Recommendations for heater fuse and holder
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@dragonn One more thing I am a little worried about: these fuse holders have fairly large wires going in and coming out of - much larger than those I use for the hot end heater cartridge. Will I not create a high contact resistance at the connection points? Or doesn't this matter bacause the wires to the hotend are already appropriately sized?
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@wilriker That holders are just designed for much higher currents then or hotend have, but this isn't a problem if you put the right fuse into it. And yes, wires for hotend are appropriately sized. So no worry about that.
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@dragonn Thanks for confirming.
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And another question: what would be the appropriate rating for the hotend fuse? I just took the same 7.5A fuse as is now used with Duet 1.04 but then I realized that this also covers the steppers so it will probably be too large for just the hotend.
I do have a 12V 40W heater cartridge which is run with 13-13.8V effectively making it a 52W heater.
This evaluates to 3.83A current.I think a 5A fuse would be better, right? Or even just as "low" as 4A?
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5 or 4.5A would be right. 4A could be to close. It could happen that you hotend draws ~4A when it is cold and starts heating up (resistance is lower when temp is lower).
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@dragonn Thanks. AFAICT there are no 4.5A automotive fuses so 5A it is.
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@wilriker didn't check if 4.5A exist but yes, 5A will be fine too.
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5A at 12v is 60 Watt. So the question that needs answering is, in the event of a MOSFET failure, will a 60 Watt heater on your printer get hot enough to cause a fire? The only way I know is to tune a 60 Watt heater and see what the firmware reports. In the thread that I linked to, people were saying that an appropriate size fuse would be 10 to 15 percent above the heater wattage. That's why I started this thread. So it seems that inline automotive fuse holders are NOT the answer if appropriate size fuses are not available for that type of holder.
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@deckingman said in Recommendations for heater fuse and holder:
5A at 12v is 60 Watt. So the question that needs answering is, in the event of a MOSFET failure, will a 60 Watt heater on your printer get hot enough to cause a fire? The only way I know is to tune a 60 Watt heater and see what the firmware reports.
In my case with 13.8V this would already nearly be a 70W heater. Anyway when PID tuning my heater with 12.6V already gave me a warning that if left on continuously it could reach something around 750-800°C which is more than "adequate" to start a fire.
In the thread that I linked to, people were saying that an appropriate size fuse would be 10 to 15 percent above the heater wattage. That's why I started this thread. So it seems that inline automotive fuse holders are NOT the answer if appropriate size fuses are not available for that type of holder.
I could reduce my voltage a little bit (to 13V max) and use a 4A fuse in this case. But of course this would be rather a workaround than a real solution.
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@resam In this video he uses a 19V PSU to power a 12V 40W heater which then becomes a 100W heater - but I assume this only makes the process faster not worse.
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I'm wrong - ignore this post.
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@resam I was also wrong it is even 109W.
