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Why are motors not current limited?
On Tue, 24 Apr 2018 00:33:48 +0100, Wayne Boatwright wrote:
On Mon 23 Apr 2018 12:59:29p, Jimmy Wilkinson Knife told us... On Mon, 23 Apr 2018 20:08:41 +0100, Wayne Boatwright wrote: On Mon 23 Apr 2018 07:39:07a, Jimmy Wilkinson Knife told us... On Mon, 23 Apr 2018 15:34:12 +0100, Clare Snyder wrote: On Mon, 23 Apr 2018 05:11:13 -0000 (UTC), Wayne Boatwright wrote: On Sun 22 Apr 2018 05:53:35a, Jimmy Wilkinson Knife told us... On Sun, 22 Apr 2018 13:19:20 +0100, Wayne Boatwright wrote: On Sat 21 Apr 2018 11:45:29a, Jimmy Wilkinson Knife told us... On Sat, 21 Apr 2018 19:34:56 +0100, Wayne Boatwright wrote: On Sat 21 Apr 2018 10:30:54a, Jimmy Wilkinson Knife told us... On Sat, 21 Apr 2018 17:34:51 +0100, Clare Snyder wrote: On Sat, 21 Apr 2018 16:29:06 +0100, "Jimmy Wilkinson Knife" wrote: On Sat, 21 Apr 2018 16:13:43 +0100, Uncle Monster wrote: On Saturday, April 21, 2018 at 9:57:48 AM UTC-5, James Wilkinson Sword wrote: On Sat, 21 Apr 2018 15:50:07 +0100, Uncle Monster wrote: On Saturday, April 21, 2018 at 9:42:58 AM UTC-5, wrote: On Sat, 21 Apr 2018 12:35:25 +0100, "James Wilkinson Sword" wrote: How hard can it be to put some kind of electronic limiter on a power tool so if you over-stress it, it doesn't consume enough current to melt the coils? I assume something like this must be done on electric cars, or instead of stalling the engine, you'd wreck the motor. Most motors that are to be used unattended do have thermal overloads in them. I guess hand tool manufacturers assume you will stop before you burn up the tool I've been on construction sites where I'd cringe when I heard workers abusing both hand-held and table saws. One of the things I was always repairing/replacing were the power cords on circular saws where some genius carpenter got it caught in the blade. o_O I did that with a hedge trimmer once. -- You folks use 220vac 50hz as I recall. Did you have a lot of sparks or did the fuse blow immediately? o_O [8~{} Uncle Fused Monster The only observation I made was the trimmer stopped running. Of course I had a proper 3A fuse in the plug, not the 13A standard everyone seems to use. And no I don't have any form of circuit breaker, earth leakage or otherwise. North american stuff doesn't have fused plugs. We fuse the feed circuit. But you might have a table lamp or a heater plugged into that circuit. In the UK we fuse according to the appliance. It also means we don't have to run a seperate wire to every ****ing outlet. Is that why your plugs are so damned large? They're an easy size to get hold of. Your mickey mouse ones are pathetic. Do you have tiny little hands or something? And we had them that large before fuses, it ain't the fuse that takes up the space, it's because they can take 13 amps. Over 3 kilowatts on any device we like, no need for special circuits with different currents and voltages, just one standard plug and socket for anything you like, anywhere in the house. I can plug a computer, a lamp, a hairdryer, a vacuum cleaner, or a clothes dryer into the same outlet. OK, I undeand. Apparently at some point the US considred convertng to a system similar to that in the UK, but because of the already existig proliferation of both low and high volage devices, wiring, sockets, and plugs in the US, it was deterined impractical. At that point in time, there was not such a proliferation of such devices in the UK. Why would it be impossible to make all your future plugs the same, but containing a fuse? And you could gradually move over to the higher voltage too to simplify things. New appliances could run on the higher voltage, in fact switched mode power supplies would run on either. I never said it would be impossible, but at this late date it would probably be economically unfeasible given the millions of devices from generating stations down to single households. I'm also not suggesting that either system is better or worse than the other. What works in either country happens to work and no one on either side of the ponnd seems to have a problem with their own system. Personallhy, I don't really care. I was only curious some physical attributes of the UK system. Back in about 1954? Ontario Hydro decommissioned the old 25 hz system in the remainder of Ontario to switch up to 60 hz. This required the replacement of all induction motors, ballasts and clocks in the affected area. At that time it was a major hassle, but not a disaster, due to the relatively small number of induction motors and flourescent lights in use, as well as clocks. Can you imagine a changeover of that magnatude today? Particularly changing operating voltage - which would require changing anything with a transformer, a universal motor, a light bulb, etc AS WELL as the inductionmotors and ballasts which needed to be changed for the frequency shift??????? It would be a MAJOR disruption to ALL life in North America. To say it wouldn't be impossible is pretting a pretty litteral and restrictive definition to the word. At that time they did not decommission all the 25 hz generators - they installed HUGE rotary frequency converters which have only now been decommissioned with the overhaul od the last generating stations - with some industries in New York STILL running on 25 hz up untill the conversion in 2006? when the 25hz generators at the old Rankine station were decommissioned. But it isn't a sudden change in voltage. 240V is already in all American homes. You just move stuff over as you buy new things and use the higher voltage instead of the centre tap. Eventually the centre tap is obsolete. Homes would have to be rewired to handle 240 volts. When every homeowner has to have that done, it's a major undertaking and is not cheap to do. You have yours, we have ours, and I think we just need to agree to disagree. But you already have 240V. I'm tired of arguing over this. The 240V wiring in our houses is prdominately for electric ranges and electric dryers. The 120V wiring throughout the rest of our houses would not support 240V. Yes it would. Is it not true that you have double outlets with 120V on each, where neutral to each is actually the centre tap, and the live to each is opposite ends of the 240V? So you could remove the neutral and make a 240V outlet right there. Thus, every houses would have to be completely rewired and either additional or replacement power panels would have to be installed to support 240V for the entire house, not just for the range and dryer. It's not cheap to completely rewire a house or change out the power panel. All outlets and switches would also have to be replaced because they're not rated for 240V. Since I doubt that you have any intention of moving here, it's rather a moot point. Nuff said! As I said before it can be a gradual process. Just like electric cars and electric charging points, we don't change over from petrol overnight. -- When a clock is hungry, it goes back four seconds. |
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