Simple Add on Battery??

The Prius does not have a generator in the simple term. It has two motor generators that is each MG can act as a motor or a generator at any time. MG1 is used for starting the petrol engine (ICE) and can assist with powering the car or producing electricity to be used by MG2 to power the car or both can power the car or produce electricity to charge the battery and act as breaks. The motor generators run at at a higher voltage than the battery (500volts for the MG's 201.6volts for the battery). The MG's are 3phase variable frequency AC the battery is DC.

There are add on units but these generally only charge the existing battery (do a search on Engineer system).

 

Hi John, and welcome to the community!

There are ways to do this, but not as simply as you describe. The good news is there is a lot of good info out there from 7 years worth of tinkerers The main challenge is not adding the extra battery, but convincing the Prius to make use of the extra energy available. Since Voltage is not a reliable indicator of the state of charge (SOC) of the NimH battery, the battery controller uses an approach referred to as "coulomb counting" to track how much energy goes in and out of the battery to estimate its SOC. In this sense the controller "knows" how big the battery is, and won't use more energy from an additional battery without "tricking" it in one way or another. There are several primary ways to do this that have evolved over the years.

1) Closest to your suggestion is the approach taken by the Enginer conversion. This runs current from the kit in through the current sensor to the battery to make the extra current look like energy coming from regen. The limitation to this approach is that the hybrid controller also has current sensors up at the MGs/inverter so it "knows" that this current is not actually coming from regen. If the mismatch between the current coming out of the inverter and the current going into the battery is large it assumes a fault has occurred and triggers an error condition disabling the electric drive system. The limit seems to be in the neighborhood of 16A. The Enginer kit uses a large capacity 48V Li battery connected through a dc:dc converter to feed current back into the NimH battery and/or inverter/motors in a controlled manner to avoid exceeding this limit. The result is a very inexpensive PHEV conversion that avoids the complexity of having to "trick" the Prius controllers, but the limited amount of current available makes it unable to sustain EV driving for a long time under many conditions. The real strength of this kit IMHO is in supplementing the NimH battery current over a long commute, though there are people that have learned to drive it right to get decent results on shorter or stop and go kinds of drives.

2) The next approach is to add on a PHEV pack and controller to "trick" the Prius into believing that the stock NimH pack has more energy than it thought, and consequently using it. This started with the original cal-cars open source project in ~2005. They found that by using contactors to connect a >240V battery to the system on the battery side of the current sensor, they could get the battery controller to enter a "recalibration" mode referred to as SOC Drift. Basically if the voltage on the pack exceeds certain preset limits the controller will revise its coulomb counting derived SOC to accommodate for errors in the counting accumulated over time. This had to be done carefully to avoid overcharging the NimH pack, so the added PHEV controller would dynamically connect and disconnect the PHEV pack to try and keep the calculated SOC high but not overcharge. The big advantage to this approach is there is no limitation on how much current the PHEV battery can deliver into the system, making sustained EV driving more feasible.

This evolved into the "SOC Spoofing" approach, that was use by a number of conversion companies, and may still be by some. In this case they found that if the controller "listened" for the battery controllers SOC report on the CAN bus and then immediately rebroadcast a different SOC value, the hybrid controller would ignore the battery SOC and just use the rebroadcast value. Now the SOC could be artificially maintained at a high enough level to force the hybrid controller to use more electric drive for as long as the PHEV pack held out, and let the PHEV pack use a slightly lower voltage to avoid the danger of overcharging the NimH battery. This had the advantage of being a more reliable way to set a given SOC, and didn't require the contactors to switch the battery in and out all the time, which was also a reliability concern. As I recall the "CAN View" controller popular for many years with diy converters began as the cal-cars controller, and evolved into an SOC spoofing capable controller.

SOC Spoofing in turn evolved into the approach now used by a number of conversion companies that puts the new PHEV controller between the stock battery controller and the rest of the CAN bus. Its a similar result, but instead of relying on the "SOC spoofing" which could be somewhat unreliable as multiple conflicting messages were all on the CAN bus at once, the PHEV controller can now just decide which messages from the battery ECU to pass along to the rest of the system, and which ones to block and/or modify. If I remember correctly, the hybrid interfaces BMS+ works this way. Plugin-Supply and others may also use variants of this approach.

3) The "ultimate" evolution of this concept in some opinions is to just remove the NimH pack and stock battery ECU all together. Now you don't have to worry about intercepting the stock controllers messages, because they don't exist. However the PHEV controller is now responsible for providing all the data that the hybrid ECU expects to see from the battery ECU to stay happy. I believe this approach has been used by some commercial conversions, and is essentially the approach used by Toyota in the PiP. This approach has largely been beyond most DIY converters, with the notable exception of a project undertaken by a user on this board that goes by peef. There is now an open source project by user jdh2550 to recreate and expand on peef's work and make it more accessible to the general community.

Rob

 

Some good info/resources:
The original home of the cal-cars open source PriusPlus project. Now mostly historical, but still some good learnings and insights that drove later conversion methods:
PriusPlus - EAA-PHEV

Hybrid Interfaces BMS+, also maker of the now (I believe) discontinued CAN View.
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Work by lopezjm2001 to recreate the CAN View functionality on a standard development board:
My Duinomite Mega Canview V4 equivalent Project | PriusChat

Good thread on a project to adapt the BMS+, originally designed for adding multiplt stock NiMH packs to a single large Li add-on pack.
Planing CanView and BMS+ conversion with lithium | PriusChat

Thread by pEEf on his complete pack replacement conversion project:
Update and technical details on my PHEV project | PriusChat

JDH2550's thread on recreating/building on pEEfs approach with an open source project:
YAPiP - recreating pEEf's approach | PriusChat

Reports on a user who's gotten particularly good results with an Enginer kit. (as well as some of the drama that can happen with the small companies trying to build these kits):
107 mpg. 1,100 mile tank. Enginer system back on track. | PriusChat

Reports from a user who's getting good results from a Plug-in Supply conversion. (as well as some of the drama that can happen with the small companies trying to build these kits)
Plug-In Supply DIY | Page 12 | PriusChat

 

Wow... Thanks much for the excellent in-depth reply.

I learned lots from it.

The thing that gets me is that car manufacturer's don't do what tech companies do when it comes to sparking innovation by strategically open sourcing aspects of their technology. For example, Google, Twitter and Facebook have annual events where they bring all the best hackers they can find and feed them and give them the type of code access that they need to innovate new ideas. Of course the integration/execution of new code ideas for internet companies is way easier than the integration/execution of new technologies in a motor vehicle.

Perhaps the solution/goal for long term innovation is this:

Hey Toyota!

Please build us a 2014 PriusChat Edition Prius!

This car would be specifically designed with loads of extras, especially firmaware flashing opportunities, lots of easter eggs too... We need a car designed specific to inspiring the most talented tinkerers and modders to further advance this car's technologies.

Imagine if we had a decent GUI that would make it easy to adjust and then save all the car's primary settings for each specific driving condition? Once you have finely tuned these settings and saved them, then the car can learn your driving routes and choose the appropriate settings for each scenario automatically.

What if we had a developer tool kit that would allow us to add hardware and add software/firmware to car? (for example: sensor controlled grill blocking vent system)

Another example is how the new Hybrid BMW will use topo maps so the car knows how much recharge is available going down the other side of the mountain and thus then knows how the limit how much power it can discharge going up the mountain.

Point being, the future of cars is about the car being way more responsive to site-specific driving conditions for not just fuel economy, but for helping the driver from avoiding traffic, not getting lost, text loved ones if airbags deploy, or car loses traction for extended period of time, etc.

And all these innovations ramp us up to the self-driving car that have already logged 300K miles on public roads. How do you think Google plans to introduce their car to the market?

So for all these reasons and many others: I wish Toyota would become an even greater leader in the advancement car technology by offering a 2014 PriusChat Edition Prius!

 

Thanks camper, that would be awesome I think a lot of the reluctance to work with the "hackers" has to do with the stakes/liability. If your app crashes, nobody dies I wish there was a way for more collaboration, but I think Toyota does deserve some credit in that I don't think they've ever taken action to try and block people from experimenting & modifying their vehicles. The same certainly can't be said for some tech companies. To some extent its clear to me at least that the converter community is a big part of the reason we have a PiP though. They proved it could be done, could be effective, and created a lot of buzz driving demand. Toyota spent years saying it wouldn't make sense, and no one would want it. Then they gave in and built it

 

or you can trade in on a pip!

 

Exactly!!!

 

Exactly!!!

 

Wow! Loved your earlier post. Prior to pEEf's project car post, he posted Battery ECU secrets and teardown (warning: geek content) | PriusChat.

I, Danny, cproaudio (I think), Jack Chen (of Enginer ), efusco, and a few others (?) all had the privilege of driving pEEf's project car at Green Drive Expo last year.

Unfortunately for us, it seems that he's moved onto Leaf projects and EVSE upgrades now. There are some folks on MNL who are clamoring for cool stuff from him like My Nissan Leaf Forum • View topic - LEAFSCAN - The Ultimate Instrument for your LEAF!.

 

I think what you're looking for once it's fully developed and available is a separate system that will sell for around $3k. It will puts electric motors on your rear wheels: Turn Your Car Into a Plug-In Hybrid for $3,000 | Autopia | Wired.com

 

I'm not sure if you realize that there is no dedicated starter motor in the Prius. MG1 and MG2 are integrated inside the power split device. To give you an idea, see links below:
Prius Palm Mileage Simulator - you may have to click the Planetary Gear Set link
Toyota Prius - Power Split Device

Graham's Toyota Prius (under Understanding the Prius)
Hybrid Components

 

Other problem do arise one being speed limitation of the stock system to about 40+mph in electric only mode above this the engine has to spin (without fuel) to stop MG1 over speeding and destroying itself.