Heater Cartridge Safety Questions
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@gnydick said in Heater Cartridge Safety Questions:
I have 2 questions...
- What is the maximum advisable wattage for a heater cartridge?
- Assuming trustworthy build quality, is this safe to use on the duet2?
- That's a difficult question to answer. If you look solely at the current capability of the various boards, you'll see that the heater outputs are rated at 5 to 6 Amps.
https://docs.duet3d.com/en/User_manual/Connecting_hardware/Heaters_extruders
Using a 12v heater with 12V supply that would give you a maximum of 60 to 72 watts depending on the board. Using a 24V heater with 24V supply would give you a maximum of 120 to 144 Watts.
But if you put a 144 Watt heater into a small hot end with very little mass, and if the Mosfet failed closed circuit, then it could reach a temperature that might melt aluminium - it would almost certainly cause a fire if it came into contact with something easily combustible. So while a 144Watt heater might be "safe" in a large hot with high thermal mass, it might not be safe in a small hot end with low mass.
- 115 W at 24V is 4.8 amps so should be "safe" as far as the heater output capability of the board is concerned.
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I would like to add that it also really depends on what you are doing. If you are pushing a really large volume of filament through a really large nozzle than it might be ok. The picture shows a nozzle that goes with the kit but I didn't see the nozzle size.
Even if you are using a 1 mm or larger nozzle and intend on printing huge amounts of filament real quick, this should only be attempted by someone who REALLY knows what he/she is doing!
I personally wouldn't attempt to run this heater on 24V because of the danger involved .... but then I don't do base jumping or bungy jumping either .....The table of output power vs temperature seems odd to me - while resistance does go up with temperature, they are claiming that the heater only puts out 46W at 280C and there is no mention of anything special for the heater that would account for this reduction in wattage when the heater is hot.
I suspect this is really a 50W heater with a really creative way of selling. Not unheard of in Chinese products. -
@jens55 It looks to me like a clone of E3D's Revo Heater core which uses a PTC heater.
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@deckingman, that would explain the wattage table but would lead me to wonder why nothing was said about that feature. Seems to me that this would be a game changer feature.
How lucky do you feel ? ...
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@gnydick 115 watts? Why?
You can max out a Volcano at ~280C with 30 watts. Very rarely is a heater cartridge the limiting factor, maybe if printing PEEK in a CHT or Volcano.
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@jens55, lol. Yeah, I pretty much want to print fast. My kinematics can keep up and so can my cooling, but even the volcano copper block doesn't hold enough juice sometimes. My prints come out brittle and flake apart because the net temp by the time the extrusion touches the print, it's pretty much solidified in the air already.
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@gnydick, what temperature is reported by the current heater. There are two (or more) aspects to liquefying the filament. The most obvious of course is the hot end temperature. If you push too much material through it, you might see a drop in temperature shown on the temp graph. The other aspect is how fast the heat is conducted from the nozzle and hot end to the core of the filament. This is something that more wattage isn't going to help you with and is IMHO the bigger issue.
If you see a drop in the hot end temperature then a more powerful heater can help but if the temperature that you see is mostly constant then a replacement heater isn't going to do diddly squat.
I am assuming you have already increased the temperature of the hot end to let you extrude marginally more material but don't forget that this is really not the way to go as it is easy to overheat the outer material and still have the inner material too cold. In moderation, it can help.
Also, what happens to the filament when the flow rate drops due to the nature of the model? This can really throw all kinds of wrenches in the works. There is no such thing as a free lunch - if what you are printing requires a constant high flow rate then sure, optimize for that .... but be aware that you loose quality in low flow/high detail situations.
The Volcano is known to cause all kinds of drooling issues. You could also go with the Super Volcano but I can see the drooling issue being magnified by the Super Volcano (I tried the Volcano and have discontinued it's use, I never tried the Super Volcano)To increase your extrusion rate, you can go with a number of different newer technology hot ends other than the volcano. These usually come with a bigger heater as well. There are a number of better hot ends out there that can flow more material and you can also go with the special nozzles that have a modified interior to allow more heat transfer to the filament. I don't recall the name of these at the moment.
Anyway, the Volcano is outdated technology and better solutions exist.YMMV !!!
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@gnydick I second pretty much everything that @jens55 has said. My current hot end design has 6 inputs and two heat zones, the primary purpose of which is to print multiple different filaments using the same nozzle. But a secondary "side effect" of this design is that I effectively have 6 melt chambers fed by 6 individual extruders. So I have at least 6 times the surface area of a single hot end. When feeding all 6 filaments concurrently, each individual filament travels at one sixth of the speed. So each filament spend 6 times longer in the melt chamber than single input would. This is important because as @jens55 rightly points out, it takes time for the heat to reach the core of the filament.
Just out of interest, I did do some test prints just to see what the melt rate capability would be. With a 1.5mm diameter nozzle, I printed a vase in 73 minutes using around 130 metres of filament. But a simple vase is about all I could print. Filament oozing is a huge problem so I could never print anything with any sort of detail. Essentially, in this high melt rate configuration, the hot end is untamable at lower speeds or short moves. The other issues with big nozzles (which you need to use to leverage high melt rate) is that you need a massive amount of cooling. Even then, it takes time for the previous layer to cool, so if you try to print anything with a small footprint, you'll end up with a shapeless blob.Edit. For the sake of completeness, here is the video of that print https://www.youtube.com/watch?v=gc8AciHjf4I
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@gnydick said in Heater Cartridge Safety Questions:
@jens55, lol. Yeah, I pretty much want to print fast. My kinematics can keep up and so can my cooling, but even the volcano copper block doesn't hold enough juice sometimes. My prints come out brittle and flake apart because the net temp by the time the extrusion touches the print, it's pretty much solidified in the air already.
(Assuming you're holding desired temperature as measured by the thermistor), that's not the heater's fault, that's exceeding the laws of physics constraining the nozzle in question.
Solutions include making the nozzle longer so heat has more time to transfer, or improving the internal geometry (like a CHT nozzle) to increase surface area inside the nozzle.
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@deckingman nice! Did you machine the 6 chamber hotend? Videos, cad files?
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@gnydick said in Heater Cartridge Safety Questions:
@deckingman nice! Did you machine the 6 chamber hotend? Videos, cad files?
Yes I did - I documented my journey on my YouTube channel - link is in my signature.
