Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: chevblue2 on April 27, 2008, 08:07:04 PM
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Hi
First post here and have a question on selection of a power supply for my bench top mill.
I am using a 3amp stepper3 3 axis control with 304oz 6v 2amp unipolar steppers.
Everything is wired and working,now my question is, what voltage and amp power supply would
you guys recomend?
I have read in past post art saying 60% amperage of all three motors.I have used 12v 10a with ok results.
In stepper3 manual 24v seems to be the max.
This is my first cnc project and I am planning on buying another 3axis control board but for now trying to squeeze
a little more out of this one.
Thanks in advance!
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Generaly if your control board says 24 VDC max I would not exceed that, typicaly if you were to use a 24 volt transformer, full wave bridge and some filter caps you would see about 28 VDC on the output. What exact controller board do you have a link to the manual would help out answering your question.
Kristin
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Thanks for the reply!
Cannot find manual on net
But the web site is stepper3.com
drive is stepper3 rev 0c model stepper3 roc
manual says 1v above and 6-10 times the amps listed on stepper when using a common power supply
When i use these v and amps(7-8v 12a), ipm and velocity must be set low or i lose steps
When i used 12v i got better performance but motors were getting warm.
Might be time for a better drive
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I took a quick look and cannot find the product, can you post a direct link to your board?
Kristin
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Stepper motors are normally run at several times their working voltage. It does not hurt them.
If your motors are rated at 2.0amps at 6 volts, then you would be better to run them at 24 volts, or even 30v. If your driver boards only go up to 24 volts them stick to that.
The driver board SHOULD have some way to limit the current output to each motor. Each driver board, therefore needs to be set at the motor rating - 2.0amps, so the current to the motor is not exceeded.
You therefore have your answer - your power supply needs to be 24volts - capable of giving 6.0amps. You needs a capability of 6.0amps just in case all motors are drawing 2,0amps simultaneously - perhaps not likely, but possible.
Your problem will be to ensure that, when the motors are not drawing full current, the voltage on your power supply will not rise above 24 volts and therefore damage your drivers.
On my system I use 2 x 12volt batteries in series to give 24 volts and as much current as I need - without any danger of exceeding the "safe" voltage of my drives. I have just replaced two of the drives with Gecko drives which are OK up to I think it is 70 volts, so really the problem does not arise - but my third driver, for my Z axis is a 24 volt 2.5 amp drive - so I have to keep within those limits.
I charge the batteries up overnight - no problem
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I just read you post again - for your second project I WOULD NOT buy a three axis board.
Buy three seperate single axis boards - if anything goes wrong you can change the faulty board - and you do not have to change the whole thing.
A little more expensive to start with, but much more flexible in the end, particularly if like me, you start to uprate your system and want to replace single boards.
My motors are 220Ncm motors rated at 2.5amps at 7.5 volts - but they are 8 wire motors. I bought 24volt 2.5 amp drives and wired the motors in series. The result was reasonable (to my mind) - but my speeds were dissapointing. I wired the motors in parrallel and the results were much better - a 7 fold increase in speed (later cut to 4 to increase accuracy) - but then my drives were not powerful enough to drive the motors - which needed more CURRENT.
As I say, I have changed the two main axis to Gecko drives - which give me capability of 7 amps at (I think) 80 volts - but I still run the third motor on the old Routout 24v 2.5amp drive.
I had one Gecko given, I had to buy one, (and the financial master turned her nose up at that), so I am not quite sure when I am going to get the third axis done.
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Jim,
you need to get yourself a new financial advisor :D
Hood
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I didn't say financial advisor - I SAID FINANCIAL MASTER
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Well get yourself a mistress :D
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The 60% (actually 66%) rule of thumb applies only to chopper drives. I think yours are LR drives. Check your documentation. If they are LR drives then your PS current will be more than the combined current of your motors - in some cases, substantially more.
If you can up your voltage to 24V then your motors will stall at roughly twice the speed thay do at 12V. However your PS current will also substantially increase. Without specs it's impossible to give figures. But you need to know these specs to avoid damaging your PS, drives and/or possibly your motors.
Uni-polar LR drives are ok for some jobs (often used in printers for example) but generally speaking they are cheap because - well they're cheap!
For your next project I'd recommend bi-polar chopper drives. There are many good makes available.
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Thanks to all with replies,you guys are great
Kristen heres the web site with the drive, sorry took so long for reply
http://stepper3.com/shop/product_info.php/cPath/54_64/products_id/51
Thanks for bi polar chopper drive info,
The motors i am running are 8 wire so i was looking ahead for next drive.
I think i can run the in bipolar and be 450oz
Anyway thanks for bearing with me!
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I just had a look at that site - the drives you are looking at seem to be 3 amp spec.
I also started with 8 wires motors - rated at 2.5amp @7.5 volts and thus bought some 2.5 amp drives.
8 wire motors have two pairs of two windings, and can be wired together in series, or parrallel - or just using a single winding
I wired mine in series. Without going into a lot of maths which we did in the last post (see "how do I wire my steppers") - if you wire the motors in series you use roughly 1/2 the rated current.
If you wire up using just one of the two windings on each side - you use the rated current.
If you wire up in parrallel - I think we decided you use 1.666 x rated current.
The big thing about it is the power from the motors. I was satisfied in series (my first go) I was pleased to have everything work - but could not get the axis speeds up above 4 ins per minute (48,000 pulses per inch) no matter what I did.
I decided to wire them in parrallel - and the difference was amazing - I could get up to 10 times the speed. Even using a single winding, I was up to 5 times the speed.
The problem was - of course - that having done all this - my drives were not powerful enough to sustain about 4 amps continuously - and I have now moved on to Gecko drives - which are rated up to 7amp at about 80 volts.
CHECK THE RATING of your motors and find out wether the quoted current is through one winding or two. If you measure the resistance of a single winding and check it against the spec that will tell you - E = IR - mine were 3 ohms resistance - which gave me 7.5 = 2.5 x 3 which told me that the quoted rating was for only ONE winding in the motor and there were two.
The drives you are looking at seem relatively expensive - so I think you should be able to perhaps invest in some more powerful ones which will staisfy your needs for quite some time.
Drives cards can be limited in current, so buying too big is not a problem.
Sorry is you have already worked this out.
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Just read through this thread again and I'd like to ask some (rhetorical) questions.
1) what is "root2" and how does it relate to the rectified/smoothed DC voltage of AC?
2) For an LR driver - what is the max current the PS will need to supply for 3x2Amp motors?
3) If a stepper motor is standing still (holding) what current is it "drawing"?
4) How many rated currents do 8 wire motors have?
5) what is "root2" and how does it relate to single, series and parallel wiring schemes?
6) Why can 2.5Amp chopper drives NEVER source 4Amps - EVER?