60-70v unregulated power supply recommendations

[Agathon]

I just want to check that the symptoms I'm getting with my set-up is down to an inadequate power supply. Here they are:

• Losing steps on rapid travel
• Drives trip "sensorless stall detection"
• I also get an occasional message from Mach3 saying something like "one or more of the drives exceeded the 25000 kernal setting".

I've got the current settings at maximum.

[Neale]

I just want to check that the symptoms I'm getting with my set-up is down to an inadequate power supply. Here they are:

• Losing steps on rapid travel
• Drives trip "sensorless stall detection"
• I also get an occasional message from Mach3 saying something like "one or more of the drives exceeded the 25000 kernal setting".

I've got the current settings at maximum.

Point 1 - could be a number of things. On rapid, I would expect the stall detect to come in, but I suspect that it's not just the motor being overloaded. Could be tied in with point 3 below?

Point 2 - I get this if I try to work the motors too hard (mainly, that just means trying to go too fast. In my case, the motor speed is getting close to the stepper motor's corner speed, the point where torque starts dropping rapidly). I found that increasing current helped (torque depends on current) and I have ignored the actual numbers; I've turned up the current to the point that the motors run just a bit too hot to touch which is fine for steppers. Increasing voltage helps, as it allows the motor current to rise more rapidly. The driver will stop the motor being overloaded, but the higher voltage gives the motor that bit more of a kick at the start of each pulse.

Point 3 - sounds like you are trying to drive the motors with too many microsteps. Using my machine's settings as an example - 5000mm/min with 2005 ballscrews means 1000RPM. I'm using x8 microstepping, so 1600 pulses per rev. That works out at just under 27K pulses per sec. The Mach3 kernel speed is tied up with its ability to generate accurately timed pulses, and maybe you are pushing its limits. I'm using Mach3 but with an external motion controller which takes over the pulse generation and frees you from some of these Mach3 parallel port issues.

I may have made some false assumptions in that bit of reasoning so don't take this as gospel! First thoughts based on what you have said, though.

[Clive S]

I just want to check that the symptoms I'm getting with my set-up is down to an inadequate power supply. Here they are:

• Losing steps on rapid travel
• Drives trip "sensorless stall detection"
• I also get an occasional message from Mach3 saying something like "one or more of the drives exceeded the 25000 kernal setting".

I've got the current settings at maximum.

I believe you are using about 36V smps at present it will be night and day difference on 70V toroidal

[Agathon]

I believe you are using about 36V smps at present it will be night and day difference on 70V toroidal

Just want I want to hear Clive.

I'm just being cautious and will look into all that Neale mentions too.

Many thanks again, David

[Clive S]

Just want I want to hear Clive.

I'm just being cautious and will look into all that Neale mentions too.

Many thanks again, David

I have given you the list in post #7 just build it any probs just ask. Its all been done before many times tried and tested. Good luck.

[Agathon]

OK, so I've built the power supply (625 VA). Ignore the overlong DC wires in the pic - I've left them long as I'm not sure where I'm going to permanently mount a fuse holder. On that topic, what size fuse should I fit for the output? The temporary set-up has a 20A fuse, but if I go with a 20mm fuse holder the largest fuse is 10A. Would a time-delay fuse work given the short peak over-current demand?

[Clive S]

You have gone to town on that. Have you fired it up to see if you are getting around 68V DC if so fine. Are you going to mount the tx on a ali back plate? Re the fuse if you are going to make a control box use din rail fuses and fuse to each drive

[m_c]

Only the input to the transformer should be fused.

Fusing the output is more likely to blow up your drivers, than protect anything.