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Posted by Wayne Weedon on August 23, 2006, 5:37 pm
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Peter Harrison wrote:
> Hope they have some 4 core flex. That seems unnaturally hard to find in
> small amounts.
B&Q normally has 4 core flex in 1.5mm2, quite good enough for a small
motor as fitted to a Myford.
Wayne...
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Posted by Adrian Godwin on August 23, 2006, 6:17 pm
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> Hope they have some 4 core flex. That seems unnaturally hard to find in
> small amounts.
>
I've bought 4-core flex with a braided shield (which is recommended for
inverters to reduce RF interference) by the metre, from City Electrical
Factors. This was in Cambridge, but they have branches all over the place.
-adrian
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Posted by Christopher Tidy on August 21, 2006, 5:42 pm
Please log in for more thread options Steve wrote:
> Greg wrote:
>
>>
>>>Its probably an odd voltage now, but not so much in the past.
>>
>>Funnily enough 220V DC has stayed with us, it's a common battery voltage in
>>large UPS systems, I mean large as in the battery is the size of a fair
>>sized room 8-)
>>Greg
>
>
> Shame they don't have motors within UPS systems (or do they ?).
>
> I have wondered for some years how we ended up with the mains voltage
> we did. I had assumed it was a balance between a high enough voltage to
> reduce resistive losses and a low enough voltage that a shock would
> wake you up and not be deadly. No doubt the CEGB decided, but I am not
> sure how. Maybe the same criterion is used in UPS systems.
>
> I am a little anxious about setting up the 220V DC within my lathe
> enclosure as I don't want a shock from it, though I have had many mains
> shocks without anything other than a BIG wake up call, but we had a 2kV
> DC source in a lab I worked in and I was told it was deadly - so I
> treated it like a cobra.
Were you by any chance the guy at the centre of that well-known story
about surviving a shock from a pole transformer? :-D
Chris
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Posted by Greg on August 21, 2006, 6:02 pm
Please log in for more thread options > Shame they don't have motors within UPS systems (or do they ?).
Yes, cooling fans, but 230V AC from memory.
> I have wondered for some years how we ended up with the mains voltage
> we did. I had assumed it was a balance between a high enough voltage to
> reduce resistive losses and a low enough voltage that a shock would
> wake you up and not be deadly.
that and the basic economics of cheap, maintainance free transformers all
over the place instead of rotary machines, it's also far easier to switch.
> I am a little anxious about setting up the 220V DC within my lathe
> enclosure as I don't want a shock from it, though I have had many mains
> shocks without anything other than a BIG wake up call, but we had a 2kV
> DC source in a lab I worked in and I was told it was deadly - so I
> treated it like a cobra.
People should treat mains voltages as deadly since they can be, yes ok
plenty of us have had shocks and are still around but when you get too comfy
with something that's the time it bites back. I've had a 2kV shock off a
scope but that doesn't make it safe 8-).
> My grandfather (also a model engineer) couldn't feel mains.
That's the point, everyone's different.
Greg
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Posted by Christopher Tidy on August 21, 2006, 5:36 pm
Please log in for more thread options Steve wrote:
> Greg wrote:
>
>>I would have thought 250V DC was a very odd voltage for a
>>motor of this size.
>>
>>Greg
>
>
> Its probably an odd voltage now, but not so much in the past. The
> standard mains AC supply is relatively new thing, and many locations in
> the UK had DC supply into the late 1930s and some through the war. DC
> was typically supplied at 400 to 500 volts on a three wire system,
> where the central wire was earth and lay roughly between the two. A
> motor/generator set called a balancer acted to trim the voltage either
> side of earth.
>
> I suspect the requirement for DC motors at this voltage died out when
> the CEGB finally managed to get us all onto one system - this was
> started in 1927, but took a long while to implement.
>
> I have a 1940s/1950s lathe that uses an old GEC motor 1HP at 220VDC
> with 170V field coils as part of a variable speed drive system. One of
> the USA Monarch lathes had a similar system, but they probably worked
> at lower DC voltages, as the AC over there is lower voltage.
>
> I have not seen a modern motor that has a similar specification, and
> would be interested to know if such a thing exists.
Steve, that sounds a lot like a motor that I have. Probably weighs about
25 kg, is about the size of a large pumpkin, and has something like a
5/8" shaft. I'm saving it with the intention of using it to drive a very
large Van de Graaff generator, but as yet it's a project I haven't got
round to. Unfortunately my motor hasn't got a data plate. I'll take a
picture tonight or tomorrow and post it to see if they're the same.
Best wishes,
Chris
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> small amounts.