The Hot End with Water cooling and the Fan Problem Part 1

As I have decided to use an Titan Aqua Klon instead of a standard E3D V6 Klon, this creates some problems.
Before we start I should mention that all fans on the MK3 are running with 5V, not 24V.

Let us start with the Parts list:

Titan Aqua Klon for 1.75mm 24V with NTC €63,63
120mm Radiator €13,62

50x140mm Water Reservoir €10,19

PWM Water Pump with Tacho signal  €13,62

Besides that I will need some tubing, pneumatic fittings and a 120mm silent fan(noctua).

Tests will show if the radiator and the water reservoir is big enough or if I need to increase them.

The blower fans I bought are useless to me unless I want to turn the monitoring function in the software off. Those are advertised as MK3 parts, but have no tacho signal. You need a 3 pin version for the MK3.
2x Blower Fan 5V €3,89 (Don´t buy these!)

But those are hard to come by. I have not found one in Aliexpress or ebay for cheap, so I am going to order this fan from Prusa. Yes, that will be the only original part on my built.
Strange that I found the Einst Rambo board, the filament sensor and the P.I.N.D.A probe, but cannot find a 5V radial blower 3 pin fan with tacho signal.

Original Prusa Print fan with tacho signal €7,27

But I will keep looking into this, maybe I can find another source. I you know a source leave a comment below.

Before we go into details I would like to explain why a tacho signal is important. I read quite often that a fan failed on a 3D printer.  For example if you have a lot of stringing and some filament string get into the hot end fan and block it. So what can happed is that the whole hot end get to hot then, not just the heat block. And maybe you habe a 3D printed mount for your hot end, which might work fine in normal condition when the heat sink of the hot end is cooled down by the fan.
But if this fan fails, the disaster takes its course and quickly the shit hits the fan. This could be the how some of the fires caused by 3D printers started.
Luckily Prusa monitors the fans with the tacho signal and turn the heat element off when the fan has a problem. If this is required for the print cooling fan as well or just for the hot end cooling fan is arguable. But Prusa monitors both.

So for my water cooling I have the following problem. There is no fan to cool down the hot end, that is done by the water cooling. But what if the water pump fails? What about the missing tach signal form the fan?
Sure, I could simply remove the fan monitoring feature in the firmware, but I consider this as an important security feature.

My Water pump is a 12V PWM controlled, so we have 4 pins (Vcc, Ground, Tacho, PWM). The Hot end cooling fan is a Noctua NF-A4x10 5V with only 3 pins (Vcc, Ground, Tacho).

So first problem is that I have a 5V signal form the Einsy Rambo board that usually powers up the hot end fan. My Water pump is 12V and needs for sure more power then the little fan.
The solution is quite easy, I will use a MosFET that is triggers by the 5V from the board and switches the 12V for the pump. OK, I could also just use a "normal" switch and switch the pump on/pff manually. But hey, where would be all the fun in the built?
What about the PWM? According to the specifications of PC mainboards, the pump should run always a full speed when there is no PWM signal. We will find out if this is true once the pump has arived.

For the next problem we have to understand how the tacho signal works. In fans with tacho signal there is a high sensitivity hall-effect sensor that detects the rotation of the shaft providing with two pulses per rotation, where the north pole generates a positive pulse and the south pole a negative pulse. The output of the hall sensor is usually weak and not a square wave. So a differential amplifier amplifies it, and a Schmitt trigger provides the switching hysteresis to reshape it into a TTL (5V) square wave.
As my water pump was designed to be used in PC´s I assume that the output tacho signal is 5V as well, even the pump runs at 12V. So in theory there is nothing I have to perform on the tacho signal. I will confirm once the pump has arrived.

One thing I am thinking of adding is a small fan controller with a temp sensor. The sensor will be added to the cooler and controls the fan speed of the 120mm water cooler fan based on the water temperature. The fan I am planing to use is the 120mm Noctua NF- F12 as this fan is optimized for radiators.
And of course I need to design and 3D Print a mount for the radiator that fits to the Ikea Lack enclosure.

For the print cooling fan there is not much todo, except to design a mount to attach it to the Titan Aqua klon somehow.