The files section has a data pack for the Erskine drive unit including a typical circuit diagram, set up data and most component values. So far as I'm aware it has everything that is readily available out in the wilds of the internet. I've not found anything else of significance since I compiled it. The Erskine unit takes its power from the auxiliary drive transformer in the main control box. The standard UK circuit diagram has all the details.
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My Drives Direct box connects via 5 pin plugs with both neutral and earth available so clearly all the connections are available. Many years since I hooked it in so i don't recall details.
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Start-up power ratings are confusing.
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Basically a Drives Direct box won't reliably start any motor above half its power rating. Essentially it has to run in its designed short term overload mode to deliver the start up current demanded by the motor. All perfectly safe, it's designed to do it, but the size of the internal capacitors limits ?how much current can be drawn for how long.
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In normal one VFD per motor mode everything soft starts drawing only enough current to accelerate from standstill so the VFD doesn't have to supply the high start-up current needed when running from utility power (or a Drives Direct box). So the capacitors and everything else inside can be much smaller and the device correspondingly cheaper. Drives Direct style boxes that an be used as an effective substitute for utility power aren't made commercially because Mighty Great Big Electrics Inc would need to make them about 4 times the rating of a VFD for the same size motor so the market doesn't really exist.
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When setting up fuses, overload trips et al on a Bridgeport motor you generally need to cope with a peak short term current capability of 150% of the rated normal load current. But all the standard control gear handles this.
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Clive
