DC motor drive - on the cheap!

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Thread Starter

Bill Bathke II

Have a 170 or 180 VDC brush, permanent magnet motor with a gearbox drive that would make it ideal to cobble into a potter's wheel, but all of the drives I've looked at cost more than just buying the %$$@&* wheel complete! Can anyone point me towards a DIY design (I know how to etch PCB's, wire, program (if req'd - nearly any language), etc., but lack both the theoretical background and/or the tools (Spice, P-spice, or the like) to design it myself - need a simple (probably PWM) contoller, accuracy no big deal so don't need a tach, or other feedback (beyond back EMF), adjustable with a pot in a footpedal, to let me use this FREE motor (1 HP, I think) - drives I've looked at start around $400 - $500, can buy a nice portable half-horse wheel for $440.
Any ideas?

Thanx in advance...
Bill II
 
K

Ken Emmons Jr.

What about a Triac light dimmer circuit from Home Depot with a bridge rectifier in front of it? Rectified Line is 170Vpeak, so you are safe. Its probably the simplest and cheapest PWM available. Just make sure the device can supply enough current for your motor, you probably want to over-rate it because of the startup surge of the motor.

I may have missed something, but I think this will work fine. You will not get full speed of the motor, but for quick and dirty it is worth a shot.

~Ken
 
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William Sturm

Have you called some of the "OEM" style DC drive vendors, such as Minarik, KB, or Dart? I suspect that they all have stripped down drives that are under well under 100 dollars.

Bill
 
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Michael Griffin

I can't point you to a DIY design that I would recommend, but off the shelf DC drives come in a fairly wide range of types and prices. KB Electronics makes low cost SCR and PWM drives that you may want to look at if you haven't already. The cheaper industrial ones are typically the SCR drives.

To use a 180V motor at rated speed, you will need to supply the drive with 220/230VAC. If you don't need more than 50% speed, you may be able to use a 120VAC supply (if that's what you have where you live).

The KB Electronics web site is "http://www.kbelectronics.com/". You may wish to bypass the main page however and go straight to "http://www.kbelectronics.com/catalog_chassis.htm" as they have a horrible web site that needs some sort of special browser plug-in to get past the main page. Down at the bottom of the page they have links to the rest of the site. This is the manufacturer; you'll need to find a local distributor to get a price.
 
Look around on eBay. I saw several drives under $100 that would suffice. At that price point you'd end up spending less than the equivalent in time and components to build one.

You'll probably need a 230V/1PH AC source to power the drive, and motor full load amp rating for a 180V/1HP motor is on the order of 5 armature amps at full rating.

You may have other options depending on the gearbox ratio - if it isn't necessary to run at full speed you may able to use a 120V source (nominally for a 90V DC motor) and run the motor at half speed or less. Also, it you don't need the full 1 horsepower at full speed (and stay appreciably lower than full load amps throughout the speed range) you might even be able to use a smaller HP rated drive successfully.
 
Place a value on your time. By the time you add the time you'll spend on researching, buying, building, debugging etc. plus material cost you'll have spent well over what you could buy a dc motor drive for. Not to mention the headaches. Years ago drives were relatively expensive. Not anymore.
 
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Curt Wuollet

Relax and look up "kb electronic" drives should start about $100 or a little less if you can find discount dealer. And unless you have a well equipped junkbox it would be hard to build for much less.

Regards
cww
 
R

Richard Fritts, NSM, KB Electronics

Michael,

Thank you for recommending our speed controls, however I am concerned over your comments regarding navigating our website. Please contact me directly so I can learn more about your difficulties. You can E-mail me at [email protected] Thanks.
 
M

Michael Griffin

In reply to Richard Fritts, NSM, KB Electronics - You have said you are
concerned over my comments regarding your web site in my reply to Bill Bathke
II on DC drives in May. I should point out that these comments were incidental
to the primary subject of the reply, and I had no criticism regarding your
products themselves or of your company in general.

I think perhaps any discussion regarding your web site would however be better
conducted here than off-list. Other people may wish to learn from this as
well. Anyone who isn't interested in how web sites work or how they can be
used to communicate with customers, or in web based MMI design can probably
skip this message without missing much.

When I visit your web site (www.kbelectronics.com), all I see is your logo, a
few "motto" type lines of text (e.g. "a complete line of motor drives"), two
tiny links to "email" and "search", and three large boxes stating "click here
to download plugin". There is no obvious means of proceeding further into
your web site. So far, your web site is not making a good impression.

If I was not already a long time customer and knew what sort of products you
had, I would probably give up at that point. There are other companies that
sell drives. As it was, I was able to use "Google" to find a "back door" into
your web via another page Google had indexed, and to work from there to find
the information Mr. Bathke was looking for.


I am not an expert on web sites, but I probably know more than many of your
other customers so I could look at the HTML source code of your web pages to
see how your site works and what the problems were. Keep in mind that most of
your customers would probably just give up and go somewhere else if they had
a problem.

First however, I need to cover some background. If you are not familiar with
what Adobe Macromedia "Flash" and "Shockwave" (which I will simply refer to
collectively as "Flash") are, I'll explain it a bit here first before
proceeding with what I think is wrong with your web site. "Flash" is a
proprietary animation player which is an optional "plug-in" to most web
browsers. This operates in a manner similar to the Adobe Acrobat Reader
browser plug-in (Macromedia was by the way recently bought by Adobe). Most web
sites don't use it at all, and for the few that do have it, the main use for
it is animated advertising (i.e. third party ads which pay for advertising
space on entertainment sites) or some simple games and amusements. Unlike
"PDF" files, it cannot really be considered a "mainstream" web technology.

Many people have their web browsers set to block "Flash" because it uses a lot
of bandwidth (this is particularly a problem for people on dial-up modems),
and they aren't all that interested in seeing third party animated
advertisements anyway (which is the main use of "Flash"). It's also been
proven to be a potential virus vector. I don't have it installed at all in my
main web browser (remember, this is an *optional* plug-in).


The problems with your web site can be summarised as follows:

1) The entry page into the site depends upon an optional proprietary product
(Adobe Macromedia Flash) but does no detection and offers no alternate
navigation. Not all of your customers will have Adobe Macromedia "Flash"
installed (or they will have it blocked), and they are unlikely to install it
just to view *your* web site.

From the HTML source code, I can see that "Flash" is used for an animated
logo, some sort of intro animation, and an animated menu. Particularly
critical is the animated menu, which is used to get past the first page.
Without it, nobody is getting in to your web site as it is now unless they go
in through a back door.

The normal way of dealing with this is for your web server to detect whether
"Flash" is installed in the client browser, and if not to re-direct them to
an alternate page that does not use "Flash". Alternatively, you could just
use a conventional menu system instead of the animation (see additional
reasons for this below). The animated "Flash" logo could probably be changed
to a conventional animated "gif" (or just drop the animation). You could keep
the intro animation, but just have it only on the "Flash" version of the
entry page.


2) Your web site depends upon javascript for certain important functions
(search, menus), but does no detection. The normal way of dealing with this
is to detect whether javascript is disabled (almost all browsers have it; but
many people just turn it off when not using it), and to re-direct to a page
which asks the potential customer to turn it on. Better still is to design
your web site to not need it. I didn't see anything on your web site which
couldn't be done just as easily without it.


3) Your web site seems to use a "pop-up" ("function popMeUp(url,w,h)") via
javascript. I have no idea what this does, as it won't "pop-up". "Pop-ups"
are obsolete and should not be used. Most modern web browsers will block
"pop-ups" either inherently, or via third party security products. "Pop-ups"
are mainly used by disreputable ad companies to bombard people with multiple
ads, or by hackers trying to crash your computer (this is why they are
obsolete).


4) Your web site uses "cookies" to store search information, but does no
detection. Many people turn "cookies" off for security reasons. You do have
some very small fine print explaining how your site uses "cookies", but the
customer would have to scroll down to the bottom of the page to see it. You
could do detection and respond in a manner similar to that for javascript,
but I doubt it's worth the effort. Many times the cookies would just get
automatically deleted by the browser's cookie manager at the end of the
session anyway. In this application, I doubt that having cookies on your web
site is worth the effort. The information you have in your explanation on
enabling cookies by the way, is at least 8 years out of date.


5) The search function page says: "Your Browser's 'Back' button has been
disabled. Please use the navigational tools provided in this program". The
"back" button on my browser works just fine on this page. If there is some
reason your web site needs to disable this button, it isn't working as you
intended. Unless there is a very good reason for disabling browser buttons
though, it is usually best to leave them alone.


6) Your web site uses "Flash" and javascript menus. Neither of these types of
menus will work with tabs. All modern web browsers have tabs, and even
Microsoft's very archaic "Internet Explorer" is getting them in its next
version (whenever that comes out). Your customers who have modern web browsers
are not going to be happy trying to navigate your site as if it were still
1996. Conventional HTML menus would work fine.


7) The javascript drop down menus don't always appear in the right location.
For example, if I put the mouse cursor over "Products --> KB Fan Speed
Controls", a menu with "Panel Mount / Wall Mount / Chassis Mount / Plug-In"
appears. However, it appear up near the top of the page (over your static
logo) rather than next to "KB Fan Speed Controls". I would have to be very
quick with the mouse to be able get up to the sub-menu before it closes up.
This makes navigation somewhat difficult. I tested this by the way with
several different models of web browser.

Also, if you move the mouse in a pattern which is not expected, the menus
don't necessarily close up properly before another one drops down over it.
You can end up with several menus "stuck" in the down position. This is a
minor cosmetic issue, but it doesn't look very professional. One of the
problems with using drop down javascript menus is that they take a lot of
debugging to get them to work right.


8) There are lots of errors in the HTML page code. If I run the first page of
your web site through an HTML validator, it shows 26 errors. If I run the "DC
DRIVES, CHASSIS" page through, it shows 69 errors. A lot of web browsers will
try to work around HTML errors, so it does happen to look "OK" in my web
browser. This does however indicate possible future problems.


As for what you could do about the above - In general, you have what should be
a fairly simple web site suffering from being over complex and in some ways
"broken" by dependence upon a few features which are not really necessary.

If we have a look at what is powering your web site we see:
Operating System: Linux
Web Server: Apache/1.3.27
Scripting Language: PHP/4.3.3
I would guess you also have a database behind this - probably MySQL.

This is a very common "stack", and I wouldn't change it. PHP give you a
dynamic web site, so the user interaction can all be done through the server
side. The problems I have mentioned above therefore are all in the
application code.

The layout of the actual catalogue pages and other similar pages looks OK
(except for the javascript menus). Correcting all the points I have raised
above (except the HTML errors) would involve changing the front page, the
menu system, and the search function. Since the site is written in PHP, just
about any experienced web programmer could change this for you. I don't know
what your content management or administration pages look like, but since the
customer can't see them they are not relevant to this discussion.

QA testing of a web site intended for access by the general public
(e.g. customers) is a bit different from testing web sites intended for
internal company use only. You don't control the browser type or
configuration of your site visitors. Public facing web site testing normally
involves accessing it using several different web browsers (at the least
MS-IE, Firefox, Opera, Safari; for MS-IE test with at least two different
versions). Testing should also involve setting the optional web features
(javascript, cookies, "Flash") on and off to test the fall-back behaviour.


I hope the above has answered your question.
 
C
Hear, Hear!

I see way too many broken sites that I _need_ to use. I too am a big fan of, and recommend, KB drives. Glitz is important, I suppose. And the LAMP stack is the way to go if you would like everybody to be able to use your site. But web developers need to test and refine their creations for usability. And yours isn't a particularly bad example. I see many that will only work with one version of IE. And plug in features should only be used where they serve a purpose and then should be widely available. Writing to Firefox is a lot more portable than writing to IE, which often isn't portable even between versions. This is important as web presence and content is becoming important to customers, especially outside business hours. So kudos for starting right, just have the web wizards fix it. And test it with a few browsers before signing the check.

Regards
cww
 
K

K.V.Subramanyam

Hi, people just confusing you. I have done it very cheap. I bought an electronic (Triac based) AC motor (in my case ceiling fan) regulator for Rs. 100/- (US$ 2.00) connected a 1N5408 inseries... that's all, I got my cheapest DC motor regulator. All the best...

kvs
 
I have tried this , but it only works at high speeds. At lower speeds (higher dimmer resistance) the motor keeps turning on and off. Can anybody tell me why?
 
T

Tomy Zacharia

Dear Subramanyam,
Just curious or say confused. Your approach should work with AC supply and you would get half wave rectified DC output. What happens if your power source is say 200 VDC. Moreover ceiling fan motor regulator (at least the ones available in my part of India) are rated to 200/400 W (might be resistive as these are designed as lamp dimmers). So after half wave
rectification (power also reduced to say half or even less), how do you control a 1 Hp motor as mentioned in the original post?

Tomy Zacharia
 
K

Ken Emmons Jr.

It's hard to say why it would turn on and off. Perhaps the circuit needs a minimum load, especially at low current. You could try putting a resistor to ground in front of your bridge rectifier. Make sure the resistor can handle full power of the curcuit.

~KEJR
 
Hi Bill,
Suggest you look into a KBMD-240D DC drive suitable for 120 or 240 VAC input and 90 or 180 VDC output. Maximum rating is 3/4 HP at 90 VDC. Since the potters wheet application is usually just intermittant at maximum load this drive will be OK. The list price should be around $150.00. We have been manufacturing it for about 25 years. It is not PWM. You can look at our website and check out a local distributor near you. We also offer PWM in NEMA-4 enclosures. They are more expensive.
 
I too have a 180VDC gear reduction motor that I'm trying to use. I use it currently to drive a grain mill at a nice 30 or 40 RPM. (this is using rectified 110VAC). However, I'd like to use it as a variable speed motor with a faster top end. But where I'm going to use it, I don't have access to 220.

Any one see any reason why I couldn't use a voltage doubler diode array with a rheostat before the doubler/rectifier? Would this be dangerous without a transformer to isolate the connection? For the record, the motor only pulls about 18W at 180VDC.

Thanks!

mike
 
K

Ken Emmons Jr.

Use a transformer and/or a Variac as a brute force method, but I would not run your motor over rated voltage. You could burn out your motor or cause a fire. There are ways you can pulse your motor for short times, but not with this kind of circuit.

~Ken
 
C
Any direct line rectified circuit is going to be equally hazardous and a transformer would seem to solve your problem at moderate cost. I'll mention how below A rheostat is a very inelegant means to control a motor and the place for it would be after the rectifier/filter. Voltage doublers rely on charging currents that are much greater than the average output current for reasonable load regulation and the rheostat would limit the charging current and would probably be less linear than you would like if placed before the doubler. Now for a little better solution, albeit still without isolation. If you take any small 24 V control transformer and connect it as an autotransformer and use the present rectifier and capacitor if voltage ratings will permit, you will get your boost without as grossly exceeding the motor voltage rating and with better load regulation which I would think matters with a grain mill. An even better solution would be any approx. 1:1 xformer at 110 V or more with the common adjustment taps , This would let you bump up the voltage a little and provide isolation.

Regards
cww
 
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