D
Don Kelly
Guest
On 14/07/2014 3:40 PM, Dan Coby wrote:
be cobbled together from surplus equipment such as a 5-7.5HP 3 phase
motor driven by a single phase motor <1HP at an estimate.
I should think that this is the cheapest alternative.
It is bulky but it means that the original 3 phase 3HP potor can be
kept. Capacitors can help.
However, the sizing of the original motor is probably based on the load
current at start -and a HP rating to fit this and also fit an rms HP
limit equivalent. It may be that a 3HP single phase motor -capacitor
start designed for max torque near standstill would do the job as the
duty cycle is the same as before.
Check the specific info for the original motor and a replacement. The
single phase replacement will be expensive and there would likely be
mounting problems.
It's a bit of a toss up- mainly economics
--
Don Kelly
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Such rotary phase converters have been commonly used in the past and canOn 7/14/2014 9:00 AM, DaveC wrote:
I need to provide jog function on a machine (run the motor for a few
seconds
under load) without use of VFD**. It was done on this small printing
press
with a 3 HP, 3-phase motor but the customer has no multiphase power so
Išm
changing to a 220 ³single phase² 5 HP motor.
Is there any inherent issue with starting an asynchronous motor under
load? A
3ph motor does this with ease, but can the same be said of an async
motor?
Should I be looking at a particular design of async motor?
Also, reversing an asynch motorÂis this a straightforward thing to do?
I'm
thinking about bringing the directional wiring inside the motor's
terminal
box out to separate contactors. I'm also thinking about
cross-connecting aux
contacts in the contactors to eliminate possibility of actuating both
simultaneously and some kind of timer relay to provide delay between
forward
and reverse actuation.
Any observations or experience youšd like to share would be greatly
appreciated.
Thanks!
** The customer has said ³absolutely no VFD². Apparently his business
neighbor has had nothing but troubles with VFDs (blowing the supply
fuses;
smoking at least one VFD) and he is terrified of them. Itšs an emotional
issue, not a logical one so no amount of discussion can change his mind.
Wešve tried.
Does your customer have any objection to a non-electronic converter? A
common means of running 3 phase motors from a single phase supply is via
the use of rotary phase converters.
http://en.wikipedia.org/wiki/Rotary_phase_converter
Dan
be cobbled together from surplus equipment such as a 5-7.5HP 3 phase
motor driven by a single phase motor <1HP at an estimate.
I should think that this is the cheapest alternative.
It is bulky but it means that the original 3 phase 3HP potor can be
kept. Capacitors can help.
However, the sizing of the original motor is probably based on the load
current at start -and a HP rating to fit this and also fit an rms HP
limit equivalent. It may be that a 3HP single phase motor -capacitor
start designed for max torque near standstill would do the job as the
duty cycle is the same as before.
Check the specific info for the original motor and a replacement. The
single phase replacement will be expensive and there would likely be
mounting problems.
It's a bit of a toss up- mainly economics
--
Don Kelly
remove the cross to reply