Anet A8 Hardware Specifications

A8 Stepper Motors

The original ANET A8 uses 4 identical Nema 17 type stepper motors and the newer 24V A8 Plus also uses the same motor !

The Nema 17 specification defines the mechanical front attachment plate of the stepper motor. It does not specify anything else so do not assume that motors are interchangeable even if they are the same physical size and are sold as 3D printer motors.

Both A8's use the 42SHDC3025-24B stepper motor for all three Axis and the Extruder. This has the electro-mechanical specification shown on the right.

If you buy a replacement you will need to match or better the Torque and Current ratings.

There are newer Nema 17 motors with a 0.9° step angle that could help with printing accuracy but they would require recalibrating the steps/mm in Marlin.

A8 Stock Heated Bed Specification

The Stock heated bed is 12V 1.2Ohm i.e. a 10 Amp Peak Current.

This needs a minimum of 1x18AWG wire, and is probably better with 1x16AWG.

Evan at 16 AWG = 13 Ohm/km i.e. 48mV/m that is 0.48W at 10Amps so will run warm.

However it is common to see a pair of smaller gauge wires used rather than a single larger cable. Given the frequent bending motion of these cables whilst in use, you should monitor the state of these cables by checking the temperature of the cable and connector looking out for any hotspots developing.

Replacement Heated Beds now come with the heater elements split into two halves with 3 wire connections, where there is a common middle connection. Typically wiring across pins 1 and 3 gives two heating elements in serial and is for 24V 5Amp operation. Wiring 1&2 together across 3 gives two heating elements in parallel and is for 12V 10Amp operation.

Stepper Motor and Driver Temperatures

The following readings are actual measurements taken from my stock A8, before the Main board replacement, and are provided for reference.

This was done to enable a check, once I had the new board installed, to see if I was overdriving the motors and needed to dial down VRef and/or use the standalone reduce hold current option of the TMC2208 (ground the UART pin). They are long run stable temps (lots of short jogs on XY) and the ambient temperature was 21.7C

From the initial test with SKR 0.8VRef readings I needed to dial down the VRef on all motors but not to reduce the hold current as the Z motors are still pretty cool.

The Extruder motor is cooled by a constant 12V fan so it never really got hot, i.e. less than 30C. So much so that I have now added a PWM board to slow down the fan and reduce the noise levels without increasing the motor temperature.

However the E Driver runs the hottest at 47.3C at a VRef of 0.73V.

Note: With UART mode it is possible to dynamically change the stepper currents and I found that the X&Y motors, with low accelerations, will operate with just 250mA, so even my preferred 523mA may be slightly overdriving them.

If you increase the maximum movement speed of an Axis then you will need correspondingly higher currents.

Thermistor’s, Pull-Ups and Shorts

Both the Anet and SKR boards use a 4K7 pull up resistor, so, there is no need to change the ANet thermistor configuration.

The Anet uses the same Thermistor for both Bed and Hot End 3910 NTC (Negative Temp Coefficent) – Marlin Type 5 100K. The 3910 is no longer available and it looks like the 3950 is the replacement.

https://www.thingiverse.com/groups/anet-a8-prusa-i3/forums/general/topic:27359

https://www.thingiverse.com/groups/anet-a8-prusa-i3/forums/general/topic:13600

Warning: One of the most common causes of failure on the SKR Board is a damaged Hot End Thermistor, or its wiring, shorting to the 12V Heater circuit. Be careful when installing or changing the Thermistor. It may well be worth considering changing the Thermistor for the metal encapsulated type HT-NTC100K Thermistor.

Zonestar 2004 Display

Warning: Do NOT use the ANET 5V Zonestar 20*04 display unaltered. The 5V on the switches will damage the 3.3V SKR boards ADC Input if not the entire chip.

See: https://github.com/bigtreetech/BIGTREETECH-SKR-V1.3/issues/4

It can be modified but for the time and cost you should just buy a replacement. If you really want to use it then the hardware and firmware changes are discussed here.

See: https://github.com/MarlinFirmware/Marlin/issues/14552

Heating Times

Following PID Calibration my Hot End takes 2:00 minutes to get from 20C to 200C and the Bed takes 2:50 minutes to get from 20C to 60C (with slic3r my startup gcode will heat both at the same time).

Power Supply

The stock power supply provided with my Anet A8 was a 12V 20A supply with no cooling fan. I have installed a Volt/Current meter on the supply to monitor it. The currents that I have measured are:

Nozzle Heater 3A
Bed Heater 10A
Mainboard and Display < 0.5A
5 off Steppers at 550mA each 2.75A
I have not seen the demand exceed 16 Amps and it typically runs between 8 and 12 Amps whilst printing.

If you replace the power supply allow at least 50% headroom ie buy a 25A or 30A supply as the cheap power supplies coming from China are peak burst current rated and not average use current rated. They really overdrive the outputs and will burn out if you load them at 100% capacity for any length of time.

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