Wow, Itâ€™s been a long time since Iâ€™ve had something to update on here. Iâ€™ve done pretty much nothing to the motorcycle in 6 months. Iâ€™ve been busy, Iâ€™ve moved, and most of February and March was spent with friends who moved and had birthdays. The guys helping me with the fabrication have been slammed as well. Now that that is all over, Iâ€™ve hunkered down and decided to get serious!
I didnâ€™t like the fact that my battery test setup didnâ€™t cut out automatically at a set voltage and temperature to protect the battery, so I bought a CBA-II and a temperature sensor to help automate the test. I increased my discharge current ability, but now I can just walk away. So far the tests look good and I love the graphs from the CBA so far. It gives me all the information automatically (Ah, Watts, temperature, voltage). I want to set up â€œBurst Modeâ€ on the CC400/CBA setup so I can alternate between 2 currents with 2 associated durations. For instance, set the CBA to 5A, and set the CC400 to alternate between 15A continuous and 75A for short bursts. This will allow me to check that the cell can discharge at 2C continuous and 8C bursts. From that, I can look at my CBA output and get the voltage at 2C and 8C and calculate IR for each cell. Its gonna take a while, but hopefully I can catalog all of the batteries. I better get to work, thereâ€™s 160 cells to test!
Another big thing to announce that Iâ€™ve found some help on the mechanical side. A guy at work who goes to ITT has 2 classmates that wanted to do an EV project for their senior project. I talked with them a bit and theyâ€™ve decided to use my project as their final project. Theyâ€™re mechanical engineering students and wanted something real world, not just a drawing of something. Iâ€™ll do the electrical, and help with ideas on the mechanical, but for the most part, that is their project. Iâ€™ll be working with Aston and Bryan on getting the bike finished by June 4th, when they have to present. We wonâ€™t have the bike street legal, but itâ€™l be drivable. I can work on the lights/paint after its done.
I also decided to sell my AC15 and Curtis 1238-7501 (AKA AC18) combo. Why? well, I decided to buy an AC20 off a friend of mine. Itâ€™l fit in the same motor mount, but itâ€™l stick out 1.5â€³ more. I sold my AC18 to a fellow board member on ELMoto, so I know itâ€™l have a good home.
So this week, I removed the old motor and shipped it, and readied the chassis for the AC20 motor. Aston and Bryan came over and we made foam mockups of all of the batteries (160 of them) in groups of 55, 55, 25 and 25 to fit in the chassis. We think we can get everything in without cramming everything in. At this point it looks like those groupings will get us the 160 without any issues. Weâ€™ll probably go with steel for a battery box and make it somewhat easy to remove out of the top of the frame. We measured and everything looks like itâ€™l fit. Iâ€™ll have some photos and drawings soon.
So this weekend, Iâ€™ll probably fit the motor in the bike and get some of the Headway batteries tested on my discharger. Iâ€™ll throw them on a single cell charger for a bit to charge them up, let them rest for 24 hours or so, and then do a burst mode discharge to ensure they can do 80A (8c) and estimate their IR. I want to catalogue the cells by barcode so I have a â€œfileâ€ for each cell. This will prove useful in matching as well as future use. I may decide to measure these cells again at a later date, so I have some real world data on % capacity loss after XX cycles.
Anyway, thats it for now. Hopefully we finish by June without any hiccups.
frodus wrote:definately a slow build eh?
It’s been a slow summer. I’ve been too busy this summer to get much done and David moved his shop. I haven’t posted lately, but I have been doing things on and off. I’ve also been riding my SV650 a bit. Really glad I got this to practice on while the bike is being finished. I’d rather learn on this than the eVFR. I wouldn’t want to drop either, but I’d rather drop the SV650 (Has frame sliders) than the eVFR with rare fiberglass fairings.
A few weeks ago I decided I wanted to bin my cells. I borrowed an IR meter from a friend. It’s an AC impedance meter and I realize it won’t accurately give me the DC impedance, but it will allow me to organize the cells into groups of similar IR values. I spent a few nights with my girlfriend testing the cells and writing their IR value on them (she’s awesome!). I got ~150 cells that measured between 5.0-5.9mOhm and like 30 between 6.0-6.9mOhm. One I thought was above 7, but was just the leads not attached correctly. I had some cells that were test-cells and some that were showing low voltage, so I set those aside for testing and further study/destruction.
Now that I had boxes of cells, I noticed some had a tiny number of rust specs on them. None of the rust was very bad, but I wanted to get a pack with as little or no rust on it as possible. Some of the ends where the epoxy is applied seems to have been contaminated, and in some cases appeared between the case and blue plastic covering. After organizing the cells, I have ~165 cells that are near 100% and are between 5.0 and 7.0mOhm. The rest are extras and will be used if I need to replace a cell. I plan on putting a small pack of 16 cells together in a 4s4p 1/2kwh arrangement as a test pack that I can also use with an inverter for portable power (could be used as a small emergency pack to charge the bike).
So after sorting the cells, I got the water-jet cut copper buss-bar de-burred and ready for assembly. I used groups of the same IR value to assembly each parallel group. This will ensure that all of the cells share the current as equally as possible. I think I need some longer Stainless Steel screws. The screws that came with the cells seem to be all over the place with regards to quality, and some of the threads were easily stripped. Despite 2 screw issues, the pack went together well and It measured 36.38V (~3.3V/cell). Here are some pictures of building the 11s5p smaller pack (located above the motor):
I’m going to David’s tomorrow and turning the pack over to him so we can start on the plastic holders/battery box.
I also re-started my Discharger project. I’ve gathered most of the pieces and put together a schematic. I’ve gotten help from a few friends Bob Simpson and John Muchow (designed the CC400 discharger I’ve got). I think we’ve addressed any issues that were lingering and figured an easier way to stop charging when an alarm is triggered. I’ve got a sort of Interlock right now. The Low-voltage alarm, Over-current alarm, Over-temperature alarm and Emergency Stop are all wired to a latching relay. If any of them trigger, the gate of the FET is pulled low, and the discharging stops. The contactors are only there to connect/disconnect the battery, and not to stop the test. Here’s a pic of the parts and of the schematic:
Anyway, that’s it for now. I’ve cut down on my social obligations and renewed my motivation for the discharger and eVFR. I’ll probably start building up the larger front pack this week if I’ve got time.
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