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Posted by DrollTroll on October 6, 2008, 3:39 am
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Awl --
With single phase, what are the pro's/cons with having a 3 ph compressor
motor with starting caps, vs swapping it out for a single phase motor?
The tradeoff I see is a wiring pita vs. the grunt/mechanical pita and $$ of
a single phase motor, with likely a modified mounting.
I would like to put the starting caps/running caps on relays, that switch
in/out, as well.
--
DT
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Posted by Todd Rich on October 6, 2008, 6:48 am
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> Awl --
> With single phase, what are the pro's/cons with having a 3 ph compressor
> motor with starting caps, vs swapping it out for a single phase motor?
> The tradeoff I see is a wiring pita vs. the grunt/mechanical pita and $$ of
> a single phase motor, with likely a modified mounting.
> I would like to put the starting caps/running caps on relays, that switch
> in/out, as well.
How big is it, and have you considered a VFD running your 3 phase motor
off of single phase power?
I'm running a 15hp 3 phase motor on my compressor. Admittedly, I need a
100 amp line to do it though.
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Posted by DrollTroll on October 6, 2008, 11:43 am
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>> Awl --
>
>> With single phase, what are the pro's/cons with having a 3 ph compressor
>> motor with starting caps, vs swapping it out for a single phase motor?
>
>> The tradeoff I see is a wiring pita vs. the grunt/mechanical pita and $$
>> of
>> a single phase motor, with likely a modified mounting.
>
>> I would like to put the starting caps/running caps on relays, that switch
>> in/out, as well.
>
> How big is it, and have you considered a VFD running your 3 phase motor
> off of single phase power?
No, I hadn't. But it is an idea. About 5 hp.
Certainly caps will be cheaper, but wiring relays, start/run is going to be
a pain as well.
Plus, I will have to de-rate the motor, and possibly put a smaller pulley on
it.
Keep in mind that this is a scenario where the motor is starting under
near-full load, which might be some electrical wear/tear on a VFD.
At least I *think* it is starting under full load (tank pressure).
Is there a way to set up an air compressor so that the motor starts under no
load? Only with a clutch, I would imagine, or "almost no-load", where some
vent bypasses the compressor head to air, or sumpn, and then closes.
So much drama....
--
DT
>
> I'm running a 15hp 3 phase motor on my compressor. Admittedly, I need a
> 100 amp line to do it though.
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Posted by Don Foreman on October 6, 2008, 5:57 pm
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wrote:
>
>>> Awl --
>>
>>> With single phase, what are the pro's/cons with having a 3 ph compressor
>>> motor with starting caps, vs swapping it out for a single phase motor?
>>
>>> The tradeoff I see is a wiring pita vs. the grunt/mechanical pita and $$
>>> of
>>> a single phase motor, with likely a modified mounting.
>>
>>> I would like to put the starting caps/running caps on relays, that switch
>>> in/out, as well.
>>
>> How big is it, and have you considered a VFD running your 3 phase motor
>> off of single phase power?
>
>No, I hadn't. But it is an idea. About 5 hp.
>
>Certainly caps will be cheaper, but wiring relays, start/run is going to be
>a pain as well.
>Plus, I will have to de-rate the motor, and possibly put a smaller pulley on
>it.
>
>Keep in mind that this is a scenario where the motor is starting under
>near-full load, which might be some electrical wear/tear on a VFD.
>
>At least I *think* it is starting under full load (tank pressure).
>Is there a way to set up an air compressor so that the motor starts under no
>load? Only with a clutch, I would imagine, or "almost no-load", where some
>vent bypasses the compressor head to air, or sumpn, and then closes.
>
>So much drama....
Many (if not most) compressors do not start under full load. There is
an "unloader" in either the pump output or in the controller.
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Posted by on October 6, 2008, 7:25 pm
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> wrote:
>
>
>
>
>
> >>> Awl --
>
> >>> With single phase, what are the pro's/cons with having a 3 ph compressor
> >>> motor with starting caps, vs swapping it out for a single phase motor?
>
> >>> The tradeoff I see is a wiring pita vs. the grunt/mechanical pita and $$
> >>> of
> >>> a single phase motor, with likely a modified mounting.
>
> >>> I would like to put the starting caps/running caps on relays, that switch
> >>> in/out, as well.
>
> >> How big is it, and have you considered a VFD running your 3 phase motor
> >> off of single phase power?
>
> >No, I hadn't. But it is an idea. About 5 hp.
>
> >Certainly caps will be cheaper, but wiring relays, start/run is going to be
> >a pain as well.
> >Plus, I will have to de-rate the motor, and possibly put a smaller pulley on
> >it.
>
> >Keep in mind that this is a scenario where the motor is starting under
> >near-full load, which might be some electrical wear/tear on a VFD.
>
> >At least I *think* it is starting under full load (tank pressure).
> >Is there a way to set up an air compressor so that the motor starts under no
> >load? Only with a clutch, I would imagine, or "almost no-load", where some
> >vent bypasses the compressor head to air, or sumpn, and then closes.
>
> >So much drama....
>
> Many (if not most) compressors do not start under full load. There is
> an "unloader" in either the pump output or in the controller.
Methinks that an 'unloading check valve' is a standard commercial
item, useful for smaller compressors. This valve is placed between
the compressor and air receiver. After compressor shut-off this valve
bleeds off the pressure between it and the compressor, allowing the
compressor to start against atmospheric, instead of tank, pressure.
Wolfgang
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