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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
My past reading about which spindle to choose suggested that Huan Yang was a well used and reliable manufacturer of the most popular 2.2KW water-cooled design but that there were plenty of less reliable copies available from other suppliers, especially with regard to the VFD. This is why I decided that buying a combined set of spindle and matching VFD direct from that manufacturer's own shop was the obvious choice.
I have been very pleased with the spindle and VFD so far, it has worked perfectly and the majority of the VFD settings were factory set to the recommended values I found on this forum.
Fair enough! It seems to be the go-to set-up at that price point. Although, in all fairness, I can't seem to find any alternatives either (other than units looking exactly the same, but with different logo)...How do you find the noise level? In youtube videos it seems a bit noisy, especially the VFD.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
I hope you are not disappointed!
One thing to be very careful of is the quality of your soldering inside the 4 pin plug to the spindle. If soldering is not one of your strong points, practice until it is :welcoming:
No probs on the soldering side of things. I have a full on micro soldering setup at home along with microscope and various electronics kit. I like to repair any of my tech at home as I am actually qualified in electronics test and service mechanics and have a City and Guilds certificate too.
If you think soldering is hard try hand soldering an 0203 component under a stereo microscope. Even a bit of static will lift the component if you are not careful. I’ve gently touched the board with the flux syringe before now and had the resistor, or whatever, just vanish.
I also made an emergency stop interface for my CNC. I can watch my machine from another room on my iPad and if something goes wrong I just say Computer SCRAM and it hits the emergency stop on the machine from wherever I am in the flat. It’s actually safer than the amount of time it would take to reach my machine on crutches and I’m not sitting in front of a noisy machine for 1hour plus when it’s doing 3D carving of curved surfaces.
So yeah... soldering is a good skill to have.
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Re: Was about to get a toy- then I did some research...
neoMorph,
I've made a few DIY surface-mount circuit boards but 1206 is my stock size for resistors and 0.05" pitch for chips so I'm sticking Stone Henge monoliths together by your standards.
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Re: Was about to get a toy- then I did some research...
As far as noise is concerned, the VFD has a fan which is noticeable in my workshop but not intrusive. The actual spindle is quiet enough that I'm happy to stand next to it when it's running. However, once it starts cutting then the noise makes me put on ear defenders!
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1 Attachment(s)
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
neoMorph,
I've made a few DIY surface-mount circuit boards but 1206 is my stock size for resistors and 0.05" pitch for chips so I'm sticking Stone Henge monoliths together by your standards.
It’s easy enough to solder 0603 with practice but I prefer to stick to 0805. I tend to buy my surface mount parts in sample books and top up when I use them. Helps keep track of the tiny suckers lol.
Regarding the plug, if it’s the type I think then I already have several in my current CNC build. Even have some 7 pin ones. Those are hard.
Is it these ones?
Attachment 27215
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
NeoMorph
Similair just larger and bit more HD.
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Re: Was about to get a toy- then I did some research...
I always have difficulty judging sizes from pictures. Usually have to get my callipers out.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
but 1206 is my stock size for resistors
You could row all the way to Aus on a 1206! :drunk:
0603, less than that and you're just being a masochist.
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2 Attachment(s)
Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
NeoMorph
I always have difficulty judging sizes from pictures. Usually have to get my callipers out.
They look like GX16?
The spindle will take a GX20.
I've been soldering lots of 7-pin GX16s and 4-pin GX20s this weekend.
Tip number 1: Get someone to help hold stuff. Failing that, grab a vise or something. And like ten of those helping hands things.
My technique (who knows if its good, but it seems to work). Tin the wires. Prep the pin with a decent amount of solder. Then flow it whilst simultaneously heating the wire, and bring the two together asap. Reflow once you're happy its in a good place to avoid a cold joint. Can be a real PITA when you're dealing with very short cable ends to keep it looking tidy.
Oh and DON'T forget to put everything on the right side of the damn panel. Spot the error below...
Attachment 27216Attachment 27217
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
AndyUK
They look like GX16?
The spindle will take a GX20.
I've been soldering lots of 7-pin GX16s and 4-pin GX20s this weekend.
Tip number 1: Get someone to help hold stuff. Failing that, grab a vise or something. And like ten of those helping hands things.
My technique (who knows if its good, but it seems to work). Tin the wires. Prep the pin with a decent amount of solder. Then flow it whilst simultaneously heating the wire, and bring the two together asap. Reflow once you're happy its in a good place to avoid a cold joint. Can be a real PITA when you're dealing with very short cable ends to keep it looking tidy.
The vice is a must. If you put a socket (plug) in the vice and plug in the plug (socket) you're soldering then the socket (plug) will support the pins in place and help avoid distortion through overheating the plastic, though if you're as quick as you should be this won't be a problem. You're using the same method I do, just keep everything clean before tinning, don't twist the wires with sweaty fingers and clean the iron on a sponge between each application. Don't try using a gob of solder that's been sitting on the iron for a while. Sleeving over each pin will prevent shorts between pins or pins and the case.
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Re: Was about to get a toy- then I did some research...
I’ve got half a dozen or so helping hands that I use. Some are missing arms, some have been modded with mounts for plugs to be held without distortion. I usually make them out of wood as it doesn’t transfer the heat into the plastic that way.
Same goes for PCB holders. I used to lust after a decent pana-vice but they are crazy expensive for what they are. If you are any good at putting together a CNC then you could make a better one.
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Re: Was about to get a toy- then I did some research...
Hi again, I've been somewhat occupied with work lately, hence, the radio silence. I've got offers on nearly all main components and the intended design seems to be within budget. One loose end is the aluminium plates which I'll have to have made for me and to that end I wanted to ask a practical question (as I have very limited experience working with metals); what tolerances do you use on screw holes? More specifically, I'll probably end up using a combination of M5, M6 and M12 screws and 20mm aluminium plates.
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Re: Was about to get a toy- then I did some research...
I think you probably mean clearance hole size rather than tolerance? Google "metric clearance hole chart"
Edit: Or if I've misunderstood then ignore the above.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Doddy
I think you probably mean clearance hole size rather than tolerance? Google "metric clearance hole chart"
Edit: Or if I've misunderstood then ignore the above.
Precisely, tolerance, not clearance. And just for the record (and before anyone posts a lmgtfy-link :) ), I did try to google it before asking on here but using highly scientific terms like "screw hole sizes" did not yield me any useful info. Anyway cheers, I got exactly what I needed!
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Re: Was about to get a toy- then I did some research...
I think Juranovich meant tolerance of holes being in the right location.
I’ve seen makers use the rails with hole transfer punches to make sure the holes are in the right place. Put the rail on the plate, loosely clamp down one end and then measure and tap to the right distance from the edge. Do the other end the same and then go back and forth until both end are perfectly aligned before clamping down hard... then one final measure to make sure the rail hasn’t moved.
Then if that is all correct, just go down the holes with the correct size hole punch and tap in the locations for the holes. Follow up with a drill press or a mag drill (you can even rent them according to my friend) and Bobbie’s your auntie.
This way, you won’t measure the hole spacing wrong and drop a hole out of position that would knock out the following holes too. Simples, as a certain Meercat would say.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
NeoMorph
I think Juranovich meant tolerance of holes being in the right location.
I actually meant tolerance as Doddy pointed out, but what you describe is also something I'd probably had come back to ask at some point :)
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Re: Was about to get a toy- then I did some research...
As I'm trying to get the whole picture I've had to dip into the electronic side of things. Now I've got offers for steppers, drives and torodial transformers, but I'm a bit unsure on how to size them properly, or specifically how to size the PSU. The specs are as follows:
- NEMA 24 closed loop steppers at 4.5Nm holding torque, 5A, 0.75ohms, 2.4mH (all phase values).
- Drives rated at 20-70VAC or 30-100VDC, 8A peak.
- 420W torodial transformer 220 to 70 VAC, 6 A
Firstly, as the drives can take AC, is there any need to convert the output current from the torodial transformer to DC? As I've understood in case I go for AC to AC I could simply connect the first winding to the mains (with fuse for safety) and the second directly to the drives? Also, assuming no DC conversion, is it safe to use a 70VAC rated torodial transformer to power the drives rated at max 70VAC?
Now, if I've understood correctly the total amps my 4 steppers will draw is roughly 2/3 of the sum of the rated amps of the steppers, i.e. 4*5A*2/3=13,33A. So the PSU would have to supply (rounded up) at least 14A? As the torodial transformer is rated at only 6A, should I consider wiring several in parallel to get more amps or would it be better to simply look for a beefier one to supply all the current i need?
And so the voltage. This has me the most confused, some recommend to not over do the voltage for fear of getting components burnt, while others prefer higher voltages in order to not lose out on max performance (however, in these cases drives usually have some sort of voltage regulators). Now, if I've done the math correctly the Vmax of my parallel wired steppers is 32*√(2.4mH) = 49.6V., so well within the 70VAC outputted by the torodial transformer so as to get the most out of the steppers, BUT (and see first question above) would I run the risk of overheating my drives/steppers with this setup? The drives I've been offered (Lichuan LCDA86H) do list "overvoltage protection", but this sounds to me more like a fuse type protection than active voltage regulation.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Firstly, as the drives can take AC, is there any need to convert the output current from the torodial transformer to DC? As I've understood in case I go for AC to AC I could simply connect the first winding to the mains (with fuse for safety) and the second directly to the drives? Also, assuming no DC conversion, is it safe to use a 70VAC rated torodial transformer to power the drives rated at max 70VAC?
If the drives take AC, don't bother rectifying it into DC. Go straight from the transformer to the drives. Don't daisy chain them though. Size the transformer by taking the max motor current (e.g. 4A) times the number of motors (3 or 4), so lets say 12A, then reducing by 1/3rd, so 8A. Don't go too overboard on the VA of the transformer, get what you need. Bigger transformers can suffer from large amounts of inrush current which can trip the power and just be a pain without other compensation.
Quote:
Originally Posted by
Juranovich
Now, if I've understood correctly the total amps my 4 steppers will draw is roughly 2/3 of the sum of the rated amps of the steppers, i.e. 4*5A*2/3=13,33A. So the PSU would have to supply (rounded up) at least 14A? As the torodial transformer is rated at only 6A, should I consider wiring several in parallel to get more amps or would it be better to simply look for a beefier one to supply all the current i need?
Well clearly I should have read ahead because you already know the method. Oh well, not editing it now. No just get a larger VA transformer. You probably need 1000VA based on your 13.3A current, but that seems a little high? Most of us have 500-600VA transformers when turning into DC, perhaps someone can shed more light on this.
Quote:
Originally Posted by
Juranovich
And so the voltage. This has me the most confused, some recommend to not over do the voltage for fear of getting components burnt, while others prefer higher voltages in order to not lose out on max performance (however, in these cases drives usually have some sort of voltage regulators). Now, if I've done the math correctly the Vmax of my parallel wired steppers is 32*√(2.4mH) = 49.6V., so well within the 70VAC outputted by the torodial transformer so as to get the most out of the steppers, BUT (and see first question above) would I run the risk of overheating my drives/steppers with this setup? The drives I've been offered (Lichuan LCDA86H) do list "overvoltage protection", but this sounds to me more like a fuse type protection than active voltage regulation.
I think most people tend to ignore Vmax and just give them as much as the drivers can manage, then limit the current on the drives so they don't burn. Typically with 3.2mH motors with a Vmax around 58V people use 68V (convenient toroidals are available). Basically I think you want the motors to be warm but not burny hot (demagnetisation occurs when they hit a certain temp).
The overvoltage protection you talk about is interesting though - what do the drives spec for the voltage?
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Re: Was about to get a toy- then I did some research...
What AndyUK said about larger transformers tending to pop breakers and blow fuses due to high inrush current is right. The less is said about the time I was working on a DIY boost converter for my electronics course, and blew out the power to an entire wing of the YMCA I was living in, the better. That was back in mid 86 so they might have forgiven me now lol.
That was down to high inrush current as well.
But the good news is inrush current can be reduced pretty easily. See here...
http://www.ti.com/lit/an/slva670a/slva670a.pdf
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
AndyUK
Well clearly I should have read ahead because you already know the method. Oh well, not editing it now. No just get a larger VA transformer. You probably need 1000VA based on your 13.3A current, but that seems a little high? Most of us have 500-600VA transformers when turning into DC, perhaps someone can shed more light on this.
Yes! Pretty please! The problem seems to be (assuming 1000VA is an issue- as I'm quite unqualified to judge) that 4-4.5nm steppers seem to be rated at 4-5A and with 4pcs that quickly adds up.
Quote:
Originally Posted by
AndyUK
I think most people tend to ignore Vmax and just give them as much as the drivers can manage, then limit the current on the drives so they don't burn. Typically with 3.2mH motors with a Vmax around 58V people use 68V (convenient toroidals are available). Basically I think you want the motors to be warm but not burny hot (demagnetisation occurs when they hit a certain temp).
The overvoltage protection you talk about is interesting though - what do the drives spec for the voltage?
For the record it also lists overcurrent protection. If you're after the input rating it's 20-70VAC and 30-100VDC. Is that what you were looking for?
When your're saying to max the voltage, shouldn't there be some room for the transformer to fluctuate (upwards) from the rated voltage? In this case the transformer outputs 70V which is also the max of the drives. Also regarding overheating, is it the wattage/VA that is the decisive factor or can voltage alone cause over heating? I'm thinking if higher than rated voltage is passed through a circuit but at lower than rated current (i.e. less than rated watts are being fed), shouldn't there then be "unused" resistance in the circuit to avoid overheating? If so, is higher than rated voltage more a question of the structural integrity of the circuit? Or does it maybe manifest in the same way in the end, i.e. burning components...? In the current case the transformer outputs 70V at 6A = 420VA and the drivers can take 70V at 8Apeak = 560VA. Even if I had 4 transformers in parallel and 4 drives in parallel, respectively, the total wattage would still not exceed that of the drives' capabilities. So getting back to what you said about maxing voltage and limiting current, as the drives can take more current than the transformer outputs, I should be on the safe side?
sorry, for the ramblings, my thinking hat came on while writing this...also b/c curious! :excitement:
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Re: Was about to get a toy- then I did some research...
Quote:
For the record it also lists overcurrent protection. If you're after the input rating it's 20-70VAC and 30-100VDC. Is that what you were looking for?
If you are just going to put AC in then I would not go more that 60V AC as the mains can and does fluctuate.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Clive S
If you are just going to put AC in then I would not go more that 60V AC as the mains can and does fluctuate.
This ^^^^^
Mains electricity is very “dirty” in some areas. Stick a scope on the mains and you would be shocked to see how bad it is at times. It’s the reason if it was me I would at least have a voltage regulator in the circuit at the very minimum. Cleans up that dirty power a treat.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
would I run the risk of overheating my drives/steppers with this setup? The drives I've been offered (Lichuan LCDA86H) do list "overvoltage protection", but this sounds to me more like a fuse type protection than active voltage regulation.
Do not rely on the OV protection of these drives, they will not save you from more than just a few volts. So if you get a spike then they will fry them.
They are good drives provided you leave a good safety margin.
You need to leave at least a 10% safety margin on the voltage and I wouldn't run much above 60Vac with 70Vac Max.
Regards the Transformer I use 750Va with these drives without any issues. I wouldn't go above 750Va because you will get troubles from inrush.
Do NOT use a regulated PSU like as been suggested by one member as it could cause you troubles with voltage clamping.
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Re: Was about to get a toy- then I did some research...
I keep meaning to ask, do you guys use surge protection or, better yet , run it through a UPS to clean the mains transients from glitching out the machine and computer. I’m wondering if a domestic surge protection device would freak out. I seem to have this memory of a computer with a beast of a psu that kept freaking out because of the surge protector (think it was 1200w psu because of all the extra stuff he was using including a crazy raid array and loads of RGB). Once he ditched the surge protection the machine worked fine.
That’s why I’m thinking a decent UPS would at least let you shut down safely. Or is my OCD going overboard again?
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
NeoMorph
This ^^^^^
Mains electricity is very “dirty” in some areas. Stick a scope on the mains and you would be shocked to see how bad it is at times. It’s the reason if it was me I would at least have a voltage regulator in the circuit at the very minimum. Cleans up that dirty power a treat.
What are you on about:beguiled: You can supply a drive with a toroidal, rectifier and some caps ie DC or just use a toroidal and use the rectifier and caps in the drive.
Quote:
That’s why I’m thinking a decent UPS would at least let you shut down safely. Or is my OCD going overboard again?
I think you are going overboard a bit here and frightening new users into things they just don't need:jaded:
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Re: Was about to get a toy- then I did some research...
The fact that the drives are rated at "20V-70V" AC in is a pretty clear indication that they are very tolerant of input voltage variations. The only thing that really worries them is input overvoltage, which is why Jazz has suggested aiming at about 10% under the nominal maximum to give a bit of headroom for the odd spike, mains surge, etc. There is no point in cleaning up the raw AC input to the drives. These devices are power switching to motors, not audio amplifiers! I hung a 'scope off the DC supply to my drivers some time ago and saw something like a 10V 100Hz ripple across the smoothing caps and the drivers clearly weren't worried about that - they've been working for a few years now quite happily. There are things that need close attention, like good earthing techniques, keeping noise-producing high power cables away from low-level sensitive feeds to inputs, but the basic supply to the drivers can be pretty crude by comparison. In fact, a simple linear power supply will beat the pants off a switched-mode supply when it comes to feeding stepper drivers as you have to drastically over-spec the SMPS to cope with the odd peak load which causes it to go into shutdown or some other protective mode where the linear supply just dips a bit and carries on.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Clive S
What are you on about:beguiled: You can supply a drive with a toroidal, rectifier and some caps ie DC or just use a toroidal and use the rectifier and caps in the drive.
I think you are going overboard a bit here and frightening new users into things they just don't need:jaded:
No no no, I’m asking the question of experienced users. I’ve only got experience of an openbuilds machine at present and haven’t had the pleasure of building a larger CNC so the op’s question and your reply about mains fluctuations made me think about running tests on the local power grid.
I can’t remember the figures from my last test but I do have the kit still.
I still remember the time back in Cannock where I was sitting in offices and suddenly the ceiling fans turned into scary propellers. Turned out the distribution centre had supplied twice the rated frequency for a while... blew a ton of mainframe terminals throughout the building and only the fact that it tripped the generators protected the two mainframes we had downstairs (IBM 370/158 and IBM 3033).
That truly is a worst case scenario but check your local power. Mine is ruddy awful at times, especially around 6pm. My oven is flashing the clock timer at me because we had a brownout yesterday.
But ultimately I don’t know much about mains system and I haven’t touched anything 3 phase or high voltage this millennium... so I’m very much the noob asking questions.
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Re: Was about to get a toy- then I did some research...
From what Neale said made me do a facepalm... not at him, at me. Of course the driver will clean it up. I’m a moron.
Sent from my iPhone using Tapatalk
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Neale
but the basic supply to the drivers can be pretty crude by comparison. In fact, a simple linear power supply will beat the pants off a switched-mode supply when it comes to feeding stepper drivers as you have to drastically over-spec the SMPS to cope with the odd peak load which causes it to go into shutdown or some other protective mode where the linear supply just dips a bit and carries on.
Neale is 100% spot on and using an SMPS is asking for trouble because at some point it will bite you when it goes into protection mode. KISS works for CNC no need for over complicating the job with Surge protectors or UPS, DHL, FedEx or any other courier service...:hysterical:
Now back to these drives and the Question of AC or DC. I've used these drives with both AC & DC and in terms of performance, I've seen no differences.
However, I've never run them on machines working in harsh conditions regards power fluctuations, etc but I suspect that if the mains supply was prone to fluctuations or was a little dirty then using a DC supply would be less stressful on the drives due to larger Caps being more capable of smoothing out the power than the little caps that will be used on the individual drives.
Now I'm not into electronics so I don't know if when using a DC supply the drives still use their onboard Caps as extra smoothing.? . . my gut says they probably do.!
But that said I would always go with the simple approach if normal conditions so AC is easier and cheaper. The machine doesn't care if you run it on Everyready battery's so long as it gets a nice supply of power when it asks for it.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Now I'm not into electronics so I don't know if when using a DC supply the drives still use their onboard Caps as extra smoothing.? . . my gut says they probably do.!
If they use the same input connections for DC as AC as I assume they do then the rectifier and capacitors must still be in the circuit.
One other thing to consider: If you add an additional rectifier and capacitors to make a DC supply for an AC driver you will also increase the inrush current to the transformer and increase the risk of trips. Adding more capacitance for the sake of it to any DC supply (making Neale's audio amp PSU instead of a motor driver one) will have the same effect.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
If they use the same input connections for DC as AC as I assume they do then the rectifier and capacitors must still be in the circuit.
One other thing to consider: If you add an additional rectifier and capacitors to make a DC supply for an AC driver you will also increase the inrush current to the transformer and increase the risk of trips. Adding more capacitance for the sake of it to any DC supply (making Neale's audio amp PSU instead of a motor driver one) will have the same effect.
Yup. My brain was in full “doped up on morphine mode”... which is why I did a facepalm. It’s the reason I had to quit work. Not asking for sympathy, just stating the way things are. I seriously do not know this tech, BUT I WANT TO LEARN. It’s better to ask questions and act a fool than profess to be an expert and tell people incorrect info because “Well it works for me so must be okay”. A lot of my expertise is 20 years out of date and worked with super delicate security systems that required strong, stable power sources to detect intrusions. These days you could build the same thing for lest than 50p with tech from Asia.
But I love making things which is why I got into CNC in the first place. Anyhoo... I’m going to shut up until I can reduce my meds come spring.
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Re: Was about to get a toy- then I did some research...
Don't fret mate!
My radio/TV background doesn't allow for much ripple on a DC power supply so I was expecting to see huge quantities of expensive smoothing capacitors on a linear supply of the sizes discussed here. For this application you don't need that much.
I'm not brainy enough to use Faraday's Law to work out the inrush for a given transformer, but I suspect you need a pretty chunky lump of iron for that to be the only significant contributor to the overall inrush.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Kitwn
Don't fret mate!
My radio/TV background doesn't allow for much ripple on a DC power supply so I was expecting to see huge quantities of expensive smoothing capacitors on a linear supply of the sizes discussed here. For this application you don't need that much.
I'm not brainy enough to use Faraday's Law to work out the inrush for a given transformer, but I suspect you need a pretty chunky lump of iron for that to be the only significant contributor to the overall inrush.
Hah... try doing math when your head is on the equivalent of 10 pints of lager. I read some of the posts here and go, “Errr... what the heck? The drives can take AC direct from the transformer... that ripple is going to be awful!”, without thinking it through that the drive itself will do the cleaning.
This is the problem with someone who knows a little bit of knowledge and thinking they know what to do (that’s me btw). Unfortunately, microelectronics which is VERY pick about power stability and a CNC drive that is going to take 60v from an AC transformer is two very different things.
Unfortunately I won’t be able to get my kit for at least a month apparently... nobody appears to be working at the factory/distributors in China. They are talking 2 weeks to even start back up again and maybe longer.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Do not rely on the OV protection of these drives, they will not save you from more than just a few volts. So if you get a spike then they will fry them.
They are good drives provided you leave a good safety margin.
You need to leave at least a 10% safety margin on the voltage and I wouldn't run much above 60Vac with 70Vac Max.
Regards the Transformer I use 750Va with these drives without any issues. I wouldn't go above 750Va because you will get troubles from inrush.
Do NOT use a regulated PSU like as been suggested by one member as it could cause you troubles with voltage clamping.
Now this gets fun! So, given that I want steppers around 4Nm. They usually (based on my google searches) come rated at 4-5A and 2-3mH inductance meaning total drawn amps are in the range of (Atot_= 2/3*pcs*Arated) 10.5-13.5Atot and Vmax (=32*√mH) 45-56V.. Now based on what I've picked up in this discussion I want to give my drives as much voltage as possible (minding 10% safety margin) and restrict the PSU to 750VA due to inrush. Say I supply 60V to 70Vmax drives, that means the 750VA PSU supplies 12.5A of current i.e. steppers should be rated at 4.5A (~12Atot) or lower in order to get max performance out of them (naturally I could have higher rated steppers, but that would be wasted monies, correct?). Am I correct in this logic?
Moreover, is the performance of the steppers linearly related to the current supplied or is there some leverage at play, i.e. say I supply a stepper with 4.5A, now will a 5A (arbitrarily chosen) rated stepper perform equally well as a 4.5A rated stepper would?
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
Say I supply 60V to 70Vmax drives, that means the 750VA PSU supplies 12.5A of current i.e. steppers should be rated at 4.5A (~12Atot) or lower in order to get max performance out of them (naturally I could have higher rated steppers, but that would be wasted monies, correct?). Am I correct in this logic?
Well, it depends on how many drives you intend to use now and in the future. Maybe you might add a 4th axis.? In this case, the 750Va allows a little overhead. However, what I didn't mention so as not to confuse the issue is that I've also used 625Va without any issues. But I knew this machine wouldn't need 4th axis because it was fitted with a 4th Axis that was powered from a separate smaller PSU.
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Originally Posted by
Juranovich
Moreover, is the performance of the steppers linearly related to the current supplied or is there some leverage at play, i.e. say I supply a stepper with 4.5A, now will a 5A (arbitrarily chosen) rated stepper perform equally well as a 4.5A rated stepper would?
If using the Same Voltage then the 5A motor will have lower overall performance than the 4.5A motor. It will have a little more torque lower down the range but the RPM will be lower. This is mostly due to inductance because the higher current motor will have more inductance. It will also create more heat which robs performance.
In this case, half an Amp is neither here or there so wouldn't be a big difference and you'd hardly notice it. Thou any gains would be offset unless something else changed ie: Voltage. Everything comes at a cost.!
In a nutshell, Higher Amp's which often = higher inductance means higher voltage to reach the same speed. This is why often a 4Nm Nema23 will outperform a 4Nm Nema34 motor if using the same volts.
It's also why Large Nm Nema 34, 42 size motors require Very high or better still mains level voltages to allow any reasonable RPM's. All the machines I build that use above 8Nm motors use Mains voltage drives.
People often mistakenly think increasing the current will give more torque, which it does up to a point, but it also increases heat which affects the motor's saturation point which then creates resonance etc so stalls at lower RPM.
It's a complicated formula with several twists depending on motor spec, wiring, etc also with the advent of Digital drives allowing much better performance then Old Vmax (=32*√mH) Formula is even less relevant because the motors can be pushed harder and heat is controlled better along with resonance.
All I can tell you is that if you run the motors at the Rated current with a Voltage 10% lower than the drives Max V you'll be getting the best performance. If you need a little more Torque then increasing the current will provide a little extra but will cost in terms of heat and RPM.
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Re: Was about to get a toy- then I did some research...
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Originally Posted by
JAZZCNC
All I can tell you is that if you run the motors at the Rated current with a Voltage 10% lower than the drives Max V you'll be getting the best performance. If you need a little more Torque then increasing the current will provide a little extra but will cost in terms of heat and RPM.
After much googling and talking to my uncle who's an electrical engineer I think I've got my head around the basics of this. One thing i still find confusing however is that logically you'd want to run the motors at they're rated current but I keep reading that the drives only draw 2/3 of that assuming parallel wiring (hence psu should be sized 2/3*Atot). Now, are the drives able to supply the motors the full rated current even if only 2/3 of that is supplied by the psu (through some magic I don't understand)? Or is this 2/3-rule applied simply due to the fact that the motors are seldom simultaneously drawing all of their rated current?
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Re: Was about to get a toy- then I did some research...
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Originally Posted by
Juranovich
Or is this 2/3-rule applied simply due to the fact that the motors are seldom simultaneously drawing all of their rated current?
I think its that you'd never power all phases of the same motor to 100% of their current at the same time? But I'm sure one of the electronics experts around here will come up with a much more detailed answer! The 2/3rds rule is for parallel wiring, and for series wiring you can get away with 1/3rd.
I'd wager the answer is in here: http://homepage.divms.uiowa.edu/~jones/step/index.html (I just don't have the time to read it all!)
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
Juranovich
After much googling and talking to my uncle who's an electrical engineer I think I've got my head around the basics of this. One thing i still find confusing however is that logically you'd want to run the motors at they're rated current but I keep reading that the drives only draw 2/3 of that assuming parallel wiring (hence psu should be sized 2/3*Atot).
Be careful here when talking with electrical engineers ie: Domestic electricians or maintenance electricians because while they know how electricity and how circuits work etc I find they don't always understand or realize how different a Stepper driven machine differs to say typical AC motor system.
A stepper drive uses a chopping system to control the current/voltage that steppers require so it's not straight forward in terms of power draw etc like it is with say an AC motor connected straight to mains voltage.
The drives use a chopping system which uses PWM which only draws current 50% of the cycle on time. This power is taken from the capacitors in the DC system (AC drives just rectify inside the drives to DC) so during the Off cycle time the capacitors are recharging so only drawing power 50% of the time.
This is one of the reasons why the PSU can be sized lower than total Motor ratings. The other reasons being Not all Motors will draw full current all of the time and if they do then it's for very short periods and the Capacitors and drives will deal with any shortfall.
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Originally Posted by
Juranovich
Now, are the drives able to supply the motors the full rated current even if only 2/3 of that is supplied by the psu (through some magic I don't understand)? Or is this 2/3-rule applied simply due to the fact that the motors are seldom simultaneously drawing all of their rated current?
Above should explain this hope fully.! . . . . Don't try to overthink this, I understand the need to understand how it works but if you want to build a good machine then what's been suggested will work great. You could spend weeks or months learning how it all works and you'll still end up back at what's been suggested.
Go with what's proven to work and you won't go wrong.
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Re: Was about to get a toy- then I did some research...
The rated current of a stepper motor is the maximum permitted continuous current in each winding. This will flow in the windings when supplied at the rated fixed voltage, something you will never do in practice for the reasons Dean has outlined above.
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Re: Was about to get a toy- then I did some research...
Quote:
Originally Posted by
JAZZCNC
Above should explain this hope fully.! . . . . Don't try to overthink this, I understand the need to understand how it works but if you want to build a good machine then what's been suggested will work great. You could spend weeks or months learning how it all works and you'll still end up back at what's been suggested.
Go with what's proven to work and you won't go wrong.
This! Even though I'll probably end up building my machine according to the various suggestions I've got, I still cannot bring myself to do something without having built an understanding of my own of the matter. Hence, the occasional silly questions :)