Serious question.

"Rainbow" (rainbeaux) 02/18/2015 at 12:43 • Filed to: None

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I don't know much about electric cars, but how difficult would it be to add extra cells to a Nissan Leaf? It has 192 cells standard throughout 48 modules, and there's more than enough space in the trunk for at least 24 more of those. But of course... There's a lot going on in the battery pack and I have no idea what it all does exactly. The idea here is that, if I can manage to gather enough money, I legitimately want to build a Leaf-R. I figure the 107 stock horsepower could be raised significantly with all the space that Nissan left open. I'm just curious if that's something that can be done at home with normal tools and lots of patience, or if it would need to be taken to a shop.

RamblinRover Luxury-Yacht > Rainbow 02/18/2015 at 12:47

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If it were as simple as just "more battery", it would be pretty easy - just make sure you build in parallel so the voltage remains the same. Unfortunately, I'm guessing the battery management is aggressively managed with a computer model, so the management computer needs to be brainwashed appropriately. I'm also not sure about heat dissipation from having extra cells in the space - that might be a problem to some degree.

Sir_Stig: and toxic masculinity ruins the party again. > Rainbow 02/18/2015 at 12:50

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Added in parallel you should be able to add as much as you want, the voltage will stay the same but your amperage will go up. If you want to make it faster you would need to find out a lot more about how the motors are regulated.

CalzoneGolem > Rainbow 02/18/2015 at 12:52

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It should be pretty easy if you know what you're doing but these packs have enough juice to kill an elephant.

saabstory | fixes bikes, breaks cars > RamblinRover Luxury-Yacht 02/18/2015 at 12:52

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I would argue that more batteries equals the potential for more power and that more power would necessitate new batteries because you'll be using more energy quicker. The main problem with this plan looks to be weight/weight distribution rather than power or battery life though.

Sir_Stig: and toxic masculinity ruins the party again. > saabstory | fixes bikes, breaks cars 02/18/2015 at 12:55

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It depends on how the motor power is regulated.

RamblinRover Luxury-Yacht > saabstory | fixes bikes, breaks cars 02/18/2015 at 12:58

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A lot of it would be in managing discharge not to fry the existing circuitry - one important element of the aforementioned charge computer "brainwashing". That management would keep temps down in the compartment, too, but getting the balance right so as to still allow better performance (and not just longer range) would be tricky.

jariten1781 > Rainbow 02/18/2015 at 13:04

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You'd probably need to pull out all of the computerized management systems and go with a more simple custom controller. I'm sure recoding them would be more difficult than anything else unless someones cracked Nissan's system and it's all open kimono. With the new controller you'll probably have to modify all the inputs (throttle, regeneration if you're going to keep that around which is probably as big a project as anything else, charging etc.). You'll also probably lose all your instruments in the process so you'll have to rig something up for that.

It's not trivial, but it should be doable with enough time an money. At least you wouldn't have to worry about OBDII compliance since electric cars are exempt in all state inspections I'm aware of.

Snuze: Needs another Swede > Rainbow 02/18/2015 at 13:55

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DO NOT mess with those battery packs if you don't know what you are doing. The amount of power in a single 12V car batter can KILL you. It's also not just the electric shock you have to worry about. You need to be extremely careful about the tools you're using and conscious of electrical safety at all times. We had a Chief when I was in the Navy who was replacing the battery in his car. He was tightening down the terminals on the new battery and for some reason was using a really long wrench. He dropped it and by sheer chance it bucked the terminals of the battery and the thing exploded, killing him in the process.

That said, here's a few thoughts. If you connect batteries in parallel, you get more amperage. This means extended range, but not more power. Connecting in series gives you a higher voltage. That means more power for the same current draw, or the same power but at lower current draws. Ideally you'd want a combination of batteries in series and parallel to produce more voltage and have more available current, so you can get the power and maintain the same range.

But you can't just throw batteries in there willy nilly. Everything... the motor, controller, wiring, and the controller are all designed to operate in a specified voltage range. You would need to replace wiring, and reprogram or possibly replace the controller to allow for operation on higher voltage. You would also need to upgrade the cooling system to handle the extra heat, and possibly upgrade the motor depending on how it's wound.

I'm not trying to discourage you but this isn't a task for the feint of heart.

Tekamul > Rainbow 02/18/2015 at 13:56

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More battery won't give you more power at the wheels. You would need to change the power controller.

I'm guessing the system in a leaf is very complicated. It's managing current delivery, heat, battery life, regen, etc. Your easiest path is probably to get a Leaf, and ditch the entire power control and charge system. Replace it with a simple off the shelf power controller, and target higher currents.

You can reuse the batteries, but you would want to add additional cell packs. The 24kW pack is 48 modules wired serially, each having 4 cells, arranged as two parallel pairs wired in series. Each cell is 3.8V. So that's ~360V. If you add more modules, you can bump up the voltage, but that means the controller and motor need to be adjusted. Also, those are some seriously high end batteries, expect extra packs to be expensive. I think the full pack is $15k.

I think you'd be better off going with a custom build. Grab something light, like a Miata or civic, and add your own batteries, controller and motor.

Mattbob > RamblinRover Luxury-Yacht 02/18/2015 at 14:09

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yup

Mattbob > Rainbow 02/18/2015 at 14:13

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I would not touch it. You would have to have a in depth knowledge of their charging, and battery balance schemes to even begin to think about making changes to one of those systems. It's not like adding some AA's in series to a flashlight to make it last longer. The hardware may not even be there to handle the extra batteries, depending on their balancing scheme(there are quite a few methods). That is before you get into heat dissipation etc etc. Doing a whole control system with open source methods would probably be easier unless you had support from Nissan. And remember Li-ion batteries can explode if you don't treat them right. I am probably forgetting some more details about why this was a bad idea, but my class on this subject (I took a class on this exact subject) was like 4-5 years ago now.

Mattbob > Sir_Stig: and toxic masculinity ruins the party again. 02/18/2015 at 14:13

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nope, its much more complicated than that.

Sir_Stig: and toxic masculinity ruins the party again. > Mattbob 02/18/2015 at 14:15

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Well yeah, but without schematics I can't really go into a more detailed analysis.

Sir_Stig: and toxic masculinity ruins the party again. > Mattbob 02/18/2015 at 14:18

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Adding batteries in series won't make the flashlight last longer, adding them in parallel will.

Mattbob > CalzoneGolem 02/18/2015 at 14:19

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"Pretty easy if you know what you are doing."... Isn't everything?

CalzoneGolem > Mattbob 02/18/2015 at 14:24

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Pimpin' ain't easy.

Mattbob > Sir_Stig: and toxic masculinity ruins the party again. 02/18/2015 at 14:25

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In my haste to convince someone not to do something stupid I made a typo. I'm an EE, I do this shit all day long. Also technically it would make it last slightly longer. If it is an incandescent bulb, the nonlinearity of the resistance would make it last longer with double voltage and double mAh.

Mattbob > CalzoneGolem 02/18/2015 at 14:26

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this is the best answer.

Sir_Stig: and toxic masculinity ruins the party again. > Mattbob 02/18/2015 at 14:36

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I also work in EE, and I would agree it's not a great idea do mess with electric cars without having a degree on it, but that part just stuck out at me. Also tons of flashlights are LED now so overvolting could cause problems.