[SOLVED] How do I calculate the reference voltage for Melzi board stepper drivers?

Hi everyone,

I have bought a Melzi board and some 17HS8401 (1.8 A) stepper motors. To make the Melzi deliver 1.8 A current to the motors, I need to set the reference voltage of the stepper drivers like described here (Reprappro Mendel instructions). I have found this source to help me calculate what the reference voltage should be if I have a A4988 stepper driver. I have two resistors marked with "R050" on each driver.

However, the black stepper driver chip on my Melzi says "4988ET A1316 935T" instead of just "A4988" as I expected. I have not found any datasheet or even a description of A1316 driver, and hence this question to you:

What does this difference in marking mean?
Or, to be more specific:
Is it safe to use Vref = 1.8 * 8 * 0.05 = 0.72 V as reference voltage?

Edited 1 time(s). Last edit at 07/14/2013 09:15AM by tobben.

When doing an image search for "A4988" i found several chips with markings similar to mine (example), so I guess I should be fine. I'm still interested in details about what this marking tells me though.

Great thanks from me too, soldering solved the problem with brand new Melzi and old Nemas-17.

If the motor has a label of 1.8A, that is a max, and does not mean that you need to actually have 1.8A in it to work. However if you insist to get close to this number, both stepper driver chips and the motors will run quite hot, and under worse operating conditions you have more chances of bad stuff happening.

The point of adjusting the motor current, is to find a minimal current level at which your mechanics function normally without missing steps or without any issues. The aim is to get this minimal level for many concerns but also for efficiency. Any current more than that is basically wasted.

I would set the vref to a low level, like for a current of 0.5A, make some observations, then increase perhaps to a level like 0.8A, afaik i think the latter number is reasonable for most machines. Perhaps for z and extruder to have like 1.0A and x and y 0.8A, or anyway something like that range. At least my opinion.

Thanks for the answer, NoobMan! You are right. I figured it out after burning a chip last summer...

Check out the web app I released yesterday: [tobbelobb.webfactional.com] An article with this ref-voltage-knowledge would be very welcome indeed

Edited 1 time(s). Last edit at 04/15/2014 09:40AM by tobben.

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torbjornludvigsen.com

The relation between current peak adjustment and vref is vastly different, first bewteen chips and manufacturers, and second because different values of Rsense are used. So i dont think there is anything generally valid here, except the basic idea. The exact formula has to be taken, from chip datasheet and the Rs resistors have to be checked on the board documentation. This is for each case in particular. Also not even the basics are 100% valid, there just a few chips which do not even use Rs for sensing but other methods, so this is to speak of diversity.

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The point of adjusting the motor current, is to find a minimal current level at which your mechanics function normally without missing steps or without any issues.

To get the best performance you should use the highest current that the motor or driver can handle without getting too hot. Higher currents give better microstepping linearity because the ripple current (which gives an offset) is comparatively less and higher torque gives less backlash due to friction.

I use Vref = 0.5V which gives 1.25A on a Melzi for 1.7A motors.

Edited 2 time(s). Last edit at 04/15/2014 12:59PM by nophead.

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[www.hydraraptor.blogspot.com]

I stand corrected then

And /bow and ty Mr Nophead for the better information.