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
  #61  
Old Tue 06 August 2013, 03:38
KenC
Just call me: Ken
 
Klang
Malaysia
Your quest for world domination still would not require all 5 motors running at the same tim... so you can take it easier with your PSU VA rating. IMHO, 4x5.65A would be rational.

**PS,
Btw, I use 9801 too, it works wonderfully with 3A direct drive 24 teeth 1/8step, I bet you will use the belt reduction, hence I assume you won't be needing anything more than 3A per motor to dominate the world
with that, you can have even smaller PSU....
Its not about money or being cheapskate on parts, its about appropriate...

Last edited by KenC; Tue 06 August 2013 at 03:44..
Reply With Quote
  #62  
Old Tue 06 August 2013, 04:53
Fox
Just call me: Fox
 
Amsterdam
Netherlands
Hi ken, thanks for all the info. Good to have first hand experiences. Yes, I am using 4:1 reduction. Are you driving the motors at the higher (+20%) voltage !?
Reply With Quote
  #63  
Old Tue 06 August 2013, 07:09
KenC
Just call me: Ken
 
Klang
Malaysia
nope, used 32*sqrt(mH) =56.34V, custom wound a 40V tranny & get stable 54V dc (loaded). no rocket science involved....
Reply With Quote
  #64  
Old Tue 06 August 2013, 08:08
Fox
Just call me: Fox
 
Amsterdam
Netherlands
ok, so ignore the +20% recommendation of Gerald it is, to be on the safe side.
I just thought he said that because it's the difference between the regulated and unregulatedpowersupplies under load, and was curious about that assumption being correct.

But...... your calcution seems to be faulty, or am I making a mistake ? 86HS9801 motor Deitech ? V4.1*32=64.79 V ?

Last edited by Fox; Tue 06 August 2013 at 08:14..
Reply With Quote
  #65  
Old Tue 06 August 2013, 09:38
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The plus 20% comes from my personal experience - We have increased the voltage of our 4 tables to about 20% over the conservative Mariss formula value, to give really good cutting performance. If there is a heat problem, it is really simple to control the heat with the current setting.
Reply With Quote
  #66  
Old Tue 06 August 2013, 09:48
KenC
Just call me: Ken
 
Klang
Malaysia
Sorry, yours is the correct numbers, I made a mistake in my coil inductance.
Tend to forget numbers...
I can still remember I didn't go there because my motor driver is 80V max, , a big fluctuation in my line voltage & I risk burning all the drivers. I wasn't brave enough...
Also, 80V rated capacitors are a lot cheaper than a 100V one. again, one won't use 80V DC on a 80V rated capacitor unless one crave for fireworks inside the control panel.
Reply With Quote
  #67  
Old Tue 06 August 2013, 10:00
Fox
Just call me: Fox
 
Amsterdam
Netherlands
Hey Gerald,

Ok so there's goes my theory, but (your) experience counts... Since 77 V is very close to the max 80 of my drivers, I will follow your example but a bit conservative... and probably make it a nice round number in the lower 70-ties volts area.

@ Ken Thanks ! I am so out of my comfort zone with these electronics I already got afraid that I was the one with a stupid beginner mistake again
Reply With Quote
  #68  
Old Tue 06 August 2013, 10:05
KenC
Just call me: Ken
 
Klang
Malaysia
No wories, I came from the same dark corner too.
My example may not be the right one but its mine

End of the day, learnt from those before you & apply common sense.

PS, I don't use Gecko...
Reply With Quote
  #69  
Old Tue 06 August 2013, 11:32
Fox
Just call me: Fox
 
Amsterdam
Netherlands
- me neither (LEADSHINE AM882).

- Ah the Darkside...yes...and Gerard is our Yoda,

I must say sometimes I really hate(d) it* that the info/theory is scattered over the forum/internet, or stuff 'seems' contradicting, but even so.... I feel Gerald was right with this approach. I've already learned sooooooo much, it was not easy, and very time consuming.....but when it is finished it will be my machine, and I will know every inch of it. If I want to repair/change/ improve on it in the future I can.

* Often I have only a 2-3 hours I can spend on it in a week, an hour or less a day. It becomes then very hard to make significant progress, which frustrates, because when you start to understand it, you have to put it away again, and the next time you look at it, you read something else and you are left second guessing yourself and losing a lot of time catching up again....

But I am (slowly) getting there and my questions directly related to this thread are answered...so I will continue in my build thread as to not pollute this thread.
Reply With Quote
  #70  
Old Tue 06 August 2013, 16:51
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
There are several "unknowns" in the use of the 86HS9801 motors used with a Leadshine stepper driver. Geckodrive published the formula for use with Geckodrive stepper drivers. No one should assume that the same formula is safe to use with other stepper drivers. It would be prudent to contact Leadshine and get their recommendation.

If the 86HS9801 motor motor is used at full Amps with a Geckodrive stepper driver and if it is loaded to the point that it will miss steps if pushed any harder, it will be generating about 80-degress C (yes, I have tested that on my testbench when I used a 86HS9801 stepper with a G203v stepper driver). You will have to read the data sheet for that stepper motor to see what temperature the insulation can handle, but 80-degress C is hotter than I have chosen to run my motors. Reducing the load also reduces the heat generated - all other things being equal.

Reducing the current that is pulled by a stepper also reduces the torque of that motor. Reducing the torque means that the motor will not be able to cut as deep as one might hope.

In a general sense, voltage determines the speed of a motor under a light load. Current determines the load that the motor is able to handle. However, both voltage and current are interrelated. In a resistive load, voltage X current = watts. The higher the voltage or the greater the amount of current being drawn by the stepper motor, the higher the heat. Many modern stepper drivers have an "automatic" current reduction feature that reduces the current by 50% or more whenever the motor is idle for more than 1 or 2 seconds. That reduces the heat. In a 3-D cut, the motor may be required to make short moves at short intervals, never coming to a complete halt for the time required to enter "reduced current mode". In that situation, the heat will build up faster than expected.

I use an infared thermometer to measure the heat produced by the stepper, the stepper driver and the load. For my peace of mind, I keep the stepper's temperature at 60-degrees C or lower and the temperature of the G203v at 40-degrees C or lower. Because I use Geckodrive stepper drivers, I use Mariss's formula to determine the maximum voltage, then I choose a voltage at or less than that voltage.
Reply With Quote
  #71  
Old Wed 07 August 2013, 00:41
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
The 86HS9801 motor has Rated Current (A) = 4.0 and Phase Resistance (Ohms)= 0.98. The voltage marked on the motor would thus be 4.0 x 0.98 = 3.92 Volt.

Most websites and producers (other than Geckodrive) would still tell you to aim for 20 to 25 times marked motor voltage. That is 78.4 to 98 volts for the 86HS9801 motor.

Geckodrive will tell you 32xSQRT(4.1) = 64.8 Volts

I suggest 1.2x Geckodrive = 38xSQRT(4.1) = 77 Volts

Mike Richards has mentioned before 0.75x Geckodrive = 24xSQRT(4.1) = 48.6 Volts

The choice is yours!
Reply With Quote
  #72  
Old Wed 07 August 2013, 01:54
KenC
Just call me: Ken
 
Klang
Malaysia
Fox, nobody said learning is gonna be easy, but its not impossible. Shriving through this treasure trove is the time best spent on the internet for me.

Don't forget voltage rating of other component parts in the system.

PS, careful with your current(A) selection, bigger A require fatter cable which = more money, more weight. mind you, cable cost is significant investment.
Reply With Quote
  #73  
Old Wed 07 August 2013, 23:15
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Ken, you do a lot of texture cutting, where your Z-motor is moving very slowly and almost continuously . . . . . . . does that motor get much hotter than the X or Y motors? Our experience is that the Z is cooler than the X or Y motor. The motor with the biggest cutter load gets the hottest.

Modern drives seem to have completely cured the "hottest condition at low speed/hold" which was apparently the plague for earlier (over 10 years ago) drive technology. Mike Richards, when saying "In a 3-D cut, the motor may be required to make short moves at short intervals, never coming to a complete halt for the time required to enter "reduced current mode". In that situation, the heat will build up faster than expected." appears to be referring to another era of drives that don't apply here anymore. Same applies to his logic on heating caused by selected motor voltages.

Our experience is that running a motor hard, fast, deep causes the most heating today. The earlier era experience was that the most heat came when the motors sat still, doing nothing.
Reply With Quote
  #74  
Old Thu 08 August 2013, 01:47
KenC
Just call me: Ken
 
Klang
Malaysia
I don't know what was the history of motor theory, my understanding of electric machine operation is based on electromagnetism which I nearly forgot after I left school.

All my motors are hottest when not in motion. Heat is produce from the coil resistance.
I configured full current when stop.
In static mode,
P static=IR & I=3A, R=coil resistance (Constant)

In dynamic mode, all electomachanical machines the current fluctuates according to load, the theory is way to tedious to get into, in layman terms, its like pushing a shopping trolley, you need more force to get it up to speed, & when in motion, you need less force to keep on the speed, if you run into a ramp, you need to apply more force to keep climb at the same speed & if the trolley is full its harder to push than an empty trolley...

In the stepper motor case, its identical, when it need to generate more force, it will ask for (draw) more current from the power source, its not greedy, it only ask for as much current it need to do the work..., . but wait, the driver has a max current setting, hence the motor can never draw full current it asked for all the time & it also won't be asking for the full current all the time, so on average, the current that passes through the motor coils will be lower than when it is stationary. I can lay out pages of equations & maths to proof this but I'll leave it for noobs who has the energy & interest to do the chore
Unfortunately, I can't get away without an equation,
P motion=IR, I= less than 3A, R=Coil resistance (constant)

hence P static > P motion

My Z-motor is the coolest of all motors. I reckon like you said because its lightly loaded. Especially, when it has the highest mechanical ratio of all 3 axis. (Ball Screw)

Actually, the temp difference between the X & Y motors are 2~3C, I consider they are at the same temperature, but Z-motor runs 5~10C lower, unless my IR temp gauge lied to me.

Conclusion, Cold motor is one that isn't working hard, hard working motors gets hot... Ain't that familiar

Our aim is to make sure motor don't get too lazy, yet not slave drive them to a burn out...

*More on operating V & I.~
We have a choice of using higher voltage or heigher current to achieve the same power.
P=VI
In transmission application, higher V is prefered, because P=IR, R=wire R, & wire R is proportional to wire length.
In short distance, higher I is prefered, because low V is safer to work with (still dangerous nevertheless.)
My personal preference is always go for lower I possible, as fire is almost always caused by high current. & if select your component's Voltage rating carefully, high V isn't that dangerous (still dangerous nevertheless).

Last edited by KenC; Thu 08 August 2013 at 02:03..
Reply With Quote
  #75  
Old Thu 08 August 2013, 02:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Thanks Ken, you confirm our experience; in 3D cutting, the slowest moving, lightly loaded motor is the coolest.

It is surprising that you have chosen "full current when stop". Most of us opt for the current reduction feature.
Reply With Quote
  #76  
Old Thu 08 August 2013, 02:06
KenC
Just call me: Ken
 
Klang
Malaysia
In 1/2 current, I can move the gantry with 1 hand push. in full current, I need 2 hands to move the gantry... Hence, full current. Its not what others do, but I like it that way, give me peace in mind...
Reply With Quote
  #77  
Old Thu 08 August 2013, 06:57
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Ken,

What motor do you use on your Z-axis and what is the gear ratio on your Z-axis? You wrote that you're using a ball-screw. Two popular screws from Automation4Less have pitches of 5mm per revolution and 10mm per revolution.

A 7.2:1 geared motor with a 1.25" pinion has a "pitch" of 13.8mm per revolution. A motor with a 10:1 gearbox and a 1.25" pinion would move an axis the same distance per revolution as a ball-screw that moves 10mm per revolution. A motor with a 13:1 gearbox and a 1.25" pinion would move an axis the same distance as a ball-screw with a 5mm pitch.

In any case, when attached to a ball-screw, a motor would only have to produce a maximum of 70 oz*in of torque to match the 700 oz*in of torque produced by a PK296A2A-SG7.2 geared motor. Even a little PK264 motor could easily handle that much torque.

What I'm guessing is that your machine with a ball-screw on the Z-axis would only draw a fraction of the current that would be required if you used rack and pinion on the Z-axis. If it only pulls a fraction of the current, it will only produce a fraction of the heat.
Reply With Quote
  #78  
Old Thu 08 August 2013, 07:12
KenC
Just call me: Ken
 
Klang
Malaysia
Exactly, that what I call lightly loaded. or in another layman term very much over sized motor. I'm using 86HS9801. 640oz-in. I think the motor work harder overcoming the gas spring than the actual work I really can't remember what the pitch was 5 or 10... its chinese & I got it off ebay, stuff from Automation4Less & Oriental motor are too dear for me.

I didn't do much math as that was not important since I have too much power for Z-axis, I only do maths when this are marginal but its obvious that the overall mechanical advantage of ball screw is a few time over a direct drive. move 5~10mm per turn, vs 24mm (Pitch circumfrance of Mod 1 is the number of teeth in mm) one turn... I leave the details for you to ponder.
Reply With Quote
  #79  
Old Thu 08 August 2013, 08:13
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Mike, we have rack&pinion Z drives and always the Z is the coolest motor. Identical 7.2 geared motors on all axes.
Reply With Quote
  #80  
Old Thu 08 August 2013, 08:15
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Ken,

Thanks for the quick response. As you said, your Z-axis is lightly loaded so it won't draw much current.

If I've done the math correctly, a 24mm pitch diameter gear would move an axis about 75mm per revolution or about 7.5X futher than a 10mm pitch ball-screw, so if your motor were used with that 24mm pitch diameter spur gear, it would have to pull about 7.5X more current than it pulls with your ball-screw to move the same load. Of course there are other factors involved.

In 3-D work, the cutter is normally lightly loaded simply because much of the fine detail work requires a small cutter and a small cutter could not handle a heavy load without breaking. However, in 3-D work all three axes are constantly moving, usually short moves. Depending on the way the software is setup, short moves may never get "up to speed" which means that those moves are in the high-torque range of the motors. High-torque moves mean that the motor is pulling more current than it would pull in a low-torque situation. Depending on the weight, moving the X-axis and the Y-axis can take a lot of torque, especially when the moves are short. (One of the tests that I run to quickly heat up a motor is to move the motor constantly 1/4" CW and then 1/4" CCW with just enough pause between directions to allow the motor to come to a complete stop before changing direction. That "test" heats things up quickly.)

I think that the proper test in a 3-D cut would be to measure the heat of the motor that has to work the hardest. A lightly loaded motor would not develop much heat - just like you said, but the motor(s) moving the heaviest load would develop the most heat. Modern motors can handle about 80-degrees C rise with a maximum temperature of about 100-degrees C. That also assumes a duty cycle of 50% or less and a large heat-sink on the motor.

When all factors are considered, an efficient machine can be built that can handle the required job. Even if not all the factors are known, the price of the components is low enough that changes can be made as required. That's the "price" that's part of a do-it-yourself design. Commercial machines have been put through that cycle as many times as required until the machine does what it is supposed to do within the safety envelope required by whatever government regulations that may exist where the machine is sold and used.

Thanks for your input.

Last edited by Richards; Thu 08 August 2013 at 08:26..
Reply With Quote
  #81  
Old Thu 08 August 2013, 08:41
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,

You posted while I was responding to Ken. I agree that the Z-axis on your machine should run the coolest because it would normally be handling the lightest load. Of course heavy cuts with a large diameter cutter could load the Z-axis enough that that motor would pull as much current or even more current than the Y-axis motor or the X-axis motors, but almost always the Z-axis on my PRT-Alpha ran cooler than the other axes. The exception was when I was surfacing a new piece of MDF. I used a 1-1/2" cutter at a little more than 1/8" depth of cut at 15" per second. The "heavy" cut was necessary to get past the tightly packed material so that the vacuum system could do it's job properly.

Having the same style motor/gearboxes on all axes and the same rack/pinion driving system on your machines would remove some of the variables. The only variable would be the load presented to the motor, which would be influenced by the weight of the axis and the load on the cutter.

I think we're all in agreement on why the Z-axis motor would normally run cooler.

Last edited by Richards; Thu 08 August 2013 at 08:47..
Reply With Quote
  #82  
Old Thu 08 August 2013, 11:33
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Which motor are you then referring to when you say:

Quote:
Originally Posted by Richards View Post
. . . . In a 3-D cut, the motor may be required to make short moves at short intervals, never coming to a complete halt for the time required to enter "reduced current mode". . . . .
Reply With Quote
  #83  
Old Thu 08 August 2013, 13:09
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,

In a 3-D cut, all three motors are primary motors. They all move more frequently and for shorter distances than when cutting 2-D. In a 2-D cut, usually, the Z-axis goes to depth and then the XY axes move the cutter through the cut. In a 3-D cut, any of the motors may move in conjuction with or separate from the other motors. It entirely depends on what the tool path requires.

When using a Geckodrive G203v, the manual states: "AUTO CURRENT REDUCTION: The G203V reduces motor phase current to 71% of the set current value 1 second after the last step pulse is sent. The G203V also changes to a special recirculating current mode to nearly eliminate motor heating."

Other Geckodrive stepper drivers may have different times and different values when they enter auto-reduction mode (which I called "reduced current mode".)

In some of the 3-D cuts I've made using 1/16" ball-nosed cutters, each move was barely visible, but all three axes moved contineously. None of the axes ever paused long enough for that stepper-driver to enter auto-reduction mode.

Once, when I set the pots on my PRT-Alpha to mimic a G203v, I noticed that the depth of cut on 2-D cuts had small variations, depending on the length of the cut. For instance, when edge cutting a piece of MDF, sometimes the cutter rose one or two hundredths of an inch along the 96" length of cut. I have no idea how a G203v would actually handle that cut, but in the twelve seconds that it would take to make the cut (96" at 8" per second), eleven of those seconds would have been in reduced current mode. Comparing the Alpha stepper driver to a G203v is comparing apples to oranges, but if anyone ever suspected that entering reduced current mode was affecting the cut, he could simply insert a command to lift or lower the cutter 1 step every half-second so that the G203v never entered reduced current mode until the cut had been finished. The motor would run hotter, but the cut would be more consistent IF reduced current mode was affecting the cut.
Reply With Quote
  #84  
Old Thu 08 August 2013, 20:57
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
You have often mentioned you tested motor heating on your test bench by simulating 3-D cuts. Now it is clear that you don't actually know what happens in the real world with 3D cuts. I have now become very suspicious of what you actually do at this "test bench". We have had to replace 4 costly toroidal transformers because our real world told us our MechMates were underpowered for a very wide range of cutting types. Lots of others building MechMates have built them underpowered, following your advice.
Reply With Quote
  #85  
Old Thu 08 August 2013, 23:46
KenC
Just call me: Ken
 
Klang
Malaysia
My cut with Dia. 50mm ball nose cutter 90% of the time, & I feed them deep, 8~9mm to be exact, 50~90min at one go. So Its not exactly light cutting load. Actually, most loose steps are caused by tripped spindle
On the Plasma table, the Z is hottest because its lazy & get the most rest (not moving).

I'm lucky that I design/built my own stepper motor system, I would want my motor any hotter that it already is which is 40~50C. 80C is good for brewing Chinese tea, not for my machine drive.

Gerald, how many C degree did you increased with +20% V?
Reply With Quote
  #86  
Old Fri 09 August 2013, 00:51
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Ken, it is not practical to exactly measure the temperatures because there are so many variations depending on the job at hand. However, everyone in the workshop has a regular habit of laying their hands on the motors . . . if they can't hold them for about 3 seconds or more, then they consider reducing the cut speed or depth, or consider whether the cutter is blunt. (Also a lot of work with a big ballnose)
Reply With Quote
  #87  
Old Fri 09 August 2013, 06:49
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Gerald,

You know that I use a 500VA transformer on my bench when I'm testing four motors. I use a 250VA transformer when I test single motors. You recommend a 300VA transformer for use with four motors. It was not my recommendation that caused your transformers to fail. You can cast any aspersion that you wish on my methods, but I have never lost a transformer, a motor or a stepper driver.

The temperature of a motor is directly related to the voltage used and the current drawn. The amount of current that a motor pulls is directly related to the load on that motor. There is no black magic involved. Ohm's law was developed in 1825. Since then anyone who wanted to know the relationship between voltage, current and heat only had to plug in the variables. It works in the CNC world just like it works in all of electronics.

Ken is absolutely correct. His motor is properly sized for the job. Depending on the pitch of his Z-axis ball-screw, his motor pulls less than 1/5th the current that your Z-axis PK296A2A-SG7.2 motor pulls. Current running through a transformer causes the transformer to heat, just like current flowing through a motor causes the coils inside the motor to heat.

If you've had problems with overheating motors, overheating drivers or overheating power supplies, it's not because you followed my advice.

Last edited by Richards; Fri 09 August 2013 at 06:51..
Reply With Quote
  #88  
Old Fri 09 August 2013, 08:10
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
My transformers did not fail, they were selected at too low a voltage.
Reply With Quote
  #89  
Old Fri 09 August 2013, 08:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by Richards View Post
If you've had problems with overheating motors, overheating drivers or overheating power supplies, it's not because you followed my advice.
People who follow your advice will never experience any overheating . . . but they won't experience the cutting performance that is intended from the MechMate either.

People who follow my considered advice will get the performance, and know how to tune for max. performance, without going over the heating limits and without having to change expensive transformers.

Last edited by Gerald D; Fri 09 August 2013 at 08:24..
Reply With Quote
  #90  
Old Fri 09 August 2013, 09:00
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Okay Gerald, have it your way. Meanwhile, those who follow Mike's (Metalhead) suggestion to use a properly sized motor with a belt-drive will never need to exceed maximum voltage or tweak current to keep their components from overheating.

It's up to the builder to decide whether he agrees with the laws of physics and correctly sizes the components that he uses or whether he wants to overdrive undersized components to get the performance that he desires.

You do it your way and I'll do it mine.
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 00:37.


Powered by vBulletin® Version 3.8.3
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.