Rambo Fan outputs?

[sthone]

OK... so I want to do is completely ditch the Extruder fans on my M2's as I don't see them serving any purpose with the V4's. I know they are wired in series with the case fan so they both draw 24 volts. I was reading the wiki on the Rambo and it lists the "Extruders + fans and logic at 5A 12-35V" Is the output for FAN1 always at 24 volts (firmware controlled somehow?) or can I just rewire the single case fan directly into FAN1 and it will just draw the 12 volts required?

I know just enough about electronics to get myself in trouble and I don't want to let the magic smoke out of my boards.

-Steve

[jsc]

That's brave. I don't recommend removing the extruder fan, it prevents heat creep. Without it, the top portion of the extruder will get hot enough to melt plastic, and then you get a jam. And yes, all the fan outputs are always at 24V.

[sthone]

I don't think heat creep with the V4 would be an issue though as the hot end is totally separated from the actual extruder.

So if I do this I guess the easiest option would be to get a 24 volt fan for the case then.

Thanks for the info...

-Steve

[jsc]

Oh yes, probably true, although why design in a fan then?

Yes, a 24V fan is the way to go, although you could drop the voltage with a resistor, or feed it smoothed 12V using PWM and an RC filter. More work, and no point.

[sthone]

Oh yes, probably true, although why design in a fan then?

Best guess... two fans were needed for the V3B for sure. After they switched to the V4 instead of purchasing all new 24v fans for the case (who knows how much stock of 12 volts one they had left) just keep using up the old stock of 12 volt fans and harnesses up.... least that's what I would do if it was my business after all it can't hurt to have two fans. I'll soon find out if its need or not whats the worst that could happen.

-Steve

[Tim]

I know they are wired in series with the case fan so they both draw 24 volts.

I'm not sure what the present setup is for fans, but I have an older M2 that I converted to 24V, and I have the electronics case fan and extruder fan wired in series. Fans are going to be either 12V or 24V, so if they're wired in series, they must be 12V fans, so that the 24V across them is divided in half so each fan sees 12V across it (more or less. . . actually it's a pretty poor setup for a voltage divider, as the fan loads are constantly changing, and the midpoint should be connected to the output of a 12V regulator to keep it from moving around. . . although if you install a 12V regulator, then you might as well use it to drive both fans in parallel). If your fans are wired in parallel, then they would be 24V fans (anyway, the voltage rating is written on the front of the fan). You can run a 12V fan with a 24V output + PWM, as Jin said, although I wouldn't necessarily recommend it. It's much easier just to buy a few 24V fans.

[sthone]

So I disconnected the two 12v fans and just put a single 24v one in the electronics box and after a quick test without the extruder fan (1 1/2 hours at 230°) I really didn't see much temperature changes in and around the filament drive.

I took some reading with one of those laser type temp gauges and around the tip of the filament drive where I'd expect the creep to be and it was still only around 60-100°C (same as with the extruder fan) The area behind where the fan is went from maybe 35°C to only 65°C that was the biggest change. I tested it on my printer with all the plastic bits printed in PETG so I really don't see there being any problems there with the temps. I plan on moving it to my printer with the all metal hot end so there should be any problems there either. I don't know if it's really any quieter without the extruder fan as the 24v one spins a lot faster but my original case fan was making some crazy noises so it was worth swapping out anyway and I don't have to worry about sticking allen drivers through the fan blades any more.

-Steve

[Tim]

my original case fan was making some crazy noises so it was worth swapping out anyway

Yeah, this is a property of having the two fans in series and expecting them to act as a voltage divider with a drop of 12V across each---it comes pretty close in steady-state, but definitinely not at startup. The fans are a constantly changing load so it is possible to get voltage oscillations between the two, or at least some very complicated and undesirable dynamics. My extruder fan is the one that makes all the crazy noises, not the case fan, but I expect I'm getting the same noises you are (or rather, were). When my first fan started doing that, I ordered a replacement fan from MakerGear, but after a few days that fan started making noises as well. The noisy mode quiets down after some time (10 seconds to half a minute or so), but it is quite loud and annoying while it lasts. I am going to try adding that 12V regulator I mentioned in the last post; I think that will solve the problem while keeping the 12V serial configuration. Or maybe it's a lot easier just to get two 24V fans and call it done.

The extruder fan blows not only on the hot-end, but also on the extruder motor gears. Is there any evidence that they really need to be cooled down as well?

(Edit) From the discussion with Ed Nisley on the "Nema 17 dampers" thread, the 12V regulator will only work if you put the two 12V fans in parallel and drive them both at the same time from the 12V regulator output. This doubles the current, but the fans are a very small part of the total current being drawn by the M2. The Final Word on the subject is that putting fans in series is just a Bad Idea.