RE: [CAD_CAM_EDM_DRO] Re:low cost stepper driver

I have to agree with Ron here. Trying to turn a cheap Chinese stepper driver
into a good driver is akin to trying to turn a Yugo into a Toyota. If you
start with junk you'll wind up with junk.



There are two separate questions here: Why are these stepper drives so
cheap. A big problem with cheap 'no-name' products imported from the East is
that many of the parts are from unknown origins (i.e. they are likely
counterfeit.) Even large companies and defense contractors are fighting this
problem of bogus parts (and spending a lot of money doing so). The guy
making $10 stepper drives has no incentive (or budget) to worry about the
authenticity of the parts he is using. A friend of mine was running short on
an part last year and no US suppliers had stock so he bought a reel from a
broker in the East that had been recommended to him. The parts were
counterfeit, they pulled each part from the reel, sanded off the part
number, and re-stamped it. He was out a few thousand bucks but at least he
found out before using a bogus part that could have caused many thousands of
dollars worth of boards to not operate properly.



Another problem is that when you are designing a product to meet a price
point you achieve that by throwing out all the stuff that is absolutely not
needed to make it work, i.e. all the safety stuff. You also use parts with
ratings that are right on the edge of being acceptable, i.e. use 16V
capacitors when you normally would have used 30V.



Then you come to the usage scenario / target audience. The monolithic
stepper driver chips that most of the cheap stepper drives use work great if
you run them within their design spec. There are millions of these types of
chips in everything from photo copiers to inkjet printers. The companies
designing the machines spend a lot of engineering time/money to endure that
they are operating the driver chips with their performance specifications.
They will test for things like having enough airflow to keep things cool,
having a power supply whose output voltage does not spike up above the
drivers limits.



When operating in the hobby world things are different though. Things are
built much more with the 'seat of the pants' method and often cobbled
together with spare parts. (Nothing wrong with either of these methods BTW.)
In the case of the stepper driver, the chips used will often have a maximum
power supply voltage of 28V, anything above that and the chip will be
damaged. So the average hobbyist will put together an inexpensive 24 power
supply with a transformer, rectifier and large capacitor. While the rated
voltage of the transformer might be 24V it could easily put out over 30V in
an unloaded state. So now you are hitting the driver chip with more voltage
than it is designed to handle and it fail.



If you operate these driver boards in their proper range of operation and do
a good job with the wiring you will likely get many years of service. If the
board was built with sketchy parts then it might fail in a month or less.



Just some things to think about.



Jeff Birt

Soigeneris.com



From: CAD_CAM_EDM_DRO@yahoogroups.com
[mailto:CAD_CAM_EDM_DRO@yahoogroups.com] On Behalf Of Ron Ginger
Sent: Monday, October 01, 2012 6:24 AM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: [CAD_CAM_EDM_DRO] Re:low cost stepper driver





On 10/1/2012 6:15 AM, CAD_CAM_EDM_DRO@yahoogroups.com
<mailto:CAD_CAM_EDM_DRO%40yahoogroups.com> wrote:

>
> Posted by: "artgartg"lists@... <mailto:lists%40toynbee.org.uk>

artgartg

> Date: Sun Sep 30, 2012 7:44 pm ((PDT))
>
> I've been looking for suggestions on modifying these chinese boards to

improve reliability. Unfortunately Yahoo stripped your pdfs from the
archived mail. Would it be possible to put them in the files section please
?

>
> I have found some articles on the web, mostly related to improving the

optoisolator circuits. There are comments too about power sequencing, which
these boards do not usually do correctly.

>
> I'm also interested in the reason these boards fail if a motor is

disconnected in use, and wonder if it's feasible to add some protection.

>
> -adrian

How long and how much effort do you want to put into maing a low cost
board into a better board? Why not just buy a better board in the fist
place. There are a number of good quality drives around now for not much
more money than these cheap drives that are good industrial quality
drives. Keling is one good source, but there are others.

brings to mind an old saying about making a silk purse out of a sows ear.

ron ginger





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