| | |
Has there actually been a lot of failures caused by the timing issue? Violating design requirements is not a good practice, but it will not necessarily result in damage.
There have been GOBS of failures of these drivers, but there is no way to know for certain if this is what caused those failures. However, when the data sheet for the chip says "don't do this" and every driver out there IS doing this, it seems like a good place to start, doesn't it?Originally Posted by H500
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)
A lot of the failures on the small SMD stepper driver chips come from the enthusiastic specs. These tiny chips are designed for bubblejet printer use which is intermittant use at lowish currents and with low dynamic loads. The max amps spec are definitely enthusiastic, ie if rated for "3 amps" that does NOT mean "3 amps all day long driving a big dynamic CNC machine".
The last stepper chips that had more realistic specs were the SLA series, (as used in the SLAmStepper and Hobby CNC boards) that have a much larger chip die, larger body package and greatly increased heatsink surface compared to any of the cheap disposable type SMD stepper chips like the TB6560.
The SMD chips (like the TB series) are just not meant for proper machinery! They are meant for infrequent use, in small throwaway consumer devices like bubblejets and laserprinters.
I totally agree that the SLA is a better chip. It beats the TB6560 on every metric except one: It's quite a bit more expensive. And... cheap sells over quality it seems. It's also bipolar, and everyone is (incorrectly) convinced that bi-polar is better. It isn't, and I can prove it, but get people to listen... that I can't do. LOL.
techref.massmind.org/techref/io/stepper/connections.htm
However... The TB6560 is also available in a full sized package just like the SLA. It doesn't have the SLA's spec's, but it is a full sized chip. Most of the boards that use it, mount the full sized chip as if it were SMT, by actually cutting a hole in the middle of the PCB, but it CAN bet setup vertically just like the SLAm:
techref.massmind.org/techref/io/stepper/SLAm/SLAm_bld.htm
Here is one example:
pminmo.com/toshiba-6560
Now that is dead on! Half the cheap crap Chinese TB6560 drivers are advertising 3.5 amps when the datasheet /very/ clearly says that is a peak rating. For example:
CNC TB6560 3 Axis Stepper Motor Driver Controller Board | eBay "High power, maximum 3.5A drive current."
I guess you can claim that is a language difference issue, but I think it's a bald faced lie.
I mean, the Linistepper using discrete drivers (TIP122's) that are rated at 8 AMP (!!!) peak, and 5 AMP's continuous, but we NEVER say the driver can do more than 3 AMPs and we have all sorts of scary warnings about how you must have huge heat sinks to drive even that much. Why? Because it isn't practical to drive more than 3 amps in microstepping modes before the heat will overwhelm the driver and kill it. Now, with a CPU fan heatsink, in half step mode, you could probably get away with 4 or maybe even 5 amps drive, and wouldn't that be a great advertising bullet, but it wouldn't really be honest. And we couldn't offer more than a 7 day warranty (seriously, go check the ebay listing, the warranty is 7 whole days!) much less total customer satisfaction like we do.
Ok, this is turning into an advertisement. Sorry. My point here is that Roman is right, the TB6560 is a little guy that is being advertised at far more than it's actual ability.
And my point in this thread is that even with all of that aside, it STILL can't work right because the drivers that use it violate the datasheet requirements. Even if it does work, every single time you power it up, there is a percentage chance that it is going to fry. Eventually, you are going to power on, and it's going to lockup the wrong way and let out the magic smoke.
Every TB6560 driver design that I have seen is a ticking "bomb", which is going to fry eventually because it violates the chips operating specs for the power up sequence.
A design that doesn't violate those specs would be cost prohibitive (I think, I could be wrong here) unless it is part of a larger system where the power supplies are controlled by the main units logic.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)
(with apologies in advance for the possibly rambling, incoherent thinking out loud to follow)
The peak vs. average current discussion is an interesting one, and it should probably not be limited to discussions of driver chips alone.
For example, I haven't found an unambiguous discussion about motor winding current ratings either. Can you even trust that when two different motor manufacturers specify a current rating, those current ratings mean the same thing? Or, is there a game of specsmanship going on with the motor ratings as well as the driver ratings?
The ratings (for the cheap Chinese motors, anyway) seem to be loosely specified at best. Should they be tightly based on specified holding torque ratings as well as temperature rise ratings, so that they respect the envelope of all of the other maximum ratings, or are there some unwritten assumptions underlying the max current ratings, such that they are getting away with ignoring or violating other constraints? Maybe there are other relevant internal construction details that can vary from manufacturer to manufacturer that are hard for the average buyer to quantify (for example, variations in the quality of the materials used, permeability variations, eddy current losses, internal geometry, or whatever).
Also, while the ratings may be valid for operation with a low voltage and un-chopped current supply (either for holding the rotor stationary or for single stepping), are there any rules of thumb for adjusting the winding current ratings for chopped operation or microstepping?
Where this all might make a difference is in helping the user choose an appropriate driver and driver setup that is a good match for their motors. Then again, maybe all of this is a "don't care", because as long as the motors work "good enough", nobody really needs to worry about such details (as opposed to the driver current rating discussion, because it's much more likely to smoke the driver chips than it is to damage the motors or get marginal performance, so motor metrics are probably much less of a concern for the average user).
It would seem that this is fertile territory for some experimentation, but maybe I'm just overthinking this. It's also possible that you have such a discussion on your site and I have simply overlooked it.
Your point is valid, but the failure rate on these boards does not appear to be any higher than with other chip based designs. Most of the complaints on this site were related to rough running and missed steps, due to the improper design of the opto couplers.
I would guess that most of the failures would be caused by people disconnecting the motors while the power is on, or by people using a power supply voltage too close the 40v breakdown limit of the chip.
You may be right, and again, there is no way to know for sure, but posts like these:
How I fixed my Chinese TB6560 controller (updated)
How I fixed my Chinese TB6560 controller (updated)
How I fixed my Chinese TB6560 controller (updated)
How I fixed my Chinese TB6560 controller (updated)
How I fixed my Chinese TB6560 controller (updated)
How I fixed my Chinese TB6560 controller (updated)
Make me think that this power on issue is a significant failure source. Notice what they are saying: no motors were connected or disconnected, no changes made to the isolation, etc... These were systems that /were/ working just fine and after nothing more than a power off / power back on, they are suddenly fried.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)
I bought the 3 axis from ebay and the first time I cycled it off it blew out a driver when I turned it back on.
The dealer replaced it with a 5 axis unit that I have not even tried to power up
for fear of blowing this one as well.
I have read through and bought the timing ic's and I have some darlington arrays I am considering using on the feild coils input,I am just not sure if it will do anything for it if the ground is shared.
Sorry to hear you got caught in this. I'm impressed that the dealer replaced it... most have this 7 day limit on returns... how long has it been since you got the replacement and if you don't fire it up before the warranty runs out, how are you going to get it replaced if it does fry when you do fire it up?
In the same time it will take you to make all these changes, you could have built and be running a good quality kit like the Linistepper. Well, assuming you have 5 or more wires on your motors and don't mind running them in Unipolar mode... anyway, my point is that these cheap controllers are a false economy.
James hosts the single best wiki page about steppers for CNC hobbyists on the net:
http://www.piclist.com/techref/io/steppers.htm Disagree? Tell him what's missing! ,o)
I intend to fix my 3 axis board with the posted corrections and use it for testing.
Isolating the back EMF from the circuit should be fairly simple.
You are quite right about the linistepper and I did actually consider building that one,until I found this cheap one already to go and I thought it would be easier, oh well.
It is just great that we have guys here that contribute to solving problems and debugging electronics.
I am always impressed with folks who create solutions and not just post negative stuff.
Today i did the modification needed for the correct power sequencing.
*** Disclaimer ***
theese is not a quick mod and if not done correctly can damage your board/motor/burn your house etc. So i do it only if you feel comfortable at doing such a things and at your very own risk.
*** end disclaimer ***
The idea is simple: using the spindle relay to activate the motor supply.
Here is how i did. (Please note: i used orange/red circle to denote trace cutted or removed components, green for solder joints).
1) Cut the trace that goes from the power jack positive lead to the diode from the underside (red circle) and solder the wire to power the 12V regulator.
2) Connect the two pins of the optocoupler (upper green circle). This make the relays going always on, as soon as there is the 12V power supply.
Optional: i bridged the three Capacitor with the red wire(look further for an explanation).
3)Cut the trace that goes from the power jack to the diode (from the upper side).
4)I replaced the three pin spindle connector with the two pin power connector. Min is positive supply(side with red band), GND is GND. Skip the MOut pin.
5)Remove the optocoupler with the red circle (the other were removed for other kind of modifications).
How does it works:
The motor supply is switched via the relays. The relay is connected so that it will switch on everytime, so, as soon as the +5V supplu has a reasonable volage, it will switch on.
The power to the regulator is feed via the wire soldered at step 1 so the logic side is always powered as soon as there is supply.
The three tb6560 supply circuit (capacitors ) are not shared they are separated by the diode that is put on the supply rail for each IC.
I connected the three capacitor together so that the back EMF from least loaded motor can be recovered and used by other more loaded motors, with less risks that the supply voltage varies beyond safe limits.
What do you think?
Alessio
That is interesting work, although it would be easier to understand and follow the circuit modifications that you have made if you could possibly mark your changes on a schematic (such as the one contained in the zip file attachment to the first post of the 'How I fixed my Chinese TB6560 controller' thread - that post is at How I fixed my Chinese TB6560 controller (updated) )
Posting Permissions
| | |
LinkBack URL
About LinkBacks
