Planning EV Race Car

Duncan said:

No not even close - triple it $90,000...

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That was my first thought.

A perfect combination of all-out race performance and street type range, at this point, isn't really going to happen. You're going to compromise one or the other.

mahedyaj said:

...The issue is I wouldn't be able to fit an 85kWh pack in the car. If I'm lucky I can maybe fit a 65kWh pack...

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For 150 miles in a fast race vehicle, you're automatically talking about the highest power density Lipo cells available, just to build a pack capable of meeting your goals, without weighing more than, and being half the size (or more) of, the vehicle you're putting them in. Your biggest issue then, is going to be cycle life. You go from the thousands of cycles road-going, daily driver, EVs talk about, to hundreds of cycles - meaning you start planning very carefully when and how often you'll use them.

mahedyaj said:

...I draw the line at 90k for batteries.

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You may not make it then. When researching the same thing for the Inhaler, I priced just the cells for a high-power Kokam-based pack at around $50K (much less range, but possibly more power than you're after?). That's not including connections, case - and most importantly BMS - you're not going to run these cells without a really good BMS, unless you just like the thought of roasting money over an open flame.

So, with great deals/partial sponsorhip, one $50-100,000K battery pack, if it's in your budget, fine. One or more a year, and you start to see why we only see occasional all-out performance demonstrations from the fastest, most powerful, EVs. It's a bit different than that 1200hp dino-burner that just wasted $200 in race fuel at the track.

To add insult to injury, generally, the faster you charge and discharge them, the lower the cycle life number gets...

mahedyaj said:

Thank you for your help. From what I'm seeing, these batteries can only be charged at low voltage. I need to be able to charge them faster. This would work as a 12v for the electronics but not as the battery pack...

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Those are 12v replacement battery packs made from lithium cells. YOu will charge your pack at pack voltage, with a charger made for it. How fast is dependent on how much $$$ you spend. The LiPo cells, with good BMS, can generally take a pretty fast charge rate - so it's a matter of how much charger you are willing to buy/can afford, and how much power you can safely tap from your source.

mahedyaj said:

...I am in the process of drafting an email to Rimac Autombili, what questions should I be asking about their battery packs? ...

...Sorry if these are dumb questions, clearly I'm new to this.

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We're here to help you learn. You might want to wait a while on that letter to Rimac, because if they get the sense that you don't know what you're doing you'll probably get a pleasant blow-off or no reply. Most companies are very busy and get bombarded with requests from well-meaning, curious, but out of their league enthusiasts; and they're also constantly thinking about liability, negative feedback/word-of-mouth from misuse, etc...

dougingraham said:

Firstly, just about any battery with enough range to go 150 miles will have high enough output...

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I don't think you can say that, that easily. "High enough output" is relative, and depends on the intended application. My idea of a high output pack used to be a LiPo pack that could supply a Shiva, without significant sag, for as long as my foot would stay down. Now, my idea of a high output pack is one that will provide enough voltage to spin an AC motor to 10K, without sag, and at drastically reduced current levels. Intended use, component choice, and vehicle specifications, all have a say in what constitutes high output. As usual, we're shooting in the dark here, because we don't have any of that, as solid data, to work off.

Anyway, your numbers agree and make the point that it's just not practical, at this time to try to accomplish both goals in the same pack.

mahedyaj said:

Okay. So what about swapping multiple packs around. Let's say that the price isn't a big deal. If I had multiple (5?) smaller pack with enough range for 80 miles, would I increase cell life? The way I think about it is that if I deplete one pack to 10% and I put it to charge (outside of the car) while the next pack is swapped in I would only be depleting at a faster rate.

What matters more, getting to 0 SOC or running through the SOC quickly?

Is BMS always separate from the battery module?

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You never want to go to 10% SOC, definitely not 0%, unless you like buying cells and building packs. The rule of thumb around here seems to be 20%. I generally figure 25% SOC with LiPo, just to give them a little extra margin.

As for 5 smaller packs, the same rules apply. How quickly are you discharging them, how often, and how fast are you re-charging each one? If having more lets you charge the others slowly, while one is in use - maybe. The problem I see is you're going to push a smaller pack harder for the same performance, so did you just eat your own lunch?

major said:

Heck, I'd go to 0% to win a race Done it a number of times. What hurts is hitting zero SOC 50 yards from the finish line while leading a 9 lap race at Laguna Seca

Zero SOC isn't zero voltage. The battery can take it. It's racing so I ain't looking to get 3000 cycles. I don't want to carry any extra battery mass than I need to finish the race.

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We (not specifically you and I) have had this type discussion here a few times. There's all-out racing, with Nitro Top Fuel and Funny Car drag racing at the extreme, where you leave nothing on the table. Everything is expendable, parts, fuel, oil is constant loss, etc, etc. Then, at the other extreme, there is bracket-level amateur racing, where vehicles and parts are expected to last for a season. It's all in what type of racing a person is engaging in and what the competition is doing.

9th lap at Laguna Seca, I assume in a championship series, where the bike is headed back to the shop to be gone over with the proverbial fine-toothed comb, and everyone else in contention is willing to risk it all - yes, leave nothing on the track.

I'm a grudge racer (formerly a street racer) and a part of the game there is to always have something left in it - never show your full hand. And, always be ready for the next sucker, errr, I mean challenger, to try you after watching you just squeak out a victory...

Again, it's all in what you're after and I am surprised at the tendency of such a science-based community to draw lines in the sand so quickly.