Question on starter size
 

Hi,

I am going to make a phase converter similar to the two stage unit you have.
One thing I have been unable to get a definitive answer on is sizing the
ider starter (mag). So... running a 10HP ider off single phase, do you size
the starter the same as if you were suppling it with 3 phase, or do you have
to up size it as if you were suppling a 10HP single phase.

Your set up is similar in that I what to start a 10HP idler with a size 2
starter (rated 15HP @ 230/3P or 7.5HP @ 230/1P)

Any clear opinions on whether the size 2 is fine or undersized????

Thanks,
Glen
"Ignoramus29580" wrote in message
.. .

http://igor.chudov.com/projects/17.5-Phase-Converter/

I need to do a few extra things, like adding a pushbutton (which I do
not have yet, I bought it on ebay yesterday), some crimpable butt
splices and ring terminals, and preferably adding a second motor
starter instead of a definite purpose contactor. The starter would add
overload protection, which the 10 HP motor has but 7.5 HP motor does
not yet.

i

Question on starter size
 

glensmith wrote:
Hi,

I am going to make a phase converter similar to the two stage unit you have.
One thing I have been unable to get a definitive answer on is sizing the
ider starter (mag). So... running a 10HP ider off single phase, do you size
the starter the same as if you were suppling it with 3 phase, or do you have
to up size it as if you were suppling a 10HP single phase.

Your set up is similar in that I what to start a 10HP idler with a size 2
starter (rated 15HP @ 230/3P or 7.5HP @ 230/1P)

Any clear opinions on whether the size 2 is fine or undersized????

Hi Glen,

You should size the starter for single phase as you have single phase
entering the convertor. Presumably you have a starter with three sets of
contacts, and you use two sets for single phase operation or three sets
for three phase operation?

The rating of the starter will be based on the current which the
contacts can handle. For a single phase motor the equation giving the
power in terms of line voltage V and line current I is:

P = I * V

For a three phase motor it is:

P = 1.732 * I * V

Given that I and V are the same in this case, one would expect the three
phase power rating to be 15/1.732 = 8.6 hp. The manufacturer has
obviously chosen a 7.5 hp, which is a nice round number. What machines
do you plan to run from your convertor? Technically you should probably
go for a larger starter, but if you're only going to run your convertor
lightly loaded and don't insist on doing everything by the book, you'll
probably get away with it. But if I was building the convertor myself I
would go for a larger starter.

Best wishes,

Chris

Question on starter size
 

Correction: one would expect the single phase power rating to be 8.6 hp.

Question on starter size
 

Ignoramus4758 wrote:

snip

I agree with your post, but I want to note that size 3 starters are
very expensive, even used.

In this case Glen should probably make his choice based on what he
intends to run from the convertor. The size 2 should be fine for a 3 hp
Bridgeport (say) but could be inadequate for a bad ass welder like yours
:-).

By the way, I like your pics of the new phase convertor. I missed the
pictures when you first posted them, but just saw them now. Nice job.

Chris

Question on starter size
 

Hi,

The largest load will be a 10HP (+ 1HP feed motor) wide belt sander. It
will have a heavy starting load due to the inerta of the steel rolls. I
will also want to run a 3HP dust collector at the same time. The smallest
load will be 1.5HP. So everything from 1.5 to 14HP at one time.

For idlers I have a 15HP, a 10Hp, a 7.5, and a 5HPavailable. I believe
(hoping!!) that I can get away with 15HP of idler. Have max of 60amp 240
single phase supply but I am going to try with 50amp first (much less work).

Haven't decided whether a single 15HP would be the way to go or a 10/5
combo. (more complicated).

Thanks,
Glen

"Christopher Tidy" wrote in message
...
Ignoramus4758 wrote:

snip

I agree with your post, but I want to note that size 3 starters are
very expensive, even used.

In this case Glen should probably make his choice based on what he
intends to run from the convertor. The size 2 should be fine for a 3 hp
Bridgeport (say) but could be inadequate for a bad ass welder like yours
:-).

By the way, I like your pics of the new phase convertor. I missed the
pictures when you first posted them, but just saw them now. Nice job.

Chris

Question on starter size
 

glensmith wrote:
Hi,

The largest load will be a 10HP (+ 1HP feed motor) wide belt sander. It
will have a heavy starting load due to the inerta of the steel rolls. I
will also want to run a 3HP dust collector at the same time. The smallest
load will be 1.5HP. So everything from 1.5 to 14HP at one time.

In that case I would look for a larger starter.

For idlers I have a 15HP, a 10Hp, a 7.5, and a 5HPavailable. I believe
(hoping!!) that I can get away with 15HP of idler. Have max of 60amp 240
single phase supply but I am going to try with 50amp first (much less work).

My guess is that you'll probably get away with a 15 hp idler if your
convertor is well balanced. Don't take this as fact, though: ask Jerry
Martes or Bob Swinney. They seem to be the phase convertor experts in
this group.

Of course you can also build a prototype phase convertor quickly, check
that it does what you want, and then build a housing for it.

Best wishes,

Chris