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IssacZachary
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 6:53 am

mux wrote:European new Leaf owner chiming in here - I'm planning to do basically exactly the same mod that ATKAM and Collink did. It really seems to be as simple as hooking up contactors on the RLY V signals on the main battery connector, however, I would like to be extra super sure if there are no other issues to take into account.

I'm an electronics design engineer by trade and would be able to make this mod decently professionally. If ATKAM/Collink are willing to share their notes, I can formalize them and make them into a proper tutorial. I'm also interested to know if it isn't possible to tap off the battery wiring going to the on-board charger, as that is extremely easy to access without the need for a bridge or lift.

The real interesting thing about this is the ability to get additional capacity economically. I can get new 2900mAh (10Wh) 18650s for $2.04/pc, meaning a 96s20p pack would be $3916, doubling the range of the car. At 46g per cell, it's only 88kg or 200lbs of extra weight. Of course, the contactors, wiring, additional firewall, secondary BMS and so on will cost a bit extra on top, but it's significantly less than the price premium of a new 40kWh car.


Have you checked out Leaf Xpack on YouTube? He has some informative videos as well as one big mistake that can be avoided by wiring contactors to the same signal that activates the main contactors and not the pre-charge contactors.

As far as I understand only about half the weight of the 24kWh Leaf Battery are the cells. So the actual cell weight is around 300lbs. But I also understand that a lot of the extra weight is for structural ridgitidy, perhaps for safety concerns.

I get what you're saying about price. I can't afford a Tesla Model 3 or a Bolt right now. But $3,000 or $4,000 I might be able to handle. And it doesn't all have to be at once, the battery could start out small and grow as I have time and money to add cells. The battery management system would be expensive though, about $1,000 in itself for a good system.
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mux
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 8:49 am

I should have probably specified as well: I specialize in power electronics and lithium ion batteries (people around me are starting to recognize me as 'that guy that eats 18650s for breakfast') so I'm planning on using a BMS of my own design. A BMS does not have to be expensive, they just are because they're usually specialized and low-volume.

So for me at least, I expect to land, all-in, at about $5k for at least 20kWh of added capacity, with something that should be decently designed, at least much more so than Leaf XPack.

And yes, I've followed him over his journey. He has a slightly different Leaf though, the newer one. Makes it different, and I don't know exactly in which ways. I hope somebody can tell me about splicing into the battery wiring from the charger instead of having to tap off the main battery connector, because it would make a DIY pack so much easier to wire in.

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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 9:18 am

I too am looking to build a add on battery for my leaf. I am just gathering info right now. Why do you think taping in to the DC bus at the charger is preferable to taping in at the main connector? Is it for environmental reasons, the connection will be better protected there?
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EVDRIVER
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 9:21 am

I'd be interested to see the safety strategy for packaging these additional "packs" How they are safely contained, deigned for weight distribution and accidents, isolated, etc. To date I have yet to see one project completed with a safe design. There is a reason the traction pack enclosure is so heavy. What many people think it costs to do such work vs what it actually costs to do properly is usually a surprise in the end, at least for those honest enough to admit it. Anyone that has built a quality EV conversion and accurately documented the costs can relate to this. To safely design a pack in a car is no small feat and people with extensive experience with small hobby packs on the internet are now attempting to work with lethal high voltage. I've seen some scary comments posted that reveal a complete lack of knowledge of HV traction systems and safety. Years back an "experienced" person was killed tinkering with a LEAF pack so please be careful or buy a used longer range EV.
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lorenfb
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 9:50 am

mux wrote:I should have probably specified as well: I specialize in power electronics and lithium ion batteries (people around me are starting to recognize me as 'that guy that eats 18650s for breakfast') so I'm planning on using a BMS of my own design. A BMS does not have to be expensive, they just are because they're usually specialized and low-volume.


That's the difficult part versus just using another Leaf battery with it's BMS, i.e. a custom BMS with all the balancing circuitry and processor
for the 18650 cells.
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jkenny23
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 9:55 am

lorenfb wrote:
mux wrote:I should have probably specified as well: I specialize in power electronics and lithium ion batteries (people around me are starting to recognize me as 'that guy that eats 18650s for breakfast') so I'm planning on using a BMS of my own design. A BMS does not have to be expensive, they just are because they're usually specialized and low-volume.


That's the difficult part versus just using another Leaf battery with it's BMS, i.e. a custom BMS with all the balancing circuitry and processor
for the 18650 cells.


Just want to add that you can buy a Leaf BMS for around $75-100 and it should have no issue balancing/monitoring an 18650 pack assuming the cells are well matched to start with. There's another engineer WolfTronix who has reverse engineered the microcontroller and can swap in a new one with more features also.

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IssacZachary
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 9:59 am

EVDRIVER wrote:I'd be interested to see the safety strategy for packaging these additional "packs" How they are safely contained, deigned for weight distribution and accidents, isolated, etc. To date I have yet to see one project completed with a safe design. There is a reason the traction pack enclosure is so heavy. What many people think it costs to do such work vs what it actually costs to do properly is usually a surprise in the end, at least for those honest enough to admit it. Anyone that has built a quality EV conversion and accurately documented the costs can relate to this. To safely design a pack in a car is no small feat and people with extensive experience with small hobby packs on the internet are now attempting to work with lethal high voltage. I've seen some scary comments posted that reveal a complete lack of knowledge of HV traction systems and safety. Years back an "experienced" person was killed tinkering with a LEAF pack so please be careful or buy a used longer range EV.

Agreed.

I'm not sure which is truly more dangerous, but for the record working on any vehicle can be dangerous. People have been killed by working on gasoline and diesel engines too. For an example, if a diesel develops a leak in the high pressure system it can hypodermically inject diesel fuel directly into your body. The only remedy for not dying is to have the affected limbs amputated immediately. (That's why I keep a skillsaw handy when I'm working on my VW diesel... Just kidding!)

Anyhow, there's a recent flood of cheap LiFePo4 batteries on eBay and Amazon at a stellar price, close to $100 per kWh! So a 30kWh pack would cost around $3,000. The main reason I'm attracted to the LiFePo's is that they are not flammable. So that eliminates one danger. As far as weight goes, personally I wouldn't add 600lbs to the rear of the vehicle. Maybe 200lbs at most in the trunk. If I build it any bigger I'd put mine on a trailer where weight could be better controlled. Yes, that would make the high voltage cables more exposed, but good insulation and a good contactor shutoff system ought to help reduce that danger considerably. And with LiFePo's the box on the trailer could be made out of something non-conductive like plywood or fiberglass.

The reason there are people like me interested in this mod isn't because it's the safest thing to do; rather it's very cheap. If I can take a $7,000 vehicle and add $3,000 in batteries and go 130-150 miles of range that's about a third the price of a Leaf 2 with about the same range. I don't think that driving my 1985 VW Golf or my 1972 VW Beetle is also the safest thing either. But I have a limited budget. Now someone did mention that I should be able to get a Prius Prime for about $10,000, which if possible I'd do that instead of fidgiting with the high voltage on my Leaf.
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mux
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 10:07 am

mmmike: Like I said; in the 2011-12 Leafs, the charger is essentially already in the car trunk, under a plastic cover. Undo a couple M6 bolts and you have access to the HV bus (charger side), CAN and a bunch of other signals. Seems like a very convenient place to work compared to having to put the vehicle on a bridge and working underneath. All this said: I'm working off of videos and trying to work my way through the service manual, I have not touched any of the covers in the car or worked on it. I like to be prepared.

EVDRIVER: Totally agree. However, I don't think it is fundamentally possible to make the design 100% safe. In fact, the Leaf's battery pack is demonstrably unsafe in some cases; there have been at least two documented total vehicle burnouts, including the passenger compartment, due to faulty charging and consequently pouch cells bloating and catching fire, taking the rest of the car with it. The steel container did very little to stop this from happening. This is also not the purpose of the container.

What I believe the designers to have done, and this is of course speculation, is that the container is designed to detach and move independently from the car in the case of a collision, reducing the weight that the local chassis needs to decelerate in case of front and rear collisions in particular. That way they could design the rest of the car like any other car and did not have to take the battery pack's crash characteristics into account in the rest of the spaceframe. The battery compartment could then individually be designed so as not to cause immediate danger when it bumps into something. The shape of the container as well as the bolt position and orientation seem to indicate this kind of a design strategy.

Design for safety is not something you can do in isolation, and certainly not without proper simulations or real-world crash tests. In order to actually design a foolproof and well-designed pack, you would have to be somebody at Nissan with intimate knowledge of the car's frame and mechanics. This is obviously not a possibility. All we can do is try our best, with the best crowdsourced and engineering background information possible, to make something that could be construed as safe and reliable.

So when designing a container for an extender pack for safety, you have a fairly large design space to work with. It will have to cope with:
- Charging, discharging safety. Undervoltage and overvoltage checks, balancing, temperature checks, cooling. This is the BMS
- Service safety; presenting a safe state of the vehicle when the vehicle is off and not charging; these are the contactors and interface connector
- User-facing safety: when using the vehicle normally, the battery pack should not raise additional concerns in the use of the passenger compartment and trunk, nor should the user have to take special precautions when loading the vehicle. No loose packs on the rear seats, no walls with explosives behind them that get triggered when you callously throw a wood axe in the trunk.
- Crash safety: high physical load tolerance, crush safety and should not present a fire hazard to first responders

From what I understand, there is a decent amount of void space under the trunk; this would be a prime location for the extender pack. Out of the way for users and very easy to package. This takes care of most user-facing safety. Disconnecting the pack and installing a first responder's loop should take care of service safety. It being in the rear of the car, away from the passenger cage (would it be?), in the rear crumple zone (very rare to face impact) also makes it relatively impact safe. There is no way to avoid a massive fire when the pack is impacted, but the immediate danger can be avoided with a fire break. Like the firewall in an ICE car, this only has to be one or two inches of (supported) stone wool to be effective enough. The only thing I would package very carefully are the contactors; I'd put those in semi crush-proof containers, just so they fail open.

Now, don't take this as disparagement to anyone, not in the least because I'm just as much of an idiot with safety sometimes, but you are totally right that most conversions are very slap-dash. Leaf XPack is probably the best example of somebody seemingly not even being aware of the safety issues and doing some exceedingly dangerous things (e.g. the parallel/serial relays on a dodgy switch). I don't condone that kind of work, but on the other hand he does provide very valuable and pioneering information to this community.

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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 10:25 am

mux wrote:The real interesting thing about this is the ability to get additional capacity economically. I can get new 2900mAh (10Wh) 18650s for $2.04/pc, meaning a 96s20p pack would be $3916, doubling the range of the car. At 46g per cell, it's only 88kg or 200lbs of extra weight. Of course, the contactors, wiring, additional firewall, secondary BMS and so on will cost a bit extra on top, but it's significantly less than the price premium of a new 40kWh car.


That 204 $/kWh, not bad.
Consider cell holders, nickel strips and spot welding (preferably with Tesla style fuses), rugged custom box + everthing you've mentioned and I believe you be a bit far from 3916$ and 88kg.
If you value your time, the total cost will be WAY off.

128 kg of VW hybrid modules weigh 128kg for 17.4 kWh, and are WAY simpler to put together.
215 €/kWh.

jkenny23
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Re: Extra Battery, How to Integrate with 24kWh Traction Battery?

Sat Jan 13, 2018 10:35 am

IssacZachary wrote:Anyhow, there's a recent flood of cheap LiFePo4 batteries on eBay and Amazon at a stellar price, close to $100 per kWh! So a 30kWh pack would cost around $3,000. The main reason I'm attracted to the LiFePo's is that they are not flammable. So that eliminates one danger.


I'm not sure you can mix chemistries that easily, the discharge curve of LiFePo4 batteries is rather different (flatter) than Li-Ion, though it looks like 112s would work for the maximum voltage.

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