Z axis invariably stops while trying to home

Hi,
I've got a home brew printer I'm trying to get to work, but I've noticed a frustrating issue: while trying to home, the z axis seems to eventually stutter to a stop. Replacing the DRV8825 controller on the z, or just waiting for a while seems to restore functions, but not for long.

I'm thinking the print bed might just be a bit heavy (big chunk of aluminum) and current draw might be exhausting the controller which has a good 400mm to home (long axis). but it doesn't even get very hot (quite cool actually, has a cooling fan on it). The motors are also cool to the touch.

Has anyone experienced an issue like this? Don't know what I can be besides manually lift the stage (not trivial to do, have to hand-spin the motor shafts for a long time) and only do z-home from up close, but even then I don't know if it'll last through the print. I have the arduino RAMPS combo driving the thing, with Marlin firmware. Thanks in advance.

Edited 1 time(s). Last edit at 06/23/2016 10:54PM by anvoice.

Sounds like the driver is overheating, you need to lower the stepper current. A heatsink on the driver chip doesn't cool it properly. These drivers use the pc board for cooling, so the heatsink needs to be on the pc board side. To make room, just use two 8-pin stackable headers to raise it up and move the fan to blow on the heatsink underneath.

Edited 1 time(s). Last edit at 06/24/2016 12:57PM by stephenrc.

Thanks, will give that a try, but I'll have to wait for the stackable headers. In the meantime, I'll try monitoring the temp under the PCB board to see if it's indeed overheating (the heatsink on the chip is not).