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printing - hotbed problems

Discussion in '3D printers' started by Rodm, Feb 13, 2017.

  1. Rodm

    Rodm Veteran
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    Hi,
    I bought an Anet a8 as a way to get started - learn a bit before moving on to bigger builds. after a few newbie - learning curve moments all seemed to be going well. I'm pretty sure my print settings are conservative and should not be challenging the machines (toys) capabilities. layer height .15, shell 1.6, bottom / top thickness 1.2, fill density 10, print speed 40, print temp 240 using abs, had been setting bed temp at 100. then I had to drop temp to 90 or bed would not get hot enough to start print. at first I thought my basement work area might be a bit cold for bed to keep up so I set up a small heater to blow warm air at the bed. Its printing now set at 90 and bed temp reads 75, so the drop in temps is progressing. the bed heats up, control panel seems to work fine. I'm thinking it a heat bed problem. its obviously not a real good heat bed to start so if its bad I would rather upgrade than try to figure out how to get a replacement from Anet. So a few questions for the skilled and honorable openbuilds crew. does it seem like I'm on the right track? Is there something else I should try? what would you recommend as a replacement - upgrade?

    thanks,
    Rod
     
  2. Kyo

    Kyo Master
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    I find the cheap heat beds (depending on source) can struggle with getting up to temp. I chucked one heat bed I got off ebay in the bin as it never did get up to temp properly.

    One mod you can do to help keep the bed at a constant temp is to add a layer of insulation. I find cork sheet to work really well in this regard. You can pick up multi packs cheap online such as this pack "here" and trim to size and stack it to your heat bed. I am not familiar with the anet a8 but I assume it uses a standard 200mm bed? If so for a upgrade I really like the reprap mk3 aluminum beds "here".
     
  3. snokid

    snokid Master
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    the heat bed is just a resistor, then there's a thermistor on the bottom.
    ok if it's getting warm just not warm enough, could be a few problems.
    things to check....
    check the thermistor on the plate did it come loose, just tape it back on if it did.
    check the wires to the bed 12v + & - could be a loose connection.
    lastly power supply could be underrated for the bed.
    Bob
     
  4. Rodm

    Rodm Veteran
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    Thanks Guys,
    Well I did a bit of checking and some web surfing about your suggestions and for other ideas. Power supply seemed to power bed fine at first. 12v 20amp output. It seems it would not be considered underpowered but not a lot if any extra juice. I saw a youtube video that talked about a power supply not being adjusted properly and only putting out 7.5 amps +/- so it could not get up to abs temps. He adjusted - fixed that. I have not had a chance to check and no clue how to adjust. It worked fine - now its not so I don't think that's the problem. That said it did preheat for pla to 60 in just afew minutes. I don't have any pla to try a print with. Preheating for abs flat lines at 92. Everything seems fine with hotplate. nothing seems lose, connections look good, no sign of discoloration or charring anywhere, bed or board. One warning I was glad to find was about the extruder heater coming loose. I checked and it was, pulled out with barely any effort. What do you like to print with. I'm using abs because it came with kit. Is this a good general print filament or would pla be better. I want to get things fixed either way. I guess when I get a chance I'm off to the depoe for a test meter. Anyone know how I would adjust the psu output? Normally I would not try to adjust what's an inexpensive psu and replacing - upgrade would be my choice.... from what I've learned the wires, board, ect... are questionable if power draws increase over its design.
     
  5. snokid

    snokid Master
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    T2) My PCB heatbed never reaches the required temperature, or takes too long to reach the required temperature.

    This is probably the most common problem with heatbeds that RepRap builders have to deal with. It can have various causes:

    D2a) Turn off your printer completely, and measure the resistance of your heatbed using a multimeter: it should not be higher than 1.2 Ohm. If it is higher than 1.2 Ohm, your heatbed will not get enough current and will not dissipate enough heat to reach the required temperatures.
    S2a) Return the heatbed to whomever sold it to you and make sure to get one with a proper resistance!
    D2b) If you have measured the resistance of your PCB heatbed and it is lower than 1.2 Ohm, you need to check the voltage across the heatbed terminals when it is heating up. If the voltage is significantly below, say, 11.7V, then again your heatbed will not get enough current and will not dissipate enough heat to reach the required temperatures.
    S2b) Make sure you are using electrical cable with a proper gauge (14 gauge recommended) to connect the heatbed to the controller board. And again, make sure your power supply provides the proper voltage under load conditions. Change components as required.
    D2c) Make sure you have the PCB traces on the upper side of your heatbed!
    S2c) Flip the PCB heatbed if required.
     
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  6. Rodm

    Rodm Veteran
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    Thanks,

    D2 - S2c ?
    Upper sides of heat bed? Silver side is up. Black side with solder connections and warnings - lettering down. seemed to be the same as instructions and build video. Is that wrong? I can see how that would effect quality of print but not sure it would cause issue I having. I'll try to get rest checked out tonight or tomorrow.

    Thanks
     
  7. Craig Anderson

    Craig Anderson Well-Known
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    I have had heatbed problems like those described above. Most of the problem with my printer was trying to power a heatbed with 12 volts. I replaced my PCB heater with one that runs at 120 volts. Now I can go from cold to 120 C in 6-7 minutes and it stays where I set it.
     
  8. JustinTime

    JustinTime Master
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    I too switched from the 12V heat bed to 120V heat bed. I bought a 3mm aluminum plate on eBay, 12" x 9". The heater has a adhesive backing that sticks very well to the aluminum. I power it with an SSR. My bed now gets to 100┬░c in about 4-5 min.
     
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  9. Rodm

    Rodm Veteran
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    Hi,
    I finally got a chance to go get a multimeter. A klein mm300. 600v, 10a, 2m. I followed the instructions for dc v up to 20a and get a 9.8 reading. Voltage at outlet and polarity both fine. I tried using the voltage adjustment on psu(12v, 20 amp) set all the way its 14.4 at psu and -13.2 at connector to bed.. temp could not make 110 stalled at 109 in reasonable time. Seemed to hold 100 ok and heat up from there to 105 in ok time. reset to just above 12 then -11.5 at bed. Heat up slow
    at this setting extruder holds close to set temp +/- 2.5, bed temp stalls at 89. At 14.4 extruder temp ran about +5 but bed good but no better than 109. Is it ok or safe to run at 14.4 setting? Or is this a sign something needs to be fixed or replaced? I'd be lying if I said I completely understand what these readings mean, I'm having fun figuring things out but would prefer not to start a fire!

    thanks again,
     
  10. snokid

    snokid Master
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    sounds like voltage is about right out of power supply, 12.8-13.6 should be plenty safe.
    I don't know what board the anet has, but adding a mosfet would be a good idea. A mosfet is pretty much a relay. With a mosfet it takes the work away from the motherboard and as a plus you can add another power supply to power the heatbed. Adding another power supply you can give just the bed 24V if it will take it and your problems will be gone.

    Or you can give up on the pcb board heater and go with the 120v AC oil pan heaters like mentioned above, then you can have an external temp controller for your bed heat.

    Trying to print ABS in an open frame printer isn't the easiest thing to do. Try the Ikea lack(sp?) table enclosure mod that many I3's use.

    hope this helps
    Bob
     
  11. Rodm

    Rodm Veteran
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    Thanks Bob,
    It's nice to know what's safe. I got started with the a8 as a way to learn - prep myself for a cnc build. I had been interested in 3d printing before and after reading and seeing how usefull they are openbuild wise it seemed a great way to start. As much as I prefer to upgrade than just fix, the parts are already starting to show up for my cnc project. So for now I'll settle for safe and working well. I'll adjust psu to the 13.6, do a Moffet (I had read about and liked that idea) and put a cabinet together. I hope that works well enough till the cnc is up and running.
     
  12. Craig Anderson

    Craig Anderson Well-Known
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    My 120 volt heater is a PCB......designed for 3d printers......what is an oil pan heater? My heater is controlled by a SSR, but it is controlled by my Smoothie board, so I have internal control of the bed.
     
  13. Kyo

    Kyo Master
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    Oil pan heaters are basically the same as silicone heaters sold by 3d printer stores (think Keenovo). Powered by mains and are self adhesive. Used to pre heat the oil to reduce wear and tear on your engine.

    op_heater.jpg
     
  14. Rodm

    Rodm Veteran
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    hello!
    So I was pretty happy following the advice and figuring out the psu adjustment. I thought the mosfet? Was all I was going to need to do for now. Between the great advice here and a youtube video showing how to do test towers in cura for temp and flow I was racking up some nice prints. Well so far even using all the lucky charms the larger prints like the frame supports still lift and warp, darn!! I like the new hot bed idea. Would prefer to stay with a set up that keeps control in the code - one power supply. The one Kyo recommended is 24v and can be 12. More power always seems like a good idea to me. I've seen the 5v step downs? to power boards, is there a 12v step down I could use off a 24v psu to use the new bed at full power and not burn up the rest of the printer?
     
  15. snokid

    snokid Master
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    what board did they put in your printer? might be able to handle 24v...
    Bob
     
  16. Rodm

    Rodm Veteran
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    The Anet a8 is a Chinese knock off of a pursa i3. I don't remember seeing any none anet markings anywhere and that only marker one ortwo things. I'll take a better look in the am. I've read - heard too many smoked this or that stories to expect it could handle the extra power.
     
  17. Rodm

    Rodm Veteran
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    so if I updated psu and hotbed to 24v and the board goes up in smoke how involved is the fix - next upgrade?
     
  18. evilc66

    evilc66 Master
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    Have you tried glue sticks? ABS slurries? Those will help some, but might not be the final solution. Success at this point with ABS is more likely going to come from using an enclosure rather than increasing the board temperature. Smaller parts don't warp and lift as readily, as the stresses put upon the part as the upper layers cool and shrink is less. Larger prints need to be kept warm throughout the print to prevent the upper layers from shrinking. Increasing the temperature on the bed will just make lifting happen later in the print.

    Now, an enclosure doesn't have to be fancy. I've seen people use garbage bags as a quick band-aid fix. Rubbermaid/Sterlite storage boxes placed over the printer work well too, and many are available clear so you can see what's going on.

    In my opinion, increasing the bed temperature should only be done if you are having trouble getting the first layer to stick at all. Seeing as you can get it to stick, but it's lifting later in the prints says to me that you have enough heat.
     
  19. Rodm

    Rodm Veteran
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    Sticking isn't a problem. I'm using blue tape and my first layer height at .85. Things stick realy well. Also used my fill density to 20 it had been set at 10. I haven't printed anything big yet with those settings but the small stuff is working well. The bed holds 105 pretty well. Yes the lifting is happening later. I've walked away 2 hrs into a print with all going well. A few hrs later and it's messed up. I have a cabinet idea I'm going to put together. I guess I'll wait and see. That and try some PLA.
     
  20. evilc66

    evilc66 Master
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    The big advantage you would see from a change in heater (especially if you increase the wattage rating of the heater) is faster heat up times. I'm sure the factory heater takes forever (relatively speaking) to get to 105C. I went a little overkill on my last printer with a Keenovo 750W 110v AC heater mat under a slab of 1/4" thick aluminum tool plate. If I turn on the hot end and the bed at the same time, the bed hits it's target first ;)
     
  21. Rodm

    Rodm Veteran
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    How do you have the power and te
    How do you have the power and temp control set up?
     
  22. evilc66

    evilc66 Master
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    Heater is controlled through a solid state relay. Input signal for the SSR is connected to the same port that a DC heat bed would be connected to.
     
  23. Rodm

    Rodm Veteran
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    do you run 110 power from ac in lugs on psu or a separate cord to outlet? do you have a link for relay? is it the mossfet think I've read about?
     
  24. Kyo

    Kyo Master
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    About 1:56 in Tom covers hooking up a ssr. Legit Fotek relays work well.

     
  25. evilc66

    evilc66 Master
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    You can run a separate cord, or you can tie into the AC input for the DC power supply. Same difference. I chose to wire it to the AC input on the power supply.

    As Kyo posted, the Fotek SSRs are the way to go (there are other more expensive options, but these are the best on the more budget friendly end of the spectrum). These are readily available through Amazon, eBay, etc...

    These are different than MOSFETs. MOSFETs are DC switches basically. You can't pass AC through them without letting the magic smoke out. What is inside an AC rated SSR is a triac, which is an AC rated component. If you would like to see what's inside and a description of how it works, take a look here:

     
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