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A123Systems Acquires Hymotion to Develop Market for Plug-in Conversions

Lithium-ion batter maker A123Systems has acquired Hymotion, Inc., a fabricator of aftermarket plug-in hybrid conversion modules. These Battery Range Extender Modules (BREMs) can be easily installed in the spare tire well of most hybrid vehicles, enabling current production models to become plug-in hybrid electric vehicles (PHEVs).

The Hymotion acquisition provides A123Systems access to critical early IP on plug-in hybrid systems technology as well as valuable experience with engineering BREMs using A123Systems’ Automotive Class Lithium-ion batteries. Terms were not disclosed.

A123Systems CEO David Vieau stated in testimony to a Senate subcommittee this week that the company plans to begin marketing BREMs in 2008. (Earlier post.)

With 5 million hybrids expected on the road by the end of 2010, we feel there is a significant opportunity for an interim aftermarket solution allowing consumers to experience the oil and CO2 reduction benefits that PHEV upgraded vehicles provide.

—David Vieau

The fleet market has been an important testing ground for PHEVs. The Hymotion systems will continue to be available to the growing fleet market.  Over the coming months we will work to reduce delivery times to fleets by standardizing packaging and in anticipation of having a consumer ready system for early 2008 introduction.

—Ricardo Bazzarella, Co-founder and President of Hymotion

A123Systems and its partner Cobasys are working with GM on advanced battery development for use in the Saturn Vue Green Line plug-in hybrid SUV. GM has also awarded a development contract to Johnson Controls–Saft Advanced Power Solutions, LLC, a joint venture between Tier 1 automotive supplier Johnson Controls and Saft, for that project. (Earlier post.)



The tricky part will be to convince consumers to get an aftermarket product now when they might expect that Toyota will have a production version by 2009 or 2010. The Toyota version should be cheaper and better optimized with respect to emissions issues.

Ron Fischer

Hymotion's emphasis has been on government fleet conversions. A number of local politicians have passed laws requiring cities to buy PIHEVs for their fleets if possible. Conversions are what's possible now and for the next few years. The type and number of PIHEVs available from major automakers is likely to be limited for some time.

This is a wise move on A123's part.


Which hybrids have the more powerful motors? Can the software on any of them be tweaked in order to use just the motor and not the engine up to 40 mph or so? If so, these BREM's might be quite popular as the price starts to drop. Why wait til 2009 or 2010 or even later, to maybe get a slightly better product if you can have a good product in 2008?



Do you have any cites for Toyota's production of plug-ins? I'd love for it to happen, but no concepts are out that I know of.


Buying a PHEV kit isn't a hard decision for me - too bad they're not available this year. Even if I buy a new PHEV when available, chances are I'll keep my current car (with the kit installed) for a second car.


I'm not so sure there is as big of a market for this as A123 thinks there is. How many owners of Prius, Camry, and Escapes are willing to drop $10K - $3.5K Tax Credit + Alternative Minimum Tax offset for an upgrade? Two hundred, maybe. Get the cost down to around a thousand bucks, then you might get one or two thousand people willing to upgrade their current hybrids.

I agree that consumers would rather wait for the Toyota production PHEV.


You don't go after the average consumer with this product. You go after the government user.

I don't try to sell a $15,000 Spectrum Analyzer/receiver to Jimmy down the street. I sell it to the government user who needs it...there may be 4 or 5 Jimmy's who want to buy it from me but they are not the target market, and I don't market it to Jimmy.


ZIV, the Toyota Camry Hybrid has a large 105 Kw motor, but the electronic control system does not utilize it fully, perhaps to avoid a large draw from the battery.
The A123/Hymotion modification, when and if available, might be able to supply more power to the motor if the electric control system allowed or was modified to allow, full motor utilization.

It only takes about 21 KW's of power to barrel down the road at 60 miles per hour, so if you drove that fast in an all electric mode, for one hours, you would draw 21 KWH from the battery and go 60 miles. If you only had 5 KWH of draw down available, then you could go about 15 miles.

So the reason the electric control system starts up the ICE at about 40 miles per hour seems to be two fold, to avoid a drawdown rate in excess of about 20 KW, and to avoid depleting the 1.3 KWH battery in the unmodified configuration.

In summary, given the current battery limitations, the design of the Prius and Camry make the most of the situation. Given a larger battery with a higher rate of draw down capability, like the A123 battery, a smaller ICE and a larger motor, or motor utilization, is in the picture.

The 2009 Prius promises to paint that picture! Time will tell.


I've been going to for years now to find out when consumers can get a PHEV kit.

Since they have a new owner, maybe they will update the FAQ area of their website:

"Our PHEV kits are currently available only for government and fleet use. However, we are working to ship PHEV kits for consumer use early in the new year, 2007."

The new year would be 2008 and early 2007 has already come and gone.

I want a plug-in hybrid as I only drive 20 miles per day on side streets and cannot stand stopping/paying for gas.



Toyota’s electromechanical transmission employs two electric motors/generators, and only one could be used as traction motor, so max electric power is ½ of what is reported on, say, Yahoo autos, or about 50 KW for Camry hybrid. Enough to highway driving, but only if you are light on throttle.

Shaun Williams

You've go to admire A123 for grabbing their markets by the throat. Premium DeWalt battery packs, RC batteries of choice and now; let's buy a PHEV startup!

They may have a product just good/cheap enough and leadership aggressive enough to be the disrupter from left field that begin the paradigm shift away from ICE's. A little more help from visionary legislators could make a big difference.

Still not sure whether the Cobasys-GM connection will bear fruit though.


Hi Andrey, a fully utilized 50 KW motor would provide more than twice the power needed to travel at a steady state of 60 MPH. If your view is correct, and I am not disputing it, then the Prius drivers that reach 38 MPH on electric only do so using only a 25 KW motor. See my point? The Camry could go much faster than 40 MPH in the electric mode if the battery had more capacity both for energy storage (5 KWH vice 1.3 KWH) and for power (50 KW rate of usage verses 25 KW rate of usage.)
And if my view is invalid, I will be happy to revise my figures and my understanding.


The Toyota Synergy Drive does use two electic motors, which refers to the two electric motor generators, one used to drive the wheels and the other used to recharge the battery from engine power. In the Camry, the larger one is rated at 105 KW @ 4500 RPM. In the Prius, the drive motor is rated at 50 KW.


People already complain that the Camry hybrid does not have enough trunk space because of the batteries. If you put more batteries in there you have less space for luggage.

This obvious point is a marketing principle. Make sure your prospective customers are willing to make that trade off before you start spending money designing any of this.


Van, Camry and Prius engines MUST rotate at highway speeds. It's not a matter of battery power, it's the way the system is designed.

In Toyota's HSD there is no neutral, the engine is always mechanically connected to the wheels. The connection is via the power split device (PSD), a planetary gearset with three shafts. One shaft goes to the engine, one to the wheels and one to a motor/generator (MG1) which controls engine RPM. To keep engine RPM at zero when the car is moving forward, MG1 must spin backward. Once you reach about 40 mph MG1 is spinning backward as fast as it can. Any faster and it would overspeed and suffer damage.

There is no easy way for a retrofit to get around this electro-mechanical limit. I guess you could replace MG1 with a higher RPM motor or build a replacement PSD or final drive unit with different gear ratios or something, but that increases difficulty and cost significantly. The other option would be a software tweak that allows the engine to rotate but not receive fuel. The Prius operates this way in some situations (as does Honda's latest Civic Hybrid), but a rotating engine creates drag so it's not terribly efficient.


Thanks for the insight, but I see no limit for MG1 RPM, except the 10,000 RPM listed, which would be much faster than 40 MPH. The drive shaft rating of MG2 (105 KW @ 4500) suggests MG1 would not be in an overspeed condition at high speed, i.e spinning backwards at 4500 RPM.

Therefore I still maintain that the reason the MG2 does not supply more than about 30 KW of power to the drive shaft is battery power draw limitation, not mechanical overspeed, in the 2007 Camry. Where have I gone wrong?


I agree when is Hymotion going to supply us with the batteries we want early 2007 is past. Why do they give them to fleets first then consumers second. I had the same problem when I ordered my Prius to me it seems like those who can well afford to pay for gas get to save money and the consumer is denied this right so save any money whatsoever.



I understand your point about going after the fleet market, but Ricardo Bazzarella was quoted as saying, "Over the coming months ..... and in anticipation of having a consumer ready system for early 2008 introduction."

I have a 2007 TCH, which I bought in July 2006. I wouldn't really consider a conversion until I am beyond my warranty, July 2009. At that point my car has depreciated to, let's say, roughly roughly $15K. Would I want to drop $8K on a conversion on an "older" car when the 2010 models (hopefully) would be PHEVs? Some folks might. I would consider $1000-$2000 to convert, but not much more than that, unless the fuel savings was compelling.



MG1 has a max limit of 10,000 rpm, but loses the ability to control the engine at around 8,000 rpm. The control logic, in order to leave a large margin of safety, orders MG1 to start rotating the engine at around 6,000 rpm. The equation that expresses the relationship between MG1, MG2 and the engine is:

MG1 = 3.6 * Engine - 2.6 * MG2

At zero engine rpm, 6000 MG1 rpm corresponds to 2300 MG2, or about 39 mph (MG2 is hardwired to the wheels with a ratio of about 59 rpm per mph). Much of this is described in the following PDF file:


I have heard that retrofitting a car with the Hymotion system ruins the emissions control strategy, so that emissions of CO, HC, and NOx are no longer legal. That may not be a problem for a few hobbyists, but I'm not sure that it would be allowed to happen in large numbers.


Steve: All they need to do is make sure the catalytic converter is kept warm. I've seen several ideas on how that can be done.


Hi Doggydogworld, thanks for the link, but I seem to lack the compute skills to access it. So I do not understand why the "engine loses the ability to control engine speed" at 8000 RPM. One would think if you could offset engine rotation by rotating the sun gear at 6000 RPM, you could do it at 10,000 RPM.

But in any event, unless I can access your source, I am in no position to dispute it. Let's leave it that the numbers do not add up as far as I can see.


Van, if you paste the tinyurl link into your web browser's "address" box and hit the enter key it should take you there.

Toyota engineered MG1 to sustain 10,000 rpm without breaking apart, but it can't produce much usable torque above 8,000 rpm due to back EMF. One of MG1's jobs is to apply torque (through the PSD) to crank the engine for starting.

At 52 mph with the engine not turning, MG1 would be at 8,000 rpm and would lack the torque to rotate the engine for starting. If the car accelerates (for instance if on a downgrade), MG1 rpm will increase above 8,000 rpm and still have no way to start the engine. At about 65 mph MG1 would hit 10,000 rpm and be in danger of overspeed. To avoid reaching this potentially unstable condition, the Prius fires up the engine when MG1 hits about 6,000 rpm and still has plenty of reserve torque available to crank the engine.

There was really no reason for Toyota engineers to allow >39mph EV mode. Usable battery energy is only about 500 Wh, and some of this gets used up accelerating from a standing start. Battery drain at higher speeds, say 50 mph, would be in the 10 kW range, so you'd only be able to sustain 50 mph EV operation for a minute or two. If you want more detail I recommend a Yahoo Group called Prius_Technical_Stuff:

Their files section has a lot of good data and the people there know 100x more about Prius internals than me.


Again, thanks for all your effort to put me on the right track, Doggydogworld, your explanation seems sound to me. I could not access the site, the first address brings up a page that says this page redirects you to "you second address" but when I click on "proceed to site" I get a 404 message saying the webpage cannot be found.

Consider this, at 7500 MG1 RPM, the engine start sequence is initiated. The engine starts rotating with no fuel, spark or compression. As the engine speed increases, either MG1 slows down or drive shaft speed increases. So when the engine speed reaches 1000, either MG1 is rotating less than 7500 with available torgue to start the engine, or the MPH of the vehicle in stealth mode could be as high as about 60 MPH, without any mechanical changes.

But all this is not what Toyota has done, and they know best. Also it seems you cannot put a Toyota Hybrid Drive into "Neutral" when on a downgrade where gravity would allow you to go above 60, because MG1 would overspeed to destruction and could not restart the engine. So apparently the "Neutral" position only operates below 39 MPH.

In any event, when the 2009 Toyota third generation HSD comes out, we will see if the stealth mode limit is still 39 MPH. For example a more robust MG1 capable of 13,000 RPM with torgue at that speed more than enough to start a possibly smaller ICE. Time will tell.


In the first quarter of 2008, A123 Systems and Hymotion plan to market a $9500 USD add-on for the Toyota Prius. This cost, which includes installation, is expected to increase your Prius’ fuel economy to 150 MPG in the city. Pretty dang impressive! If it works reliably and safely: I do have some minor qualms about installing a massive lithium ion battery in my car ...


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