4 stepper motors for Z-axis, amperage

axiom

since my bed is very large, I have 4 stepper motors for the Z-axes, each with 1.8 amps.
In the Config tool you can only specify one value for the motors. Do you have to add the amperage so that you can use the entire power?
Or does a Duet5 expansion board make more sense?

deckingman

@axiom The motor current setting (M906) applies to each and every motor driver on an axis because all motors must be identical and therefore must have the same current setting. Assuming that you have connected each motor to it's own driver chip, your 1.8Amps is per motor.

Mandragora

It depends on if you want to control all 4 motors individually for bed traming. If yes, every motor needs to be connected to individual stepper driver. So each will have its own set of parameters, which will be identical if you use the same kind of motors.
Other option is that all motors will be working together as one and bed traming will be done manually by turning screws of each motor. In this scenario all motors could be connected to 1 stepper driver. There are actually 3 ways to connect 4 motors to 1 driver.

All motors are connected in series. That way they will be seen as one 1,8A motor but with 4x higher inductance and resistance. It might work on low inductance motors and or high supply voltage, so you can actually create enough torque for desired speeds. Each motor will get exactly same current = same torque.
All motors in parallel. They will act as 7,2A motor which is to much for most boards unless you will decrease actual current by a lot. Another issue is that current for each motor might not be equal due to differences in resistance and inductance - manufacturer tolerances. This might result in different torque of each motor, so if actual torque will be to close to actual required, some motors might loose steps - very bad.
Mixed set up. You connect in parallel 2 sets of motors, where a set of motors are 2 motors connected in series. This way you get "best of 2 worlds". Current of 3,6A but not so high required voltage for supply.

I personally have 3 motors, each on separate driver which is best. I experimented on three 1,8A motors connected in parallel on 6HC board which worked on dry runs (but I also work on 37V supply). I don't know about that during printing.

I hope that will give you general idea.