What happens if the fan fails

I suspect you will get a filament jamb pretty quickly as the heat from the heat block will transfer across the heat break and melt/soften the filament in the tube. The fins will gradually get hotter. Pray that the fan keeps working ;-)

Mike

 

They get pretty hot, like 100C.

But over 60C should be a trip point if you're printing PLA, as that will cause the filament to heat up and jam

 

The neato solution would be to replace the fan for one of the 3 wire ones which has a speed pulse output. Then it's a simple circuit and a FET to disconnect the heater and fire a reset at the controller board to stop the print if you don't see a certain RPM from the fan.

 

That's why they dropped from a 40W to 25/30W. The most you can get that to heat up is like 400C, below the melting point of anything that could cause damage

 

thanks for this information

 

Wouldn't the maximum temperature on the fins be what you set the hotend to?

 

Not really, no. The setpoint is actually measuring inside the heater block, which will actually be hotter than even the skin of the block. Add in the thermal barrier in the heat break, you reduce the amount of energy being transferred into the heatsink. The heatsink will then dissipate this heat via radiation and convection. It will still get burning hot, but not the same temp as the setpoint

 

@e3duser : Is this with or without the fans blowing ?

 

I have actually had a fan failure, so I can report what happened: nothing. It just jammed.

I was printing ABS at 255C. The hot end jammed about an hour into a 10-hour print. I'm pretty sure the fan never started, and it ran the entire 10 hours with no active cooling.

My extruder setup is all plastic, installed on a 12" Prusa i3v (MakerFarm). The extruder, groove mount, mounting shelf, X carriage and and a rear fan shroud with 1mm clearance from the fins are all printed ABS parts and they all survived. I just freed up the fan, cleaned off the glass and started again. I probably have 200 hours on the printer since.

 

IMHO the problem is not the temperature of the heat sink and it's fins but the temperature of the Heat Break.

As the heat break gets hotter, so molten plastic can rise / exist higher and higher up this tube.

Which is a great place for a jam to occur.

(Pushing rigid filament down a tube is easy, pushing molten plastic not so much...)

Even if it didn't quite jam, imagine what happens when you finish the print: the whole mass goes rock solid.

That means that, when you want to print again, first of all you have to heat up not only the heater block and nozzle but also the heat break to melting temperature before you can even think about ramming more filament in. And, because the molten plastic is a lot stickier in the tube than freely moving filament, it will take a lot more force to get things going. Which your extruder might not manage.

I watched Tom Sanladerer's latest review http://toms3d.org/2016/05/04/review-up-to-500c-dyzeend-x-and-dyzextruder/

He makes an interesting point: the heat exchanger in question has much finer aluminium fins with the consequence that the whole structure can be lighter and the fan SMALLER (for an equivalent amount of cooling). I wonder what the logic is behind the V6 heat sink? Structural strength?

In any case, we might be able to SLOW the fan down a bit to make it quieter. That it is running flat out is just an accident of the system, the fact the Rumba has no controller for this, the the supplied voltage is 24v and that that is the rating of the part!