ANet A8 42SHDC3025-24B Stepper Motor Specification
The ANET A8 uses 4 off Nema17 type stepper motors. The Nema 17 specification defines the mechanical front attachment plate of the stepper motor. It does not specify anything electrical so do not assume that motors are interchangeable even if they are the same physical size and are sold as 3D printer motors.
Note: The 24V A8 Plus uses the same motor !
The A8 uses the 42SHDC3025-24B stepper motor for all Axis and the Extruder. This has the following electro-mechanical specification.
| Stepper Motor 42SHDC3025-24B Specifications | |
| Rated Power | 14W |
| Rated Voltage | 3.96V |
| Rated Current | 0.9A |
| Rated Speed | 1000rpm |
| Rated Torque | 0.34NM |
| Holding Torque | 0.4N.M |
| Step Angle | 1.8° |
| Step Angle Accuracy | ±5% |
| Phase | 2 |
| Resistance | 4.4Ω±10% |
| Temperature Rise | 80K Max |
| Ambient Temperature | -20℃~+50℃ |
| Ambient Humidity | 90% Max |
| Insulation Resistance | 100 MΩ Min. ,500VDC |
| Size | 42*42*40(mm) |
| Weight | 280g |
All we really need from this table is the Rated Current 0.9A (900mA) in order to set up the stepper drivers.
A8 Stock Heated Bed Specification
For Reference:
The Stock heated bed is 12V 1.2Ohm i.e. 10 Amp Peak Current.
This means a minimum of 1x18AWG wire, and probably better with 1x16AWG.
16 AWG = 13 Ohm/km i.e. 48mV/m or 0.48W at 10Amps so 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 cable 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. Wiring across 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 and after the Major Upgrade 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
| Board | Room Temp. | X Driver
Heatsink |
X Motor | Y Driver
Heatsink |
Y Motor | Z1
Left Motor |
Z2 Right Motor |
|
ANet |
21.7C | – | 34.8C | – | 36.9C | 29.0C | 30.0C |
| SKR TMC 0.8VRef 650mA |
20.7C | 45.0C | 41.3C | 49.0C | 45.7C | 30.9C | 29.5C |
| SKR TMC 0.73VRef 523mA |
21.1C | 42.3C | 34.0C | 47.3C | 32.9C | 26.6C | 26.4C |
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.
Note: The E motor is cooled by the extruder fan to less than 30C, however the E Driver is the hottest at 47.3C for 0.73VRef.
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 523mA may be overdriving them.
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.
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.
Caggius Interweb 