Power Supply Question

[ricks]

Power supply question.

I recently had intermittent lost steps in the X axis. The same file had run 22 times, then the lost steps began. After pulling and reseating every wire in the Wago connectors, checking the speed test in diagnostics (85%), pulling the motors away from the rack and checked for binding, I decided to dig into the controller and check things.

My machine is a 4G upgrade (might call it a 5G, I'm running five Gecko 202's. I have two motors on the Y axis). All motors are the PK296A1A-SG3.6. My X and Y rails may be heavier than the normal PRT, they are C channel iron and large angle iron parts with solid aluminum to hold double BW rails. I was cutting at 3 ips.

As Shopbot suggests, when I got the upgrade a couple of years ago, I turned the power supply up to close to 60 volts. I now measured the power supply at 47volts. Turned it back up to just below 60volts and it hasn't lost a step since.

My question is, is this a normal occurrence for a power supply when it ages or is this evidence of it failing?

I'd also be interested in buying an off the shelf power supply, with more power, if someone knows of an exact model.
(I don't think I want to build one).

Thanks for any help.

Rick Samish

[richards]

You can use a power supply up to 80VDC. Antek makes the 70VDC model PS-4N70Rxx (where xx is the value of for the secondary voltage). That power supply costs between $95 and $125, depending on the secondary voltage(s).

Your motors pull 1A maximum per motor, so a power supply that gives you 5A continuous would be adequate. I don't know whether you'll need other voltages or whether you already have an auxiliary power supply to furnish the 5V and 12V (and possibly other voltages) that you might need.

Most power supplies do not drift; however, if there is an adjustment pot, you can always put a drop of clear nail polish on the pot's dial to keep it from creeping with vibration.

[ricks]

Mike,
Thanks, that's exactly what I wanted to know.

My existing power supply is the Mean Well SP-300-48 (DC output 48V 6.25A).
The V+ and V- are the only wires going to the board.
The control box has a regular computer 250W power supply that supplies the 5V and 12V.

Is there any advantage to having the new power supply, supply all the voltages, and eliminate both older supplies?

Thinking of vibration, my control box has always been on a concrete floor, not attached to the Shopbot.

Thanks again, and for all your posts in the past, can't tell you how helpful they've been.

Rick Samish

[richards]

If you decide to replace your power supply, I would keep the regular power supply and only replace the Mean Well SP-300-48 with a toroidal-based power supply.

It is common practice to add a large 10,000uF (or larger) filter capacitor to all stepper motor power supplies, even switching power supplies.

Because of the nature of a stepper motor, a toroidal based non-regulated power supply is usually preferred over a regulated switching type power supply. A switching power supply usually is designed to be used when the output current consumption is fairly stable (like a computer). A stepper motor draws a differing amount of current depending on its speed and its load, so it taxes a switching power supply.

The filtering capacitor helps a switching power supply to deliver adequate current exactly when that current is needed. Of course, a linear power supply (non-switching) MUST have a large filter capacitor (or a bank of smaller capacitors).

The standard formula for computing the size of a filter capacitor is: (80,000 X Amps) / Voltage. In your case, with a 48V power supply: (80,000 X 6) / 48 = 10,000uF.

The proper sized capacitor will keep any ripple to a minimum (5% or less).

[ricks]

Thanks Mike,

I'm going to replace the Mean Well with the Antek.

Rick