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  #1  
Old Mon 10 November 2008, 16:43
William McGuire
Just call me: Bill
 
Weiser, Idaho
United States of America
Total power consumed by a working MechMate - your workshop wiring . . . .

I've been talking to a couple of CNC folks and we were discussing the various input voltages for the control box and they made me realize that:

If you use a 120 volt source (as here in the United States) and a 600 VA power supply, and a 15 amp Milwaukee router, the amperage needed for just the router (15 amps) and the power supply (600 VA/120 volts= 5 amps) is 20 amps... with no room for any excess.

I don't know if the geckos and proxies, etc. would come under that amount or add to it, but it might be something for electrical novices (like me) to take a look at before purchasing a large power supply when considering 120 volts input...

Unless, of course, I am entirely wrong...
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  #2  
Old Mon 10 November 2008, 19:15
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
Bill,
Dont forget that you can have a 300VA supply or a 1200VA supply but if you are only using 150VA at any one time, then that will be all you would draw. So you are not drawing the rated amount from the supply al the time but really only what your load is requiring. Also your router will not draw 15 A all the time either. If it drew that much on startup it would pop the breaker on a standard 15A circuit. I would recommend though, to have separate circuits for your router and for the control side of things. Does this help at all?
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  #3  
Old Mon 10 November 2008, 20:53
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
A standard 15A breaker can handle more than 15A for a short time, so starting up can normally be handled. Plus, the router and power supply don't start at the same time. However, when power supplies get way too big, their transformers & capacitors do draw a huge start-up current, causing breaker trip problems. Bill, you are still very safe.
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  #4  
Old Tue 11 November 2008, 07:14
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Bill,

I ran some tests a few weeks ago to see just how much current a stepper motor draws. The test showed that current is basically proportional to torque; however the current draw vs torque curve was not totally linear. In other words, the higher the torque requirement, the greater the need for current. I had setup a PK299-F4.5 motor, wired half-coil, with an 80k resistor so that the G203v could deliver up to 4.5A to that motor. Here are the data from the latest test for the amount of current that the motor was drawing as it stalled at certain speeds:

300 inches per minute - 2.98A
400 inches per minute - 3.60A
500 inches per minute - 3.52A
600 inches per minute - 3.80A
700 inches per minute - 4.14A

There is a little glitch at 500 ipm, but that could have been the method that I used to stall the motor (a gloved hand clamping down on a three-inch pulley).

Since it is probably poor practice to run the motor too near its stall torque because of the possibility of missed steps, keeping the motor at 80% or less maximum torque seems to pull only about 50% to 60% of the maximum current that the motor pulls at full stall torque.

In other words, the PK299-F4.5 motor that was wired for 4.5A pulled closer to 2.5A when used normally.

One side note is that the temperature of the motor rose to about 60 degrees C. (room temperature was 20 degrees C.).
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  #5  
Old Tue 11 November 2008, 23:12
William McGuire
Just call me: Bill
 
Weiser, Idaho
United States of America
Mike... my setup will have a 600VA toroid with 56 volt output to the geckos. I will therefore be running the motors (PK296A2A-sg7.2) full coil.

As I still had the ability to put in a special outlet in my garage, I used 10AWG wire to supply a 30 amp 120 volt outlet. In my box, I'll have a 15 amp fuse (for the router), a 5 amp fuse (for the power supply), and a 1 amp fuse (for the E-stop circuit directly after my disconnect and before any relays or contacts. This will hopefully give me some extra room to play with. I guess, after the fact, it would have been just as easy to use a 240 circuit to begin with...

but then I would not have had the opportunity to introduce a 30 amp 120 volt circuit to the forum...
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  #6  
Old Wed 12 November 2008, 07:16
Richards
Just call me: Mike
 
South Jordan, UT
United States of America
Bill,

Your steppers are rated at 2.1A per motor when wired full-coil. So 4 X 2.1A = 8.4A. To find the AC output of the transformer, 1 / SQRT(2) X 56 = 39.59VAC and then finding the required VA rating for the transformer, 8.4A X 39.59VAC = 332VA.

In other words, you have a good safety margin in your calculations. Worse case, and depending on the efficiency of your transformer, you would be drawing less than three amps from the AC line feeding that transformer. Your router will probably be pulling well under 75% of its rated 15A, even in heavy cuts. (I never ran a watt meter on my PC 7518 before I installed a spindle, but others have said that the router produced about 1-1/5HP before it started to bog down.)

I had some of the same worries with my little 50A 240VAC panel that feeds my whole shop. According to the figures that Shopbot sent me, pre-purchase, I should not have been able to run the Shopbot with a spindle on that circuit; however, I commonly run the Shopbot with 3hp spindle, 2 FEIN vacuums, a 1-1/2hp 240VAC dust collector and a PC7518 (router table) all at the same time. So far, I've never had the sub-panel's circuit breaker trip.
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  #7  
Old Wed 12 November 2008, 18:41
William McGuire
Just call me: Bill
 
Weiser, Idaho
United States of America
Thanks guys...

Always a big help...
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  #8  
Old Thu 13 November 2008, 10:35
gmessler
Just call me: Greg #15
 
Chicago IL
United States of America
Mike,

You have a great way of taking a bundle of snakes and lying them out straight.

Thanks for all your help!
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  #9  
Old Thu 13 November 2008, 11:10
domino11
Just call me: Heath
 
Cornwall, Ontario
Canada
I think Mike must have tested all possible configurations of steppers that we would use on a Mechmate at least twice from all the data in his posts.
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  #10  
Old Wed 14 January 2009, 21:28
sprayhead
Just call me: Francis
 
sydney
Australia
Quote:
Originally Posted by Richards View Post
Bill,

I ran some tests a few weeks ago to see just how much current a stepper motor draws. The test showed that current is basically proportional to torque; however the current draw vs torque curve was not totally linear. In other words, the higher the torque requirement, the greater the need for current. I had setup a PK299-F4.5 motor, wired half-coil, with an 80k resistor so that the G203v could deliver up to 4.5A to that motor. Here are the data from the latest test for the amount of current that the motor was drawing as it stalled at certain speeds:

300 inches per minute - 2.98A
400 inches per minute - 3.60A
500 inches per minute - 3.52A
600 inches per minute - 3.80A
700 inches per minute - 4.14A

There is a little glitch at 500 ipm, but that could have been the method that I used to stall the motor (a gloved hand clamping down on a three-inch pulley).

Since it is probably poor practice to run the motor too near its stall torque because of the possibility of missed steps, keeping the motor at 80% or less maximum torque seems to pull only about 50% to 60% of the maximum current that the motor pulls at full stall torque.

In other words, the PK299-F4.5 motor that was wired for 4.5A pulled closer to 2.5A when used normally.

One side note is that the temperature of the motor rose to about 60 degrees C. (room temperature was 20 degrees C.).

HI

I always thought that a Stepper motor draws 100% of the rated current at all times...

How much current is going through a stepper when it is stopped, holding it's position? That is, forgetting about the automatic current reduction done by the Gecko.

Francis
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  #11  
Old Wed 14 January 2009, 21:32
sprayhead
Just call me: Francis
 
sydney
Australia
Also,

Would I be able to use a standard GPO from the garage and make an extension with an RCD and a CB to supply the MM or the light circuit of my garage would be not suited?

thanks
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  #12  
Old Wed 14 January 2009, 23:03
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
GPO = General Post Office?
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  #13  
Old Wed 14 January 2009, 23:11
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by sprayhead View Post
I always thought that a Stepper motor draws 100% of the rated current at all times...

How much current is going through a stepper when it is stopped, holding it's position? That is, forgetting about the automatic current reduction done by the Gecko.
There are so many myths around stepper motors! Here is a measured observation:

Quote:
Originally Posted by Gerald D View Post
Today I tried another experiment, with a good ampmeter in the transformer's output, before the rectifier . . . . .

I wanted to see how much current is needed for a holding/static motor with quite a high torque on it. This would be the case for 2 or 3 of the MechMate motors when cutting out cabinet parts - only 1 or 2 motors would be moving for the cutting action, the rest will be holding.

The shocker for me was that a loaded static motor and an unloaded static motor draw exactly the same current!

Taking a A2A geared motor, clamping the body in a vice, and then forcing the shaft to turn while the motor is energised, made no difference to the ampmeter reading. With the transformer at 35VAC, an 18k resistor on the G203V, the transformer current draw was 0.38 Amp. Putting a 36k resistor on the G203V raised the transformer current to 0.49 Amp.

This means that a stationary axis will never need more than 12.3 VA, if it has been stationary for more than 1 second. If the current reduction had not yet kicked in, the VA's could be 17.5.

My next experiment will be to put a peak-hold ampmeter onto a hard working MM table and see what that does.

At this this stage I cannot fault the conventional advice of sizing a power supply on two thirds of the motor's total peak current demand.
So, if an axis is stationary, it draws no more than 20 VA, the same as used by a 20 Watt light bulb.
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  #14  
Old Thu 15 January 2009, 06:14
sprayhead
Just call me: Francis
 
sydney
Australia
Quote:
Originally Posted by Gerald D View Post
GPO = General Post Office?
Hi Gerald

Here Down Under, GPO for a sparkie is a General Power Outlet.
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  #15  
Old Thu 15 January 2009, 06:58
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Let's try and talk your language . . .

Over here, any GPO will be protected by a RCD somewhere on the premises. The wiring to that GPO will be protected by a CB somewhere on the premises. That means we can plug a MM control panel, plus its router, into any GPO, even in a bedroom. You might find the CB tripping because the wiring to that GPO is too thin, but generally we have 2.5 mm2 wire and 20 Amp CBs or 1.5mm2 wire and 15 Amp CBs. A single phase MM with a big Makita router running at full load draws about 10 Amp off a 230V circuit.

The picture changes drastically when you add dust collection and/or vacuum holddown that is when the power requirement doubles or trebles.
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  #16  
Old Thu 15 January 2009, 10:39
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
...my power often "trebles" when I try to draw to much out of one GPO I couldn't resist Gerald.

Sean
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  #17  
Old Thu 15 January 2009, 11:16
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
I think your voice trebles while your power trembles
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  #18  
Old Fri 16 January 2009, 15:01
smreish
Just call me: Sean - #5, 28, 58 and others
 
Orlando, Florida
United States of America
oh gosh, now I am caught in that darn "usable" language barrier again
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  #19  
Old Fri 16 January 2009, 18:04
sprayhead
Just call me: Francis
 
sydney
Australia
Quote:
Originally Posted by Gerald D View Post
Let's try and talk your language . . .

Over here, any GPO will be protected by a RCD somewhere on the premises. The wiring to that GPO will be protected by a CB somewhere on the premises. That means we can plug a MM control panel, plus its router, into any GPO, even in a bedroom. You might find the CB tripping because the wiring to that GPO is too thin, but generally we have 2.5 mm2 wire and 20 Amp CBs or 1.5mm2 wire and 15 Amp CBs. A single phase MM with a big Makita router running at full load draws about 10 Amp off a 230V circuit.

The picture changes drastically when you add dust collection and/or vacuum holddown that is when the power requirement doubles or trebles.


Thanks, From a photographic memory i think that the light wires at my Garage are very close to 1mm in diameter, solid core. That makes them 2.5mm^2.
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  #20  
Old Fri 16 January 2009, 23:00
dragonbreath
Just call me: Bill
 
Gibsonton florida
United States of America
hello world wide people as a newbe to this site my word may not mean much so here is my 2 cents or what ever curency yo use when i put my shop up which is a small welding machine shop in a detached garage i pulled 220volt 50amp from the house kept blowing breakers i contacted my local power company got permits and had a meter set on the garage 125amp wired the garage next to every 110 outlet i put a 220 outlet everything that i can run on 220 rewired motors on lathe and mill fans coompressor well you get the idea i haven't had any problems since so you us guys that have detached garages this might be a consideration oh by the way the 2 meters togather my power bill is only half or what it was when i was pluged into the house got a commercial rate on the garage
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  #21  
Old Fri 16 January 2009, 23:54
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Quote:
Originally Posted by sprayhead View Post
. . . the light wires at my Garage are very close to 1mm in diameter, solid core. That makes them 2.5mm^2.
Wrong - dangerous assumption!

For solid core:
1 mm2 wire has a diameter of 1.13 mm and is typically protected by a 10 Amp CB
1.5mm2 wire has a diameter of 1.38 mm and is typically protected by a 15 Amp CB
2.5mm2 wire has a diameter of 1.78 mm and is typically protected by a 20 Amp CB

Check that wire core diameter with a vernier/digital caliper. (The ground wire could be thinner). You can also see what is embossed onto the PVC cover of the wire - the wire size should be labelled there.
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  #22  
Old Mon 19 January 2009, 00:53
sprayhead
Just call me: Francis
 
sydney
Australia
Quote:
Originally Posted by Gerald D View Post
Wrong - dangerous assumption!

For solid core:
1 mm2 wire has a diameter of 1.13 mm and is typically protected by a 10 Amp CB
1.5mm2 wire has a diameter of 1.38 mm and is typically protected by a 15 Amp CB
2.5mm2 wire has a diameter of 1.78 mm and is typically protected by a 20 Amp CB

Check that wire core diameter with a vernier/digital caliper. (The ground wire could be thinner). You can also see what is embossed onto the PVC cover of the wire - the wire size should be labelled there.
ouch!

I'll find where the Circuit Breaker is, shut it off and call out Mr. Vernier for a measuring inspection.

I assume the building is about 50-60 yrs old. I don't think there is an RCD for my garage circuit.

thanks
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  #23  
Old Tue 20 January 2009, 18:30
servant74
Just call me: Jack
 
Nashville (Tennessee)
United States of America
I have been told that here in the US, a ShopBot with a router before doing dust collection or vacuum hold down should have 2 15A 110V circuits. One for the router and one for everything else. Dust collectors or vacuum hold downs can each have motors larger than a 3.5HP router. In the US, RCD are called GFI (Ground Fault circuit breakers) I think.

Sizing the electrical needs planning tool.
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  #24  
Old Tue 20 January 2009, 19:13
sailfl
Just call me: Nils #12
 
Winter Park, FL
United States of America
I thought I was going to have to upgrade my power supply to my garage when I moved the machine to my garage. But I did not upgrade. My garage is supplied by a 15A breaker that also supplies power to a bed room that I use for my office. In the past when I ran my table saw, I would have to reset the breaker when the blade got jammed when I was cutting wood. This happened many times. I have yet to have to reset the breaker. The power needs are very low. I have run a shop vac at the same time I have been cutting and there still has been no problem.

Do I think I should upgrade? You bet I should. When I add the dust collection I am sure I will need more power but for now I am good. I hope that I get busy and have to move to a new place.

Last edited by sailfl; Tue 20 January 2009 at 19:18..
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  #25  
Old Sat 31 January 2009, 18:03
sprayhead
Just call me: Francis
 
sydney
Australia
a couple of common electrical wires

The one on the right is 1mm^2 and the cores measure 1.1mm in diameter in my digital vernier.

Tho one on the left is multi-stranded and I am not sure how much the area section measures. It's definitely thicker.
Attached Images
File Type: gif wire gauges.gif (137.5 KB, 329 views)

Last edited by sprayhead; Sat 31 January 2009 at 18:07..
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  #26  
Old Sat 31 January 2009, 19:21
Gerald D
Just call me: Gerald (retired)
 
Cape Town
South Africa
Count the strands and measure the strand diameter. The rest is school maths:
cross section area = pi X diameter X diameter / 4 (pie_dee_squared_over_4)
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