Help With Dc Load Meter Led

[dannystooblue]

I have seen one control panel for a home made cnc that had a christmas tree like load meter with led's. I know almost nothing about electronics and have managed to kill one dc servo. I have since added an inline fuse to protect the motor but didnt really know how large to use. i know that the motor can handle more than it is rated for for short periods but would like to see how much it is using. the motor is an electrocraft e243, its rated to 4.5 amps the best i recall, maybe 5amps. could anyone steer me in the right direction?


Danny

[Al_The_Man]

I would think that your drive should be set to go into current limit correctly before cooking the motor, this is the normal way to protect the motor and drive.
Normally fusing is not used between drive and motor, only in the drive power supply.
The LED display you saw was probabally a Bar Graph Led unit, you can get these that incrementally change colour as they progress up, e.g. Green/yellow/red etc, these need other electronics like shift registers etc to complete a current display, I have not seen off the shelf meters of this type.
Al.

[pastera]

The LM3914 will drive a bar display easily - you would need to add a current sense and amp to get the sense signal in the range of the LM3914.

You shouldn't need a load display to protect the motor. The servo drive should be set to trip on motor over current. Setting the drive to allow the motor to work in the non-continuous torque range is not a good idea.

Aaron

[Alex_Cole]

I myself have been thinking about this issue to try to detect how much my servos are pulling.

Let me ask this question, Can you use a amperage panel meter to try to monitor your servo motor?

If you have a servo that pulls like 3A max could you get a 5A panel meter and hook it up inline with your servo and find out how much it is pulling. If you can then this would give you a visual reference to if your servo is pushing too hard and might burn up. Mabe one of the experts in the electronics side of things might be able to answer this question.

AC

[gar]

070513-0942 EST USA

If you have a permanent magnet brush type DC motor, then the armature current is approximately proportional to mechanical output load torque. If you run the motor with no external mechanical load at the speed you intend to make measurements at, then the difference between the actual load current and the no load current is a better measure of output torque. I think an ammeter is a better method than an LED bar graph. A Fluke multimeter would be a good means to determine what range panel meter is needed.

If you have a so called brushless DC motor, really an AC synchronous motor with permanent magnet rotor and some sensors, then the motor controller probably provides a DC output voltage proportional to load.

.

[Al_The_Man]

Most modern drives, whether DC Brush, BLDC or AC sinusoidal are PWM controlled, the voltage is constantly turned full on or off, the resulting current waveform can be more trapezoidal in appearance, so it is often difficult to get a meaningfull reading in the normal sense with conventional meters.
Although the The DC Brushless motor and the AC sinusoidal type are constructed almost identical, (three windings), the DCBL is known as such, due to only two windings being energised at the same time, The AC can have all three energized.
I would think it would be more practical to measure the current in the DC supply side to the drive.
Al.

[dannystooblue]

I guess I should go back to the gecko setup then because i sure did smoke one motor that was over taxed. It has been a good while since i have set them up, but i only remember one power setting. for some reason i thought i rememberbered it being a voltage limit, not an amperage limit. i am not great with electronics so forgive my ignorance.

Danny