Custom Heat Pad and thermistor question
-
@wingtip nozzle sock and tuning it as a tool will be a good idea once that's all in place, but that's a good first step. Show's it heats up anyway. If you set a temp does it hold steady?
-
@phaedrux yes but i already knew that when i heated it up to tighten the nozzle
so im good to copy that m307 line in its entirety to the config file and save? then do pid tuning on the bed or should i do it now and enter both lines then save and restart?
-
Either copy the line or just send M500 to automatically save the results to config-override.g. Then add M501 to the end of config.g to load that file. Whichever you prefer.
-
Well I had some interesting things happen while trying to PID tune the bed. Being worried about heating up the glass to quickly as this was my first ac powered bed, when i sent the command to start the tune i also entered a P command to cut the pwm to 40% to ease into heating up the glass. It was very slow to say the least but it was heating up. When it first put power to the bed it had a slight odor to it that i just assumed was the new pad.
Eventually it got up to about 60c (i set it to go to 80c) then failed saying that the temp couldnt be reached. Im unaware if it was at that moment is when the failure occured or when i tried again later after letting the bed cool fully and i then let it rip at full pwm In hopes that it just timed out the first time and would heat faster at 100%. But after noticing finally the power switch to the bed wasnt lit i removed the switch and found the fuse had melted the internal plastic around it and eventually blew. the fuse internally was only 5 amp. I need to find a new switch that can handle a little more amperage. I wouldnt trust re using this one with a new fuse since the housing got so hot.
This is the switch i used (bought 2 years ago for this project) https://www.amazon.com/gp/product/B07C1567XW/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1
and here was the results
-
Well let's see, you installed a switch/fuse/socket combo that has a 5A fuse installed with a switch that is rated at 10A and you run between 12 and 13A (depending on your line voltage) through it.
Can you see a problem with this arrangement?
Find yourself something that is rated at 20A and you will be golden.
BTW, the power cords that plug into that particular plug are usually rated at between 5 and 10A and make for a nice heater when you draw that much power .... but then you like to do unconventional things so don't let me keep you from exploring this method of powering your printer. Like the arrangement of your print bed, it likely will work for a while before biting you in the rear. -
@jens55 as i said i bought the switch 2 years ago and its been installed for a year or so... Of course i see the problem now
Im already looking at a new switch and some assorted fast blow fuses better suited that will be ordered shortly.
Not sure why your being such a prick about my way i built the bed.... it will work and has been working on my other printer for years.... but by all means continue shaming something different. I dont care if it does fail, at least im experimenting and having fun... -
@wingtip, trying to explain why I am giving you a hard time will come across as snarky so I will not explain myself.
On the other hand, in the spirit of trying to help - do not install fast blow fuses, they are inappropriate for this application.
Saying "I don't care if it does fail ...." is fine in low voltage low power situations but not when you are playing with line voltage and high power heaters. Failure has the distinct possibility of burning down your house...
-
Now now, no need to be snarky here. Pretend it's a maker space and we're all just here to help each other out and learn while we go.
@wingtip that sucks. At least the fuse did what it was supposed to eventually. Likely a slow blow version.
Replacing the socket entirely would be a safe bet. Getting a fuse rated for the draw obviously.
Given the draw of the bed it might be a good idea to put it on it's own fused socket.
I should have asked about that detail earlier on.
@jens55 said in Custom Heat Pad and thermistor question:
do not install fast blow fuses, they are inappropriate for this application.
I'm curious about this. I've been using a "fast blow" fuse on my bed heater and it hasn't been an issue. Fast blow still isn't very "fast". Is the concern that it would blow too quickly?
-
@phaedrux, yes, fast blow fuses blow .... well ... fast
If you were to measure the cold resistance on your bed heater and calculate the current based on that rather than the normal operating current, then you get the minimum fuse size for that heater for a fast blow fuse. A regular fuse can be rated based on the operating current of the heater.
There are very few instances when a fast acting fuse is used and you usually pay a premium for them.
A regular fuse will allow for start up surges such as charging up large filter capacitors or heater start up current but will still protect the integrity and safety of the electrical system. A fuse will have specifications how long it will take to pop at how much overcurrent. A regular fuse is just more tolerant of surges and odd events while still making sure that the supply wiring will not be overloaded.
If you use a fast acting fuse but over-rate it (ie a 10 amp fuse when your normal draw is 5A), the fuse will tolerate start up surges and work just fine but you paid a premium for no additional protection.
I am sure there are other reasons that I am not aware of at the moment. -
Further to my comments about electrical safety .... one needs to look at the whole system and not just an individual component. If you design a circuit at that kind of voltage/power level, you need to be aware of the details of the entire system. Replacing the inlet receptacle with a version that handles 20A will not help you if the cord from the receptacle to the wall is only rated for 10A (or less). Ampacity charts are readily available.
It is bad ju ju if one is designing and building stuff related to line power without being fully aware of all the details. If you throw in the use of Chinese components, you really need to have a good understanding of what is what.
As an example of that, Chinese SSR's are known to be over-rated so the prudent designer would use either a 20A rated brand name device or a 40A (or higher) Chinese no name or clone brand. In both cases it is good policy to use a heat activated fuse on the bed in addition in case the doo doo hits the fan. Again, shit like this can easily burn down your house. -
I would like to add that using a fuse that is rated at a much higher draw then what you normally use (and using a higher rated fast blow in order to not trip it) is not recommended for obvious reasons.
