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ANET A8 Heated Bed Upgrades

by Deve Krehbiel

The All-Important MOSFET

The first thing we must address is for safety reasons. Do not ignore this step! It turns out the Chinese manufacturer of the A8 did not build enough into their current/amperage specifications. This results in burned out main boards, discolored wiring, and the possibility of a fire. To eliminate this issue, we need to add a small circuit board that contains a Mosfet. A Mosfet is a special type of transistor that controls the current of high current items and completely resolves this issue. Enter the "Little Driver" by Digital Sqrt. Sure you can get a Chinese Mosfet board, but aren't we fixing this problem because the Chinese manufacturer played fast and loose with the spec in the first place?

Right out of the box it was apparent that someone did their homework. The wires are clearly labeled and they even include very heavy duty terminal ends. I suggest you use the included heat shrink so there is no chance of the wires touching each other. Connections are simple. The A8 Main Board has two terminals, 12 volt positive and 12 volt negative labeled POWER in the corners of the board. Simply use the provided thick wires and wire from the POWER terminals on the Main Board to the POWER+ and POWER- terminals on the Mosfet Board. Then, connect the two thick wires coming off the Heat Bed to BED+ and BED- on the Mosfet Board per the Drawing.

The Heat Beds Control (thin wires) go from the two wires on the A8 Main Boards HEAT BED screw terminals as shown and then connected to the Mosfet board at CN1. Be sure to observe Negative/Positive orientation. This is what gives the new Mosfet board the control. Digital Sqrt even made the board so the mounting holes line up with the Chinese model so if you are replacing an old one, no re-drilling is necessary.

The board works exactly as advertised and I highly recommend this product. I like that it doesn't generate heat, does its job perfectly and I can spend my time concerning myself with other things. We wish Digital Sqrt much success! Not convinced? Go to their website at and check out the documentation page. Very well written and very well engineered. We were so impressed with this little gem, we made a very nice little enclosure for it for mounting to the side of your A8.

Nifty Little Enclosure for the Little Driver

The Anet A8 comes with a heated bed just like the more expensive models and masking tape is already applied to the Aluminum surface. Masking tape is what many people use for the surface. There are many other ideas, but that is how the A8 comes from the factory. If you Google 3D Printing Heatbed Sticking you will get a gazillion ways to make your prints better adher to the surface. You can try all of the tricks.. Hairspray, GlueStick, Acetone/ABS, Glass, PEI, and on and on OR you can take my experience and just cut to the chase. It's completely up to you.

We are going to fore-go all of the above with a few exceptions. We are going to get perfect results each and every time afterwards. We will not be looking back! This will cost you a little bit, but you saved so much on the Printer, there is no excuse to cheap out on certain things, this being one of them. First get yourself a piece of glass. Not just any glass! Regular window glass cut to size is a very bad and dangerous idea. The reason for this is because every now and then, the Heat beds proximity sensor looses its mind and the nozzle trys to destroy your bed. This can happen due to a power glitch and it happens very rarely. Nonetheless, it will break that kind of glass and you will have glass all over the place. Do not cheap out on the glass!

The Glass

What you want to get is a 220mm x 220mm x 3mm piece of Tempered Glass. The ones I get off Ebay are nicely sanded on all sharp surfaces and work perfectly. They call the stuff Boroscillic Glass. To make a long story short, since they use Boron Trioxide they have a very low tendency towards thermal expansion and they are more resistant to Thermal Shock. The cost of one piece of this is about $23. Just do an Ebay search for Boroscillic Glass 220x220. This is only the first step and sets us up with a perfectly flat surface for the next step.


Now we need to add the sticking surface. Enter Polyetherimide (PEI). This is a very special thermoplastic that provides high strength at elevated temperatures and outstanding dimensional stability meaning the Print will stay put without using anything else. You also want a thick piece of PEI and not some .3mm thin stuff that ends up being ruined very quickly through normal use. Get in the very least a .8mm thick piece that is 220mm x 220mm. Do a search on Ebay or Amazon for PEI Ultem 1000 220x220 .8mm. Expect to pay roughly $20 a sheet. But do not stop there! Make sure it comes with a sheet of 3M 468MP Adhesive.

Applying this PEI to the Glass is NOT fun nor easy. I warn you up front it is hard so be really on your game when you attempt this. The problem is the adhesive really works! You have to start it perfectly and then with a credit card as a spreader, slowly, VERY slowly and carefully press it down to the glass first. Then remove the protective film on the PEI sheet and then press the PEI down. Really push with that Spreader and get it down good without air bubbles. Its not easy. Did I say that enough? (Don't answer until after you have tried it). Alternately, you can use book binders to hold the PEI down to the glass. The good news is, PEI lasts a VERY long time. I change my PEI out about once a year. I do that because of gouges I made when lifting the prints, or the head getting a tad low and scraping on the PEI sheet. You can actually sand this PEI smooth again with 600 grit paper if you wish.

The only problem with using book binders is, every once in a while you will decide to print something that is very big and nozzle may hit the binder and snag on it and cause a minor catastrophy. As time goes by, you will get better at getting that Adhesive to lay down correctly. There is good news... The good news is, PEI is TOUGH. I always test the PEI that comes in prior to installing it by swiping one side with Lacquer Thinner, which is what I routinely use for cleaning the surface anyway. If it clouds up and gets nasty and discolored, someone tried to sell you Lexan or some other plastic. Get your money back! (This happened to me!) I put the book binders on so you can see what they look like.

The Hardware

Next we need to scrounge up some non-standard hardware. We are going to do something unusual but very effective. We are going to remove your ability to level your bed! Trust me. Get yourself 4 Hex Female Standoff Insulators (metal) that are 12mm or 1/2" with 3mm threads. Also, while you are at it, get at least 4 22mm or 1 inch Flathead Stainless Steel Screws. I get this stuff at McMaster-Carr. While you are waiting for those to come in...

So you have your PEI adhered to the Glass. Now you have some printing to do to finish this wonderful setup. Lay the glass on the clean aluminum surface minus the masking tape. Use two book binders on all 4 edges to ensure the glass does not move for now. With a little 3D Printing, we are going to fix this problem once and for all. Its always good in this business to have those medium book binders just in case.

The Glass Bed Hold-down System

I made this Glass Bed Holddown System using Fusion 360 which is currently free to hobbyists. Below is the STL files for printing direct as well as the main Fusion 360 files. This way you have everything you need to customize this system. No more book binders after this! This system consists of:

2 Left Corners
2 Right Corners
4 Bolts
4 Nuts
Fusion 360 Zip

Print 4 of the nuts and bolts and 2 of each left and right clamp. STL Files ready for 3D Printing Fusion 360 Files ready for making changes.

Print the above at 100% Infill or completely solid. These parts get a lot of abuse. Best to use ABS but I have always printed them in PLA and have never had a problem. Do not skimp on those standoffs. They must be 12mm or 1/2" and the screws must be flat head so they do not protrude above the Aluminum bed surface. This system is made for the Heat Bed, 3mm glass plus .8mm PEI. If you do not do this exactly right, things will not fit together nicely.

Remove the Heated Bed from the table by removing the 4 screws holding it down. Remove the springs and store them for posterity. Put one standoff inside the hole in the plastic bolt, then run the 22mm by 3mm flat head screw down through the bed and bracket assembly. Be sure the plastic screws are pointing front to back. Do this on all 4 corners.

Next we slide the corners into the plastic bolts observing front to back orientation. Make sure they slide into the bottom bracketry as they are designed to do. Look that over before starting them. You will see the track the corner is supposed to take. Slide them in nicely and install the back ones first, then put the round plastic nut on them and tighten them down. Do not overtighten, snug is fine. Do the same for the front except install the glass/PEI combo, THEN tighten the front corners down. From now on, to remove the glass, just loosen the two front ones.

A side benefit to this system is, it is CHAIN friendly. With or without a chain, these corners really do the job. See the photos if you do not know what a chain is. It is merely a way to protect the wiring system from the abuse of the table going back and forth repeatedly. I highly recommend you install a chain. It takes patience and a little work, but worth it. Soldering is required.

The Heated Bed Chain Modification

Once you have printed the 16 chain pieces that you snap together and have the two ends printed, you will be rotating the bed 90 degrees so the connector is on your left facing the printer as shown. Be very gentle when removing the connector from the heat bed. They made these beds really cheap and the printed runs can lift off and ruin your day. Don't force anything. Heat it sufficiently to remove it properly, then place a pad of solder on the runs where your new wire will go. If you are a fanatic like me, use replacement SILICON wire. It is very flexible and very unlikely to break ever. Do a search for 14 AWG Soft High Strand Flexible Silicone Wire. You can get 20 feet for about $8. It is things like this that make this printer better than the more expensive ones over time.

The Chain Links

This was not worth my time making in Fusion 360 when Thingiverse has decent ones already. Go here and download the files. Print them at 100% Infill. There are certain things we do not cheap out on by making them less solid. You need 16 Chain Links. Print the Heatbed and Frame ends and everything nicely snaps together.

With Support turned on, print the frame mount upright like in the 2nd top left photo at that Thingiverse link. The Heatbed end just goes as flat as possible and the links as well.

The Heat Bed

The Heat Bed that comes with the A8 will do nicely, but when it comes to replacing it, there is a slightly better alternative. I find it works well and spreads the heat out well. The problem is there is a lot of soldering to do since none of the LEDs, Resistors or wires are connected. In fact, it doesn't even come with those parts! When I complained about this, the company sent me the VERY VERY TINY (did I mention small?) resistors and LEDs that I can barely see, let alone solder! Here was my workaround:

The Heat Bed Replacement in question is the MKS MK3-220. You will need the appropriate Thermistor NTC 3950 (100K), a 220 Ohm 1/8 watt Resistor, a 3mm or 5mm LED (5v), 14 gauge Silicon Wire and about 6 feet of 24 gauge wire for the Thermistor connection to the Motherboard (2 wires 3 feet long). Use the LED color of your choice. All it is for is to give you an indication the Heater is heating. It is hard to see since its under the bed, but that is how this system originally worked. If you want a nice heater ON indication, extend those wires and place the LED somewhere else if you wish.

The 220 ohm resistor and LED are attached on the left side as shown. The resistor value is not critical and you can use all the way up to a 1K. It is there as a current limiter for the LED. The Red Hot wire and the Black Ground wire go in position 1 and 2 respectively. What is harder to see is the Thermistor wires. They are just behind the black wire and go side by side in that position. Orientation doesn't matter. I took two shots just to make sure. Be sure to use heat shrink tubing to protect the leads from crossing each other.

The NTC 3950 Thermistor goes in the center of the bed as shown. This is what senses the heat level and transmits that information to the motherboard. With all of the connections made, you can now thread the wires through your new chain and connect to the motherboards connections. Be sure to observe proper electrical connections and use tie wraps or something to organize the wires appropriately.

Bed Leveling Sensors, the Real Story!

Next we will discuss Bed Leveling Sensors and exactly how to connect them. First off, I will assume you followed my advice and have a 3mm glass with .8mm PEI sheet on top. This fact alone eliminates a great deal of the conversation. The sensor that works best for that combination hands down is the Capacitive Sensor. Capacitive Sensors can see through PEI and Glass and reflect off of the Aluminum substrate. This is the most accurate sensor available for glass/PEI. I have never tested just how accurate because it gets the bed into perfect position about 97% of the time. Hard to improve on that. The other 3% is very likely anomalies in motherboard sensing capability. I never start a print without watching the start of it and I have been very pleased with the LJC18A3-B-Z/BX NPN Capacitive Proximity Switch. I use it on all of my A8's. Remember, the Inductive sensors do not see through glass and are wonky on PEI and sensors that actually touch the bed are a bad idea since they are mechanical and can wear out quickly. I am very grateful for how well these work.

First off, this is not a matter of Plug and Play. We have some work to do to properly install this sensor. The sensor uses anywhere from 6 volts to 36 volts for its power source and your A8 uses a 5 volt motherboard (in the area of it we are concerned with). 5 volts isn't enough. Fortunately for us, the A8 uses a 12 volt power supply so we have what we need, almost. We can't just apply the full 12 volts to the motherboards pin for sensing the Z axis. That is too much and we will burn it out. We need to be careful and choose just the right compromise. 6 volts is on the low end, so let's not use that. Any more than 8 volts could toast the motherboard, so let's go with 7 volts. The question is how do we get 7 volts only out of a 12 volt power supply? Enter the Buck Converter! For a grand total of about $5 we can convert 12 volts to 7 volts very precisely and just for our Capacitive Sensor. Pretty cool eh?

We COULD go with a "easier" alternative like a voltage reduction diode or transistor, but this solution is far better in that you will get cleaner, more precise voltage with the benefit of being able to check the output of your 12v power supply. This is the best solution. Once you adjust the stepdown voltage, you will never have to change it.

The Buck Converter I chose has a nice LCD display on it so we can monitor its output (or its input if you wish). I rarely even look at it anymore since they have been working so reliably for a few years of operation. But press the button on the converter and you can see the Input which is nice to monitor to make sure your 12v power supply is doing its thing. Do an Ebay search for Buck Step-down LM2596 Power Converter Module DC 4.0~40 to 1.3-37V LED Voltmeter. Now we will go into how to hook this all up!

The Capacitive Sensor has three wires. They are colored Brown, Black and Blue. Brown is POSITIVE Voltage (7v), Blue is GROUND and Black is the Sense wire. Do not assume Black is ground, it isn't. Read the side of the sensor for clarity. We will connect the Black wire directly to the Z Axis End Stop Switch connection on the motherboard. You can remove the Z End Stop Switch and put it away for an extra. I want to be extra clear about how to hook this up, so forgive me for going into such detail. Take a look at the Z end stop connector on the original A8 motherboard. The TWO-WIRE connector has Ground on the right and Sense on the left. We will use the Ground to ensure that our buck converter is grounded at the same potential as the Sensor and Mobo, and we will connect the Sense wire directly to the Black wire from the Sensor. The power to power the Sensor will come from the Brown (+) Buck Converter Output.

The sensor has a diameter of 18mm so we need to mount this to the Extruder Assembly so it can do its thing. This was also something that I didn't see a need to re-create because Thingiverse has it covered. I decided I agree with the place to mount it. And it IS plenty handy located there. Someday I will solve the problem of what a pain it is to change filament that will probably effect this mount, but meanwhile, this is as good as it gets.

Marlin for 3D Printing

The reason I am putting this here as well as in other places on the website is because the software you use will effect your bed leveling capability. The only real choice for making this Printer do amazing things without a lot of fiddling around is Marlin. It looks daunting when you start off, so here are a couple of tips to help you keep things in order. Marlin is free and we are so appreciative of the Marlin Team. There are several methods of bed leveling that are available with Marlin, but the one that I use is Auto Bed Leveling Linear. I am not an expert at this, but I know it works. I encourage anyone who understands this clearly to contact me so I can write about this better. So be forewarned, this works perfectly for me, so I feel okay with sharing.

I will not go into tremendous detail on how to set this up because there are more expert people out there you can listen to, however here is my configuration.h file for Marlin 1.8.3. If you have a Ramps 1.4 or other than the A8 Stock board, change accordingly. Be sure you save your current configuration.h file before you do this under another filename so if you have adverse problems, you can go back and start over.


I write this stuff down for you and me both. I will forget what I did if I do not write it down. Meanwhile, it would be NICE if you were to also share your setup and let me know how I can improve this document. You can always email me at I run my printers HARD and rarely stop them. They run all day and all night so the improvements have to be value added. I hope you agree with what I have done here but your ideas are very welcome!