Need help selecting an inverter [RE-wrenches]

[William Korthof]

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It might be overkill, but there are a wide range of motor controllers
that would help out a lot on the motor start up. Single phase
induction motors take a big surge to start up (on the line),
especially if there is load on them. With a solid grid source, it's
not uncommon for the startup to be 10x the running load. The

Trace inverters do a respectable job on slam-starts while not
letting the lights and other loads dim too much, but they can only
go so far especially with big motors.

The best type of motor controller is basically an inverter-drive
controller...on start up, the power starts more slowly (like 1-2 x
of full load power) with voltage and frequency to the motor set to
gracefully ramp the motor up to full speed instead of slamming it
instantly.

Other [simpler] motor starting circuits with capacitors, relays,
timers, and/or resistors are also worth considering if the problem
motor only causes a mild or occasional problem and cost is a
big consideration. Grainger is a good source; Siemens and Sq D
make a wide variety of off-the-shelf units.


/wk


At 06:36 PM 8/24/03 -0800, Greg Egan wrote:
>Darryl,
>
>I would use the Outback X-240 for balancing the legs.
>
>You might also look for ways of getting the work done more efficiently. 
>Maybe some of the equipment could use smaller or more efficient/higher 
>power factor motors. Maybe there's some incandescent lights you can 
>replace w/ FL's.
>
>I'd sure try to find a way to keep from taking those heavy SW's off the 
>wall : )
>
>Best,
>
>Greg Egan
>
>--
>Alaska Renewable Energy
>981 Gold Mine Trail Fairbanks, Alaska 99712
>Phone: 907-457-4299; Fax: 907-457-4290; Email: gegan at renewalaska.com
>URL:  http://www.renewalaska.com
>
>
>
>Darryl Thayer wrote:
>>Hi everyone
>>I have a system design problem.
>>I have a system that needs 240 volt to start and run a
>>7-HP motor with full load current of 30 amps. And
>>carry a 10-amp 240-volt motor load.   One leg of this
>>also has to start a ¾ HP 9 amp 120-volt full load
>>pump.  With miscellaneous loads such that one leg has
>>45 amps total and the other leg has 55 amps total. The operation of the 7 
>>HP motor is only for 2 to 3
>>minutes then off for 20 minutes up to several hours. However under 
>>extreame condition, it could run up to
>>30 % duty cycle.
>>I tried two SW5548 and they seem to work but on start
>>of the 7-HP motor will some times kick on overload.
>>What do more experienced people than I do in this
>>case?  I have other use for the SW’s. I do not know if
>>a soft start will work.
>>Do you think two stacked sets of two FX3648 (or what
>>ever the new vented Outback is numbered)  inverters
>>would serve the purpose?  Should I use an
>>auto-transformer to balance this load?
>>What other inverters might work from a 48 volt battery
>>set?  Can other inverters use the auto-transformer?
>>Daryl
>>
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