Phew.
All was not quite perfect, but pretty good.
The installation (right) Plenty of insulation on the back of the controls and indicators, and the touch guard goes over everything after this 🙂
The test load (below) came out well – two borrowed 100W incandescent bulbs and two 60W rugged incandescent bulbs bought new, attached to a board with three new bulb holders (and four I finally found after the replacements had been bought…) resulting in several different load combinations up to 320W. The junction box provides a place to tap-in current and voltage meters.
The load allowed the DC-51 motor speed controller current limit preset to be adjusted.
As the control was working right down one end (max is 4A and the motor max is 0.9A), and is very light in action (vibration might move it) it was hard to achieve am exact figure and 860mA rms was the nearest value that was not over 1A.
The voltage regulating trimmer was a bit of a let-down.
Initially the output could only be set up to 200Vdc (rms) with the external control and the internal ‘max’ trimmer both set to max.
Even after shorting out one resistor (which prevents the optional (and dangerous) external ‘stop’ switch shorting internal rails if both controls are set to minimum) with solder to get more range, the output would still only reach 213V dc. Further simple (resistor-swap) mods would have changed time constants, so these will only be made if performance is seriously compromised.
The ‘IR’ speed droop compensation circuit does not have enough gain (with this motor) to work fully, so it was left full-up to get as much droop compensation as possible.
A 3d printed control panel (right) holds the new no-volt release, and other controls and indicators. I came out well, although after three other attempts. Tall components are kept away from the red ‘stop’ button to maximise the chance of hitting it in a emergency (the black H-L gearbox knob cannot be moved).
An annoying thing that needs remembering is that the motor sometimes spins briefly (well under 1s) at switch-on if the controller has recently been powered.
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October 12, 2021 at 12:04AM
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Enough of the DC-51 milling machine speed controller - Electronics Weekly
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