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Re: Toroidal transformers vs standard IE
« Reply #10 on: March 28, 2008, 11:31:49 PM »
also both are bipolar parallel motors

Offline jimpinder

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Re: Toroidal transformers vs standard IE
« Reply #11 on: March 29, 2008, 06:43:03 AM »
I think we are getting a bit "wrong way round" here.  The motor does not produce current, it draws current from the supply, via the drives. The voltage input to the motor determines how much current it draws.

As far as I understand, it is normal to run stepper motors, exceeding the rated voltage by up to 20 times.

I can see the 4.8v motor performing well, but, if the drives have some current limitation on, set it at the maximum 7 amps otherwise you might damage the drive - if the motor tries to draw its full current.

As far as the other motor is concerned, using the rule about over voltage, it would appear to need a voltage in excess of 600 - 700 to operate satisfactorily. I cannot see it drawing sufficient current at 54volts to trouble the drives, but what performance you will get is a bit of a mystery

Not me driving the engine - I'm better looking.

Offline stirling

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Re: Toroidal transformers vs standard IE
« Reply #12 on: March 29, 2008, 07:23:22 AM »
Let's go with what you've said you've got and look at what will happen.

You have 2 motors - 1 power supply so... both motors will be presented with the same voltage by your geckos i.e. the 54Vdc of your PS.

Your 65Vdc rated motor will be UNDER driven by a factor of 54/63 or ~0.8 and your 4.8Vdc rated motor will be OVER driven by a factor of 54/4.8 or ~11.5.

Now - current: your going to be using a gecko for each motor to drive them independently - yes? So... the gecko driving the 65Vdc/5.4amp motor should have its current-set resistor set appropriately so that it does not DELIVER more than ~5.4amps. Now onto your other 4.8Vdc/8.4amp motor: A gecko can deliver a MAX of 7amps so that is what it will deliver to that motor - period. Geckos, being chopper drives are current limiting devices - they will only deliver the current they are set to deliver. You can NOT "draw" more, V=IR does not apply here as it would in a simple "linear" dc circuit.

So the bottom line is: Firstly, you're under driving one motor in terms of voltage - this will affect the usable speed you can usefully get the motor to before it stalls. - will it be enough - well that depends on your application and more info would be needed to comment usefully. Secondly you're current starving the second motor and that will reduce it's torque over the whole range of speeds it can operate at. - is it enough? - same answer as before.

Regarding the often stated 10-20 V overdrive factor - this is totally dependant on application. To determine this empirically you would start by running your motor at the labelled voltage (Vx) and increase speed under the required load until it stalls. If that stall speed is insufficient for your application you up your voltage by Vx and repeat. As a rule of thumb the overdrive ratio of the voltage is proportional to the stall speed at a given load. i.e. 10 x V = 10 x stall-speed.

A couple of observations on things you've said:

I was told by Pacsci to just hook them up in parallel and go with it. Do you see any problem with this?
Yes, it's meaningless. They're FOUR wire motors - it is not possible to wire them in parallel.

I am going to be using a 54vdc 800 watt power supply with these drives.

Your 2 drives are going to require ~4.2Amps in total from your PS. Your PS can source ~14.8 Amps so that will not be a problem.
Re: Toroidal transformers vs standard IE
« Reply #13 on: March 30, 2008, 01:23:42 AM »
I don't know. I think that the system I built before had 2 nema 23 pacsci powermax II motors that were rated for
35vdc and I ran them on a 24vdc power supply.
end result, they ran great for what I needed slow speed an a lot of torque.
I think that everyone input is great, but in plain English I don't understand why
if the plate on the motor states for an E33 sigmax motor 665 oz-in 65VDC 5.4
why this motor would not give me my 665 oz-in or close to it when using a 56vdc power supply
Max rpm on this machine is going to be 180-200 rpm
?should this work yes or no.
?the other motor e33 sigmax  996oz-in  4.5vdc 8.4amps
same max rpm 180-200.
will these work with a 56vdc 800 watt power supply
yes or no.
? what should I expect to see when powered up an I make a first move.
they are 1500 rpm motors.
I think I have a large motor for what I need but this is what we have.
and I would like to use them.
It seemed to work on the other system I built, the only thing with that was the top end speed
was not there.
Anyway just thought I'd ask.
My brain is fried after working 16hrs a day
thanks,
Brian










Offline Sam

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Re: Toroidal transformers vs standard IE
« Reply #14 on: March 30, 2008, 04:02:54 AM »
The questions your asking cannot be answered with a simple "yes" or "no". What may be suitable for some, may be totally unsatisfactory for others. Allot depends on the specific application, or, as most people need/want "widest possible ranges of multiple applications". The design of the machine plays a huge part also. If your making a pick-and-place machine, for example, your requirements would not be as critical as say, for example, a hobby router capable of cutting wood, plastic, aluminum, steel, 3d embossing, and all the while keeping an acceptable level of tolerances. Nobody here is telling you "it won't work", as it very well may work perfectly for your application. Were just here to help people avoid potential mistakes we have already made. Yes, I have a pile of stuff that never made it on my machine. I admit it. Anybody that claims they haven't made bad purchases...is a liar.

Now, I'm definitely not the expert on your questions, by any stretch of the imagination. But I will try. I'm not even going to state that I am correct in my own assumptions.

Quote
why this motor would not give me my 665 oz-in or close to it when using a 56vdc power supply
Max rpm on this machine is going to be 180-200 rpm
The same could be asked at the race track. My car has 450 HP and 500 foot pounds of torque. However, at 200 mph, the torque would drop off drastically. I need some nitrous oxide (more voltage) for a boost over a wider range of speed. These figures are made at optimum conditions, and not at an industry standard. You should be able to find spec sheets on your motors. If they say 665 oz at 200 rpm's, then there ya go. I have seen spec sheets where the torque drops like a cliff face at 5 revs per second. Take advertised specs with a grain of salt.
Quote
?should this work yes or no.
Dunno. (that was easy to answer!)
Quote
?the other motor e33 sigmax  996oz-in  4.5vdc 8.4amps
same max rpm 180-200.
will these work with a 56vdc 800 watt power supply
yes or no.
If I were a betting man, this is where I would put my money!! Lets see....800/56=14.3 amps. Depending on the quality of your power supply (again, no industry standards for determining the actual performance. Power supply makers have a BAAAAD reputation for stretching the truth.) it should put out 14.3 amps. It should do the trick. Don't forget to add up the amps from the other motors for a total. If it's a cheap unit, it might not even hold up to 8 or 10 amps at 56 volts. Or it might for 15 seconds. Or it might hold up forever. If your using 3 motors, 14 amps might be on the slim side. When power supplies burn out, they can be potentially dangerous. Even a computer P/S can burn out, taking the house/occupants with it in a worst case scenario. We should think about that when we add that extra hard drive or upgrade to that power hungry graphics card. Power supplies are very important. Many times a problem outside can be traced back to the P/S. That's why lots of people build there own. They can rest assured with a high confidence level there power needs are being supplied correctly.
Quote
? what should I expect to see when powered up an I make a first move.
hopefully, movement. (ahhhh, another easy one)
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."
Re: Toroidal transformers vs standard IE
« Reply #15 on: March 30, 2008, 06:33:54 AM »
Thanks Sam,
I think what I'm going to do is what I have always done and that's just build the freakin' thing
with what I've got and see what happens.
the last machine i built was holding great tolerances +/-.0001 with no problem turning 316 stainless
this one will machine aluminium in a 8" x 10"  table
I built the x - y table and it's tight. so I'm just going to build it and go from there.
Gut feeling, I think since the machine will travel at slow speeds I don't think I'm going to have a problem.
Like I said the last one I had powermax II single stack motors and tool pressure wasn't a problem and speed wasn't either
again motors were rated for 35vdc And I ran them on a 24vdc ps the only problem was speed when micro stepping.
and I think that won't be an issue here cutting 10- 20 or even 30 ipm .375-.500" deep in 6061 or 2024
I'm going to try it.
I think that the 4.5vdc motor will fail prematurely due to the excess voltage.

Thanks,
Brian

Offline Hood

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Re: Toroidal transformers vs standard IE
« Reply #16 on: March 30, 2008, 07:48:38 AM »
The 4.5v motor will be fine with the Geckos at that voltage, its recommended that you go 5 to 20 times the rated voltage of a stepper, I have run 5v rated steppers with Geckos and 77V PSU for 5 years now and no problem.

Hood

Offline stirling

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Re: Toroidal transformers vs standard IE
« Reply #17 on: March 30, 2008, 10:33:11 AM »
KNS - I think you're right to just go ahead and build it and see what happens. With respect I'm wondering why you asked in the first place. Throughout the whole thread, no one has said it won't work. If you mean by work, will the axes move? then probably yes. If you mean will you get the performance you need then with the info you've given it's not possible to say yes or no - and again that is basically what everyone has said.

There are however a couple more issues I'll throw into the pot - make of them what you will.

Gecko say that (and I quote) "In a all cases the power supply should be no less than 4 times or no more than 25 times the motor's rated voltage. The motor may not run as smoothly as possible if the power supply voltage is less than 4 times the motor's rated voltage".

Will it rotate, probably yes.

One other thing is that with the 65V motor, you are in no way going to get the performance from the gecko that you've paid for. That poor little gecko is going to be sitting there going - why me? - I'm a thouroughbred race horse - why am I pulling this cart?

Finally a note about calculating your PS current requirements. With friendly respect to Sam, you don't just add up your motor's rated currents. Chopper drives do not draw their apparant load. The total will be at most 2/3 of the sum of the motors rated currents and with 4 wire motors it will be nearer to 1/3. hence the value I stated in my previous post.

« Last Edit: March 30, 2008, 10:36:27 AM by stirling »

Offline Sam

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Re: Toroidal transformers vs standard IE
« Reply #18 on: March 30, 2008, 02:36:18 PM »
Live and learn  ;)
"CONFIDENCE: it's the feeling you experience before you fully understand the situation."
Re: Toroidal transformers vs standard IE
« Reply #19 on: March 30, 2008, 04:44:51 PM »
Thanks, Guys
To answer your question on why I ask is really simple: To get a feel of the territory I'm about to enter.
I a firm believer that sometimes people shouldn't be afaraid to get into something that they don't know a lot about.
Just Do It.
I have found out a few things in this forum:
1) It's amazing how much information there is out there.
2) It's also amazing how differently people see things.
All can be right. They just have a different route in getting there.
I used to design and build machinery for the PVC pipe industry.
So when someone tells me to boost the voltage for a DC motor; well I really need to investigate that.
For instance try taking one of you small dc computer fans and hooking it up to your car battery!
What's the outcome... A real fast hairdryer that melts.
I have tried to pull up info from everyone and everywhere to get an idea on how I'm going to persue this.
I think I now have enough to go on.
Thanks, to all of you.
Also, when I talk to the mfg. of the items in question, they all tell me just bits of info and frankly what they said and what
you guys had said in the past posts were kind of conflicting.
So I just felt I'd ask the people that actually use the stuff not design it.
As a designer and "engineer of sorts" I have learned 1 solid fact.
That is.
I hate most Designers, Engineers, Salesmen, and architect
The reason,
They never work with the stuff they design and manufacture.
All the products I've designed and built I actually had to work on or with everyday.
So the info I get from you guys is golden.
Thanks again,
Brian
KNS Supply