Arranging 12,000, 18650 cells for a 150KW 300V EV battery pack. - Page 1
Forum section: electronics / projects

author: electrolux
author_rank: Regular Contributor
timestamp: July 09, 2015, 02:47:51 pm
content: Your thoughts on arranging 12,000, 18650 type cellshttp://industrial.panasonic.com/ww/products/batteries/secondary-batteries/lithium-ion/cylindrical-type/NCR18650Bfor a 150KW, 300V EV battery pack. Safety, weight, size, etc. The size factor should preferably be thin as possible for a low COG of the EV.This is a neat system which has given me ideas.https://www.youtube.com/watch?t=16&v=31ohCyMMRkcBTW: It's powering this motor:http://www.amracinginc.com/#!dual-core/ct07

author: electrolux
author_rank: Regular Contributor
timestamp: July 09, 2015, 04:03:51 pm
content: The size would be half a pallet of bricks.

author: teksturi
author_rank: Regular Contributor
timestamp: July 10, 2015, 07:35:24 pm
content: I recommed jehurgarcia's videos in Youtube. He is using those sells and try to replicate Tesla style.

author: nctnico
author_rank: Super Contributor
timestamp: July 10, 2015, 08:13:50 pm
content: Using solder joints in a battery pack for a vehicleThese kind of applications need spot welding for safety and current handling. Give the guys from Cleantron a call and ask for a quote on their standard packs. There is much more to making a battery pack than just connecting a whole bunch of cells together. Building an EV takes a lot of engineering already and re-inventing how to built a battery pack is not going to add much to the fun. Even though these cells are pretty safe when mistreated they can still catch fire when shorted of overcharged.

author: free_electron
author_rank: Super Contributor
timestamp: July 10, 2015, 10:45:35 pm
content: Not even close.- Where's the heating / cooling system. That is CRUCIAL. Doing it without will destroy the batteries after a few months. The pack needs to be kept within a temperature band that shifts depending on charging / using.- second problem : each of these cells has its own protection circuitry (commercially avaialble cells have this on board) . That creates small imbalances when put in parallel. You are not supposed to parallel complete cells that include the circuitry. you parallel the raw cell and then hook up the protection circuitry to the pack.base mistake.

author: TerraHertz
author_rank: Super Contributor
timestamp: July 12, 2015, 02:45:37 am
content: Quote from: free_electron on July 10, 2015, 10:45:35 pmThe tesla battery teardown on youtube (or was it here in eevblog? I don't have the link) showed that Tesla includes a fuse link on every paralleled cell within groups. Plus charge state monitoring & regulation on all the groups in series.The fuse being critical, to avoid energy of all the cells in parallel being dumped into any individual cell that short circuits.Plus there has to be enough thermal and physical isolation between cells to prevent a meltdown cascade if one goes. The mistake Boeing made with their cell packs.What I'd like to know, is how you manage group charge balancing, if one or more cells in a group have blown their fuses? So there are significant differences in the capacity of groups in the overall battery.Is that situation cause for a mandatory service? Or does the battery/car system just live with it?

author: CronusWorks
author_rank: Newbie
timestamp: July 12, 2015, 05:04:48 am
content: Quote from: TerraHertz on July 12, 2015, 02:45:37 amI'm 99% sure it just lives with it. Could be any one (or more than one) of the methods described here to balance during discharge:http://americansolarchallenge.org/ASC/wp-content/uploads/2013/01/SAE_2001-01-0959.pdfIf you didn't do something like that, you'd be limited by whichever parallel group of cells hit their end-of-discharge voltage first, in which case you might as well have lost a cell in each group.The Model S 85kWh battery has 16 modules of 6S74P in series, so the entire thing is 96S74P. Without balancing during discharge, losing one cell would effectively cost you about 1.35% of your total capacity, but with balancing, around 0.014% (if your balancing method and batteries were 100% efficient, which they are not).And +1 ondo not ever solder directly to a battery.That battery pack in that video looks like a bomb waiting to happen. If you can afford thousands of cells to build an EV, you should be able to afford a proper spot welder and time to design a safe pack.

author: EEMarc
author_rank: Regular Contributor
timestamp: July 12, 2015, 10:55:26 pm
content: Lithium ion batteries need to operate within their safe operation range. They have a minimum and maximum voltage. They have a minimum and maximum temperature. They also and a minimum and maximum current, that is somewhere between their maximum charge and maximum discharge current. To visualize it, think of a 3 dimension graph. Each axis is each of the three parameters, voltage, current and temperature. If you draw the safe operation area out, initially, would look like a cube. It will end up looking like a modified cube once restrictions are added such as limiting discharge current during high temperatures.Failure to maintain the batteries within the safe operating area will significantly reduce it's life or cause a catastrophic failure. Also, handling a cell failure such as an internal short is important. A fuseable link will prevent a bad cell from failing and shorting out other paralleled cells causing them to fail. If it does short, the other batteries will dump their charge into the bad cell and blow the fuseable link. The battery will then still operate, but at a slightly lower capacity. If one cell fails, the cooling system should be able to prevent nearby cells from overheating and failing as well. A good cooling system will prevent a failure from going catastrophic.A fast way to violate a batter's safe operation area is to solder it. It will heat the battery to too hot of a temperature. Spot welding gets hotter at the spot weld, but is much faster and applies less energy and thus less heat to the terminal and battery.Large battery packs are less able to dissipate heat and require a cooling system. A cooling system will allow for high power operation while keeping the batteries in the safe operation area and also keep the batteries at the same temperature. Batteries in the centre of the pack or batteries near a heat source will get hotter if not equalized by a cooling system. If a cell or parallel of cells is operated hotter than the other cells, it will degrade faster. As a hot parallel of cells degrades, it will prevent other batteries from charging and discharging as much while causing itself to charge and discharge more. That will accelerate it's degradation.It is also good practice to match each cell or parallel of cell's capacity so they charge and discharge as well as degrade at the same rate. Matching is best done will all batteries in a pack closely matched. That can only be done with volume battery pack production. It can also be done to a limited extent by over-purchasing batteries and then using outliers for other projects. You could also sell outliers for profit since the volume discount will be below the retail price.