The same wall as before, but now from the other side! The same wall, but now finished to be used as a form to make the real aluminium version of it! Here you see for the first time the aluminium version of the wall, still with leftovers from having glued the fale wooden wall onto the aluminium plate. The same aluminium version of the wall from the other side. As you can see, at least for an untrained miller milling the aluminium shape of the wall having an wooden form glued onto the surface of the aluminium plate is far from perfect as can be seen by the gaps seen on the picture. Two main reasons exist for this! One is definitely the inability to mill the aluminium plate exactly enough to be shaped as the wooden form. The second even more important factor is the fact that the profile of a 10 mm thick aluminium wall does not have the same shape on both sides of the plate. The hull changes its shape enough over those 10 mm, so that the gaps are a result of this. It also proofs what I had expected, that I need to take extreme effort to shape the fake wooden versions of the walls at the very precise positions were they will be placed at the end! So manual work is required to adapt the shape of the aluminium wall to the hull shape in such a way that its upper border still is at its perfect place, so that the cover placed on top will be 100% parallel to the floating level of the sailboat! The same way, starting from the wooden fake wall i made the second wall of the battery cell compartment. To ensure that the shape of the second wall was taken from the correct position were that second wall would be placed within the hull I screwed the fake wooden battery cells between the aluminium wall finished first and the wooden second wall that was going to be the form to make its aluminium version shown here. Very critical, besides defining its shape by ensuring the 100% correct final position of the second wall, I also had to make 100% sure that the shape of the form in its final position would result in the battery cells being fixed by screwing its pole between both walls were 100% horizontal, means parallel to the floating level plane, that its upper border resulted in a perfect parallel placement of the cover when placed on top of the battery cell compartment. It took a lot of effort to accomplish this, make the aluminium version of it and placing the holes drilled for the screws for the poles of the battery cells at its right positions. As you can well imagine changing from the fake wooden versions of the walls to their final aluminium counterparts made it impossible to insert the real battery cells in the battery compartment. Short circuits with all their possible consequences would be the result! So what I did the was to make the aluminium solid tubes for which you had seen the 3 mm diameter holes drilled into the wooden walls. This picture shows on the second wall not just the holes drilled with the diameter of the screws for connecting to the poles of the battery cells, but also how the 3 mm diameter holes drilled for the M3 Allen cylinder head screws used to fix the aluminium bars over which the steel sheet would be bended that would form the rest for the battery cells in the compartment, at least for those hull side. as you can also see I have drilled holes with a bigger diameter so deep into the wall, that the cylinder heads fit into those cavities and lay below the surface level! here you can see the second woll with the aluminium bars screwed into their position and the cylinder heads of the screws below the surface of the wall, so that the wall can rest fully on the desktop surface! This picture of this contribution to my thread is from an earlier phase of the construction and shows both aluminium version walls, still without any holes drilled into them, but the first wall with a second wall directly fitted behind the first wall. Well, this requires some explanations and it will change some of the information supplied earlier to you! One of the objectives that I follow during my construction of the sailboat is to have most elements not glued into the hull or deck, but screwed into their positions. Well, the walls of the compartment consist of actually two plates! This picture shows the inner of the two plates that make up a wall of a battery compartment. You can see an aluminium structure that is perfectly shaped for the hull within the compartment next to the outer wall. Inside what has been eliminated is that part of the wall where the battery cells are and as you can see from the holes drilled for the M3 cylinder head Allen screws, the sharp corners not yet adapted to the shape of the aluminium bars screwed onto this inner wall. The steel sheet that will make the bed on which the "outer placed" battery cells rest, will rest and be screwed and glued onto this wall that will have the exact shape of the steel sheet. The aluminium bars will be screwed onto another inner wall of the same kind within the compartment and next to that second outer wall. What I still have to find out is how the length of the battery cells change when they get hot. As you well know, any material that increases its temperature changes its physical dimensions and so the compartment has to be long enough to have the battery cells fit within in case the batteries get hot, but do not yet burn! If they burn everything is over! Of course I have also already spend some thinking as to how I will make it possible for gas that might emanate from the battery cells to exit the compartment to prevent pressure from building up and eventually leading to an explosion! I have postponed drilling the holes to screw both plates of a wall together, because for this I need to know where in the outer wall of a battery compartment I may have room to place those holes to be drilled in! Guess what, the inner structure of the outer walls of the battery cell compartment have a lot of stuff build in that I will present in my next contribution!
The picture of one of the "inner walls" of a battery cell compartment that will be glued to the hull of the model. So between the two "inner walls " of each of the two batter y cell compartments, the hull itself and the steel sheet is the room where using wax to get the exact copy of this space a number of molds made of lead will fill this pace and ensure that the center of gravity is as low as possible. The lead that fills that space will not reach to the upper level were the cover of the compartments sits, as parts of the space will be used to place electronics in it. Specially the DC/DC-converters that generate i.e. the 24 VDC supply needed for the release of the mechanical brakes and the DC/DC-converters that supply the 15 VDC I will use as the supply for the I2C-buses. This about 3x the tensión that bus normally has will ensure the robustness and the integrity of the data transmitted over the I2C buses. I use level converting I2C-buffers that allow to change the level from 5 VDC or 3.3 VDC used in the µcontroller or the temperature and humidity sensors located next to the LED lights I will be using on board. But that a completely different story I will continue and write about at the proper time! This DC/DC-converters are switching converters but still so generate heat that will be diffused into the aluminium and lead in the hull of my model! But there is more in this story! This graphic shows the basic circuitry required to connect the 6 battery cells in a compartment. The thick lines, black, green and red show how the 6 battery cells in a single compartment are connected in series, black being the negative pole of the resulting battery pack, red the positive pole. The thick geometry of those lines are to demonstrate that the huge amount of current will be flowing along those connections. if a short circuit happens, those thick lines will show the up to 240 A of current that might flow through those electrical links! The fine blue lines represent those lines required to measure the actual voltage supplied by the individual battery cells. As you can see, 7 of those lines are required and have to be fed to the balancer of a charging device, but also to the BMS, Battery Monitoring System, to monitor the voltage of the individual cells during times the battery are stored, inactive, in the model and during time were power consumption takes place and those battery ells discharge! All this electrical connections have to be integrated into the wall of the battery compartment so that they do not interfere with the cases of the drums i.e.! The two schematics show how the electrical connections are, the upper of the two schematics show the wall in the center, the lower schematic show the lines within the "outer" wall, means the front wall of the front compartment, the "rear" wall of the rear compartment. The reason for this is that I want to have the two main poles of the two battery cell compartment close to each other. Here I will place fuses that interrupt the power lines in case of a short circuit. But also here will be the large connectors for the power lines, the feeding into the DC/DC-converters placed at the sides of battery cell compartments. But also the full tension supplied by connecting both battery cell compartments in series will be fed into the two stepper motor control electronics! Additionally I am still thinking about how to realize the circuitry that intelligently routes the connections dependent on the operating status of the model! What do I mean with this? Well, first operating mode is one were no energy is consumed within the model, ON/OFF-switch OFF, no charging takes place! In this case the main power lines will be disconnected from the stepper motor electronics, from the DC/DC-Converters, but the BMS needs to be supplied with energy to enable it to be monitoring the battery cells and to react intelligently and adequate in case it detects i.e. the heating of a battery cell within one of the 2 battery cell compartments! An acoustic signal has to be generated by using the acoustic signal warning of my smoke detector system in my workshop that is part of my residential smoke and fire warning system! A lot of thinking will have to be invested in this at the proper time! The next operating mode is one were the ON/OFF-switch is still OFF, but the battery cells are being loaded! Here the main power lines have to be routed to the connectors for the charger, the BMS has to be disconnected and the sensing lines, the fine blue lines shown above have to be disconnected from the BMS and made available to the connector for the balancer in the charger. The next operating mode is when the ON/OFF-switch is switched to ON! I stop here describing the additional operating modes and what they mean. This will be dealt with at the proper time. Relevant is this description due to its effects on what needs to be planned, to be added and to be taken into account when deciding how to make those lines integrated into the walls of the battery cell compartments. I plan to proceed with this when I have to place the proper connecting points above the cover plates of the two compartments! I decided to present this picture here now, as it makes it easier, so I hope to visualize what I am doing. I will present some pictures how the cavities were made for the plastic parts in the aluminium wall. As you can well imagine the screws are not holding the real battery cells in position, but the wooden fake ones! The danger of short circuiting them is to big and the battery cells in sum were quite expensive! But what you can see in this picture are the screws I will be using! This are stainless steel countersunk metric screws. They still need the diameter of the heads to be reduced a bit with my lathe, but they are already at or below the surface level of the aluminium wall! Now, I decided to use 3 mm thick copper bands to connect the poles of the batteries, or so to say to implement the "thick" connection lines in the circuitry shown above. This picture shows in detail the stainless steel screw and the hole milled into the 3 mm thick copper band for one of the poles. The screw will be worked on in the lathe to fit into the diameter on the top of the hole to ensure it has the biggest possible electrical contact surface between the screw and the copper band. This has the effect, that the electrical resistance between the screw and the copper band is kept as low as possible and so the heat resulting from the Ohms law at his contact surface is as little as possible. Also you can see by the size of the screw and the copper band that both will have little problems to withstand even the short circuit case with a current of up to 240 A flowing through! of course I need to keep in mind the whole electrical chain, as the weakest spot will determine were maximum heat will be generated. Here you can see the three copper connectors, now applied using a wooden fake wall just to get a picture of it! But what can also be seen is, that the screw heads are below the surface of the copper bands! The reason for this is related to something still open to be done for the first time. All electrical conductive materials used in the battery cell compartments will get a "Powder Coating Surface". You know the surface resulting from powder coating. Those are this plastic coatings you find on many cases. Using a gun powder is blown and loaded electrically. The object to which powder coating is applied is grounded and so the powder flies and gets deposited on those electrically grounded objects. Those objects are then placed in an owen, I have an adequate owen in my workshop and after heating it the deposited powder melts building an electrically isolating coating! So the aluminium wall, prior to integrating all the stuff I integrate into the walls will get such a powder coating as an additional protection for short circuits prevention! Same happens with these copper bands, excluding the holes were the screws need to have electrical connection.
In this picture you can see, of course just using the fake battery cells, the cavities milled into the wall so that the copper bands connect the poles and are fully placed within the wall geometry! As you can well imagine and as you know that there have also to be the plastic parts inserted to prevent the copper bands to have an electric contact with the aluminium of the wall. Here my milling machines started to show that it had worn out not working as precise as I wished it did wish and needed. But you can also imagine, even if the metal parts all have a powder coating and that everything would be submerged in an epoxide bath, I had to find a textile highly resistive to high temperatures. This picture shows the sample of such an textile I got. So between the copper bad connecting the poles of the battery cells and the aluminium of the walls I would place a piece of this textile to ensure that even when the temperature would rise to a level that attacks the epoxide, this textile would keep the copper band and the aluminium wall electrically isolated. I could not imagine to do more within the walls of the battery cell compartment to prevent by any means that the copper band and the aluminium wall could ever get electrically connected causing a catastrophic damage! The fine cables used to enable monitoring of the tension of each battery cell are much thinner and in the event of a short circuit that may have up to 240 A of current flowing through them would simply melt them away. Using teflon tubes and having those thin cables covered by heat resistant silicon isolation should prevent that short circuiting those thin cables can cause a mayor short circuit. I plan to do an experiment by melting such a fine cable applying the 160 A continuous current my battery cells can supply and ensure that the cables will melt interrupting the electrical connection! i will also further analyze the possibility to a section outside the wall were a fuse can protect the cables within the wall and the electronics of the balancer! Due to the fact that the text length in my last contribution happen to be too long I will take the opportunity to show some more pictures! This picture shows the copper bands placed within the aluminium wall and how there is space between the copper band and the aluminium wall. The plastic part isolating the screw and the poles of the battery cells from getting in contact with the aluminium in the walls consist of 2 parts. On is the part with the noose that surrounds the screw on its way through the wall, the second part is just a 5 mm thick plastic circular disc. As soon as my milling machine is working well again I will mill into this 5 mm thick plastic disc the cavity to receive the 3 mm thick copper band. I assume a cavity depth of 3.3 mm will be enough to deal with the powder coating thickness, the heat resistant textile and to have the copper band be at or below the surface of the powder coated aluminium wall. What I have not yet even started to do is to mill the "channels for the cables to the balancing electronics. Besides that I only want to start doing so when the final placement of the copperbands is done, I need to decide about how to make the connection to a balancer and BMS connectors. For example those fine copper cables need to be stable enough to allow to mount and unmount the cover of the Compartment as frequently as possible. i am thinking about having a brass tube around them and have the 7 cables leave physically close to each other so that a stronger connector can ensure the mechanical stability. I am still investigating how to do this, but with low priority! Here a picture that shows a first try in milling out the cavity of the plastic part to place the copper band in it! The second technical drawing shows the dimensions i plan to apply to mill the cavities for the copper bands! Here a picture that shows the "inner wall" that will be glued to the hull with the aluminium bars screwed into position and what will be the inner wall of the second wall in this battery cell compartment, but not yet milled as the other inner wall. As I wrote earlier, I still need to investigate what extra length I need to make available for the battery cell when it gets heated to prevent the compartment to be destroyed by the stretching battery cells! Only then I will now in to the last detail exactly the position to which this inner wall has to fit and then to be glued to the hull, as soon as I know whre the screws to mount the outer wall to the inner wall can be placed! Here you can see both of the rear wall, the inner and the outer wall of the front battery cell compartment with the aluminium bars, still a bit long so that I can decide about their final length! I also think that with the fake battery cells screwed into their positions it gets evident how the steel sheet, also powder coated, will bend around the outer battery cells and the aluminium bars! You also see, as I have to confess, the shape of the outer and inner wall are quite different and that some extra work will be required. But the inner wall will be glued to the hull, so that gaps will be filled by the glue. Besides, the inner wall will be hidden from sight by the outer wall when this outer wall is screws to the inner wall! This picture allows to see how the inner wall got its inner parts removed by milling! I use the holes for the screws with the noose from the plastic part to set the (0,0) coordinate of the digital indicator of the coordinate table and can so combining the function of the rotary table and the milling machine digital indicator to track the milling as desired!