I received a Monoprice i3 today, and after a quick setup and printing the customary butterfly, I gutted it and converted over to one of my Cohesion3D Mini control boards that run the 32 bit Smoothie firmware. The usual improvements in motion, speed and configuration aside, I did this because the stock board is pulling almost 18 amps thru its 10 amp rated power terminal. That’s a fire waiting to happen! And indeed quite a few people have experienced melted terminals.
For anyone counting the amps, the printer runs at 12v.
The bed measured at 1.0 ohms, so 12 amps.
3 amps hotend. (4 ohms)
A conservative 500mA per motor = 2 amps.
And the stock board regulates its 5v logic from 12v using a linear regulator! Yeah, no.
And again, not only is it running a 12 amp bed thru a 10 amp pluggable terminal (5.08mm) but it’s also running this entire 18 amps of power in thru another single terminal of the same type.
Wow. Just wow.
Originally shared by Ray Kholodovsky (Cohesion3D)
Today’s project: converting a Monoprice i3 to run on a Cohesion3D Mini. And it is now printing a piranha.
The truth, they burn. I need to get something back from Monoprice for this, less than 5 months of use. Would like to get a new board for it one of these days…
@ThantiK the machine i reviewed (and recently scrapped) was the Malyan M150, which may or may not be based on some of the same parts. The M150 is a clone of a Wanhao machine itself, and the electronics are similar to the ones we’re seeing here, but differ in a few details (like the connectors).
But it wouldn’t be uncommon to see changes throughout the life of a product - mine came with a genuine Meanwell PSU, no idea whether they’ve swapped that out for cost-saving measures yet.
Though I agree the connectors are overloaded, a stepper running at 1 amp does not draw 1 amp from the Vin rail. The current chopper in the driver acts as a sort of SMPS, with less current in than going out.
If you want a replacement board that is a drop-for form factor replacement for the Melzi, the CloneBoard (Sailfish) is available. Quite a few people are running that. Better performance and print quality than Marlin (but not as good as 32bit of course).
Assume the motors are ~4v rated (SWAG) the average current they draw from the Vin rail is ABOUT 1/3rd the motor coil current. It gets real complicated because, on top of the PWM current control, half step positions use 141% of rated current when both coils are added together, whole step positions draw 100% of rated current, and fast decay mode allows one motor coil to help power another and decrease PSU load… it’s basically impossible to calculate.
