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Circuit design for 10.5 amp 230V 2HP motor @ 3450rpm
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ehsjr
electronics forum Guru


Joined: 03 May 2005
Posts: 863

PostPosted: Thu Jul 20, 2006 7:51 pm    Post subject: Re: Circuit design for 10.5 amp 230V 2HP motor @ 3450rpm Reply with quote

TSL wrote:
Quote:
ehsjr wrote:


Perhaps a DC example would help.
View in fixed font

+----Hot-----+-------------+
+ | | |
---------- ------- |
|Battery 6V| |Bulb 6V| |
---------- ------- |
| | --------
+----nnnn----+ |Bulb 12V|
+ | | --------
---------- ------- |
|Battery 6V| |Bulb 6V| |
---------- ------- |
| | |
+----Hot-----+-------------+

For the purpose of the analogy, call the wire labeled nnnn
"Neutral". It is easy to see why it is needed - it makes
both 6V bulbs "happy". They get 6 volts each, and will
continue to work if the other 6V bulb burns out. They will
both glow at the proper level, even if the top one draws
7 amps and the bottom one draws 300 mA.

Eliminate the "neutral" wire and those 6 volt bulbs may have
a problem. For example, if there was no neutral and the top
one tried to draw 7 amps, it would have to draw it through
the bottom bulb. If that bulb was rated only for 300 mA, it
would burn out.

The 12 volt bulb doesn't need the neutral. It gets the proper
voltage from the two wires marked "hot" with no need for an
additional current path.

In your resisdence, the incoming 240 volts comes off a center
tapped transformer, anologous to the two batteries above.
Your 120 volt appliances are analogous to the 6V bulbs. Your
240 volt motor is analagous to the 12 volt bulb.

Ed


FANTASTIC - thanx Ed. One down. Two more to go - care to take a whack
at my motor starter & brake issue, Ed?

TSL


Well, I don't have much to say about it. As I see it,
you've done the "good stuff" - brought a 60 amp line
to the location with a 20 amp circuit for the saw.
I think the additional electrical work (motor starter
& brake) beyond that is pointless. (I suppose that if
it's a new motor, the manufacturer would recommend
starting and braking circuitry as needed.)

Ed
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Rich Grise
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3971

PostPosted: Fri Jul 21, 2006 1:09 am    Post subject: Re: Circuit design for 10.5 amp 230V 2HP motor @ 3450rpm Reply with quote

On Wed, 19 Jul 2006 10:04:01 -0700, TSL wrote:

Quote:
OK, now were getting somewhere. Thank you Mr Walpert.

I am clear about the difference between the ground and nuetral in
general terms. What I am unclear about is why a 240V motor (which is
also on my compressor) does not need the nuetral? This is one of the
gaps in my understanding. It bugged me when I hooked up my compressor
but i just let it go. With what I am doing now, I'd really like to
understand why 240V seems to change the whole playing field and drops
the nuetral.


In a nutshell, the neutral is the center-tap of the 240V transformer
that feeds your house, so you get 120 to neutral on the black, and
120 to neutral on the red, and 240 from black to red. When your
device is using the whole 240, the neutral is irrelevant - when you
use a 120V item, all its return current flows through the neutral,
which is why people like to balance the loads on the two legs (which
some people erroneously call "phases" - there's only the one phase,
but the 240 is center-tapped) just because it's nice to minimize
the neutral current - it evens out the load on the halves of the
secondary of the pole pig.

Maybe visualize a loop or three... ;-)

Hope This Helps!
Rich
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Rich Grise
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3971

PostPosted: Fri Jul 21, 2006 1:13 am    Post subject: Re: Circuit design for 10.5 amp 230V 2HP motor @ 3450rpm Reply with quote

On Wed, 19 Jul 2006 10:25:44 -0700, mike.j.harvey wrote:

Quote:
Robert Latest wrote

In Europe, 3-phase 400V lines go into every
home.

No they bloody don't! European electricity supply undertakings are very
reluctant indeed to supply 3 phase power to anywhere other than
industrial and commercial users, where there is no alternative. In fact
you may as well say that domestic customers are limited to 230v single
phase.

However 415v three phase lines are buried in the street, and houses are
supplied from phase + neutral.

I don't know the exact rules in the US, but my cousin's farm has had
3-phase since I can remember, and I somehow think that if you paid for
all of the wiring, transformers, work, etc, the power company would
be happy to string any kind of power you want to your house. :-)

If I'm wrong and there's some kind of rule against it, I'd be happy
to be enlightened, so to speak. ;-)

Cheers!
Rich
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Rich Grise
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3971

PostPosted: Fri Jul 21, 2006 1:20 am    Post subject: Re: Circuit design for 10.5 amp 230V 2HP motor @ 3450rpm Reply with quote

On Wed, 19 Jul 2006 09:08:44 -0700, TSL top-posted:
[some snit]
Quote:
So perhaps we could start over.

I don't understand the problem - if you already know that stuff, what are
the questions for?

But just because I'm such a smartass, here ya go:

Quote:
Questions:

1) can and should an AC motor starter be used on my 10.5 amp 230V 2hp
3450rpm drive motor to give the motor longer life - and if so should
an electric brake be installed also? What are the theories and
pros/cons?

Yes, and I wouldn't try to use an electric brake on a motor that old
without talking to the guy who's selling the electric brake, and maybe
having the motor checked out by a motor shop.

Quote:
2) what is the difference in design between a transformer rated
switch @ 120V 50/60htz versus a "full voltage" switch with identical
rating - are the contacts supposed to be different? I ask because I
noticed in my quest for the AB switches (bought used to save money)
the contact blocks for the switches appear identical in both design
and model # regardless if they are rated/listed for transformer power
versus full voltage (which I'm assuming is raw power from my house).

You'll have to ask the guy who's selling you the switch.

Quote:
3) what in blazes does the "L1, L2, L3, etc" and "T1, T2' T3, etc"
tags mean in motor circuit and wiring diagrams? I'm assuming that
"common" is the nuetral. And when the nuetral and ground from my box
(WA state) are joined, how, if at all, are they to be distinguished
at the motor?

This is the generic "line - terminal" question which has been answered
already.

So, what's the problem?

Thanks,
Rich
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Rich Grise
electronics forum Guru


Joined: 24 Mar 2005
Posts: 3971

PostPosted: Fri Jul 21, 2006 1:22 am    Post subject: Re: Circuit design for 10.5 amp 230V 2HP motor @ 3450rpm Reply with quote

On Tue, 18 Jul 2006 23:10:47 -0400, John Perry wrote:

Quote:
Another Wally wrote:
"TSL" <WestCoastJagLTD@msn.com> wrote in message
...


3) what in blazes does the "L1, L2, L3, etc" and "T1, T2' T3, etc" tags
mean in motor circuit and wiring diagrams? I'm assuming that "common"
is the nuetral. And when the nuetral and ground from my box (WA state)
are joined, how, if at all, are they to be distinguished at the motor?

Nuff for now. TYIA!
TSL

I would suggest you get a qualified electrician in to wire up these items,
it is evident you don't have a clue.



Heck, just tell him straight out that he can't use that motor. It's
unlikely in the extreme that his home provides the 3-phase power he
needs to drive that motor. That's what his electrician is going to tell
him.


He doesn't have a 3-phase motor. He's got a 240V, single-phase motor.
That question was just a red herring.

Cheers!
Rich
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