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gary wrote:I like the idea of the extra DC motor - will be very interested in how it goes.
gary wrote:Because of resonances there are "hot spots" in the speed characteristics of a stepper that prevent it reaching a particular speed. It may be possible to bring a stepper up to any particular speed (with, say, a DC motor) and for it to run quite happily at that speed.
None-the-less, as I have hitherto mentioned, running the stepper at a higher voltage with a suitable current limiting resistor is always an option you could try.
harry dalek wrote:perhaps i should of went with MOSFETS.
gary wrote:harry dalek wrote:perhaps i should of went with MOSFETS.
Considering you want something along the lines of 10 times the stepper rated voltage I think that's a big yep.
EDIT: OTOH I don't think you are exceeding the rated voltage (of the outputs) - are you SURE you are not exceeding the devices current carrying capacity? (500mA) In other words is your current limiting resistor large enough?
Can you post your circuit including the resistance of the stepper motor windings (or the specs of the stepper if you have them)?
gary wrote:Harry,
stepper 1:
I = V/R = 12/(10+8.3) = 0.66 amps = pfzzzttt!
stepper 2:
I = V/R = 12/(10+4.2) = 0.85 amps = pfzzzttt!
Actually, the ULN2003 are rated for 50V (according to my data sheet) and you would probably want to get the voltage somewhere up towards that to get the speed you are after. You just have to make sure the series resistor keeps the current below .5 amps (say .4 amps), and is of a power rating large enough to dissipate the heat.
For instance:
Stepper 1:
for 12V R = V/I - Rs = 12/.4 - 8.3 = 22 ohms (5 watts)
for 40V R = V/I - Rs = 40/.4 - 8.3 = 92 ohms (15 watts)
Stepper 2:
for 12V R = V/I - Rs = 12/.4 - 4.2 = 26 ohms (5 watts)
for 40V R = V/I - Rs = 40/.4 - 4.2 = 96 ohms (16 watts)
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