Re: [CAD_CAM_EDM_DRO] Re: can amps be mixed with motors?

Sounds great, I am going to give it a try!

Mark Vaughan wrote:

>
> That's sort of right Tom.
>
> If the bigger motor is for the same voltage, it will behave OK until
> you ask
> more than 500W from it, then it may pull more current than your drive can
> handle.
>
> The problem is this hi current condition could occur under light work, due
> to initial acceleration.
>
> Think of the motor as a variable resistor, the more power you want, the
> lower the resistance will drop, down to a fixed level. On the bigger motor
> this fixed level will be lower and pull more current. Also think of the
> resistance as being bouncy, so it can bounce down to this low level quite
> quickly during transient conditions, the more bouncy the better the torque
> speed response of the motor. As it bounces down to the lower level,
> you may
> not see much current spike on an ammeter, it will be for a very short
> time,
> but a short time is all that's required to pop the fets in your drive, and
> normal fuses aren't quick enough to offer protection.
>
> The normal method to run a big motor from a small drive is to add a series
> power resistor so that the combined resistance seen by the drive is
> the same
> as that of the smaller motor.
>
> The resistance values you are looking for are the stall value, you can
> measure this with a good digital ohm meter across the motor terminals
> while
> it is stationery. You can also calculate it knowing the stall current and
> supply voltage. Don't worry about wasting power in the resistor, during
> normal use the extra resistor will be very small compared to the operating
> resistance of the motor which is much higher, it only becomes
> appreciable at
> stall or heavy acceleration conditions when the motor resistance drops
> to a
> low value to grab more current.
>
> Without the resistor you may be OK. With it there is a much higher
> probability you will be OK.
>
> If you want to look at a simple write up for diy'ers. Rutex publish this
> method on their site, look for a download document called mystique.
>
> Dr. Mark Vaughan Ph'D. B.Eng. M0VAU
>
> Managing Director
>
> Vaughan Industries Ltd, reg in UK no 2561068
>
> Water Care Technology Ltd, reg in UK no 4129351
>
> Addr Unit3, Sydney House, Blackwater, Truro, Cornwall, TR4 8HH, UK.
> Phone/Fax 44 1872 561288
>
> _____
>
> From: CAD_CAM_EDM_DRO@yahoogroups.com
> <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
> [mailto:CAD_CAM_EDM_DRO@yahoogroups.com
> <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>] On Behalf Of caudlet
> Sent: 30 January 2007 19:57
> To: CAD_CAM_EDM_DRO@yahoogroups.com
> <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
> Subject: [CAD_CAM_EDM_DRO] Re: can amps be mixed with motors?
>
> --- In CAD_CAM_EDM_ <mailto:CAD_CAM_EDM_DRO%40yahoogroups.com>
> DRO@yahoogroups.com <mailto:DRO%40yahoogroups.com>, "toolspindoctor"
> <clarkfamily5@...> wrote:
> >
> > I have a used Yaskawa motor and amp. The motor turns out to be bad
> > and needs to be replaced. It was a 500watt motor. Can I use a 750
> > watt motor with an amp rated at 500 amps and just expect less than the
> > rated power or will it blow the amp?
> >
> > thanks!
> >
> The draw of the motor is in voltage and amperage. You *have* to use
> the right voltage, then the motor "demands" the amount of current
> needed for the load. If you use the 750 Watt motor and place it in a
> situation where it needs over the 500W the supply can furnish, the
> best thing that can happen is that the amp has some form of protection
> against overload and will just shutdown. If not you have a blown Amp.
>
> If the 750 motor is rated at the same voltage as the old 500 and you
> are confident the load will never exceed the 500 level (or the amp has
> electronic overload protection) then it would work and actually not
> run at less power than the old motor. Of course you can't get 750W
> from a 500W (I assume you meant Watts instead of 500Amps!) supply. As
> long as you don't ask it to then there should be no problem.
>
> Watts is a measurement of power consisting of (roughly) the applied
> voltage and the demanded power from the motor and it's load.
>
> So the simple answer is that as long as you match the voltage of the
> old motor and you don't let the load exceed what the old 500 Watt saw
> it should work. This is a bit like putting a bigger fuse in when one
> blows. It will work as long as things don't go into overload.
>
> Tom Caudle
> www.CandCNC.com
>
> [Non-text portions of this message have been removed]
>
>
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