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Discussion in 'CNC Mills/Routers' started by Gargoile, May 7, 2016.
A stock C-Beam with a CNC shield with DRV8825's
Gargoile published a new build:
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You asked about using a 12v power supply.
Use 24v, at least. Set the drivers for 2 amps, fit the heatsinks, blow on them with a fan.
Why? Stepper motors operate better at higher voltage, but the current needs to be limited.
The 8825 chip on the drivers does the current limiting for you.
The high voltage means that the rise time of the magnetic field in the motor is shorter, meaning it can accelerate faster, and ultimately turn faster. This also gives it more holding power, which is what allows it to maintain a constant cutting speed.
Thanks David (good name that is what my mother calls me). So would it be better to max the voltage on the Protoneer shield to 36v? What kinda current rating would I be looking for in a PSU? Say my motors are rated for 2.8A per phase. Would it be 2.8 x 2 ( 2 phases per motor) x 3 ( 3 motors) = 16.8A. So maybe 20A?
.66(2.8 x 3)= psu current. 6A should do.
a rule of thumb with electronics is never use use them at their maximum, they last longer that way (-:
so, driver max is 36v, use about 80% of that, say 28 to 30v, though I'd be happy to run at 24v. my tests at 24v at just 1 amp into a NEMA23 stepper makes them pretty impressive. bump up to 2amps and I think you will bend leadscrews before you stall the motors.
David, Joe I appreciate the help. So would something like AC 100 240V 50 60Hz 150W DC 24V 6A Power Supply Adapter Transformer BGF 54 | eBay be sufficient or should i be looking at something along the lines of http://www.amazon.com/Crazy-Regulated-Switching-Power-Supply/dp/B00HF3G4SW ?
I came up with the 2.8A per phase off the OB parts store 23's, assuming these would be the one's supplied with the kit, but you know what they say about assumptions.
Save yourself some brain damage and use a gshield. I got a 24v 6.5A power aupply Meanwell.
Well Jimmy it might be too late for me to prevent the brain damage. But if you could elaborate as to why you think the gshield is a better option I'm all ears, thanks.
It's just a more complete and robust set up. Don't get me wrong...what you have will work fine and should drive your steppers with plenty of power. I started with the same set up. I have since bought a real Arduino and Gshield to run the C-Beam. If you have already spent the money just use what you have.
I believe this depends on manufacturer.
I've noticed that when dealing with products from the east that this is generally a good rule of thumb for cheap electronics as some will mark up their product performance specs. to appear more competitive against price. I think that they are also much more liberal with the idea of safety factors and international standards than the west and European manufacturers.
However, some Chinese manufactures are actually competent enough to hold a high standard and they do very well internationally over the long term. Others will depend on flooding the market with cheap junk until the public catches on to their shenanigans. Take for instance the cheap analog TB drives that are all over the **** place atm. We see it day in and day out on these forums that these drives are junk performance wise. Yet, noobs jumping into the water react to the cheap packages that are in every crevice of the web and they eventually end up tossing them out when they finally wake up to the reality of dsp.
So far from my experience in industry I've noticed that keling(automation technologies) and leadshine offer components that will hold up and are accessible to the homebrewer(leadshine prices are mostly industry though). I'm no process controls engineer, but I work intimatly with them on a day to day basis. The consensus is that these two check out for reliability and service. So I chose them for components of my build. The thing about them is that they do business like just about every other Chinese company (and many US companies trying to make offbrands) in that they'll produce the same quality components on the side rebranded and at lower cost! Whenever I see that happen in the US the quality usually suffers if they go to the east for supply. This is because it is still a difficult task to locate then interact with an eastern business that has the capacity and knowledge to produce quality components within a standards guideline(unless you're like Apple and walk in flashing the cash).
Ahh. Anyways, I've gone on enough of a tangent and you're a pretty smart guy already Dave. I think my point was, if you choose the right brands then you can push the components well past their ratings because of the overhead left for by safety factor. Some manufacturers will even clue you into this in their documentation if you're technically savvey enough to hack through it. ABB for example, in their 1billion page vfd manuals (where different series use different fault codes and some have seperate drive alarms that look like faults when reported from the drive!!) will tell you that the drive can perform above the drive rating for an x amount of time. Parker stepper and servo drives are notorious for being complete savages, so some guys buy them underrated to save a few bucks on a project expense and just push them harder, but you have to be a controls engineer to set them up to begin with. Gecko, I see from time to time in the field, is more well known by the diy community(for their willingness and effort to bridge the gap and support us), because they offer drives that can handle the abuse and that's reported to us by us. Vampire drive anyone?
Point being, run it as rated. Report it if it fails and report if it takes an *** kicking daily. The community will take note, the entry level will benefit, the industry is then forced to keep up.
Edit: what's funny is that you'll see some eastern manufactures struggling with how to include their quality engineering considerations into their spec sheets. For example, I'm using the MX4660 on my custom nonOX build. The drives are rated 48V 60Vmax. When asking them if it's okay to supply 52V instead of 48. Instead of saying no the drive is rated 48V end of story(and removing 60V from the manual altogether), they broke everything down into a study for the application based on loads, accelerations, etc to determine if the back EMF will pop the internal fuses. When the data came back I was impressed because they sent me a 15 page study (with graphs and measuring equipment screenshots) of the scenario. I can't say that they'll do this for everyone, but ****, gotta give recognition when it's due right? You could say that I'm biased after that. Can you blame me? Glad I took the advice from those process controls guys. lol
Sorry again for the article guys.
Thanks All. Build has been updated. Bundle gets here tomorrow! Stay tuned for more updates shortly.
Hey Joe, would you care to share the name of that company so that I can spend my money with folks who care about what they do for a living? Heaven knows there are far too many of the other sort. Feel free to PM it if that makes you more comfortable.
Which company Larry?
I'm pretty sure Leadshine supplies Wantai and Longs with some drives.
For instance: Here is a nice little drive from Leadshine that would be more than sufficient to drive common 2.8 and 3.0A NEMA 23 steppers.
But hey!! What do we have here in our own parts store?
Links are broken. I'm on my phone atm.
Those DQ542MA drivers are tops! I have been using them in all my builds for a couple years. It's great to see them in Open Builds parts store - I really try to order everything I can from them, so the addition of these makes just one more reason to place the next order.