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03-06-2005, 02:19 AM
Is there a way to figure out the amps/volts needed for a stepper motor if yuo have the Ohms? I have several stepper motors and I need to figure this out because there is no ID on the motors. I have the Ohms readings.

Newzed
03-06-2005, 02:37 AM
Before you can calculate power, you have to assume a specific voltage E.

Then W(power) =EI or W =· I(RxR).· Since you don't know the current I, the the equation becomes W = E(E/R).

now you have W, so I= W/E.

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Sid Weaver
NEW! 4 MB EEPROM

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03-06-2005, 03:27 AM
Could you explain this in easier terms? Sorry, but my algebra never was that great. You said rxr. Is that resistance x resistance??

Newzed
03-06-2005, 03:39 AM
Yes - same as R squared.

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Sid Weaver
NEW! 4 MB EEPROM

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03-06-2005, 03:52 AM
OK, So what is I ? Amps??

Newzed
03-06-2005, 03:59 AM
Yes.· I take it you do not know Ohm's Law.· That, and the basics 0f algebra are fundmental to working with electronics.

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Sid Weaver
NEW! 4 MB EEPROM

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Paul Baker
03-06-2005, 04:13 AM
Ohm's law is V=IR or voltage equals current times resistance. To solve for any value you must know the two other values. Just knowing ohms is not enough. If you can figure out what voltage is supposed to placed across the coil, your good to go, solve for I, multiply that by the number of coils that can be active at any one time, multiply that by the voltage and thats the power needed to drive it. Most power supplies split the values, they have a rated voltage and a max current draw. Any supply rated for the required voltage with a current rating higher than what you need is sufficient.

SPENCE
03-06-2005, 04:29 AM
Unless they have snuck something thru in recent years, the formula is still e=ir. It may be v in electrical and motors since they aways want to push electrons backwards but in electronics, and micros are part of that field, it is e for voltage, not v. This stems from the origin electro motive force.

73
spence
k4kep

03-06-2005, 04:39 AM
So if I put a 24v 1.5 Amp Power Supply to my Controller board, what will this do to a motor that only requires 12V and vice versa? The reason I ask is this: I had a 12v 500Ma Power adapter I was using to test my motors. After using it for 1 of the motors the power supply got hot and then stopped working all together. I am assiming that the Motor requires either higher voltage or higher amps, one of the two. Is this correct?

steve_b
03-06-2005, 04:44 AM
E or V....when all you have is a voltmeter and you're a hobbiest...you just want to know if it's AC or DC!!
This could easily break in to the electron or conventional flow (uhoh...I may have just started it! haha).

Anyhow, here's a quick diagram that may aide you in figuring out some of ohm's law.· I have an absolutely assbackwards way of 'figuring' out math problems and can't even explain it...but I refer to this 'triangle' all the time.

Now, you really should go through those free texts that Parallax gives you!· There are explanations of ohm's law through some of their texts and from the sounds of it, it can only help you!

Anyways, you could call ohm's law one of the root formulas!· things stem from this.
The power calculations would be next....
Power (watts) = Volts*Volts/resistance
or
Power (watts) = current * current * resistance
or
Power = current * Volts

Through all these calculations you should make sure you know what values you're using.· a 10kohm resistor is 10,000 ohms.· 1mA is 0.001Amps.
So when you're doing your calculations these might screw you up....use a calculator...even if you think you know it!·

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·

Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

steve_b
03-06-2005, 04:52 AM
So if I put a 24v 1.5 Amp Power Supply to my Controller board, what will this do to a motor that only requires 12V and vice versa? The reason I ask is this: I had a 12v 500Ma Power adapter I was using to test my motors. After using it for 1 of the motors the power supply got hot and then stopped working all together. I am assiming that the Motor requires either higher voltage or higher amps, one of the two. Is this correct?

You have to be careful the typs of 'power adaptors' you use.· Some are not regulated and could potentially mess some of your \$\$ items up!

Your 12V motors were running at twice their rating voltage....which means they were drawing more than intended.· Was it the power supply that got hot or the motors?!·

If you were to use a transformer (which is what's most of these regulators are) in a normal circuit.· Lets say that from the primary (call it the input if you like, but they will work in both directions) you have 20Volts across it's terminals and say 1Amp.· Well, if this is a 'step up' transformer, we can expect the voltage to be higher on the other side.· If the ratio of coils from the primary side to the secondary side is 1:2 then we can expect 40Volts on the secondary (output in this case) but only half the amps!· It's similar to the "Law of conservation of Energy"....you can't get more out than what you put in.· So, if you figure out the power with the equations I provided, P=I*V=1amp*20Volts=20Watts on the input.· So you can't have more than 20Watts on the output...so if you double the voltage, you half the current (P=I*V=0.5amp*40volts=20Watts).· Now, to be honest, you lose some power from the resistance in the coils (nothings perfect!).

Anyhow, this can get pretty wordy....but since you are pretty green to electronics, I STRONGLY recommend you pick up a book or do some googling!· You can learn a lot by doing the lessons that Parallax provides....but you can't run without crawling!

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·

Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

03-06-2005, 04:58 AM
Thanks for the advice. It was the power supply that got hot. I sometimes get ahead of myself, but figure it to be the only way to learn!!! Trial and error has always been part of life!

Paul Baker
03-06-2005, 05:18 AM
SPENCE said...
UNLESS THEY HAVE SNUCK SOMETHING THRU IN RECENT YEARS, THE FORMULA IS STILL E=IR. IT MAY BE V IN ELECTRICAL AND MOTORS SINCE THEY AWAYS WANT TO PUSH ELECTRONS BACKWARDS BUT IN ELECTRONICS, AND MICROS ARE PART OF THAT FIELD, IT IS E FOR VOLTAGE, NOT V. THIS STEMS FROM THE ORIGIN ELECTRO MOTIVE FORCE.

73
SPENCE
K4KEP
·
www.yahoo.com (http://www.yahoo.com)·search: Ohm's law

Page 1

#2 http://jersey.uoregon.edu/vlab/Voltage/
#4 http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmlaw.html
#5 http://www.grc.nasa.gov/WWW/K-12/Sample_Projects/Ohms_Law/ohmslaw.html
#7 http://www.csgnetwork.com/ohmslaw.html
#9 http://www.physics.uoguelph.ca/tutorials/ohm/Q.ohm.intro.html

#1 http://micro.magnet.fsu.edu/electromag/java/ohmslaw/
#8 http://www.the12volt.com/ohm/ohmslaw.asp
#10 http://www.caraudiohelp.com/ohms_law/ohms_law.htm

Links that refer to E and V:
#6 http://www.angelfire.com/pa/baconbacon/page2.html

#3 http://www.sciencejoywagon.com/physicszone/lesson/otherpub/wfendt/ohmslaw.htm

I believe that E is the european symbol and V is the american symbol (I don't know where the U is from). I have a MSEE, the formula is expressed as V=IR in every one of my textbooks that refer to it (6), I physically checked. Im not pulling things from thin air. Research something before you state it as an absolute fact.

03-06-2005, 05:25 AM
The link to # 6 is probably one of the best things I have seen in some time. According to the chart, I need a 6A Power Supply for my motor. I put in the 2.0 Ohms and 12V and that is what it came up with. Would it be safe to put 24 V 3A in place of this?

Paul Baker
03-06-2005, 06:14 AM
not unless the motor is rated to take that kind of voltage, You could use a DC-DC converter, but that is just making things unessesarily complicated. I'll do a quick look around and edit this post if I find a suitable supply.

Ok here's some professional supplies:

PSR 7: http://www.lashen.com/vendors/csispeco/Test_Equipment_and_Power_Supplies/Power_Supplies.asp
and http://www.starkelectronic.com/spcf.htm

pyramid ps-12kx http://www.etronics.com/product.asp?stk_code=pyrps12kx&store=&catid=4071

or if you want something cheaper, go with a computer power supply, nearly all of them provide more than 6 amps on 12V supply.

Post Edited (Paul Baker) : 3/5/2005 11:34:19 PM GMT

03-06-2005, 06:25 AM
Thanks for the help. I have a 5V Power Supply from a USB hub that seems to be running the same motor that burned out the 12V supply just fine. Unless maybe I just had a Power Supply that was going out.

03-06-2005, 06:32 AM
I have a Sonceboz 6500 Motor that seems to make my controller VERY hot using the 5V Power Supply. I am assuming I need more volts but want to make sure. The motor is listed at http://www.soncebozusa.com/hybrid_step_motors.asp#specifications However, they do not indicate the power requirements. I have e-mailed them several times with no response. If anyone knows anything about these motors I would appreciate a little insight.

steve_b
03-06-2005, 06:34 AM

you always need to check on the ratings of things you are connecting...don't assume that voltage is voltage and that Tim Taylor was right that more voltage is better!

You can sometimes get away with 6-10volts to a 12Volt motor.· This isn't bad....it will prolong the life of the motor, but understand that you no longer have the rated torque now.· So, if your load isn't too heavy, then maybe you can get away with a smaller voltage.· But going more than the rated voltage is pretty well garauteeing that your motor will die quite fast!

You'll find a dropout point if you put a small enough voltage on it.· Either it won't turn or it will chatter a bit!· So pick a voltage that will work to your needs.· So far as the current....some motors may have spec sheets with graphs that would let you know what kind of current it requires.· Not that motors require a lot of current to get started...so if you have too low a voltage the motors will hog current to try and keep turning.· All you can do from a power supply point is be sure that there's enough current available for your devices to draw from.· So if you have 4 motors that each draw 100mA, then don't have a 200mA power supply (give yourself some overhead and get a 500mA supply)!!· Again, remember that when all 4motors first start, they'll draw a crapload of current....

And a quick tip is to be sure you use a separate power supply for your motors.· The start-up current draw is enough to cause the stamp to reset sometimes!

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·

Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Paul Baker
03-06-2005, 06:39 AM
look at the above edited post, don't just be hooking up power without knowing what your doing. You'll burn the motor or the supply.

Paul Baker
03-06-2005, 06:49 AM
http://www.sscnet.ucla.edu/geog/gessler/topics/steppers.htm

seems to be a good general resource, as you can see different· motors are rated for different voltage, since you know the ohms of each coil, use ohms law to calculate·the corresponding amperage. You logic that "the 5V supply is running hot, I need more volts" doesn't hold water. Look at the equation V=IR your resistance is constant, you raise the voltage, the current rises. If your motor works at 5V, get another 5V supply that can handle more current.

03-06-2005, 07:32 AM
Current is the same as Amps, Correct?

steve_b
03-06-2005, 07:55 AM
Current is measured in Amperes (or Amps).
Voltage is measured in Volts
Resistance is measured in Ohms.
Power is measured in Watts (typically!)

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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Nate
03-07-2005, 03:48 AM
Not to be too much of a nitpicker, but I think we should give Spence more credit:

Electromotive Force (whose common symbol is a Greek "E") is measured in units of Volts (V) which in terms of SI (Systeme International) units·are kg*m^2/(A*s^3).

This comes from the 62nd edition of CRC Handbook of Chemistry and Physics (which most BS and ALL MS degree holders·should remember from their higher education days).

Saying "Voltage is measured in Volts" is redundant.· It is akin to saying that Amperage is measured in Amps.· You are mixing Quantity (Emf) with units (Volts).

Regards,
Nate

Post Edited (Nate) : 3/6/2005 8:54:50 PM GMT

Paul Baker
03-07-2005, 04:51 AM
I appologize for being harsh, I was simply trying to point out there is no consensus of what the accepted symbol is. I checked my CRC and yes, it uses E. Physics and other pure sciences have a tendancy to adopt european traditions, but rather it may be a case of those who study the theoretical verses the who apply the theory in practical applications. There is even a schism between abstract and physical theoretical pursuits. Just talk to a Mathmatician, a Physicist and an Engineer, you'll find all of them talking about the same thing but thier terminology and methodology to be quite different, so much so, that the lay person would believe that they aren't even talking about the same thing.

KenM
03-07-2005, 06:11 AM
Paul Baker said...
Just talk to a Mathmatician, a Physicist and an Engineer, you'll find all of them talking about the same thing but thier terminology and methodology to be quite different, so much so, that the lay person would believe that they aren't even talking about the same thing.
How true!

Nate
03-07-2005, 06:29 AM
I agree that many times different disciplines have different symbols for the exact same thing.· (The imaginary number as a "i" or a "j" is·one insane example)

Clarifying myself somewhat, Elecromotive Force (also known as Electric Potential Difference) is a quantity which has a SI measurement unit of Volt.· This·unit can·be expressed in SI base units as kg/(m*s^3).

This Chat Room has pretty good information compared to what is elsewhere on the Net, and I was·mostly·clarifying the somewhat muddying statement "Voltage is measured in Volts".· Emf is what is being measured, and Volt·is the SI·unit of measurement·of it.

I give this·knowledge in a friendly way and hope it is·taken as such· :). ·If what I am saying is wrong, I welcome being corrected.

Nate

Paul Baker
03-07-2005, 07:43 AM
Nate said...

I give this·knowledge in a friendly way and hope it is·taken as such· :). ·If what I am saying is wrong, I welcome being corrected.

Nate

It is taken as such and you are correct in the formal definition of EMF, but to an engineer "mass divided by meter seconds cubed" has absolutely no meaning whatsoever.·A more pratical SI definition is (kg·m2)/(s4·C) or J/C (joules per coulomb) or in lay terms the amount of energy a coulomb (6.241506×1018) of electrons possess, thats something an engineer can use.

But besides that I do concede the point about "Voltage is measured in volts" and your statements regarding it.

Post Edited (Paul Baker) : 3/7/2005 12:55:57 AM GMT

steve_b
03-07-2005, 10:19 PM
ZZZzzzZZZ· lol

I think the Original poster is nicely overwhelmed now....My original intent was to keep things simple...and granted, voltage is measured in volts might have been somewhat lame, but if he didn't know, he does now!

I think we've moved off topic somewhat!

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·

Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."

Tom Walker
03-07-2005, 11:02 PM
Perhaps I just read through this thread too quickly, but before it wandered into the "E vs. V representation of voltage in Ohm's law" territory, the poster was confused by the fact that his hookup of a 12V motor to a 24Vsupply was causing his circuit to heat up.

Without getting into any good "theory", this is not unexpected behavior. The motor was built to handle a certain amount of "force" (voltage). Assuming there is sufficient resistance in the circuit to limit the amount of current (amps), then you can get away with using more voltage than a motor is rated for...but only for brief periods of time. This is usually accomplished by Pulse Width Modulation (PWM), a method of sendign short bursts of voltage (OK purists...back off...<g>) to a device so that it averages out to be something that the device can use.

There are many threads that deal with this issue. Further reading may be in order.

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Truly Understand the Fundamentals and the Path will be so much easier...

Paul Baker
03-07-2005, 11:29 PM
I think he was stating his 5V power supply was overheating when he tried to power the motors (too lazy to go back and read through), He was also confused about what voltage to run them at because the only stat on the motors is the ohms the windings have.·It is a·stepper motor, so I don't know what PWMing the motor windings would do to the motor or it's MTBF rating. An alternate method of using a higher Voltage source would be to use a power resistor in series so the actual voltage across the winding is around the rated voltage (whatever that is).