I though that I might expand a little bit on the stepper drivers and the things that I did to modify them. First I changed the R5 and R8 resistors to 2.2k from 1k as to not fry the LEDs when I start to pulse the ABCD stepper channels. I also changed the sense resistor from a .25 ohm resistor to a .5 ohm resistor, I don't know if this was needed or if it was necessary, we will find out in the testing. Another thing that I made sure to do was to make all of the capacitors have a 50v rating (the reason that I used a through hole capacitor instead of a SMD cap) so they won't explode on me! Also if anybody knows if the sense resistors are required to be changed or if they are supposed to stay at .25 ohms then let me know
I will be testing the board and seeing if they work and doing another blog post after that so stay tuned!
I am running the makerbot stepper boards at 36 volts with no mods. 36 was as low as the power supply would go. The LED's don't seem to mind because of the short duty cycle. I do have a fan on the boards.
ReplyDeleteAlright thanks I hope that I don't have to modify my boards again!
ReplyDeleteI also run 2.3 drivers unmodified at a higher voltage 29v its only 29v as that was as high as I could get the PSU could go. The leds are brighter so may not last as long.
ReplyDeleteMy theory was that If I was running the stepper motors at x2 voltage then I would have to double the sense resistors value for the sense input on the motor driver because of ohms law. Do you know if the trim-pot is functioning the same as if were running off of 12v?
ReplyDeleteThe sence resistor is the means of measuring the current the driver is feeding the stepper motor.
ReplyDeleteThe resistor should remain the same value to maintain the ability to caculate the curent the driver is driving.
It is being used as a shunt resistor as defined here:-
http://en.wikipedia.org/wiki/Shunt_%28electrical%29
Here is an exert from the Alegro A3982 data sheet.
"The maximum value of current limiting is set by the selection
of RSx and the voltage at the VREF pin. The transconductance
function is approximated by the maximum value of
current limiting, ITripMAX (A), which is set by
ITripMAX = VREF / ( 8 × RS)
where RS is the resistance of the sense resistor (Ω) and VREF
is the input voltage on the REF pin (V).
The DAC output reduces the VREF output to the current
sense comparator in precise steps, such that
Itrip = (%ITripMAX / 100) × ITripMAX
(See table 2 for %ITripMAX at each step.)
It is critical that the maximum rating (0.5 V) on the SENSE1
and SENSE2 pins is not exceeded."
Ref Doc:-
http://www.allegromicro.com/en/Products/Part_Numbers/3982/3982.pdf
The A3928 stepper motor controler Load supply voltage can be from 8V up to a maximum of 35V.
With the logic power supply being from 3.3v to 5.5v.