Energy storage #2

Happiness is a box of batteries. 
In fact two boxes, amounting to 9,6kWh of energy. 

The first order of the day is to check the cells voltage, all where at 3,29 volts and within +- 0,01 volts, remarkable. 

While at it, the cells got christened, numbered so they may be tracked over their life. The numbers will match those on the BMS later on. A red marker was used to enhance the plus sign, just to be sure no confusion will take place. These cells have a capability of supplying many hundred, if not in the thousands of amps instantaneously. Calls for respect and caution in handling. 

Below is a sketch on how the packs are going to be installed below the floorboards as seen in the pictures in the former posting on this topic. What will be installed, with help of glassfiber and generous amounts of thickened epoxy, are two L-profiles (40x40mm) that serve as rails or tracks for the batterypacks. The packs themselves can be seen as an open chassis that essentially keep the two rows of 16 cells under compression. The sides are made up of 12mm AL sheet with four 12x12 mm rods held in place with M8 hex bolts. Two of these packs are required. Partly because handling one pack is a two man job in itself, partly because the packs need to be separated by a beam that supports the floor. The idea with the tracks also has to do with how the bilge is designed. It is not a single open space but actually three compartments. The batteries are not fitted all the way at the bottom, this would be unwise, but around 50cm above leaving around 30cm to the underside of the floor boards.  

The drawings have been handed over to the local watercutting peddler who also has this very smart Weber finishing machine so that the anodizing will come out sweet looking! Unfortunately, there is a three week backorder. 

Next issue on the agenda is the removal of the 12 volt battery system. Most items that run on the 12volt bus are electronics. All the nav stuff, entertainment, LED lights and things that you have hard to find for 24 volts, will be driven from the 12 volt service bus. Both the genset and main engine have their own 12 Volt circuits but these are all independent from the service groups, and will remain so. Thus, the idea, in the spirit of reducing complexity and lead-acid batteries, was to simply down-convert 24 volts to 12. 

The finned cast aluminium box in picture below is a 40 amp 24 to 12 volt converter. Artemis will have four of these parallelled, putting out 160 amps at 12 volts. 

A benefit of using this conversion strategy is that Artemis will now have clean and stable 12 volt power. The four converters offer a really derated installation and sporting redundancy should one fail. The installation is also done so that the 12 and 24 volt earths are kept separated. This builds a system that avoids any potential problems with potential...

To make a neat installation they will be mounted on a plate according to the drawing below. I suspect with the red anodizing, it is going to look fabulous on the bulkhead in the engine room right where the 12 volt charger once was located.

Moving on.
I guess you can figure out whats on the workbench and perhaps you can see that the diode connectorplate is a goner too. The three delta wired generator windings are taken out of the generator through the brown, blue and black wires. 

The finished result is seen below. The black and red wires go directly to the field brushes. So, the regulator is gone too. What is this about then?

The story goes back to 2007 and my buddy in the UK, we both have passion for old Jaguars and he took his refitting project to the level of also reducing fuel consumption. After all they where built when gasoline was cheaper than milk. This involved removing all the parasitic loads on the vehicle seen as a system. Such things as water pump, radiator fan, servo pump for steering all got his attention. The alternator also got a makeover. These units, based on the Lundell design, are loved by the autoindustry because they are cheap. The fundamental problem is inefficiency. As designs go, if you you cut corners it is generally going to get back at you. One such area is the rectifier. The six diodes have around 2 volts drop over them resulting in around 200watts or more of heat at max output. This has to be removed and hence the very primitive attempt at a fan. Now, two things are at work here, first the generator is typically geared up between 2 to 5 times to get it to charge at lower engine RPM´s. The other is the fact that the fan is not a linear load but a non linear one, increasing with engine speed. Of course the coils need to be cooled as well, not just the diodes so I couldn´t pull out the fan. But, you can change the ratio of engine to alternator RPM.

The alternator you see is not the actual one from Artemis but one I hade on the shelf as spare for one of my cars. It is a 140 amp 12 volt unit by Bosch. It serves as my test bench for the redesign of the engine charging system. Why bother? Well, it comes around back at you this issue of "dropping" in LFP replacement for lead-acid. The LFP batteries BMS has the job of protecting the pack and will simply disconnect it from the bus whenever it wants. It is a situation known as load dumping and can ruin your day. 

Load dumping has two effects, one is a reactive pulse that can go as high as above 80 volts the other is that alternator regulators can take around 4-5 seconds to stabilize the voltage. Todays alternators have safeguards against load dumping as it is a well known phenomena. The autoindustry even has testing norms for load dumping, ensuring the suppliers of these items can comply. Nevertheless, in a boat system the electrics is not as well regulated by industry norms so you know less about the level of ruggedness. We can be quite sure the electrical system will be more stressed now than before and I am taking measures to safeguard it.

With no diode pack in the alternator the three phases of AC has to be converted to DC. 

Above is the layout for the prototype of a synchronuos rectifier. With a bigger budget I may have gone forward and produced proper PCB´s with a bit more of a finished look, but this will do for now. If all goes to plan there will be no voltage drop to be concerned about, hence no heat loss. Hence the alternator will charge at lower RPM´s too. Bliss.

Before ending, you are asking about the regulator, no? I took it out too. What the plan for it is will be a subject for future blogs.