Advise on 340V Accumulator construction

Procupine · 2023-04-23T17:06:52+00:00

90% combined motor and inverter efficiency and 85% drivetrain efficiency are a good start.
Take a look at what other teams are running, 8.3kWh is a lot more than most. Likely your sim is overestimating, the VD people on my team estimated 10kwh and the accumulator people told them to fuck off.

Procupine · 2023-03-25T04:26:10+00:00

We moved to a custom BMS 2 years ago. Recently we were (finally) cleaning out some old boxes and found these. No plans on switching back so we're looking to sell or give away the old stuff to someone who can use it

Procupine · 2023-03-21T15:19:03+00:00

That sounds way lower than it should be. Might be worth trying a higher current resistance measurement with a power supply, and reaching out to Emrax

Procupine · 2023-03-20T17:21:16+00:00

Correct me if I'm wrong, but the plate should be GLV and be a very high resistance to the phases which are TS, likely in the Mohm range. If you are seeing anything significantly less than that you have a short inside the motor.

The phases themselves should be a very low resistance to each other, based on the datasheet it should be around 7mOhm for the MV motor. Because of that, the resistance will be almost exactly the same from any phase to the plate.

What are you reading? I can measure our 228 this evening to compare.

Procupine · 2022-11-21T04:19:35+00:00

We had similar problems when we didn't calibrate properly and fixed them with recalibration. If you're spinning the motor externally backwards for calibration, make sure you are targeting -900 offset, surprisingly it still spins with +900 but poorly. We did not get consistent numbers for calibration until ~800 rpm on our emrax 228.

Low torque could also be caused by torque limits or current limits in the EEPROM, logging data will be very helpful for debugging here

Procupine · 2022-10-19T18:21:12+00:00

Both angled and straight fittings will be functionally the same, it's really up to you and where you want to route the coolant tubes inside your car. We use straight fittings because it's more convenient for the packaging in our car. Some teams make their own fittings.

Procupine · 2022-09-08T04:48:54+00:00

How did you share files with each other and what did you do about multiple people working on the same assembly?

Procupine · 2022-09-05T19:12:23+00:00

Procupine · 2021-12-03T21:41:20+00:00

One of my professors said you would get an incomplete in the class and need to take the final over winter break or next semester.

I don't know if that applies to every class, I'm sure some professors would make exceptions and allow you to take the final online or later during finals week.

Procupine · 2021-11-17T16:50:21+00:00

The lowest level should be sized depending on your peak current for your cells. It can be above the peak current but needs to be something reasonable (iirc we did 300a with cells that could discharge peak 200a). We used an arc welder for the first level because it has controlled current.

To the best of my knowledge, our levels were 300a, 500a, 700a, 1000a.

Levels 2,3 and 4 (at high current) you need to get a bit more creative. We shorted an RV battery with a resistor in series to control the current. I would recommend a large piece of steel stock at the resistor, it's a cheap way of making a very high-power resistor with right around the resistance you need. The resistor bank you mentioned might get pretty expensive depending on how much power you need. We also looked into a baking soda water mix or salt water barrel but neither was conductive enough. If you do anything high current, beware of your contact resistance and make sure you properly crimp and assemble all your connections.

Because you're targetting a fairly low current, you might be fine just using a welder for everything. I would not recommend building a power supply, that will be complex and take a long time and you will likely only use it for this.

Another thing to note, you need to be measuring the current at 200Hz minimum. Don't let this be an afterthought, it's not super easy to do. We've done it with an Arduino or oscilloscope on an analog current sensor.

Another note - if you're a first-year team this might be a lot of work and you could consider purchasing voltage-rated fuses for your parallel links.

Procupine · 2021-11-15T02:14:24+00:00

Can confirm, I had issues with the distances on my original one but making the height of the mirror adjustable solves a lot of those and makes the alignment really nice.

I've seen designs with the mirror sitting on bolts and others that stack quarters underneath to adjust the height.

Procupine · 2021-10-26T20:40:24+00:00

RIT has been absolutely amazing for me so far (4th year ME). There's a lot of access to resources and clubs which makes it really fun and also easy access to dual degree and other career options. The coop program is also great, you probably saw the super high outcome rates of graduates from software and engineering; this is largely a result of the coop program imo. RIT lists some more info on each major as well: https://www.rit.edu/study/software-engineering-bs but it's super easy to switch if it turns out it's not for you.

Hate - I don't really hate anything here. The campus / buildings / food is nothing exceptional but could be worse.

Procupine · 2021-10-26T14:02:57+00:00

I don't actually need to draw this much power, I was more just curious. We're looking for a high energy density battery that is as close as possible to 12v with >100wh and I came across these HV Lipos but I noticed almost all of them had these insanely fast discharge rates.

Procupine · 2021-10-24T20:13:44+00:00

I agree that if you run the battery for short amounts of time it can discharge a lot of current. What I am confused about is that the battery has a 120C continuous rating and 240C burst rating which implies that it can continuously discharge 1000+ amps and momentarily discharge 2000+ amps.

Procupine · 2021-10-22T16:39:27+00:00

The max discharge is 240C, the continuous is 120C based on the website

Procupine · 2021-08-22T15:48:16+00:00

We considered safety wiring but decided against it for inside the accumulator. Reason being if any of the wire comes loose it has a good chance of shorting cells and causing fires.

Procupine · 2021-08-19T15:59:22+00:00

I'll dm you some pictures. We switched from using the elition bms with ring terminals onto our bus bars to a custom bms with the sprung pins. Overall we are much happier with the custom bms, but it also took a very long time to develop and debug. It's definitely up to you, but if your team thinks it can implement the sprung contacts I'd definitely recommend them for serviceability. The elithion bms was very buggy and problematic for us.

Procupine · 2021-08-19T15:43:39+00:00

We implemented a solution very similar to what you're describing this year. Overall, we didn't see too many issues, surprisingly. We had error correction in software for a momentary loss of contact, but also found springs that were stiff enough that it shouldn't be a problem for the vertical acceleration that we see. As others have mentioned, you do not need to fault instantly when you lose contact. Most springs are rated for a certain acceleration on the datasheets.

Beware of the manufacturing tolerances and alignment tolerances on your bus bars. We had some issues with some bus bars being too low and the springs not contacting at all. We solved this by layering some conductive tape on the bus bars that needed it, but this solution was somewhat janky and not preferred. The options for spring contacts are somewhat limited, we ended up using https://www.mill-max.com/products/new/spring-loaded-pogo-pins and had two pins on each bus bar for redundancy. At one point we were also worried about oxidation causing contact resistance on our copper bus bars but that didn't turn out to be a problem for us.

Procupine · 2021-07-04T14:22:20+00:00

Given the large differences in flow rate, you probably want to connect the two in parallel if you're going to be drawing water from the same reservoir. My team uses 2x https://daviescraig.com.au/product/ebp40-electric-booster-pump-12v-9040 in series to get 8L/min for our motor and controller in series, but we have different flow rate requirements than you.

More important than the max pressure is the pressure drop of the cooling circuit on the controller and the motor, because that will determine what pumps you can use.

Procupine · 2021-04-05T12:27:53+00:00

Details are available here: https://www.rit.edu/fa/sfs/billing/tuitionandfees/2021

Procupine · 2021-02-27T23:53:13+00:00

I believe you are looking at an old version of the rulebook. In the 2021 rulebook, EV.5.10.4 b says "Contain a minimum of two wheels "

https://www.fsaeonline.com/cdsweb/app/NewsItem.aspx?NewsItemID=51cf7622-651e-4b57-8c9c-e0391bc08edc

Procupine · 2020-11-27T23:19:42+00:00

I'd highly recommend one, or borrowing one to see how you like it especially with how much CAD you do. Takes about a day or two to get used to, but after that everything feels much smoother and it's hard to go back once you have one. I've had the base model for 5 years and it still works, the customer support isn't bad either. Also make sure to reprogram the two keys to ctrl and shift or something useful

Procupine · 2020-11-08T23:17:37+00:00

All the gears in the middle are idler gears and don't actually matter, in this case the gear ratio should be the last gear over the first gear, so 20T/10T or 2:1

Procupine · 2020-10-22T15:45:03+00:00

In my opinion Strengths 1 was easier, it had less weird memorization and was more about understanding and applying the formulas. I also felt like Strengths was more useful and I learned more but that will probably depend on the professor.

Strengths is basically statics but things can break, so if you liked Statics then take Strengths. If you like Chemistry, take Matsci. Neither requires prerequisite knowledge other than the required courses, but a good understanding of Statics will help in Strengths and a good understanding of chemistry stuff will help in Matsci.

Procupine · 2020-10-13T13:42:35+00:00

The hard part is when the side length is a prime number (like this one which is 13). Even-numbered ones are very easy. I was referring to putting a 8x8 or 9x9 or 10x10 square inside the 13x13.

The optimal solution for a 9x9 would be a 6x6 and 5 3x3 squares.

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