Power Requirements
NWUpgrades
Posts: 292
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.
Comments
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
http://hometown.aol.com/newzed/page4.html
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Sid Weaver
NEW! 4 MB EEPROM
http://hometown.aol.com/newzed/page4.html
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Sid Weaver
NEW! 4 MB EEPROM
http://hometown.aol.com/newzed/page4.html
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73
spence
k4kep
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
http://ca.geocities.com/steve.brady@rogers.com/index.html
"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."
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
http://ca.geocities.com/steve.brady@rogers.com/index.html
"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."
Page 1
links·that refer to V:
super link http://education.yahoo.com/reference/encyclopedia/entry?id=34826
#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
Links that refer to E:
#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
Links that refer to U:
#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.
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
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
http://ca.geocities.com/steve.brady@rogers.com/index.html
"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."
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.
Voltage is measured in Volts
Resistance is measured in Ohms.
Power is measured in Watts (typically!)
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Steve
http://ca.geocities.com/steve.brady@rogers.com/index.html
"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."
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
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· [noparse]:)[/noparse]. ·If what I am saying is wrong, I welcome being corrected.
Nate
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
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
http://ca.geocities.com/steve.brady@rogers.com/index.html
"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."
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...