Re: [CAD_CAM_EDM_DRO] Inverter Drives

Hi,

The inverter drives I have installed and maintained in the past were
sized in kilowatts. The largest was about 30 KW. Having qualifed my
point of view, the point Randy and Tim makes about inverter rated motors
being somewhat special is true and over heating is a big issue. But
there is a lot us gear heads and hardware hackers can get away with.

Many motors for inverter drive (and DC ones too) have seperate blower
motors for cooling. These motors are expected to operate in ranges where
the shaft driven cooling fan wont be enough because they may spend a lot
of time in acell/decel where and fan is slow and the load high. To hack
this on a std. TEFC motor, remove the fan and bolt on a pancake (muffin)
fan of suitable size to the fan guard, hook it to 120vac and relay it so
it comes on with the drive and you have the same thing (cooling wise).

If you keep the speed range reasonable say 40-80 hz or something like
that and the load reasonable and use the varable speed to cover the
speeds in between the belt/gear changes you will get good service out of
it. Watch the motor temp, use a gage or thermal switch on/in the motor.
I have seen drives that took a temp probe input from the motor/s as
alarm/feedback but I hav'nt seen that on the little drives.

Hack On!
Mark

cnc002@... wrote:

> In a message dated 5/11/2003 5:24:47 PM Eastern Standard Time,
> timg@... writes:
>
>
>
>>Unless your motor is rated for double the speed that it gets at 60 hz I
>>would not even suggest going to 120 hz. So, I seriously doubt you need a
>>drive that will let you go above that. An exploding armature is not a
>>pretty sight.
>>
>
>
> Tim is correct, and also if the motor is NOT inverter rated you will have
> problems with overheating at slower speeds causing premature failure of the
> motor. It is usually safe to go up to 70 Hz on a 60 Hz rated motor but I
> would not recommend going any higher and you wouldn't want to go much slower
> than 1/4 the motors rated speed and then not for long periods of time, again
> unless the motor is inverter rated. Those motors have special care taken and
> use different "potting" and coating compounds and internal designs to take
> the extra heat generated when the fan on the motor is not turning fast enough
> to cool it as normal
>
> Randy Abernathy
> 4626 Old Stilesboro Road
> Acworth, GA 30101
> Ph / Fax: 770-974-5295
> E-mail: cnc002@...
>
> Intallation, repair, service, upgrades of industrial CNC woodworking
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