I'm replacing the motor in an elderly micro lathe with a 24VDC one from an electric scooter. The power route will be mains > switched-mode PSU > switch > speed controller > motor.
What switch is appropriate here? Is it sufficient to insert a basic switch into the positive output from the PSU and take the negative output straight to the speed controller?
Many thanks.
Yes. Id probably put one on the mains side though
Thanks.
The PSU will be plugged into (and be close to) a standard switched wall socket, so I was assuming that this would be enough.
You want one rated for the appropriate worst case DC current if it is to last. That is unlikely to be a problem with most mains rated switches.
DC arc currents tend to be persistent if they occur. AC usually quench.
You may well want the sort of switch you can hit as an emergency stop.
What he says.
But if you really do need to switch DC with serious amps, you want a proper DC switch, not an AC one.
I recently had to put a manual switch on the 40 amp preheaters for a small diesel ATV (couldn't get the correct replacement timed relay) and I used one of these
If you're switching the DC side, make sure you use a switch designed for that. Luckily things like car electrics switches are plentiful.
It will be quite sufficient tor electrical safety to use a single pole switch. But this will be an expensive and probably short-lived switch for hiigh DC current into an inductive load. The PSU may not be too happy if it arcs a little on switch off. You are better getting a mains one in the right (physical) place. And, as someone else said, you can get one of those red and green button ones that locks out if the mains is interrupted so the motor does not come on unexpectedly if power is restored, and with a big red 'off' button.
You mean the right place for conveniently switching the lathe on and off?
So I would route the incoming mains supply through a switch near the lathe, then away again to the PSU and back as a direct DC 24V supply to the speed controller (also conveniently near the lathe) and then the motor?
I'm not familiar with them; I'll investigate.
Thanks.
I hadn't realised that there's a distinction. Thanks.
Right, thanks.
Is the locking-out feature also known as a no-volt release? If so, something like this?
Long URL:
depending on current, a semiconductor soft switch or even variable speed controller such as used for RC cars etc might be useful
You can buy a cheap 'servo controller;' to generated the RC signal for them
Thanks. It's been suggested elsewhere (if I've understood correctly) that it would be better to put an on/off switch (ideally with emergency stop) in the main supply to the PSU and use that to control the lathe.
I had a vague recollection that it's ultimately damaging to a switched-mode power supply to subject it to frequent turnings on and off, but perhaps I was mistaken.
It's not great on the mains side capacitors and rectifiers...a bit of inductance in series will help
Thanks. Or presumably I could go with my original idea and put the operational switch after the PSU, leaving that switched on for a whole session.
Well you are drawing a lot more current the lower the voltage. I'd imagine the wires to such a motor might well be pretty butch as well, and some on old cars are so big they would not even go into the normal ac switches. Brian
Or dig abput in the SMPSU and see if the control chip has an "enable" input that turns it on/off without having to switch the DC. Some SMPSU's have poor regulation when they don't have suffcient load.
Yes, that's the sort of thing I was thinking off. You can get them with just the red and green button and not the added rather gross red one!
Thanks for that. Yes, the massive panic switch is perhaps a tad over the top for my little Unimat lathe.
On the subject of whether to place a switch in the mains line or the 24V feed, I've been advised that a switched-mode PSU doesn't like being frequently switched on and off (as would happen if the operations switch for the lathe was before the power supply). Would a switch like the ones we're talking about be equally effective in the 24V supply to the machine?
It wouldn't work at all unless it was a specific 24V one. And the contacts on a mains one wouldn't be suitable anyway.
As a matter of interest, do power supplies like their output switched on and off any better?
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