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Posted by Steve on August 20, 2006, 3:46 pm
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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
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Posted by Greg on August 20, 2006, 3:54 pm
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> 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
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Posted by Steve on August 20, 2006, 7:12 pm
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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.
My grandfather (also a model engineer) couldn't feel mains. He had a
live workbench and didn't realise until my father visited and got two
shocks off it (the first one being blamed on static). He could also
test the HT leads on cars to tell you which was good and which bad by
sticking his finger in the spark plug socket.
And they call me thick-skinned !!
Steve
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Posted by Peter Harrison on August 20, 2006, 8:27 pm
Please log in for more thread options Well, in a fit of madness, I bought a variable frequency inverter. These
are easy to find and I rather thought that finding a motor would be as
simple.
Daft really but what can you do when the buying mist descends?
I have spent (wasted) the last couple of hours trying to find out
exactly what motor spec I will need. My lathe is a Myford Super7B.
All I seem to have discovered is that the output shaft is 5/8ths. No
doubt they can't be had anymore and I will not be able to fit the
current pulley to the new motor.
Can anyone tell me what the mounting dimensions are. I could go and
measure mine but it is a bugger to move until I actually come to swap
out the motor. I would rather not have to do it twice. In any case, I
seem to need the actual frame size and, probably, some more modern NEMA
equivalent.
Also, it turns out there are 2-pole and 4-pole motors. What on earth is
all that about? I was only just coming to terms with the idea of star
and delta winding. Nobody mentions what their motor is so I assume that
can be adjusted internally to either configuration.
Can anyone help me with the appropriate motor specs? Oh, and a supplier
or two would be nice.
Pete Harrison
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Posted by david.sanderson@bem.fki-et.com on August 21, 2006, 3:28 am
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Peter Harrison wrote:
> Well, in a fit of madness, I bought a variable frequency inverter. These
> are easy to find and I rather thought that finding a motor would be as
> simple.
>
> Daft really but what can you do when the buying mist descends?
>
> I have spent (wasted) the last couple of hours trying to find out
> exactly what motor spec I will need. My lathe is a Myford Super7B.
>
> All I seem to have discovered is that the output shaft is 5/8ths. No
> doubt they can't be had anymore and I will not be able to fit the
> current pulley to the new motor.
>
> Can anyone tell me what the mounting dimensions are. I could go and
> measure mine but it is a bugger to move until I actually come to swap
> out the motor. I would rather not have to do it twice. In any case, I
> seem to need the actual frame size and, probably, some more modern NEMA
> equivalent.
>
> Also, it turns out there are 2-pole and 4-pole motors. What on earth is
> all that about? I was only just coming to terms with the idea of star
> and delta winding. Nobody mentions what their motor is so I assume that
> can be adjusted internally to either configuration.
>
> Can anyone help me with the appropriate motor specs? Oh, and a supplier
> or two would be nice.
>
> Pete Harrison
Try Newton-Tesla, Tel: 01925 444 773 or http://www.newton-tesla.com
They supply replacement VSD drives fro Super sevens, including motors.
Im a satisfied customer, they were really helpful remotoring my
Harrison L5, but no other connection
Dave
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> motor of this size.
>
> Greg