nema17 dampers

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jdacal
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Re: nema17 dampers

Post by jdacal » Wed Sep 02, 2015 1:03 am

I got my Noctua fan today, but I ended up removing it from the enclosure. It doesn't seem to work well in series with the 30mm fan on the e3D. The extruder fan slowed down way too much. Will have to work on a way to wire them directly to 12 volts I guess.
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insta
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Re: nema17 dampers

Post by insta » Wed Sep 02, 2015 1:05 am

There's two independently controllable 24v outputs on the RAMBo (FAN1 & FAN2) ... I'm about 2 dead fans from converting all my shiz to 24v fans across the board, and using the auto-temperature & controller enable features to flip them on or off.
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jdacal
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Re: nema17 dampers

Post by jdacal » Wed Sep 02, 2015 1:07 am

insta wrote:There's two independently controllable 24v outputs on the RAMBo (FAN1 & FAN2) ... I'm about 2 dead fans from converting all my shiz to 24v fans across the board, and using the auto-temperature & controller enable features to flip them on or off.
You wouldn't happen to know what resistor and wattage I would need to put in series with a 12 volt fan to drop that 24 down to 12 would you?
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Re: nema17 dampers

Post by innkeeper » Wed Sep 02, 2015 1:37 am

The formula for resistance is:

R = E /I
or
voltage / current = Resistance

divide the voltage you want to drop across the resister by the current the fan needs and you will get the resistance value.

example: 12v / 0.1a = 120 ohms

the other thing is the wattage, so we need a higher wattage resistor then is actualy disipated power.
formula for power is:

P = I X E
or
current x voltage = wattage

0.1a * 12v = 1.2W

in this example, you need over a 1.2w resister, id opt for a 2w.

having said all this, the actual current a fan will use is dependent on the backpressure the fan has, it is not a constant current device and will not necessarily run at he current rating on the fan, but a bit less in many applications. so the actual value is less easy to come to but using the rating should get you close enough.
the real way to know the current is to measure it and use that value.

however, if you cant to that, usually fans are pretty resilient and can handle a bit of over voltage if you use the rated value as your calculation.
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Re: nema17 dampers

Post by Kulturfolger » Sat Sep 05, 2015 10:11 pm

jdacal wrote:I got my Noctua fan today, but I ended up removing it from the enclosure. It doesn't seem to work well in series with the 30mm fan on the e3D. The extruder fan slowed down way too much. Will have to work on a way to wire them directly to 12 volts I guess.
I tried to find a few silent 24V fans but I failed. Now I use ordinary noctua fans to a seperate power supply with 10V output. 50mm Noctua for the feeder cooling and 80mm Noctua for the RAMBO Board. The Noctua within the PSU runs with the internal 12V. The fan is noisy with the air pulling outwards but rather silent with the air pulling in.

BTW: I ditched the dampers, the cant handle the belt tension, after a few days the belt went really slack and the prints went bad. To many backlash added.

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Re: nema17 dampers

Post by innkeeper » Sun Sep 06, 2015 2:48 am

i've run abut 5 spools though the machine since putting them on, no problems for me so far.
knocks wood.
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Re: nema17 dampers

Post by Tim » Sun Sep 06, 2015 4:57 am

jdacal wrote:You wouldn't happen to know what resistor and wattage I would need to put in series with a 12 volt fan to drop that 24 down to 12 would you?
For the same reason mentioned in the other thread about the 12V vs. 24V fans, I wouldn't use the fans as part of a voltage divider. Although a resistor is a constant load, so you shouldn't have all the issues that can be caused by two fans (both dynamic loads) in series. It's better to attach the midpoint between the fans to a 12V voltage regulator; the regulator gets +24V to ground as input, and keeps both fans at 12V by adjusting for the load difference.

Something like the Fairchild LM7812ACT would do nicely: 12V output, up to 35V input, regulates up to 1A (which is way more than the fans use), and costs $0.71.

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Re: nema17 dampers

Post by jdacal » Sun Sep 06, 2015 9:05 am

Tim wrote:
jdacal wrote:You wouldn't happen to know what resistor and wattage I would need to put in series with a 12 volt fan to drop that 24 down to 12 would you?
For the same reason mentioned in the other thread about the 12V vs. 24V fans, I wouldn't use the fans as part of a voltage divider. Although a resistor is a constant load, so you shouldn't have all the issues that can be caused by two fans (both dynamic loads) in series. It's better to attach the midpoint between the fans to a 12V voltage regulator; the regulator gets +24V to ground as input, and keeps both fans at 12V by adjusting for the load difference.

Something like the Fairchild LM7812ACT would do nicely: 12V output, up to 35V input, regulates up to 1A (which is way more than the fans use), and costs $0.71.
The main problem was I put the Noctua in series with the 12v 30mm fan that comes with the e3D and the loads were different so it wasn't working out too good. I have two 40mm Noctuas in series now and they seem to be working much better, but will try the regulator when I get time, I still don't think they are working at maximum efficiency.
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Re: nema17 dampers

Post by ednisley » Sun Sep 06, 2015 1:49 pm

Tim wrote:the regulator gets +24V to ground as input, and keeps both fans at 12V
Three-terminal linear regulators can only source current, so they cannot control the output voltage when it's higher than expected. When the current from the "upper" fan exceeds what the "lower" fan can absorb, the regulator can't hold its output voltage down.

The problem boils down to assuming that digital brushless DC motor controllers inside the fans behave just like 19th Century big-iron DC motors. Interrupting the supply voltage with PWM doesn't produce the expected result, nor does putting the motors in series, because they're not that kind of motor. The digital logic inside the motor requires a constant DC supply, end of story.

If you're going to all the trouble of adding a regulator, rewire the fans so they get the proper voltage and be done with it. Better to use a DC-to-DC converter, though, because a linear regulator operating from twice the fan voltage will dissipate exactly as much power as the fans and will require an absurdly large heatsink for proper operation.

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Tim
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Re: nema17 dampers

Post by Tim » Sun Sep 06, 2015 4:41 pm

ednisley wrote:Three-terminal linear regulators can only source current, so they cannot control the output voltage when it's higher than expected. When the current from the "upper" fan exceeds what the "lower" fan can absorb, the regulator can't hold its output voltage down.
Hmm, yes, you're right, I should have looked at the data sheet first. It only provides a current source, so the most it can do in response to an overvoltage is to shut off the current, which won't correct the overvoltage. I was thinking back to something I did on a chip once, controlling an intermediate value on a resistor stack with an amplifier, but that had both source and sink capability. So yes, I guess the only certain fix is to replace the 12V fans with 24V fans in parallel and call it done. Although if the 12V fans are preferred because they're less noisy, then it would be okay to connect them in parallel and drive them both from a single 12V regulator output.

Thanks for the catch, Ed.

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