When I started the project there were no chargers on the market that I was completely happy with. There was the Manzanita Micro that was left over from the Lead Acid days, it will charge Lithium but isn’t optimized for it and it has a bad habit of changing the CV voltage when you adjust the current. There are a bunch of Elcon type chargers and knock offs, Elcon being a knock off itself. They work, but if you change your pack you ship it back to be reprogrammed. That simply doesn’t work for me. There are the high end chargers like Brusa, but that’s not in the budget. There’s also the fact that virtually the only time LiFePO4 cells can be dangerous is if overcharged, this is where the dc/dc charging concept came from. This system is safe and reliable but not optimized for efficiency or speed of charge. What the market needed was a charger with user programmable outputs for voltage and current that will run from 120V or 240V without having to change any settings, one that will do accurate CC and CV stages and terminate at the right point. It doesn’t seem like too much to ask now does it? Well until recently it simply didn’t exist.
Valery at EMW has changed that, with the help of others he has developed an open source 10+kW charger platform that is available prebuilt, as a kit, or simply a BOM/Schematic and you are on your own. I went with the kit version because it needs to fit in a very specific space within the battery box so I need to build the charger to this size requirement. The version of the charger I chose has a PFC front end which means a couple of things, it doesn’t really care what the input voltage is, so it will run off of 120v or 240v just fine, as well as maximizing the power that can be drawn from a breaker (Power Factor Correction). The PFC front end takes a small hit on efficiency but is required for the battery voltage that I need to charge so it’s not really a choice anyway. By the time I was ready for the charger, and the charger was ready for me. Meaning it had gone through a few revisions and has gotten to what I believe is a fairly mature product. The electrical and mechanical design is quite nice making good use of 3D space, meaning for a 10-15kW charger it is very compact. There are two cooling options, air and water, I went with air because I hadn’t planned on plumbing the battery box for coolant lines, however if I had started the design with this charger in mind I would have gone with water cooling.
I’m a visual person and I can put just about anything together if it has pictures, however Valery’s instructions are simply text so it took me a bit before I fully understood where things are meant to go and how they connect with each other. I started with the basics soldering the PCB’s.
Then moved on to the high power components and their layout. I drilled marker holes in the heat sink using the CNC router to give faster and more accurate results.
I revised a few of the assembly instructions, including the output diode wiring. I drilled some copper blocks with the CNC router again, to directly solder 8awg wire to the blocks which bolt to the diode.
Inductor mounting is also revised, instead of the leads pointing up for use with flying wires to connect to the PCB, one connection from each inductor can be soldered directly to the PCB.
Mechanical mounting of the inductors is also revised and I created a c-channel beam to hold the inductors in place. This beam also becomes a mounting point for the enclosure walls.
The layout is quite nice allowing for a small overall footprint.
The charger will face upwards in the battery box of the 944 behind the transmission between the two battery banks. In normal use I can simply plug in the charger and it will just work, if I need to change settings the switches and display are front and center for easy adjustment. I designed the front panel using V-Carve pro, it’s nothing fancy but simple and functional.
Progress of the panel after drilling marker holes.
After milling and engraving.
And finally after drilling, paint fill and switch mounting. The display is simply sitting behind the panel just to see if all the characters are visible through the display hole.
A test fit on the heat sink to ensure everything is going according to plan.
The bottom panel / fan bracket was designed the same way.
With fewer holes and no engraving it was much simpler to produce.
Some 120mm x 38mm 48v fans were mounted for mock up only. I will be using 120mm x 25mm 12v fans for the actual build.
Test fitting the panel to the rest of the enclosure along with the required power brick and finger guards.
The enclosure shape and size are starting to show, unlike the assembly instructions where the charger/heat sink is mounted inside a steel box, my version uses the heat sink as the main frame OF the box.
I’m in the process of designing the side panels which will be the legs and mounting points for the charger. The left side is quite simple but the right side is also the mounting point for the main control board of the charger. The input/output connections will be made on a terminal strip on the front of the charger (the top as the charger is viewed in the above pictures). The external wiring for BMS input and J1772 compatibility will also be mounted on that panel.
EMW is creating some great products to fill some important holes in the market. I will also be using the Deluxe version of the EV display tied to my Samsung tablet that I’ve mentioned previously. EMW is also developing a controller, and although I love my Soliton1 there is potential for a higher powered street controller closer to the power level of the Zilla 2K HV/EHV but with configuration and controls possibly closer to that of the Solitons. The Evnetics Shiva is amazing but 3000A and 425V is well above my requirements and budget for the Porsche, I would love something in the 1500-2000A range.