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

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
>