Anyone got a source for a decent-sized DPDT switch. Rated about 240V, 30A would do. If it has an "off" in the middle, so much the better.
want it for a reversing switch for a single-phase motor, on my Colchester Student. Currently, the motor is only 1.5HP, and I have a 2-gang 10A rated switch pair doing this job, but it's not ideal, and in the longer term I'm going to be putting a bigger motor on it as the 1.5HP is not really enough, although it manages most things.
Colchester
Spaniards
Austin,
I'd be tempted to use two contactors, one wired for 'forwards' one wired for 'reverse' and electrically interlinked so they cannnot both engage at the same time. Drive the contactors off your current switch.
AWEM
Will the switch be actually turning the motor on & off, or just reversing the connections while a contactor (or something else) switches it on & off?
Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
If the simultaneous operation of both contactors would short the supply, as I would assume, then a mechanical interlock should be fitted too. They're a fairly cheap thing that bridges the pair and makes sure you can't close both together, it's important because contactors can stick and auxiliary contacts can fail. They're standard practice when changing a load between a mains supply and generator, when you're not paralleling of course. Greg
farnell pt. number 103068
only 20A tho.
You can order their stuff through City Electrical Factors, Newey&Eyre, Buck Hickman, or Hagemeyer, failing that contact me off-list and I can get one for you
Unless they've changed their policy you can just phone Farnell with a credit card, they don't care who's money they take 8-). Greg
20 quid minimum tho, and the switch is only £3.23
And if you phone them, you might end up talking to me :.)
Note seperate on-off motor switch needed as switching from fwd to rev while motor powered can weld relay contacts. Chris
On or around Sat, 14 Oct 2006 21:14:47 +0100, Tim Leech enlightened us thusly:
generally, it'll work by turning the motor off and then operating the reversing switch. For mechanical reasons, it's probably not clever to try and reverse while it's running :-).
The presence of an "off" in the middle would add a level of protection, is all - it could be an on-on changeover, rather than an on-off-on.
The currently-fitted switches actually work ok, but are already marginal on rating. When cold, the lathe takes time to run up to speed in the higher gears [1], and if you try to start it in too high a gear, it trips the 10A cut-out in the motor starter. That can be turned up to 14A, so a bigger motor should be possible. 10A running load is more than a 1.5HP motor should need anyway, of course...
[1] when cold, it won't go at 1200 at all... although it will once it's warmed up a bit. Hardly surprising, the original motor for the model is 3HP 3-phase.On or around Sun, 15 Oct 2006 12:32:29 +0100, "Chris W" enlightened us thusly:
yeah, I have a separate starter. I only need reverse occasionally, anyway - mainly for cutting LH threads with a die.
Ah, now oddly enough I've never had a problem with that as I can always find lots of bits to buy 8-)
Greg
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