ON THE RECORD: Abe Askenazi

Zero Motorcycles' CTO explains everything you ever wanted to know about EVs—and then some.

Abe Askenazi headshot

Abe Askenazi has always been the smartest person in the room. Born and raised in Mexico City, he did his masters thesis on motorcycle dynamics and wrote a textbook on analytical engineering. For 15 years he worked as a senior engineer at the Buell Motorcycle Company, and then in 2010 joined Zero where he is now Chief Technology Officer. There are few people more knowledgeable about electric vehicles, as you'll soon discover...

Battery cell development is the Wild Wild West. Unless you're packing the little cylindricals that are used in laptops, there really are no size or shape standards. Cylindricals look like AAs; they're called 18650s because they're 18mm in diameter and 650mm in length. There are two issues in creating a pack with cylindricals: volumetric efficiency and thermal management. Liquid cooling complicates things. Also, it needs to be a very large pack. Tesla uses 18650s but motorcycles are not cars; we don't have the real estate. The other thing about cylindricals is they're metal cans that you have to weld interconnect tabs to, and that's difficult from a durability standpoint. The Fisker A123 fiasco was due to poor management of these welds.

Harley-Davidson LiveWire static side view

Most powersports equipment is based around Field-Effect Transistor (FET) technology, which peaks around 130 volts. When you go to higher voltage, you have to go to Insulated-Gate Bipolar Transistor (IGBT) technology. The car guys are at 300-400 volts, which incidentally the Harley-Davidson Livewire is 300 volts. But at the level of power that a motorcycle makes, the difference is not that impactful. It's also a safety issue: Our manufacturing is pretty high-end, but we don't have automotive levels of safety, and we can't guarantee that every dealership is going to have high-voltage safety systems in place. The standard for powersports and industrial equipment such as forklifts is 102 volts, which if you screw up will shock and hurt you, but isn't fatal. If you get shocked with a 300-400-volt battery, you're dead.

For lithium-ion cells, nominal voltage is 3.65 volts. We use pouch cells, which look like manila envelopes with little tabs sticking out the end. If you put 28 of these in series, you get 102 volts. So our cell box, what we call a "brick,"  has a stack of 28 of these things in intimate contact with one another. From a volumetric and thermal standpoint, it's the most efficient pack you can have. As for the interconnects, we use mechanical crimps and then pour in a very special compound, a form of polyurea, that casts the whole thing in stone to protect it against vibration and weather.

2015 Zero SR power pack

What we used to do was scour the earth to find the best cell that we could get for our vehicle, and then design a battery around that cell and a motorcycle around that battery. And then the next year we'd find another cell and do it all over again. That's not sustainable, so for the 2013 model year we decided to establish stable platforms. We identified two different needs in the marketplace: One is about getting as much range as possible, and so the S/DS platform is built around the largest battery we could fit. And then for the FX platform, we've got this military contract that specifies 60-second charging. Well you can't really do that, but if you have modular batteries that you can swap in and out, then you effectively have 60-second charging. This also appeals to people who live in apartments and want to be able to take the modules upstairs to charge them.

There are three types of packs that we construct in-house. The first is what we call a module, which is a single-cell-box battery. It's hot-swappable and blind-mated, so you don't have to mess around with any connectors; you just push the module in. The FX can get by with one or two modules, and you can take one out and charge it independent of the other. Our big S/DS battery pack can accommodate up to four bricks, and we can also do a three-brick pack that has a dummy cell box. They're wired in parallel, so there's a single Battery Management System (BMS), a single current sensor, a single fuse, etc. If you did that with independent modules, you'd need four of each. We have a 5-year/100,000-mile warranty and the only reason we can do that is because we've been working with BMSs since 2006.

2015 Zero SR studio 3/4 view

The controller is like the EFI of an internal-combustion vehicle. It basically sucks energy out of the battery and meters it to the motor, which puts that energy into driving the vehicle forward. Of course since this is an integrated system, you need a "Master of Ceremonies" that oversees everything. We call this the Main Bike Board (MBB), but in the industry it's most commonly referenced as the Vehicle Control Unit (VCU). When you have two modules connected in parallel with different states of charge, the natural thing would be to short-circuit—the one battery wants to even out the voltage with the other. So the MBB monitors the state of charge of the independent modules and discharges the one until it's level with the other, and then continues discharging both. Same thing with charging. When we introduced this system in 2013, nobody else had figured this out yet, so we have a patent pending on it.

You don't actually get 100 percent torque all the time. There's a position sensor on the motor that tells the controller where it's at. To get the thing spinning, there's a lot of information going back and forth. So it takes a little bit to be able to deliver full wattage. And then you are at maximum torque, but at higher speeds you have this thing called back-EMF (Electromotive Force). The motor starts fighting itself because it wants to become more of a generator than a power-producing thing, and torque starts dropping. So there is a range from around 50-4,000 rpm where you are at maximum torque.

Zero Motorcycles headquarters

We won't see widespread battery swapping any time soon. We can't even decide on a standard cell size, let alone a pack size! An Israeli company called A Better Place, their whole business model was you'd come into the gas station and they'd swap your battery pack in less than 5 minutes. But how many different battery packs can they afford to carry? The battery is the most expensive part of the vehicle. Every gas tank is different, yet the way you fill it is the same. So what needs to happen is the way you charge batteries needs to be the same.

Internal-combustion engines are not going to get smaller. There's nothing that's going to cut a chunk of real estate out or take 100 lb. off. And it's going to happen for us—there are chemistries being developed right now that are quadrupling energy density. So if the range of a four-brick battery is enough for what you're doing today, then when energy density quadruples you're going to be able to get by with a single module and you'll have shed 130 lb. And now you've got all that extra real estate too—you won't need saddlebags! The future design possibilities become really exciting.

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2015 Zero SR studio photo #1

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Abe Askenazi.

Harley-Davidson LiveWire.