Wanhao i3, Part 4

The printer has to print at about half speed now (~20 mm/s). While waiting on parts, I did some more research into ways to improve it.

First, I figured out the cause of the weird SD card power thing. Turns out that the SD card slot is powered from the FTDI chip, which can't supply the required current. This causes the SD card to not mount sometimes. When it does mount, scrolling through the print file menu cases the screen to dim and the extruder fan to spin. Jetguy on youtube shows a hack you can do to power it from the input power, but I haven't bothered yet. Like many chinese made things, it works...sort of.

There is a flaw in an older version of these boards where the temperature sensor isn't grounded correctly. This causes +/-10 C temperature fluctuations. Wanhao has since fixed this problem, and mine doesn't do this.

On the topic of electronics: These melzi boards have another major flaw. The screw terminals used for the heated bed are not meant to pass high continuous current. This has caused many connectors to melt and boards to fry. This is why one of the most recommended modifications is the "MOSFET" mod. The "MOSFET" mod is common among cheap printers. It is essentially a separate circuit board with a power MOSFET. The board takes the original pins from the Melzi as control input, power and gnd directly from the PSU, and outputs pwr and gnd to the heated bed. This eliminates the bad connectors and reduces current flow through the Melzi (or other) board. 

That being said, I think that a minority of the boards have this problem, otherwise many more would have melted by now and Wanhao would have done something about it. Remember, Wanhao i3's are rebranded as the Maker Select v2 and Cocoon something-or-other, so they've sold thousands of them. Most connector overheating (in general) is caused by arcing from loose connections, so perhaps people didn't check this. I bought my printer used with ~1200 hours on it. I opened up the electronics fully expecting the connector to be fried. Nope, everything was in perfect condition...no sign of discoloration. So I left it alone for now. I purchased a pair of power connectors I may replace it with. I may also do the MOSFET modification. Still deciding. 

The problems I've been having with the hot end had me thinking about how I would design it better. The first thing I would do is place the thermistor as close to the nozzle as possible. The thermistor should ideally be encased in a thermally conductive material in a threaded stud or cartridge, not just poked into a hole like in the MK10. The heater block should clamp around the heater core for better heat transfer. The nozzle should have a large contact area with the heater block (large/long threads). Replace the PTFE tube with a stainless steel tube with a heat sink attached to it. Put all that together and I pretty much just described the E3D v6 hot end, haha. It has a far superior design to the MK10. Unfortunately, installing one has three downsides: 1. You need to print a new mount for it (some on thingiverse), 2. you lose quite a lot of Z height because it is relatively long, 3. you have to reflash the repetier firmware on the Melzi board with the E3D v6's thermistor table (Instructable). A popular upgrade for these printers is the "micro swiss all metal hot end". This replaces the tube that holds the PTFE tube with a SS one that doesn't need a PTFE tube. It also has a new aluminum heat dissipation block that clamps on to it instead of one that uses a grub screw. But ultimately, this doesn't fix fundamental problem with the MK10 heat block: 1. the thermistor is poked into a hole surrounded by air, held in by a washer/screw, 2. It doesn't increase the heat transfer area between block and nozzle. It really only solves the PTFE tube problem. A genuine e3d v6 hot end costs ~$70, while a micro swiss all metal upgrade costs ~$50. E3d J6 clones cost ~$20. If I were to spend the money on one of these, it probably makes more sense to go for the e3d v6, genuine or clone.

The titan aero solves the space problem, and upgrades the extruder, but the other two problems with the E3D v6 remain. ~$150. That's about 50% of the original cost of a new one in the US, and a little more than 50% of what I paid for mine used in the UK. 

Another popular thing to replace is the whole electronics board. RAMPS has a superior design to the Melzi, and is also fairly inexpensive. You can get a full arduino, RAMPS, and stepper drivers for ~$70. Even cheaper if you buy the cheapest chinese parts. 

At this point, a philosophical and practical question arises. At what point does it stop being a Wanhao i3 v2.1? At what point is it not worth upgrading/fixing? I think the line is crossed when changing any major mechanical or electrical components, such as hot end, extruder, control board, Z-axis carriages, etc. I think I'd be better of in terms of time and money buying a better printer, such as a genuine Prusa MK2S kit (~$800). Considering I've already spent over $400 on this printer (excluding filament, spare parts, etc), adding ~$120 for a genuine Mini-RAMBo, ~$70 for an e3d v6, ~$70 for a better extruder, ~$50 + many hours for fixing the Z axis carriage design...the MK2S looks like a pretty good deal. I really think there is a strict quality vs. cost (cost = $+time) line that can't be beat for 3D printers. You buy a cheap printer, the quality will be bad unless you invest time and money into it. You buy an expensive 3D printer, the quality will be great with little additional $ and time. Of course, you can have a printer that is expensive and gives bad quality, but you can't have a cheap (including time!) printer that produces excellent quality prints. From what I've experienced so far, this printer is above that line, i.e. it has not been a good deal.

Updated to-do list:

1. Fix hot end with new parts
2. Fix SD card power?
3. Add MOSFET board for heated bed
4. Print more stuff
5. Shorter inner spring for extruder
6. Install new heater core, add connector
7. PETG Diii (or custom) cooler
8. Enclosure if I ever decide to print ABS

List of mods I won't be doing to this printer:

1. Upgraded hot end
2. Upgraded extruder
3. Replace Melzi
4. Z axis carriage overhaul (to fix rattling...see earlier post).

I want to get this printer consistently printing at the quality I was seeing before the nozzle clog. I don't think I'll be able to improve the quality significantly beyond that without some major investments in it that would be better spent on a better printer.