Help with correct vRef

Back story is I have had my printer for few years and I was told not to worry about setting it with a meter just tune it to where it doesn't skip steps and leave it. I have had nothing but issues with my extruder where the hobbed gear slips I think maybe due to the extruder being too hot causing the slip. It is fine if its an 30min print but any longer its it will slip for sure.

I have ramps 1.4 with china pololu 4988. The resistor values on the board say R100 a pair of them so I assume that these are the sensing resistors. (I can not read the board to see if it is r7 and r8 its smeared)

The motors I am using are 1.8a/phase (if I am reading it right.)
X, Y, Z
[artofcircuits.com]

And for E It just says 1.6a I don;t know if that is per phase but I assume.
[www.phidgets.com]


So here are my questions.

1. Would this be the correct way to figure out my vref for 90% of max?
1.6 * 8 * 0.1 = 1.28 * 0.90 = 1.152v


2. Is 90% too much? What do you recommend?


3. Do I have to double the value of the Z to provide it twice the power since it is running 2 nema's?

Thanks in advance for your help

PS.
I checked the vref values as they are set now and they are lower then I expected.
X = 0.547
Y = 0.753
Z = 1.195
E = 0.469

Edited 1 time(s). Last edit at 12/15/2016 10:58PM by zerocool5878.

The formula is correct. Most people say 80% of max. current is OK, but when your stepper already gets hot at 0.46V there is something wrong with the cooling
Is it a direct drive all_metall extruder? If so, make sure the heatsink has a good contact to the extruder without crunching the fan-mount. (Use extra M3 nuts)

Do you have a fan aimed to the drivers? A stepper can be very hot without failing, but the drivers have an overtemp protection.

When your z-steppers are connected in parallel you can double up the current, but with the leadscrews, this is usually not necessary.
It is much healthier and safer to wire the steppers in series.

Hey Thanks for your reply. I ended up going with 60% of max on the x and y. 90% of max on the Z (because its driving 2 motors so its more like 45%.) And 75% of max on the E which is a geared nema direct dirve.

Everything seems to be ok now. I guess it wasn't overheating just severally underdriven. I was able to do 2 prints 1.5hrs long with no issues.

Thanks for your help