View Full Version : Power For Drivers

07-08-2007, 08:34 AM
I've just been looking at this post on the PMinMO forum from another fella that was powering his machine with a pair of piggybacked PC power supplies:

Actually toasted a few......

I have built several boards, all test out using the measurement of voltage and jumpering enable and step.

Solder in chip with low volt iron, set voltage with pot.

Set computer to setup settings given in this section.

Step motor and it steps once and poof!

He's not happy. This keeps happening. Wiring everything up, it's all humming. THen he takes a step... Blat. The consensus is that it's the lashed up PSU he's using. PC PSUs aren't good for CNC work by all accounts. It's resolved in the end though:

It looks like it was the power supply. Tried a linear 24v supply and the driver and interface board works!

Just thought this was worth pointing out.


Lee Roberts
07-08-2007, 11:49 AM
OK, thanks for that Charlie.

Looks like i need to source a power supply then, i'v got a laptop 24v Switched Mode Power Supply here i'm thinking i can use that ?

PRI.: 100-240 ~ 50/60Hz 1.8A MAX
SEC.: 15 / 16 / 18 / 19 / 20V - 6A 120VA MAX 22 / 24V - 5A 120VA MAX.

Would this be any good ?, i'v seen this power supply supplied with other controllers/drivers so i'm think it will be any advice on this ?

If you want any BEARINGS ABEC 5 - 8 PACK, i'v got a few sets for sale. i'm using them for my drive rod support.

Lee Roberts
07-08-2007, 12:19 PM
I'v just found these as well could you take a look and advise me please:

http://cgi.ebay.co.uk/24V-8A-200W-switc ... dZViewItem (http://cgi.ebay.co.uk/24V-8A-200W-switched-mode-power-supply-psu-smps-fan_W0QQitemZ200138651035QQihZ010QQcategoryZ58288Q QssPageNameZWDVWQQrdZ1QQcmdZViewItem)

http://cgi.ebay.co.uk/BN-Cabur-Power-Su ... dZViewItem (http://cgi.ebay.co.uk/BN-Cabur-Power-Supply-X-2-Single-Phase-24V-5A-120-230V_W0QQitemZ190137801341QQihZ009QQcategoryZ60839 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)

Lee Roberts
07-08-2007, 12:22 PM
See have a look at this ebay listing it has the same one as what i'v got: Ebay link (http://cgi.ebay.co.uk/4-Axis-CNC-Stepper-Motor-Driver-Controller-lathe-mill_W0QQitemZ250151218866QQihZ015QQcategoryZ26209 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem)

08-08-2007, 08:00 AM
for cnc use , i prefer old fashioned transformers , unless they are small steppers , for say a foam cutter , don't use switch mode power supplys , and be careful of pc power supplys , some of them need an additional mods to work satisfactory , just a standard transformer , diode bridge and capacitors as a guide , you need to be able to produce between 24 - 40v @ 10 - 20A

do not take the stepper voltage as a guide to power supply voltage ,
add the current rating of all the steppers and you need a supply that can give as a minium 2/3's of this
3 steppers @ 4A Each = 12A , so as a absolute minium you need an 8A supply

Lee Roberts
08-08-2007, 10:27 AM
Ok thanks for that info basher, my motors are listed below.

I managed to get them really cheap 19.90 each.

Motor Length: 76mm
Shaft Dia: 6mm
Step Angle: 1.8
Max Rated Volts/Current/Phase: 40vdc/4.2amp/2 phase
Holding Torque: 180N.cm - 254 ozf in
Leads: 4

09-08-2007, 08:07 PM
You need to be careful of how much current you push through the drivers too... It'll be in the documents you got with your driver boards. I am not an expert - by any means - but I'll be happy to look over any docs you've got.

You can achieve anything. You've just got to know the right people to ask, mainly! And the thing about t'internet -there's loads of people to ask!

As for the bearings - I'll BEAR it in mind hahahaha.


Seriously, I think I'm ok for the mo', ta.


^-- tha's me in a fancy hat

Lee Roberts
10-08-2007, 12:22 AM
lol ok np's ill pull out the paper work for the drivers tomoz and let you know.

24-08-2007, 05:19 PM
It's not just a matter of matching what's stated on the tech data sheets... but also a matter of meeting the actual peak demands of the motors when you have wired them to suit your needs.. you have to confirm that what you think is happening is what is actually happening...

Using your data as an example. Most specs are per "active" phase. that means what the motor will require with a single phase active. You state that your motors are 2 phase... however this means nothing really.... internally they might well be 4 phase motors pre-wired to run as 2 phase but with 2 actual phases active per step... this would double your current requirements at peak load if it were the case, unless the supplier has worked this out for you already and supplied this data as the rating.

I would guess that they are bipolar parallel wired internally and that the stated load of 4.2 amps is actually for 2 active phases... but this is just a guess as it common for "2 phase" motors to be supplied in this configuration.. it gets twice the torque out of the motor so manufacturers tend to do the wiring for you internally and you have less to worry about.... but you do need to confirm this is the case before spending the pennies buying something to match.

If you have this motor on all 3 axes then you would be looking for something that can output 24 - 42 v at a maximum current of 10 - 12 Amps.... generally speaking you will only ever draw about 2 thirds of the motor peak current load. It's not necessary to give the motors every volt they can use as it's doubtful that you will ever be running them flat out. Motor speed will be more governed by the acceleration and deceleration loads that you machine structure can handle than what the actual motors are capable of.

Generally speaking Voltage = Speed and Current = Power much more important to get current load sorted as this effects your torque ... most of the time you will probably be in the lower part of motor speed range but will want maximum torque... steppers supply most torque in the lower speed ranges anyway.

hope this helps....

Lee Roberts
24-08-2007, 08:53 PM
Yea it seems i cant use my motors at the full AMP's unless i upgrade my drivers and that isnt going to happen due to funding. I'm posted to your other posts on my outher posts < :? lol

I think i may start a new post where we can address verything in one go yohodi.