MechMate CNC Router Forum

Go Back   MechMate CNC Router Forum > Electrical & Electronic > 702. Power Supplies
Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Reply
 
Thread Tools
  #1  
Old Fri 28 March 2008, 12:45
kalimero
Just call me: kalimero
 
buffalo
United States of America
Need help with selecting power supply for 3X Keling motors

Hello to all,

Can somebody recommend power supply to mach my other parts :

3 stepper motors KL34H295-43-8B 906 oz/in. from kelinginc.net
3 gecko drivers G202
1 PMDX-122 board


Thank you
Reply With Quote
  #2  
Old Fri 28 March 2008, 13:07
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Have you made any calculation yourself? What do you think is the right supply voltage and VA size?
Reply With Quote
  #3  
Old Fri 28 March 2008, 14:27
kalimero
Just call me: kalimero
 
buffalo
United States of America
I don’t a have any experience with that , but if I am right 70V and 400-600 VA ??

like ps-4n70 http://toroid-transformer.com/PS-4Nxx.pdf

Correct ??

Last edited by kalimero; Fri 28 March 2008 at 14:51..
Reply With Quote
  #4  
Old Fri 28 March 2008, 21:48
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
You have several choices in wiring the motors. The Keling KL34H295-43-8B motors can be wired Bipolar Parallel, Bipolar Series or Half-Coil. If you wire the motors either Bipolar Parallel or Half-Coil, you should use a power supply that gives less than 57VDC (~40VDC would be my preference). If you wire the drives Bipolar Series, you could use a power supply up to 80VDC (~70VDC would be my preference).

The steppers can pull up to 6.1A Bipolar Parallel, 4.27A Bipolar Series, or 3.01A Half-Coil. Multiply the amps by the number of motors to get the required current rating of the power supply. (3X6.1 = 18.3A, 3X4.27 = 12.81A, or 3X3.1 = 9.3A). When you have found the Amps required, multiply the amps by the voltage to get the VA rating of the transformer (57X18.3 = ~1,000VA, 80X12.81 = ~1,000VA, and 57X9.3 = ~500VA).

Be sure to select the proper current set resistors for the stepper motors. (Bipolar Parallel 47X6.1/(7-6.1)=~320K, Bipolar Series 47X4.27/(7-4.27)= ~75K, Half-Coil 47X3.1/(7-3.1)= ~37K.

Be conservative and specify a power supply that produces a little less voltage than the maximum allowed for the wiring method chosen and a little more than the VA computed. The drives will only pull as much current as they need, so having a power supply that can supply more current than needed will mean that the power supply will run cooler and last longer than buying the minimum size required. Using less voltage than allowed will also mean longer life from the components will only a slight decrease in speed. My rule of thumb is to use about 25% less voltage than the maximum allowed (unless the maximum allowed is more than 80VDC, then I automatically use 70VDC.)
Reply With Quote
  #5  
Old Fri 28 March 2008, 22:59
kalimero
Just call me: kalimero
 
buffalo
United States of America
Thanks for your reply,

I send email to John from http://www.toroid-transformer.com and he recommend to me : PS-8N63R12 (800W 63V +12V for PMDX-122 board).
Reply With Quote
  #6  
Old Sat 29 March 2008, 01:52
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
There are various opinions on selecting the power supply voltage. These range from conservative:

Quote:
Originally Posted by Richards View Post
My rule of thumb is to use about 25% less voltage than the maximum allowed (unless the maximum allowed is more than 80VDC, then I automatically use 70VDC.)
as opposed to "risky":

Quote:
Originally Posted by Dirk View Post
I prefer to increase voltage as opposed to current to push a motor.
Well, what is the risk?

If the voltage is selected too high, the danger is damage to the drives and motors. We know that Gecko's are nominally limited to 80V (they are designed for higher, but let's not venture into that territory). I have had no problems with 75V for the Gecko's.

The motor power/torque output at a given speed is directly proportional to the voltage. Reference. Cut the voltage by 25% and you cut the power/torque by 25%. Therefore we want to keep the voltage as high as possible, without putting the motor at risk of burning out or shortening its life.

It is difficult to decide this voltage limit purely by doing a calculation. There are some guideline formulae applied, but the results can be off the mark. The best is to find someone who is using the same motors in the same application and enquire about their heat vs voltage.
Reply With Quote
  #7  
Old Sat 29 March 2008, 06:40
revved_up
Just call me: Craig
 
Hartland, MI
United States of America
Kalimero,
John suggested that same power supply to me and that is the one I purchased I haven't connected it up yet so I don't have any more information for you but it is fairly large in size 9"x6" so plan for space accordingly
Reply With Quote
  #8  
Old Sat 29 March 2008, 08:33
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The 63VDC unit is a little low for Bipolar Series and too high for Bipolar Parallel or Half-Coil. As Gerald pointed out, the higher the voltage the better the performance (as long as you know the ideal voltage for the motor and the maximum voltage for the Geckos). The maximum voltage for your motors, when wired Bipolar Series, is 114VDC; however, the Geckos have a maximum voltage of 80VDC, and because the power company can't always supply exactly the AC voltage that it says it is supplying, it is prudent to limit the voltage to 75VDC, as Gerald suggested. As you can see, 75/114 = 66% of the ideal voltage for that motor when it is wired Bipolar Series. I like to get to 75% - 80% with the Oriental Motor stepper motors that I use. So, if I had your motors, I would probably wire them Bipolar Parallel. The data sheet shows that they have eight wires, so Bipolar Parallel will give you the maximum torque with those motors. The maximum voltage (using the Gecko forumla 1000 X SQRT(inductance) ) is 57VDC, so 40VDC - 45VDC is a good 75% - 80% compromise.

I know that the Antek power supplies are popular. As far as I have read, they are robust and reliable; however, I started out with a toroidal transformer from www.partsexpress.com and a PMDX-135-8020 power supply module. That way, I could select any toroidal transformer until I found one that most perfectly matched my needs. Because building your own controller means that you might be using different motors than others use, using the PMDX-135-8020 power supply module gives some flexibility in the design process I also have the luxury of owning a Variac transformer so that I can dial the voltage up or down. That lets me find a good compromise voltage between too little performance and too much heat. Then, after I've found the ideal voltage, I can buy a transformer that gives me that ideal voltage. (That's why designers charge so much - we have to be paid for playing with our toys.)
Reply With Quote
  #9  
Old Sat 29 March 2008, 09:36
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The 63V drive offered by Antek will not damage the Gecko's - that is comfortable.

If the general experience shows that the 63V supply does not overheat those Keling motors, then the 63V supply becomes the obvious choice.

However, if we did not have the luxury of experience, I would agree with Mike and say that the voltage is too high.

Has anyone figured out yet if Keling and Antek are related to each other?
Reply With Quote
  #10  
Old Sat 29 March 2008, 09:36
kalimero
Just call me: kalimero
 
buffalo
United States of America
Richards,
thank you for your help.
I don't a have any problem with making any parts for machine , but electric .
If I buy power supply like this one:

http://www.toroid-transformer.com/PS-8N50R.pdf

PS-8N50R12 50VAC 800W

I will be OK for start? (If I need change PS I can do any time later)

Thank you

1 more question:
can Iuse any type of power supply with output like :48-50 V 800W.
I have one whit this label on box.
Attached Images
File Type: jpg IMG_2060lnp.jpg (29.2 KB, 384 views)

Last edited by kalimero; Sat 29 March 2008 at 09:48..
Reply With Quote
  #11  
Old Sat 29 March 2008, 17:08
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
That power supply should work. You will probably need to add an external capacitor to help smooth out the ripple. A capacitor of at least 10,000uF will be big enough to help. 15,000uF @ 65V (working volts) would be better. The ripple is caused when the load (stepper motors drawing lots of current) drains the small on-board capacitors faster than the power supply can handle the current drain. (Most designers add an external capacitor to switching power supplies.)
Reply With Quote
  #12  
Old Sun 30 March 2008, 00:00
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
It looks like a Tyco NP0800 Datasheet.

Take some getting used to the 3.5 second startup delay. Hope you can access the output terminals. Otherwise a fine supply with the capacitor Mike is proposing.
Reply With Quote
  #13  
Old Sun 30 March 2008, 04:13
kalimero
Just call me: kalimero
 
buffalo
United States of America
Can I use this one :

http://search.digikey.com/scripts/Dk...name=P10025-ND
Reply With Quote
  #14  
Old Sun 30 March 2008, 05:38
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
That one will work, but how will you attach the wires? Rather use one with screw terminals.
Reply With Quote
  #15  
Old Sun 30 March 2008, 12:57
kalimero
Just call me: kalimero
 
buffalo
United States of America
Quote:
Originally Posted by Gerald D View Post
That one will work, but how will you attach the wires? Rather use one with screw terminals.

I can open and connect wires inside
Reply With Quote
  #16  
Old Sun 30 March 2008, 13:45
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I hope you are not talking of opening the capacitor - probably want to open the power supply. (In my last post I was talking of the capacitor - you can buy capacitors with screw terminals)
Reply With Quote
  #17  
Old Sun 30 March 2008, 15:42
kalimero
Just call me: kalimero
 
buffalo
United States of America
I talking about power supply.
Reply With Quote
  #18  
Old Sun 30 March 2008, 23:07
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
These "switch mode" power supplies, like you have, often have a fan inside for cooling. The covers must be on for the cooling air to flow correctly. We once burnt such a power supply because the fan had collected too much dust - they are not easy to keep clean.
Reply With Quote
  #19  
Old Tue 08 July 2008, 15:16
kaartman
Just call me: Koning #20
 
Abu Dhabi
United Arab Emirates
Please revise my calculations on the same motors as what Kalimero has, I have used the formulas as was explained on how to build your own power supply and comparing my numbers to that of Richards above confuses me, this is what I have done on unipolar connection, with 4 motors
Spec sheet info : 3.01V, 4.3A, 0.7 ohms, 3.3mH
1) 3.01V x 20 = 60.2 VDC
2) 32 x 1.816sqrtmH = 58.112 V (Mariss formula)
3) 60.02 VDC div 1.414 = 42.5 VAC
4) 42.5 VAC x 4.3A x 4 x 0.67 = 489.77 VA
5) 4.3A x 4 x 2/3 = 11.46 A

Where did I go wrong, I have noticed that some of the V and A values were mixed up in #4 above with the calculations but my numbers don’t make sense on the comparison with Richards.
What would be the formula to calculate the value of the Current Set Resistor, or how to choose the appropriate one?
Thank you
Koning
Reply With Quote
  #20  
Old Tue 08 July 2008, 16:02
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
This is how I would figure the MAXIMUM suggested voltage:

1000 * SQRT(0.0033) = 57.4 VDC

or

32 * SQRT(3.3) = 58.1 VDC

Both equations give similar results, certainly closer than necessary. Without some serious testing, that voltage is the MAXIMUM that you should use with those motors. I would drop the voltage to about 45VDC so that I wouldn't have to worry about overheating things. Taking a little more time cutting is more economical (for most of us) than replacing fried motors. Time is money, so you'll have to decide how close to maximum you want to go.

In the original post, you listed three motors, here you list four motors, so if we stick to four motors, then:

4.3A * 4 = 17.2A total

The 66% figure is a holdover from the older style round stepper motors. The square motors can use more current, so I don't derate the current requirement.

Using 45V as the desired voltage, 45 * 0.7 = 31.5 VAC transformer. A 30V transformer would be my choice.

30VAC * 17A = ~ 500VA

So, a 30VAC toroidal transformer rated at 500 VA would give you approximately 42VDC, depending on your line voltage. That would be my choice.

If you need full power and full heat, then a 40VAC toroidal transformer would give you ~56V, but you would have to use a 750 VA transformer to handle the (possible) current.
Reply With Quote
  #21  
Old Tue 08 July 2008, 23:04
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
My experience with square motors, toroidal transformers & geckodrives is that the .67 factor for de-rating the VA value is very much applicable. Our transformers stay cold.

I would go with a 500VA 40VAC transformer

When transformers get too big, they can cause problems with inrush currents and tripping your mains supply.
Reply With Quote
  #22  
Old Wed 09 July 2008, 01:33
kaartman
Just call me: Koning #20
 
Abu Dhabi
United Arab Emirates
Thank you, Gerald and Mike, nice to know that my math is correct due to all your input and explinations in the power supply thread.

Take care
Reply With Quote
  #23  
Old Wed 09 July 2008, 02:06
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
You also asked about the current set resistor for the drive.

There you must find the formula in the drive's instructions sheet. For unipolar, you will use the value 4.3Amp
Reply With Quote
  #24  
Old Wed 09 July 2008, 05:45
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
The current set formula is:

47 * 4.3A / ( 7 - 4.3A ) = 74.8K

Use the closest standard value 1/4W or 1/2 watt resistor or wire two resistors in series to get a value close to 75K. A standard value 68K resistor will allow about 4.15A, which should do the job.


-------------------------------------------------------------------------------------------------

Here's a response that Mariss made on Yahoo Groups, geckodrive forum, when asked about current requirements for square motors vs round motors. It was posted Dec 21, 2005 at 3:01 pm:

Re: Power Supply's

I think something got mangled in the reply. The 4 to 20 supply voltage
rule applies in either case (round or square). The power supply current
rule is 2/3 of the motor's rated current for round motors, equal to the
motor's rated current for square motors.

Mariss
Reply With Quote
  #25  
Old Wed 09 July 2008, 06:19
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, there is an experiment I want to do one day when I have G201 or G202 drive to hand . . . . . .

Disable its current reduction by changing the jumper, connecting it to a power supply and a stationary motor, and then measuring the AC current supplied by the transformer. Theory says it should be 1.4 times the current limit set by the resistor, but I have a suspicion it is a lot less, probably 1/3 less.

If the transformer current does indeed match the drive current, then the issue of current for square versus round motors is irrelevant. The drive doesn't know what is connected to it. Or, does the transformer current into the drive change according to the motor type, even if the resistor stays constant? I can't measure that because I don't have round motors.
Reply With Quote
  #26  
Old Wed 09 July 2008, 06:34
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,

I've got some old PH299 round motors buried under a lot of other stuff in a storage unit. If possible, I'll dig them out and try your experiment.

-----------------------------------

Here's a more recent post that Mariss wrote on June 4, 2008 at 6:43 pm that gives a brief explanation about the differences between round and square motors:

Re: choosing power supply

I suggest you can pretty much ignore winding resistance and winding
voltage. There are only two electrical specifications that matter:

1) Rated motor phase current. This is the more important spec. Use
this rating to select the drive's current set resistor value.

1a) Series or parallel? You have this choice if you have a 6-wire or
8-wire motor. No choice is needed with a 4-wire motor.

6-wire motor wired full winding = 8-wire motor wired in series. For an
8-wire motor use the motor datasheet specified series current rating.
For a 6-wire motor use 1/2 the datasheet specified current.

6-wire motor wired half winding = 8-wire motor wired in parallel. For
an 8-wire motor use the motor datasheet specified parallel current
rating. For a 6-wire motor use the datasheet specified current.

2) Motor inductance. This is the other important spec. It determines
the maximum practical power supply voltage for your motor. That
voltage is 32 times the square root of the motor inductance in
milliHenries. V = 32 * SQRT mH.

6-wire motors:
full winding inductance = 4 times the half winding inductance.

8-wire motors:
series winding inductance = 4 times the parallel winding inductance.

Explanation:

Motor power output doubles when you double the supply voltage. Motor
iron-loss heating quadruples when you double the power supply voltage.
This means motor heating outraces motor power output, placing a
maximum limit on power supply voltage. This limit can be calculated
from the motor specifications.

Back when most step motors were round, expensive and 6-wire, I came up
with a simple calculation that worked well: Maximum supply voltage
equals 20 times the motor's rated voltage. The underlying principle
always was the motor inductance but the equation hid it and the
necessity of pulling a square root. Times have changed.

Motors are square, inexpensive and mostly 8-wire. They are much better
than the best round motors. What makes them inexpensive also crashes
the old, simple equation; winding fill.

The round motors used nearly 100% wire fill (the windings filled
nearly all the available space on the stator). That kept the
resistance to inductance relationship constant (R = L^2). The newer
motors don't have 100% fill because oftentimes a smaller gage wire is
used. This disconnects the resistance to inductance relationship and
makes the '20 times rated voltage' rule inaccurate.

Mariss
Reply With Quote
  #27  
Old Wed 09 July 2008, 06:45
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, I would appreciate you doing those measurements - thanks!
Reply With Quote
  #28  
Old Wed 09 July 2008, 07:37
louisvd
Just call me: Louis
 
Gauteng
South Africa
Calculation help pls

Hi Gerald (hallo uit Gauteng)

I am not an electrical person at all, have been following your threads and did my calculation on the following :
3 x PK296BE-SG7.2
1 x http://www.hobbycnc.com/products/hob...er-board-kits/

According to my calculation I will need a 30VAC T/Transformer rated at 350VA.
Is this correct ?
Also do not know how to calculate what VDC the above will give me....
Very confused help please
Thank you
Reply With Quote
  #29  
Old Wed 09 July 2008, 07:48
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
If we think of a model that shows how a stepper driver works, sometimes that helps explain why an "inductance" or a "resistance" would act one way with a round motor and another way with a square motor.

As far as I've read, the Gecko stepper drivers use pulse width modulation. That means that instead of sending a steady 5V to the coils of a motor, it sends a series of voltage pulses to the coil. The pulse has an ON time and and OFF time. The longer the ON time is active, the higher the voltage the coils "sees". Since we know that we have a power supply that gives us many times the voltage that the motor can handle, the ON part of the pulse needs to be much shorter than the OFF part of the pulse.

Because of the inductance or resistance of the coil, after a period of time, the voltage is able to force enough current through the coil that the coil's voltage rises to an acceptable level. If the voltage keep pushing current through the motor, before long the voltage would rise to an unacceptably high level and the coil would overheat. That is the reason that for the short pulse.

I've been told that a round motor has characteristics that turn a square pulse into a triangle pulse. The square motor has characteristics that allow the square pulse to remain more square. So, if we think back to our days in geometry and think of the area of a triangle compared to the area of a rectangle, we have a visual model of why a power supply that feeds round motors could be rated at about 66% of the rated current. We also have a visual model of why a power supply that feeds square motors needs to supply more current.

(There are many other factors at play, so the visual model is just that, a model. It is not intended to be mathematically correct. It is only intended to explain an electrical phenomenon or characteristic of the two types of motors.)

Last edited by Richards; Wed 09 July 2008 at 08:08..
Reply With Quote
  #30  
Old Wed 09 July 2008, 09:46
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The rule of thumb for making a CNC power supply only 2/3 of the sum of the motor requirements has been around since before square versus round motors became an issue. I always thought this was because CNC builders never ran all their axes at the same time. I did find it odd that this 2/3 rule was happily applied to 4-motor router tables as well as to 3-motor milling machines and 2-motor lathes.

While running a motor hot the other day, I did put a clamp/tong ampmeter on the transformer output, and the readings were ridiculously low. The max I saw was 0.7Amp when the current limit resistor was set for 2Amp.

Our original ShopBot was supplied with a 300VA 48VDC switch mode supply powering 4 motors rated 2 Amp each. In my ignorance I upped the voltage without thinking of the impact on VA - so my replacement supply was a 300VA toroid transformer output 52VAC / 75VDC. That transformer has been going a good few years and stays close to room temperature. While the rule-of-thumb says the transformer should be 400VA, the 300VA is coping fine. (I have actually bought a 500VA transformer to replace it, but it seems a waste to put that in when the "small" one is coping so well)

I accept the square pulse versus the sawtooth pulse as being the basis for the one type of motor dawing more nett amps than the other, but I wonder what the transformer is seeing on the other side of the capacitor?

When my ampmeter gave me such low readings a couple of weeks back, it set me thinking of a dynamometer and a proper shunt ampmeter . . . . . there is just so much that I don't know!

However, I am cautious of de-rating the old rules-of-thumb until I have seen some solid test results.
Reply With Quote
Reply

Register Options Profile Last 1 | 3 | 7 Days Search Today's Posts Mark Forums Read

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 14:03.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.