ebay board kits v 542 boards

so in another thread that i hijacked http://www.mycncuk.com/forums/showth...-Driver-Boards

i thought id start another.

i found this http://www.ebay.co.uk/itm/CNC-Router...item2a1a92096e
on ebay after being told the all in 1 boards are Cr@p,

seems alot more expensive than this
http://www.ebay.co.uk/itm/3-AXIS-CNC...ht_5121wt_1052

as i need motors etc. this is my first build so any advise on the above links..

ie what motors and psu would be suitable.

my first table will be say 4x4 to start but theres always an upgrade in size.
mainly cutting mdf and ply... perspex/acrylic

thanks

Just dinnae go near TB6560 based drivers, they are a short route to frustration.

Have just blown second 6560 in less than a month, guessing its actually back emf that kills them, this one was Y axis driver after fine engraving, lot of Y back and forth think the driver either thermally cooks or direction change kills the output devices.

Most expensive is having a piece of equipment sitting idle waiting for parts.

Personally thinking either 542 or Gecko boards to replace the fragile 6560s...

http://www.charter-controls.com/inde...b_y=0&offset=5

4X4 is actually a large table and cost of motors and drives will be a small part.

Cheers
Adam

Don't go anywhere near either of those.!!. . . Bad news.

I urge you not to rush into buying any motors or drives, psu etc untill you have fully got the design and know the components like ballscrews pitch etc and mass to be moved.

One of the biggest mistakes folks new make is to rushout and buy motors etc then regret it because they either arn't large enough or just plane rubbish like the ebay offerings.
The other often misunderstood is voltage and it's very common for folks to buy too lower voltage PSU's that don't get the best out of the motors. the other is to buy drives with too low voltage limit.
Stepper Motors work best with high voltage, a typical motor would be nema 23 at 3nm. These motors perform best with around 60-70V but it's very common for people to buy drives with a 50V limit and even more common to use 36V psu's with these drives. (Namely because they are sold in kits like this from suppliers like cnc4you etc or the only PSU's they supply are 36Vor 48V)
So as you can see the machine would be quite crippled with a setup like this and trust me it happens often because I'm always helping people who have been sold this kind of setup.

It's not difficult choosing the right setup but does need carefull attention and really if you want to get it right first time then don't try saving pennies because it will cost you pounds further down the line and lots of frustration.

Decide on the machine size, style and it's components then ask. Then and only then start buying expensive items which are critical to a good cnc machine like drives and PSU's, motors are relatively cheap in the grand scheme but can easily be crippled with the wrong choices.

thanks all for the replys, ive gone with the m542 drivers... so now ill be needing motors and psu...
what would we sudjest.. ive thought about it a like my work tools id like to invest in parts that i dont need to upgrade...
what do you think. have i made a mistake in choosing the m542 drivers, they arrived today...

m542 drivers are good, glad yours arrived.

3Nm motors will be good for that size. You could get away with slightly smaller motors but the cost saving is minimal so I wouldn't bother. These are currently the cheapest:

http://www.cnc4you.co.uk/index.php?r...&product_id=67

You want a PSU just short of 50V. The cheapest way is to buy a toroidal transformer (500VA minimum for four 3Nm motors, 35V max), bridge rectifier and capacitors to make your own PSU.

so hows this psu.... 48v 12a,,

http://www.ebay.co.uk/itm/600W-PSU-4...e#ht_500wt_715

That's good, but not the cheapest.

http://www.rapidonline.com/Electrica...-0-35v-88-3839

(They come up cheaper on eBay quite regularly.)

With capacitors and bridge rectifier (£5 max) will be just as good if not better. You can find the circuit on google easily...

Quote:

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Originally Posted by Jonathan

That's good, but not the cheapest.

http://www.rapidonline.com/Electrica...-0-35v-88-3839

(They come up cheaper on eBay quite regularly.)



With capacitors and bridge rectifier (£5 max) will be just as good if not better. You can find the circuit on google easily...

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sorry im confused, you said a transformer around 50v, the one in the link is 0-35v.. what cap and bridge rectifier would i need...

also is there a thread or diagram i could use...

Quote:

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Originally Posted by crossleymarko

sorry im confused, you said a transformer around 50v, the one in the link is 0-35v.. what cap and bridge rectifier would i need...

also is there a thread or diagram i could use...

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Due to the capacitors the open circuit voltage will be the peak voltage, not the RMS voltage of the sinusoidal waveform from the transformer. To (approximately) find the ouput voltage you therefore multiply by the square root of 2 and subtract about 1.2V for the diode forward voltage, hence 35*2^0.5-1.2=48.3V.

Bride rectifier:
http://www.rapidonline.com/Electroni...ctifiers-66254

Capacitor (3 or 4 in parallel):
http://www.rapidonline.com/Electroni...acitor-11-2993

The transformer has two 120V primary windings, so you connect them in series to get 240V then connect that to the mains via a fuse. There are two secondaries and you want the rated voltage, so put them in parallel to keep 35V but get twice the current and connect those two wires to the AC terminals of the bridge rectifier (marked '~'). The output waveform will now look similar to a loch-ness monster, so connect all the capacitors in parallel with the + and - terminals of the rectifier and double check the polarity is correct (if not they literally go bang).
If you're not sure then read up on it or just get the PSU on eBay.

quick search and found this...http://www.e-dan.co.uk/electronics/wiringtrans.html
im confident in doing this but need steering in the right direction... are all the wire colours on the tororial universal...?

Quote:

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Originally Posted by crossleymarko

are all the wire colours on the tororial universal...?

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Try this one:
http://www.arceurotrade.co.uk/projects/PSU/index.html
(I notice that diagram has fuses on the secondary side, however I did not include them since each stepper driver already has an internal fuse to protect against over-current. Also any 'nuisance' blowing of that fuse could damage the stepper drivers.)


The colours are not universal, however there is always a clear diagram on the transformer which labels which colour is which.

Quote:

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Originally Posted by Jonathan

Also any 'nuisance' blowing of that fuse could damage the stepper drivers.

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No the fuse is on the supply input. Stepper drives are damaged when the motor supply leads are interfered with.

Quote:

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Originally Posted by John S

No the fuse is on the supply input. Stepper drives are damaged when the motor supply leads are interfered with.

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It's on both sides in the diagram on Arc Euro. Stepper drivers can be damaged if the power wires are suddenly unplugged for similar reasons to doing the same to the motor wires. It's less likely but still possible since interrupting the current causes a high dI/dt which will cause a voltage spike.

ok so in stead of a couple caps.. hows this one...

http://www.rapidonline.com/Electroni...acitor-11-3234

Quote:

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Originally Posted by crossleymarko

ok so in stead of a couple caps.. hows this one...

http://www.rapidonline.com/Electroni...acitor-11-3234

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You would still ideally want two of those. No reason to spend £10 on a high quality capacitor when three £0.82 capacitors in parallel will do the job better.

Quote:

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Originally Posted by Jonathan

It's on both sides in the diagram on Arc Euro. Stepper drivers can be damaged if the power wires are suddenly unplugged for similar reasons to doing the same to the motor wires. It's less likely but still possible since interrupting the current causes a high dI/dt which will cause a voltage spike.

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So what happens when the onboard fuse goes or does that behave differently ?

overkill is my theory for future upgrades.. same with the transformer. what would you recomend for overkill..
also i read it as your stepper is rated at x volts. how is the homebrew psu regulated.. to said volts..

Never rely on colour codes being universal, not even from the same maker, just something I found out.......

Colours for the trafo linked to by Jonathan are in the PDF:

http://www.rapidonline.com/pdf/88-3781.pdf

Grey and Violet are joined, Blue is Neutral, Brown is live on primary.

Orange and Black joined are 0V

Yellow and Red joined are +V on secondary

Steppers are current driven rather than voltage, the drives take care of the current regulation just need a stiff enough power supply and will drive enough volts through to maintain current.

Cheers
Adam

so orange and black is -v on the secondry... think i get it. how you worked that out i have no idea.. as grey is 115v and violet is 0 volts.

also on the description ie. 500va 0-35 0-35.

does this mean its 70v output.

Quote:

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Originally Posted by crossleymarko

how you worked that out i have no idea.. as grey is 115v and violet is 0 volts.

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The position of the black dot on the diagram shows the relative polarity of the windings, so if a primary wire with a dot is connected to one without, and the other two are connected to the mains that's correct for 230V. If the dotted wires are connected together, then to the mains and similarly for the wires without the dot then the primary windings are in parallel and in phase, so 115V is required - i.e. ideal for the countries with 115V mains (e.g. USA). Any other connection is not permitted since it will involve connecting the windings 180° out of phase, so they'll approximately cancel and you'll get nothing.

Quote:

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Originally Posted by crossleymarko

also on the description ie. 500va 0-35 0-35.

does this mean its 70v output.

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If you put the two secondary windings in series then yes you would get 70V, however we want them in parallel to get 35V at twice the current as if they were in series. Most transformers are wound with at least two secondaries to give you this option.

Have a read through Section 8.2 of this:
http://sound.westhost.com/xfmr2.htm , you are looking at toroidal transformers, doughnut shaped, so you can be 99% certain that parallel operation is safe but it is well worth the time to quote:

Quote:

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The transformer manufacturer's specifications will indicate if parallel operation is permitted. If you are unsure, measure the voltages carefully, and avoid parallel connection if the voltages differ by more than a couple of hundred millivolts. There will always be a difference, and only the manufacturer's winding tolerances can predict what it will be. With toroidal transformers, the windings are often bifilar, meaning that the two windings are wound onto the transformer core simultaneously. The tolerance of such windings is normally very good, and should cause no problems.

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Sections 8.1, 11.3 and 12.1 are also worth a quick once over.

This is a must read for anyone playing with mains: http://sound.westhost.com/articles/electrocution.htm

If you're bored then http://sound.westhost.com/xfmr.htm is also worth looking at. In fact bookmark the site for a rainy day, there's lots of info in the Articles part and a lot of good projects too. Rod Elliott, the site owner is knowledgeable and well respected, if you are ever uncertain about anything electrical then it's always worth a visit to see if Rod has any advice.

Quote:

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Originally Posted by Jonathan

The position of the black dot on the diagram shows the relative polarity of the windings, so if a primary wire with a dot is connected to one without, and the other two are connected to the mains that's correct for 230V. If the dotted wires are connected together, then to the mains and similarly for the wires without the dot then the primary windings are in parallel and in phase, so 115V is required - i.e. ideal for the countries with 115V mains (e.g. USA). Any other connection is not permitted since it will involve connecting the windings 180° out of phase, so they'll approximately cancel and you'll get nothing.



If you put the two secondary windings in series then yes you would get 70V, however we want them in parallel to get 35V at twice the current as if they were in series. Most transformers are wound with at least two secondaries to give you this option.

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so secondry in series on the diagram would be red 70v+ , yellow and black joined. orange -v

sorry here is a good detailed page.. http://www.routoutcnc.com/PowerSupply.pdf

ok so i got it, apparently times your ac voltage by 1.4... right gonna go with it i think.. been looking at maplins,?

off the shelf 225va 2x35 3.2a,39.99. not as good as your link to rapid johnathon, i know but what do ya think.

thanks all

Quote:

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Originally Posted by crossleymarko

ok so i got it, apparently times your ac voltage by 1.4... right gonna go with it i think.. been looking at maplins,?

off the shelf 225va 2x35 3.2a,39.99. not as good as your link to rapid johnathon, i know but what do ya think.

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The proper figure is the square root of 2, which is roughly 1.412, however the rated output voltage of the transformer is with the it under the rated load, so off load the voltage is normally a few percent higher, and you need to allow that mains voltage can drift up and down, so you need to allow some margin for error.

Also check out http://www.airlinktransformers.com/ for transformers.

thanks what range of va am i looking at. ie 300va 0-35 0-35

Quote:

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Originally Posted by crossleymarko

thanks what range of va am i looking at. ie 300va 0-35 0-35

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For 4 motors you want a minimum of 500VA.

Quote:

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Originally Posted by John S

So what happens when the onboard fuse goes or does that behave differently ?

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That fuse is a much higher current rating than what you might expect (20 amps if I recall correctly). If it blows the driver is probably already gone so I bet it's more there to prevent fire.

so would 600va 2x35v cover me for all motor upgrades... dont wanna be spending twice...

why would you use axis a by the way for milling... ?

add vat to the rapid prices,, doh,,! another tenner mate. 49.50 so with caps etc how much do you acctualy save?

Quote:

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Originally Posted by crossleymarko

add vat to the rapid prices,, doh,,! another tenner mate. 49.50 so with caps etc how much do you acctualy save?

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Not so much how much you save but how much better for the drives and your machine it will be.? . . Well worth it my reply.!!!
(Remember the drives debate and back EMF in the other post.!!)