Re: From Member: where to get 2.5K resistors?

Thanks for the explanation, Danny. I learned a lot.

Cheers,

Wreno

Danny Miller wrote:

>
>
> Long story short: Go to Fry's Electronics. They have precision
> resistors IIRC. 2.4K is close enough to ideal. Or put a 2.2K resistor
> in series with 330ohms.
>
> A G540 has NO tolerance issue at all as far as the G540 is concerned.
> If a resistor is actually 2432k, it puts out 2.432A. Well, something
> "ballpark" of that. It's not extremely accurate but a 10% larger
> resistor WILL give 10% more current.
>
> The MOTOR has an issue with too much or too little current. Too little
> current and torque is reduced proportionately. Using a 2.2k resistor
> instead of 2.5k is losing 12% in torque.
>
> The motor's "maximum" current was determined by a temperature criteria.
> >From what I saw, the actual rating comes from whatever current produces
> an 80C rise over ambient. Exceeding 80C temp rise could make it exceed
> the Absolute Maximum Temp and damage the motor if the motor is used in
> the hottest environments it's rated for (50C, which IS a really hot
> enclosure). Technically, operating in cooler rooms allows you to use
> higher currents.
>
> The motor's temp rise is the SQUARE of the current. Using a 2.7K
> resistor instead of 2.5K will yield 8% more torque, but 16.6% higher
> temp rise. Since that was rated at 80C, that's an additional 13.3C
> (+24F) hotter. If your room is 24F colder than "standard", it'll
> achieve the same temp as one run at rated current in a standard-temp
> room.
>
> COOLER MOTORS PRODUCE MORE TORQUE. I don't have data to quantify it but
> all the magnetic properties of the iron core and permanent magnets DO
> decrease with temp. It's not a huge difference so don't go around
> thinking you're gonna mod this with a water-cooling jacket or compuer
> fans on the motor and get the most awesome, efficient mill evar. We're
> probably talking like 15% loss at high temps would be my expectation.
>
> Danny
>
> Jack McKie wrote:
> > Danny,
> >
> > Yes, what is the tollerance required for a G540? I don't see any
> mentioned in the instructions.
> >
> > Thanks,
> >
> > Jack
> >
>
>

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