D9 ground output problem

I am having an issue with my D9 output on ramps 1.4. The ground output on D9 seems to only give out ~2V while the positive supplies 12V. If I use ground from the incoming power and positive from D9, the fan will spin. How can I fix this? I am not well versed in electrical terms.

The D9 output on the RAMPS board is a constant positive 12v output, with the ground coming through the MOSFET. The ground is actually a PWM (pulsed) output that will vary in its potential to ground. By connecting the ground directly to your power supply ground, you bypassed the control from the RAMPS board.

I run my extruder cooling fan the whole time my power supply is on, and use the D9 output for bed cooling. You can see my wiring in one of the images at www.mindrealm.net/i3

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-David

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Check out my FolgerTech Prusa i3 (plexi) at MindRealm.net

How can the ground have 2V Or am I reading that wrong? The voltage should only be measured between positive and negative on the D9 terminal.

With a meter on the power input ground for reference, the positive terminal in D9 will always read around 12v, regardless of whether the fan is turned on in G-Code (M106). The negative terminal reading depends on the duty cycle of the PWM output of the Arduino, driving the negative (ground) through the mosfet. Technically, the output on the negative terminal is always at ground potential when on, but the pulse width makes the output seem to drop and emulate a reduced potential to ground. The D9 negative is actually turning off and on VERY rapidly when M106 is passed to the controller.

Try this.

Send M106 S0 and measure the DC voltage at the D9 positive and negative. This should show 0 volts. If any voltage is present (like the 2 volts you mentioned), disconnect the wiring that is landed on D9 and check again. If there is still voltage present, your mosfet is damaged. If the voltage goes away, something else is putting the 2 volts on the line.

Let me know what you find. (I'm following this thread and will continue to help!)

---

-David

Find me online at:
Thingiverse
Instructables.com
LinkedIn
Facebook

Check out my FolgerTech Prusa i3 (plexi) at MindRealm.net

Quote
MindRealm
With a meter on the power input ground for reference, the positive terminal in D9 will always read around 12v, regardless of whether the fan is turned on in G-Code (M106). The negative terminal reading depends on the duty cycle of the PWM output of the Arduino, driving the negative (ground) through the mosfet. Technically, the output on the negative terminal is always at ground potential when on, but the pulse width makes the output seem to drop and emulate a reduced potential to ground. The D9 negative is actually turning off and on VERY rapidly when M106 is passed to the controller.

Try this.

Send M106 S0 and measure the DC voltage at the D9 positive and negative. This should show 0 volts. If any voltage is present (like the 2 volts you mentioned), disconnect the wiring that is landed on D9 and check again. If there is still voltage present, your mosfet is damaged. If the voltage goes away, something else is putting the 2 volts on the line.

Let me know what you find. (I'm following this thread and will continue to help!)

Thanks for the help. It seems it is just a fact of clone boards manufactured to low tolerances in China. I think I'll just replace it with a smoothieboard.