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Complete heated bed kit for Ultimaker


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Posted · Complete heated bed kit for Ultimaker

Yes, that size wire is overkill but it is the smallest that vendor has in this product line and it was just a matter of convenience to buy it with the other. The wire is very flexible. However, that doesn't guarantee it is suitable to high flex situations but that is somewhat implied.

 

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    Posted · Complete heated bed kit for Ultimaker

    Usually, silicon insulated wire is high-flex stranded wire. Otherwise, the wire wouldn't be so flexible... You can easily see that when there are lots of small diameter strands instead of just a few, thicker strands.

    Silicon insulated wire is in general well suited because even the low-quality chinese stuff is still pretty good.

    Never buy PVC insulated wire of non-industrial quality - complete waste of money. :D

    High flex indeed doesn't imply high lifetime under moving conditions. I've tested high-flex fire-wire cables up to 50 million cycles and even these would sometimes fail. But it's the best thing you can do. You never get 100% maintenance free stuff...

    I bought a large stock of this wire:

    http://www.distrelec.ch/Web/Downloads/at/_d/wxHF-3KV250_dat_d.pdf?mime=application%2Fpdf

    Corresponds to AWG 14 (or 13), built up of 672 strands at 0.07mm2. Suitable for temperatures up to 180°C, and has a max. resistance of 8 mOhms per meter.

    Even if you take 10 meters of this cable, it has no noticeable resistance (meaning energy loss). The heated beds are usually in the 1 - 10 Ohms range.

     

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    Posted · Complete heated bed kit for Ultimaker

    I totally love the heated bed provided by Jason Wu on eBay: http://stores.ebay.com/3dphk/%C2%A0

     

    I did completely wreck and burn out my RAMPS controller board, but luckily had a pro soldering friend rescue the board and solder in the correct resistor. The 24 volt power supply works well... there were a few items as far as how the screws go in and how the aluminum bed sits and I'll post details, pictures, howtos and how I handled the issues ASAP... I'm using the glass with either 3m blue tape for PLA or with light heat (70 Celsius) and PET tape... or 120 Celsius with PET tape and 230 Celsius for ABS (with some light plastic sheets covering making a fake heat chamber). I gave up on Kapton tape as it's too much work to apply. Thick PET tape applies easy by just spraying some water on the aluminum first and a squeegee.

    I'm working on an online store for Jason, hopefully he'll have the patience to wait for it's completion:

    http://dev-3dpmod.gotpantheon.com

     

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    Posted · Complete heated bed kit for Ultimaker

    If I may ask, why are you using any tape with a heated bed for PLA? I just print directly on to the glass at 220c/70c for the first layer and usually with a brim to control corner shrinkage. Seems to stick very well until the bed temp is allowed to drop for removal.

     

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    Posted · Complete heated bed kit for Ultimaker

    I'd be surprised if you don't need the 4.7k resistor. The darkmatters website seems to be down. Can you describe how the temp sensor is hooked up on the darkmatters version of the heated bed? Where does the wiring go to? What does the part look like? Is it active (meaning does the part have a power source - like a chip that requires 5 volts or something)?

    Or is it just a 2 lead device? Maybe supply a photo of the heated bed temp sensor.

     

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    Posted · Complete heated bed kit for Ultimaker

    You definetly do have to solder in the 4.7k resistor on an Ultimaker 1. Maybe there are other electronics that already have the resistor in place, but the UM1 doesn't.

    It will not work without the resistor, because the resistor connects the power supply to the thermistor (making a voltage divider). Without that resistor, the electronics will always read zero.

     

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    Posted · Complete heated bed kit for Ultimaker

    You have to set that album to "public", or we can't access it ;)

     

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    Posted · Complete heated bed kit for Ultimaker

    Guys, just a few small side questions regarding bed wiring:

    Instead of using the relais, there shall be the possibility to use a thyristor to change from bangbang to PID - correct?

    Has somebody experience with?

    How would this work and which parts/FW changes would be necessarry??

    Any hint appreciated!

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    Posted · Complete heated bed kit for Ultimaker

    Hi Drayson,

    I recently bought the Jason Wu's kit. (Very efficient service, by the way!)

    I quickly decided that I should find a nicer replacement for the relay board.

    I designed a small board to easily link the UM1 electronics to the Heated bed. It's 100% solid state. No relay!

    And for the peace of mind, it's optocoupled so there is no electrical link between the Ultimaker electronics and the Heated bed power supply.

    I just received the PCBs and I'll quickly assemble a couple of them...

    If some of you find this interesting, I can share more information on this...

    ++

    Gaël

     

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    Posted · Complete heated bed kit for Ultimaker

    @ Gael, cool, I am interested as I plan on ordering the Jason Wu kit as soon as it's on stock again.

    thanks!

    Martin

     

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    Posted · Complete heated bed kit for Ultimaker

    Guys, just a few small side questions regarding bed wiring:

    Instead of using the relais, there shall be the possibility to use a thyristor to change from bangbang to PID - correct?

    Has somebody experience with?

    How would this work and which parts/FW changes would be necessarry??

    Any hint appreciated!

     

    Why would you want to use a thyristor? That's an element for AC-switching and dimming. I've never heard of any uses for a thyristor in DC applications... (Then again, I don't know everything, of course ;), especially with AC elements my education is very basic)

    The problem with a mechanical relay is, you don't want it to switch quickly because relays don't like fast switching. The best alternative would be a simple MosFET - no problems with fast switching (except maybe that you could generate some eletrical interference).

    UM heatbed mosfet wiring

    Here's how I did it. It's very simple, I didn't even use actual connectors but just soldered the wires directly to the pins of the corresponding parts.

    It starts with a LED to show me when the thing is heating. Not necessary, but informative. Then I divide the voltage by 2 (voltage divider with equal resistor values) so that I don't have the full 19V on my MosFET Gate. Again, this is not really necessary, but 19V is a bit high (my MosFET has 20V max VGS rating). Also, these resistors provide some very basic ESD protection (not really, but they're better than nothing, and a MosFET Gate is pretty sensitive).

    Then it's the simple "MosFET as a switch" hookup. Make sure that the Mosfet sits in the GND path, and not in the V+ path! As you can see, the MosFET will connect the two GND lines together, not the two V+ lines!

     

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    Posted · Complete heated bed kit for Ultimaker

    @ Gael, cool, I am interested as I plan on ordering the Jason Wu kit as soon as it's on stock again.

    thanks!

    Martin

     

    Hi Martin,

    As soon as I have some tests done that show the board is working properly, I'll share.

    For Jonny : You are right. My board is based on a Mosfet....

    ++

    Gaël

     

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    Posted · Complete heated bed kit for Ultimaker

    @ jonny, maybe youre remember - I'm basically a mechanical guy having no clue about the electronics... :-)

    Nevertheless, in my former job we used a thyristor bridge to increase/decrease/controll current introduced into a coil (eddy current dynamometer). Therefore I thought it might be the thing for controlling the heated bed instead of the bangbang full-on/off methode...

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    Posted · Complete heated bed kit for Ultimaker

    Hello all,

    I assembled my board.

    Here is a photo.

    HB01 Board Assembled

    Next step : Some tests to check everything is OK.

    I'll keep you posted.

    ++

    Gaël

     

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    Posted · Complete heated bed kit for Ultimaker

    I went the expensive way http://www.phidgets.com/products.php?category=9&product_id=3950_0

    works well in PID mode and optically isolated. doesnt even get warm

     

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    Posted · Complete heated bed kit for Ultimaker

    Ok, looks like an interresting solution, nevertheless, I've not understood it I fear...

    What I lerned now, PID is more or less a very fast bangbang via e.g. a MosFET or a solid state - isnt?

    So no slow current increase/decrease?

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    Posted · Complete heated bed kit for Ultimaker

    PID seems to be more accurate or at least more granular so that the temperature is more closely controlled to the set point and doesn't overshoot after settling in. I believe it also regulates better when the conditions change such as when the fan comes on.

    For the bed, I believe that earlier in the thread there was a discussion that regulating the temperature extremely close to the set point isn't required and that bangbang is more than sufficient.

    I went with the SSR just because I like solid state and dislike clicking....

    With both that SSR and SSRs and MOSFETs in general, you need to be aware of the turn on/off time. That SSR has a 1ms second turn on (or was it off? well whatever it was the opposite was quicker at .5ms) so the PID on/off sequence can't be faster than 100hz. Just looking at the LED, the PID looks like it is switching at 5-20hz or so so no problem there.

    In either case, the current is only on or off. Neither mechanical nor SS regulates the temperature linearly such as with say 65% current. It's always PWM.

     

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    Posted · Complete heated bed kit for Ultimaker

    Thank you very much for final clarification. Now I got it. I will stay with the relays I bought.

    Nevertheless, a linear current regulation would be a nice feature... :-)

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    Posted · Complete heated bed kit for Ultimaker

    The problem with linear regulation is that when not at 100% or 0%, the regulating part must dissipate a lot of power which is usually in the form of heat. For example, I have a bed that is 10 amps @ 24v which is 240W (power = voltage * current or P=VI). If that where linearly regulated at 50%, the bed would get 120W and the regulating part would have to do something with the other 120W.

    Have you ever unscrewed a 120W blub that was on? Very hot...

    So often the regulation is done in full on or full off model switching quickly enough that something (in this case the bed) is averaging the on and off times and smoothing the change. So if a MOSFET turns the bed on for 1/10th of a second and then turns it of for a 1/10th of a second, the on/off time is happening 5 times a second. Because the temperature of the bed can't change immediately when heating or cooling, the average power consumed is the ratio of on time to off time or in this example 50%. From the MOSFETs perspective, it is either on so the voltage across it is 0 or off so the current through it is 0. If you look at the P=VI formula, if V is zero or I is zero, the power consumed or dissipated is 0.

    Well, the caveat is that the MOSFET is perfect and in the real world, nothing is perfect. The MOSFET takes a small amount of time to transition from off to on and on to off. During this time, it is sort of in a linear mode and so dissipating power as heat. However, again like the bed, the MOSFETs temperature can't change instantaneously so it's temperature is based on the time it spends between full on or off to the time it is full on or off. This ratio is very small.

    The SSR I'm using has a turn on of 1ms and a turn off time of .5 ms. So as long as the switching frequency is low so that the SSR spends more time on or off than in the middle, it won't need to deal with much heat.

    Then there is also the fact that real SSRs, unlike the theoretical model of a switch, have a small amount of resistance. P as equals I squared times R. But MOSFETs tend to have a very low value of R keeping the power they need to dissipate low too.

    Welcome to electronics 101 ;-)

     

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    Posted · Complete heated bed kit for Ultimaker

    Thank you very much for this detailed explaination!!

    Now its clear :-)

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    Posted · Complete heated bed kit for Ultimaker

    To be honest I have to say that PID regulation might be a little better than bang bang but it also works quite well. I build head bed with a mosfet in bang bang mode. Temperature stays within 2 degrees. Using PID might get a little less deviation if you find the right PID parameters which is not an easy task. And yes you still have to supply a 4k7 resistor for the temperature control if using the 100K thermistor (have a quite new UM1 board here). The temperature readout is correct. When I measure with other means I get about 5% accurate readings. I posted a schematic on the mosfet part on

    http://www.modelbouwensport.nl/3DPrinter/3DPrinter.html

    The parts that I used were quite random choice. It is what I had laying around (except the power resistors and the power supply). For the mosfet I checked the 'on' resistance is lower than 0.01 Ohm otherwise I would have to cool it, now I don't.

     

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    Posted · Complete heated bed kit for Ultimaker

    I used the PID autotune to set up Jason's heated bed. The temperature locks on the set point quite well.

     

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    Posted · Complete heated bed kit for Ultimaker

    Ok, so just to sumarize:

    - HB from Jason

    - Solid state relais

    - PID mode in firmware with autotune option

    As soon as I'm back home, I will take a close look :-)

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