PID function. When I have time maybe I'll dig more into this. I
believe to make this work properly I would need something to digitally convert
the distance to the PLC unit. For now it works something like making the gap as
close as possible.


I rewired an old AGIE 1967 Hydraulic RAM EDM. I could post the pulse generator
only though which consist of a 555+comparator circuit. And an amplifier circuit.

Problem with vibrating ram is two problems:

1. The voltage is somewhat an oscillating voltage this means it fluctuates up
and down. The comparator will also tell go up and down because of this. The
design makes it such that the comparator is constantly comparing the ref voltage
to the spark gap ratio. This is what causes it to vibrate.

2. Window. I think there should be 3 windows. reversing (when too much shorted
or too high current) ,forward (Open) and (optimum spark gap "desired value or
spark gap"). The desired spark gap should move along with all the windows so
they don't overlap to each other.



But this isn't a mistake but just a way to improve. I use a PID function for my
spark gap which is controlled by the cheapest LOGO siemens PLC. I hooked the
analog inputs to the pulse EDM via voltage divider circuit. My ram is controlled
by a motor driver package which comes bundled together with the siemens PLC.

My ram almost never reverses but just pushes forward in a very very slow pace.


The other post is correct. It is somewhat difficult to use relays for
controlling your rams burn movement. Shorting out the relay contacts will most
likely happen since the ram reverse and sinks in a very fast manner in this
case.

Ben,  are these guys trying to say that your circuit is wrong?
or is it a case of "you do the spade work" and I will nitt pick it?
I'm happy with what I built and that I blew something up that was my fault.
Brian.

The absolute max ratings carries a note:

Stresses beyond those listed under “absolute maximum ratings” may cause
permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated
under “recommended operating conditions” is not implied. Exposure to
absolute-maximum-rated conditions for extended periods may affect device
reliability.

That means if you are not operating it with a 5V supply for the logic, proper
operation is not guaranteed, including interlocks.  I think there is enough
evidence that there are troubles with the circuit to suggest fixing the obvious
flaws and working from there if other issues are discovered.  In any case,
outputs should not be tied back to inputs unless that leads to a safe operating
state.  I would never design a circuit that would rely on the chip's
self-protection if it were easier and safer to do it otherwise.  This one is
simple.

The outputs are supposed to be able to handle the inductive kick, too.  But I
would definitely put a catch diode around those outputs.

Donald.

----- Original Message -----
From: "gst338lm" <gst338lm@...>
To: EDMHomeBuilders@yahoogroups.com
Sent: Thursday, November 26, 2009 1:18:59 PM GMT -05:00 US/Canada Eastern
Subject: [EDMHomeBuilders] Re: First burn plus problems

In reviewing the driver data sheet last night I noticed the input voltage as
well, although the AbsMax ratings indicate that 12V shouldn't kill it.

I think the comparator circuit is a red herring - it might not be working
precisely as intended, but the H-driver has an internal interlock that keeps it
from sourcing and sinking simultaneously (you can readily verify this on a
breadboard) so I don't think that's the problem either.

I'm leaning toward the inductive kick theory, but will do a little more looking
this weekend.

GsT

--- In EDMHomeBuilders@yahoogroups.com, "packrat0_15" <c.hhestand@...> wrote:
>
> I posted two files in the file section under the name comparator.
>
>  One shows the difference between your comparator circuit and what they show
on the Web and in the books on electronics.
>
> The other one shows a chart of the voltages from the circuit in the book
(first printing)   I used this voltage divider calculator;
> http://www.electronics2000.co.uk/calc/potential-divider-calculator.php
> and the voltage shown in the book.
>
> Another thing about the motor driver chip that I brought up before when people
were blowing them, is that the data sheet calls for a maximum of 5VDC on the
logic input. Maybe certain production runs of the chip can take the 12VDC input
and some can't.
>
> The last time someone said it didn't matter about the input voltage, but if
that's so why would the list it as TTL or low volt CMOS, both which are 5VDC?
>
> Cary
>




------------------------------------

Yahoo! Groups Links

Well, I hope to make my first burn this weekend.  I have only to make the
clutch, plumb in the dielectric reservoir and air, and make the electrode
holder.  I added a pic of my nearly-completed unit.

Once this works I'm going to start making some 'improvements'.

GsT

In reviewing the driver data sheet last night I noticed the input voltage as
well, although the AbsMax ratings indicate that 12V shouldn't kill it.

I think the comparator circuit is a red herring - it might not be working
precisely as intended, but the H-driver has an internal interlock that keeps it
from sourcing and sinking simultaneously (you can readily verify this on a
breadboard) so I don't think that's the problem either.

I'm leaning toward the inductive kick theory, but will do a little more looking
this weekend.

GsT

--- In EDMHomeBuilders@yahoogroups.com, "packrat0_15" <c.hhestand@...> wrote:
>
> I posted two files in the file section under the name comparator.
>
>  One shows the difference between your comparator circuit and what they show
on the Web and in the books on electronics.
>
> The other one shows a chart of the voltages from the circuit in the book
(first printing)   I used this voltage divider calculator;
> http://www.electronics2000.co.uk/calc/potential-divider-calculator.php
> and the voltage shown in the book.
>
> Another thing about the motor driver chip that I brought up before when people
were blowing them, is that the data sheet calls for a maximum of 5VDC on the
logic input. Maybe certain production runs of the chip can take the 12VDC input
and some can't.
>
> The last time someone said it didn't matter about the input voltage, but if
that's so why would the list it as TTL or low volt CMOS, both which are 5VDC?
>
> Cary
>