Heat bed connector tips

Introduction

If you own one of the popular Anet A8 3D printers, you have probably read about or experienced the dreaded burnt heat bed connector.  In this post I will talk about how and why this happens, and ways to fix or even prevent this before it becomes a problem.

Burnt heat bed connector

What is this and how does it happen

In the image seen above, the brown area on the side of the connector is heated burnt plastic.  This is caused from the metal connector inside the plastic housing getting hot.  Why does this get hot you ask?  The root cause of this problem is movement of the connector due to the wires not being secured.  As the printer is printing and moving forward and back, the wires are constantly moving from side to side.  This movement puts stress on the connectors inside the plastic housing as they are connected to the pin causing micro gaps between the connectors and the pins.  Because of these gaps the high current traveling through the connector arcs across these gaps.  Every time an arc happens, a small amount of oxidation builds up at the point where the arc happened.  As the connector continues to arc and the oxidation on the connector and pin builds up, this causes resistance.  With resistance and high current comes heat. The more the movement, the more arcing.  The more arcing the more oxidation buildup.  The more oxidation buildup the higher the resistance.  The higher the resistance, the more heat.  All this until the connector can't take it any more.  If it gets bad enough, this can start a fire.

3D printer fire

A fundamental cause of the problem

Heat bed connectorThe Anet A8 printer has a fundamental design flaw in the heat bed connector from the get go that can increase the chances of the connector heating up and burning out.  The connector used on the heat bed is a VHR-6N manufactured by JST.  The easiest is to buy a pre-made harness rather than the connector.  If you just buy the connector, then you have to have the proper crimper to attach the connectors.  There are not a lot of companies that sell a full harness that I have found.  They can be found on ebay though.  Just do a search for "JST VHR-6N harness".  You can usually get them in 1 or 2 foot lengths.  Next, if you look at the data sheet for this connector (http://www.jst-mfg.com/product/pdf/eng/eVH.pdf), it has a rating of 10 amps.  That is 10 amps per pin which is close to what the heat bed draws, actually a little less.  The heat bed has a resistance of around 1 ohm, and according to ohms law, current = voltage / resistance, so at 12 volts, the heat bed should draw approximately 12 amps. The connector has 6 pins, but the manufacturers of the Anet A8 decided to only use 4 of the 6 pins with their wiring.  The outer two pins are the power connections for the bed, and the middle two pins are for the heat bed thermistor.  Because of this, there is a potential 12 am draw on a pin rated for only 10 amps.  The ideal connection would be to use the outer TWO pins on each side, marked + + and - - on the image.  Using two wires for each spreads that 12 amps evenly over the 2 pins.  Therefore you get a current of 6 amps on each pin which is 4 amps less than what they are rated for which is MUCH safer.

How to fix the problem

So you may ask, how do I fix this issue.  Fixing this issue requires addressing the two problems discussed here, motion of the wire causing arcing, and spreading the connection of the wires on the heat bed across both positive and both negative connector pins.
Heat bed strain reliefThe first one is easy to deal with, and that is with the use of strain relief on the wire preventing it from moving the connector.  This can be something as simple as using a binder clip to hold the wire to the bed, to a bit more complex using the Y axis cable chain mod.  Basically anything that can keep the wire from moving the connector around while printing should work.
The next is to modify or replace the heat bed connector.  One mod can be seen in the image above which uses spade connectors that will connect between the two positive and the two negative pins on the connector and using the stock wire.Replacement heat bed connector  Another option is to buy a replacement heat bed connector that has all four wires and connecting both positives and both negatives together at the heat bed connection point, be that at the main board or  mosfet if you have done such a mod.

Conclusion

I hope you found this information informative.  I wrote this in the hopes that it can help new Anet users prevent some of the issues that can arise, as well as helping users that have ran into these problems to figure out the best fix for their situation.  In any case, happy 3D printing and I hope you get years of use out of your Anet printer.

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Temperature-humidity sensor

Temperature & Humidity

Description

This post will outline how I built some temperature-humidity sensors for my home automation setup to use in a couple rooms in my house.  I’ll explain some of the options I tried before coming to my final design.  I will also give you links to where you can purchase the parts and to download the 3D printer files for the enclosure.

Introduction

This originally started from an idea I had for my home automation setup to put a temperature and humidity sensor in my main bathroom.  The main reason for this was to help a small problem with occasional small mold spots on my ceiling.  This was most likely due to humidity in the bathroom.  When someone would take a shower, they would turn on the vent fan before showering, and then off shortly after.  The problem is that when the vent fan is shut off, there still may be excess humidity in the room that could eventually cause the mold.

The idea was that I could have a controller on the vent fan for the bathroom that would turn on when the humidity reached a certain level, and then would also turn off when below another level.  The two levels would factor in some hysteresis to the equation to prevent the fan from continually starting and stopping when the humidity is near a certain level.   By doing this, the humidity in the room would be dropped to a safe level before shutting off, thus preventing the mold problem.

The temperature-humidity sensor design ideas

So I needed to figure out everything I would need for the project.  My primary home automation setup revolves around MySensors nodes.  Those nodes talk to my Vera Plus automation controller.  I decided to make the temperature and humidity sensor a MySensors node.  The exhaust fan control, which I have yet to do, will be controlled by a converted Sonoff module.  For this article i’ll focus on the Temperature and humidity sensor. 

Below is a list of the things I needed to create the sensor.  The basic list was simple

  • A circuit board for the project.  
  • A micro-controller to control the sensor.
  • A temperature and humidity sensor.
  • Some kind of power source.
  • An enclosure to mount the sensor to the wall.

On to building the prototype

Easy/Newbie PCBFor the circuit board, I had a number of the MySensors Easy/Newbie circuit boards, so I thought that would be a good choice.  For that board I needed an Arduino Pro Mini, and an nRf24L01+ radio.  

Now I needed to choose a temperature-humidity sensor.  I had both some DHT11 and some DHT22 sensors.  The DHT22 is a higher resolution sensor, so I originally decided to try that one.  Through some testing with the DHT22 sensor I found that the power consumption was too high.  HDC1080 thumbnailI did some looking and found the HDC1080 sensor.  This sensor connects to the I2C bus and uses very low power.  It’s low power consumption made it ideal for use on a battery operated node.   By removing the regulator and power LED from the Pro Mini I was able to run this sensor for a week with no significant power drain on a set of 2 – AA batteries.

The last piece of the puzzle was an enclosure.  The enclosure had to be vented since I was measuring temperature and humidity.  It also needed to be able to hold a battery  or set of batteries.  I figured that I should find the battery box first, and then design the sensor enclosure around that and the PCB.  I settled on this one.

The enclosure design

I have dealt with temperature sensor enclosures before, so I had some ideas on what the enclosure should look like.  temperature-humidity wall boxI turned to OpenSCAD and came up with a basic design.  The box was vented, it had mounting tabs for the PCB and a place to hold the battery box.  temperature-humidity wall plateI decided to make it easy to remove from the wall if needed and made the wall plate with two tabs that the cover could lock on to. 

Since the creation of the first prototype wall box, I have done a couple revisions to the design.  This is what the final design looks like.temperature-humidity wall box V3
Version 3 of the wall box is highly configurable and can be adapted to other configurations if needed.  All versions of the wall box can be found on my thingiverse page https://www.thingiverse.com/thing:2186286

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Fix an oozing or leaking heat block

 Fixing an oozing or leaking heat block

Oozing heat blockIf you have done 3D printing, you may have experienced the oozing or leaking heat block problem.  This is where you have filament oozing from the heat block on either the top side by the throat tube, the bottom side by the nozzle or both.  This plastic will start to melt and drip down on your prints, and over time will burn on to your heat block leaving a big mess.  In this section I will discuss why this happens and how you can fix it.

 Why does this happen?

Incorrect block assemblyYou are probably wondering how this happened in the first place.  The main reason is that the heat block assembly became loose at some point.  This may be from movement and vibration when printing, or maybe you had to work on the assembly at some point to clean it or something else.  In the illustration on the right you see that there is a gap between the throat tube and nozzle inside the heat block.  This gap is what allows the heated filament to ooze out.  The heated plastic will be forced through the threads of the throat tube and possibly the nozzle and start pooling up at the top and bottom of the block.  If left long enough, the plastic will run down the side of the heat block and drip onto your nice print.

Now you are wondering, how can there be a gap there?  You say to yourself, I tightened the nozzle in when I re-assembled it, there can’t be a gap.  There is something you need to understand about metal.  When it is heated, it expands.  When a metal ring is heated, that expansion will be outwards.  If the throat tube and nozzle are not tightened together enough, the expansion of the block can cause this gap.  

How can I fix this?

So now you are wondering, is this something I can fix, or do I need to buy a new heat block assembly. There is a good chance you can fix this. The main thing is to tighten things when the block is heated and the metal is expanded during reassembly. This will reduce the chance of that gap forming the next time it is heated.

Heat block partsSince your heat block was leaking, you should first disassemble it and clean it.  Clean parts  reduce the chance of leaking in the future.  Remove your heat block assembly from the extruder carriage and set your printer to preheat.  preheating for ABS is probably the best as it will get your heat block to around 240 C (464 F) making things easier to clean.  With pliers holding the heat block, use a wrench or another set of pliers to remove the nozzle.  Once that is removed, your throat tube should come out easily.  Be VERY careful as the parts are extremely hot.  Use a wire brush to clean away any plastic from the throat tube, heat block and nozzle.  You may need to re-heat the parts to clean them good.  Once cleaned, you can begin to put it all back together.

Correct heat block assemblyThese first steps are easier to do when the parts are cool and you can use your hands to fit them together.  The proper way to assemble the heat block is to first thread the nozzle into the heat block, and once it is in all the way, back it off 2 turns.  Next, thread the throat tube in until you feel it hit the end of the nozzle threads.  DO NOT use pliers on the throat tube.  With the throat tube in all the way, grab the heat block with a pair of pliers and use a wrench to tighten the nozzle in place.  Once that is all together, heat up the heat block to temperature while holding it with the pliers.  This can be done with the heater on the printer, or the burner on your stove.  Don’t use a torch or it may get too hot.  Once heated, tighten the nozzle a bit more.  This will ensure that the gap between the throat tube and the nozzle will be closed not letting the filament ooze out.  In the illustration above, you will notice that after assembly, the nozzle is still not tight against the heat block.  This will allow you to tighten it again if you need to.  One more thing to note.  Do not put a nut on the throat tube and tighten it to the heat block.  This can cause more issues.  

Now you can re-assemble the extruder assembly.  Correct nut assemblyUse the nut on the throat tube to tighten the extruder assembly to the carriage to prevent the heat block assembly from spinning when printing.  Incorrect nut assemblyBe careful not to over-tighten the nut as you can easily break the throat tube.

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My personal weather station

Description

For a while now I have wanted to add a personal weather station to my home automation system. The idea was to use the data collected for things like controlling when my lawn sprinklers run.  I also plan on using temperature and humididty data to determine things like heating and cooling (HVAC) operations. In this post I will log the ongoing details of my modular personal weather station project. With the help of my new Anet A8 3D printer that I purchased earlier this year, I was able to use it to build all of the parts needed for the project. The project was started a while ago, but I didn’t have a place at the time to post my progress, so here it is.

Details

So far I am working on 4 parts to the weather station. Wind speed anemometer, wind direction vane, rainfall gauge and a temperature and humidity sensor. All sensors need to communicate to my home automation system over my MySensors network. I am hoping that I can control all data collection with a single arduino pro mini built on a MySensors Easy/Newbie PCB created by Sundberg84 from the MySensors forum. In this post I will outline each modular section of the project. All of the 3D printed parts for this have been designed in OpenSCAD and will eventually be posted on my thingiverse page.  This post is a work in progress.  Check back to see more information.

 The anemometer and wind direction vane

 The first part of the project that I started with was a combination of two sensors.  An anemometer for measuring wind speed and a wind vane for determining wind direction.weather station wind sensor This is the first prototype design of the 3D printed parts.  Some minor changes have been made since this design.  The first was to invert the center mount sections so the screws screwed in from the bottom.  This put the wind direction vane on the  piece with the square mounting peg and the anemometer was moved to the other piece.  The reason for this was to keep rain from collecting in the small screw recesses and potentially getting inside the case.  The next change which I am in the process of printing as I write this, is a new piece with a round mounting peg instead of a square one.  This was done because of a later decision to mount everything using schedule 40 PVC electrical conduit.weather station wind speed sensor rotor

The anemometer is mounted with a ball bearing that is press fit into the cap.  The shaft, a 1/4 x 20 bolt with a small rotor that has a magnet mounted in one end and that will pass by a magnetic reed switch.  The arduino will use the counted pulses from the reed switch to determine the wind speed. The anemometer cup design was borrowed from a project on thingiverse, but I can’t seem to find the original that I used.  The cups, arms and main shaft attachment are all separate printed parts that I have glued together.  This made for an easier build on my 3D printer.

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My start into open source hardware

So I decided to get my feet wet on creating my first commercially manufactured circuit boards to release as open source hardware.  For one of my automation projects Prototype switch boardI had built some custom in-wall automation scene controllers based on MySensors.  The controller consisted of 3 boards; the power supply board, the computer board (Arduino Pro Mini) and the switch board (first prototype seen on the left).   30x70 proto boardAll three of the circuit boards were built on standard 30mm x 70mm prototyping circuit boards like these.   My first fully assembled version of the controller can be seen below.  Though the design seemed to work good, they were a bit of a pain to put together.  Prototype scene controllerBuilding one controller on prototyping boards and wiring it all up took 4 hours or more.  After building 3 of them and seeing how they worked, I wanted more, but I didn’t want to spend all the time making them.  So, it was time to get my feet wet on PCB manufacturing.

The design

So I figured that if I was going to be making a number of these, I wanted the design to be flexible.  I wanted to be able to do more with it than just a scene controller.  Having the 3 separate boards made it modular.  I figured I would design it so that I could build more than just switch boards for the face of the CPU board.

The main board

Scene controller main boardFor the design of the main board I broke out all digital and analog IO lines from the pro mini except for A6 and A7.  I also have ground, raw 5 volt power plus the 3.3 volt regulated power from the pro mini available on 2 single inline header connectors.  A4 and A5 on J3 also provide I2C capabilities to the front board.  With all of these, the only limit to what can go on the front board is what you can fit in the small space..

The keypad board

Keypad board PCB design The design of the keypad board may look a bit crowded, but it was designed that way to make it flexible.  Many different keypad designs can be made from this one board.   I had gotten the idea for this type of design from a video I had seen by a guy in Australia named Jonathan Oxer.  He had designed light switches for his house and designed a single universal circuit board that allowed him to use that one board for building different switch configurations.  You can find the video here http://www.superhouse.tv/arduino-light-switches/ .  His other videos on home automation are well worth watching.  Check out his website here.   The keypads can be made with or without indicator LEDs.
4 button keypad2 button keypadStandard paddle keypadThe buttons can have any text embossed on them, or they can just be left blank. Here are just 3 examples of the many different wall switch designs that can be made using this board.  No need to have separate boards printed when you want to put together a new switch.  Just grab a board, print the switch layout on your favorite 3D printer and screw it together.  Done!

The power supply

Power supply boardThere is nothing fancy with the power supply board.  It is based on the standard HLK-PM01 power supply module that will take a wide input voltage (90 ~ 264V AC) and convert it down to the 5 volts needed to power the controller.  The output is filtered with a 0.1uf ceramic capacitor as well as a 10uf electrolytic to help stabilize the voltage supplied to the controller.  On the AC input side, a standard 0.75A glass fuse as well as a 73°C (163°F) thermal fuse is used for maximum protection since this will be used in wall.  You can never be too careful.

Conclusion

In the future, I will design  other sensor boards to be used with this controller.  This is an open source design, so feel free to take the gerbers and design your own sensors for it.  I hope you like the design.  Let me know your thoughts.

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