YAPiP - recreating pEEf's approach

Discussion in 'Prius PHEV Plug-In Modifications' started by jdh2550, May 23, 2012.

  1. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    GBS cells are rated at 2C continuous. The 100A is the sustained rate at >60mph. Most of my driving will be around town. If the batteries do puke then I'll have learned something :)

    BTW, Every GBS we've tested so far has had a larger than nominal capacity. Also, I'd rather keep a simple pack topology rather than parallel up a bunch of smaller cells. I'm lazy...

    Here's a couple of diagrams (based on that document that lopez referenced). Figure 1 shows the original setup and Figure 2 shows how it will look when I'm done.

    View attachment BeforeAndAfter.pdf
     
  2. DaveAK

    DaveAK New Member

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    I'd prefer to build an A123 pack, but I never get any of my projects finished because there's always something new to try. Tried and tested is the way to go if you ever want to get on the road. :)

    Right now I'm thinking electric Jensen again. :D
     
  3. cgates30

    cgates30 Junior Member

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    Replacing the existing battery pack and replacing the hEMC is an interesting alternative to the contactor method. How reliable is the AVR? Will those die before the pack? If there's ever a problem with the AVR then the car is dead in the water and you'd have to self support yourself getting it to work again. (a stealership wouldn't know what to do other than rebuilt the entire hybrid system for the cost of a new PiP....)

    How would the stock hybrid EMC deal with the large capacity LiFePO4 pack? I'm just thinking 3-4 years down the road when I'm ready for a "new" hobby and want to sell the car. Would it be a matter of just removing the AVR and putting the hEMC back in, or would I have to also replace the NiMH battery?

    Thanks!
     
  4. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    I'm replacing the battery ECU not the hybrid ECU. The former is a relatively simple device with just a few message of interest wherea the latter is the heart of the system and very complex. (BTW, I made the exact same mistake when talking to pEEf)

    The development board, is just that - a board for prototyping with. It won't make for an ultra reiabe system. However the Atmel chips are auotmotive grade and are top quality.

    You make a good point about reliability - however, I think the real issue is "failure mode" not "reliability". One could argue that this approach should be more reliable than the contactor method because it's less intrusive and there are less parts - hence less failure points. However if it fails there is a chance that the failure would be worse than a contactor design (although one would have to do FMEA on a specific design to know for sure). To be "picky" you wouldn't be "dead in the water" as in "stranded". You should be able to limp home on ICE power only.


    Using the stock setup with a large LiFePO4 pack would be a non-starter. All Toyota's algorithms are based on the specific NiMH pack that they install.

    However, it will actually be easier to put this system back to stock than a contactor system. Siply unplug the new bECU and plug in the old one. Unplug the new large pack and plug in the old NiMH pack (OK - you'd either have to keep that pack conditioned or source another pack.)

    Obviously all of the above is just my opinion. It would be interesting to hear from the designer of a contacor systems - the trouble is most of those folks are commercial enterprises. So, they're likely even more biased than I am ;-)
     
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  5. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Step zero is complete - sitting in my driveway is an '05 Prius. I'm just back from driving out to VA, trading in the Focus and driving back in the Prius. Ah, the things we do for "love" ;-)

    I got a high mileage car with a dying pack. 200K miles but she still drives really smoothly and rattle free. The MFD is showing the "issue with the hybrid system" icon - but seeing as the motors work (and hence the inverter) and that the battery level yo-yo's up and down I'm guessing it's just the signs of a dying pack (no capacity left). On the drive home it actually got to the stage where MG2 just gives up and shuts down. Cycling the power (and being a bit more gentle on the pack) gets things going again.

    She's also "cosmetically challenged" - but structurally sound. I'm thinking I'm going to do a vehicle wrap when I'm done. That will hide the exterior blemishes. Not quite sure what to do about the interior :-(

    There are also some other issues. However, I paid well beow market rate and the less I spend on the car the more I have for the conversion components...

    Oh, and the AVR dev board came in today as well. Hopefully I can get some sort of CAN equivalent of "Hello World" up and running this weekend...
     
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  6. cgates30

    cgates30 Junior Member

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    Well this will be interesting. Arduino-like turn around time. :)
     
  7. cgates30

    cgates30 Junior Member

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    So I have the car and interest in doing the conversion. I like the concept of replacing the NiMH pack over the contactor method, but as far as I know pEEF's car is the only one [so far] converted as such. I'm still in the mode of studying the components of the system.

    My need (want) is to get 30 miles AER in town (less than 45 mph). I'll assume 200 w-hr/mile. I'm thinking the A123 20Amp-hr prismatic cells are a good choice based on their charging/discharging ratings, price on eBay, etc. People have reported 18-18.5 Amp-hr capacity. I'll also assume 80% DOD for my cycle. Doing the math it looks like I need 8.25 kw-hr total capacity. If the batteries give 3.3 V (not sure why they're different from other LiFePO4's, but ...) and you use 70 (which is what folks are using for the contactor design, maybe this isn't optimal for the pack replacement design), then you have to make two 70-cell strings in parallel and you end up with about 8.3 kw-hr.

    This adds up to $4400 for batteries, ~$1000 for BMS, $500 charger, and $1000 misc. About $7000 plus your personal commitment. I guess I could accept half the range and squeeze below the $5000 radar and have range comparable with the PiP. I still have to finalize my own project scope.

    You bring up a good point. Going through an FMEA would be a good idea. I think in a case like this you have use discouraging language to make people 3 degrees of freedom away to realize the risk, but at least it would be written down and people can weigh in on it.

    Okay, AVR=development board, Atmel is the chip to be programmed and installed. Also, hECM and bECM are different things. We're not talking about changing the hECM, just the battery ECU.

    Good luck on getting started! At least things are coming together over a holiday weekend.
     
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  8. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Hi cgates,

    Your math seems about right to me. Personally I'd use 250 wh/mile. Although top speed around town is lower there is more stop start and accels are where you see peak draw. Also, I'd choose 72 not 70 as that will match me and pEEf. I don't know whether it's best to do 72SP2 or P272S (i.e. either connect two 72 series strings together or connect 72 blocks of paralleled cells together). I've not seen a discussion on that - but I suspect that the latter (72 blocks) is better as that's what I've more commonly seen.

    Your BOM looks about right (see mine earlier in this thread). You'll probably need a little more like 750 for the charger - unless you have something in mind?

    The one thing I haven't sourced or priced yet is upgraded springs for the rear shocks. This shouldn't be strictly necessary (because driver + pack is still within rated carrying capacity) but is recommended.

    Check out the PDF I posted for a break down of the modules and what my new architecture will look like. Also look at the document that lopez linked too (which is where I got the diagram).

    As far as commitment goes - I'm doing this entirely as an open-source for-fun-not-profit project. No commitments from me as to whether it will work or not and certainly no commitment for any particular deliverable. I have a lot on my plate with the day job - but I love this stuff and I've been wanting to do it for while and I now have everything I need. If you want to follow along that's great - but if you need me to finish first before you can complete your project then I strongly suggest you wait until I have something fully working. At any point along the way there's a chance I'll have to put it on hold due to other commitments.
     
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  9. lopezjm2001

    lopezjm2001 Senior Member

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    Upgraded springs are for additional 300 pounds weight. It lifts the rear tyre arch about two inches above top of wheels for a Prius without a PHEV kit. Since you are removing the old NiMH I would not think it would be be necessary.

    Having your wheel arch sitting two inches higher may not be a good look.
     
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  10. seilerts

    seilerts Battery Curmudgeon

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    I'd love to see info about this as well. This would be the ultimate EV conversion. Great minds think alike :D. I could get it as far as mounting a Netgain motor of your choice to the transaxle, but making the controller talk to the HV ECU and vice-versa would be an absolute devil.

    But, wow, just imagine what it could do. For those of you that think three electric motors are overkill, consider that you have three electric motors with nominal ranges of 0-5000 rpm, connected to a planetery gear set. That gives you a true CVT: an infinite range of gear ratios. With all that low-end torque, it would be fast off the line, and infinite ratios with two powerful motors would allow for high top speed, but at the same time the MG2 and the Netgain could be dialed in for an optimal cruising range. It does add more weight, which is why a single motor is usually preferred, but doing this on a Prius preserves all the conveniences like the brake actuator, regen, and A/C.

    Anyway, back to topic. jdh2550, good luck!
     
  11. cgates30

    cgates30 Junior Member

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    Sorry, I meant the commitment of the person undertaking their own conversion. I suggest anybody reading this to realize this could be a weeks/months/year, if ever completed project.
     
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  12. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Ah. Sorry I misunderstood. Yep I agree with you 100% . Reader beware!
     
  13. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Hmm I'd never thought of it quite like that. That might very well make for the ultimate EV. Very cool.

    Yet another reason for YAPiP... so I better get the darn thing working...
     
  14. lopezjm2001

    lopezjm2001 Senior Member

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    Your open source project could one day become a small business enterprise. Simillarly Dimitri started an open source thread:

    MiniBMS - open source project - DIY Electric Car Forums

    and turned it into a business, whether it was his intention to make it a busines does not matter. It would just mean you have to stand behind your product. If you end up going down this path you may want to consider if your AVR could be used with the contactor method and consider the commercial viability of using the pEEF method.
     
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  15. MJFrog

    MJFrog Active Member

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    With the battery level doing yo-yo's, it DOES sound like the HV pack is going. But just to be sure, test the 12v battery and replace if necessary. You might save a heap of $$$ over replacing the HV pack.
     
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  16. cgates30

    cgates30 Junior Member

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    Yeah, but I think his objective is to remove the HV pack anyway to make room for his non-contactor based conversion.
     
  17. chenyj

    chenyj Member

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    I would recommend to keep the stock traction battery as the backup if the lithium pack has problem/glitch.

    If the plan is to rewrite Engine ECU messages, it might be the similar task to rewrite the Battery ECU messages as well. The traction pack still has usable capacity. Why wastes it. You can use a relay (which stays on if the kit is running) to isolate the PHEV pack if necessary. Since the Lithium pack has only 72 cells instead of 76 in PIS, it would play nice with the stock traction NiMH pack.

    The spare tire well and the storage compartment should have enough space for 9KWH pack, charger and controller. The extra weight should make little difference in MPG result.
     
  18. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Project Status update: I have the toolchain set up and I can compile apps. I've managed to set the CAN baudrate to 500kbps and I can get my standalone dev board talking to a PC controlled dev board. However, I can't get my dev board talking to the OBD2 connector on the Prius. I'm making some progress - things will go quicker when I get this basic communication working.

    Meanwhile I hooked up a scantool and can confirm that the traction battery pack is bad. IT's throwing two DTCs - one for excessive voltage difference between modules and another reporting that module #13 is bad.

    I am planning on completely removing the NiMH pack - I want thist to be as electrically / mechanically simple as possible. Swap out the NiMH pack and bECU and swap in a LiFePO4 pack and new bECU. It's not really a question of which is "best" - it's that this is the goal I've set myself.

    Onwards and upwards...
     
  19. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Hmmm - not sure I like this new board. I just edited the above post but didn't provide an edit reason and it seems to have eaten all my changes... Oh well here goes again (in a separate post this time...)

    Some clarifications:

    The two DTC's being thrown are:
    Code:
    P0a80 - The difference in voltage between 2 of the blocks in the battery pack is too high 
    P3023 - block 13 is bad
    
    To clarify the design a bit more.

    • I'm using a dev board (development board) with two separate CAN ports.
    • The dev board will entirely replace the existing battery ECU (bECU). To do this it will be responsible for transmitting the existing PIDs that report battery status. It will be connected via the existing connector on the main CAN bus. It will keep track of battery status (amp draw, pack voltage, state of charge, temperature).
    • I will also unplug the engine ECU (eECU) from the MAIN can bus and plug it into the second port of the dev board. This will mean that the eECU is now on it's own SECONDARY can bus. The dev board will act as a bridge between the MAIN bus and the SECONDARY bus.
    • For normal operation it will simply pass through all traffic between the two buses unmolested.
    • For EV only mode it will intercept messages where the hybrid ECU (hECU) is requesting engine power on the MAIN bus and replace them on the SECONDARY bus with requests to spin the engine but with no power. The engine speeds required will be related to the requirements to keep the MGs within operating range. In EV only mode it will also intercept messages requesting engine warmup. EV mode is what pEEf implemented.
    • For PHEV mode (i.e. a mode that works more like a Chevy Volt) algorithms will blend EV only mode and normal operation. The decision between EV and normal mode will mostly involve engine load and throttle position. I may well implement a simple look-up based approach to achieve this (i.e. a calibration map for those familiar with such terminology). I believe this is what pEEf was intending to do but either he didn't get around to it or he didn't post much about it.
    • The difference between "normal" and "PHEV" is that the PHEV algorithms will take more advantage of electrical energy because it knows it has a bigger pack and it knows that we can safely achieve higher electric only speeds.
    • In PHEV mode one tricky thing will be what to do with engine warmup requests - because one doesn't want to demand power from a cold engine. Alternative approaches:
      • "manual warmup": Warmup is commanded by the driver. Pros: Suitable for an initial "development system" - I think this is what pEEf implemented. Cons: but it runs the risk of abusing the engine. Usage Scenario: when the driver knows he's about to exceed range or acceleration he presses a button to tell the engine to warmup.
      • "fixed warmup": Warmup follows standard Prius behavior as soon as PHEV mode is selected - and only allow selecting PHEV at the start of the journey. Pros: Toyota has already solved the issue of how best to handle warmup in this situation. Cons: not as flexible as I'd like it to be. Usage Scenario: When the driver starts the car he chooses between EV only knowing his journey doesn't involve freeways and is within EV only range or PHEV if he expects freeway driving or longer range.
      • "intelligent warmup". I've no detailed ideas yet on how to implement this scheme - but basically the system needs to be predictive and warmup the engine before demanding power from the engine. A lot of this intelligence will have to be based on what performance is possible in EV only mode. In the following I'll use speed as a proxy for load (but it needs to be load based not speed based). If I were to determine that EV only gives adequate throttle response in all cases below 60mph then I could inhibit warmup until I see a speed of 50mph. However, a more sophisticated system might also take into account actual acceleration and/or commanded acceleration. Pros: If it works then it makes PHEV the dominant mode - "set it and forget it". EV only mode would still have use for drivers who know exactly when they want to use electric only. Cons: If I don't get the algorithms right then I'll abuse the engine.
    Action plan:
    1) Get CAN communication between dev board and Prius working
    2) Use dev board as a CAN message logger to build up my knowledge of the messages first hand. I also want to build up more knowledge about ICE, MG1 & MG2 interaction.
    3) Implement a bECU replacement working with existing pack
    4) Replace pack with a pluggable 9kWh LiFePO4 pack and update bECU code to handle larger pack
    5) Separate eECU onto separate bus but with all traffic a straight pass through
    6) Implement EV only mode
    7) Implement PHEV mode with manual or fixed warmup
    8) Implement "Intelligent warmup"
    9) Rejoice.

    Progress:
    Started work on step one on 5/26. Currently have dev board connecting to a known good CAN system at 500kbps. However, it's not yet communicating with Prius.

    Next Step:
    Hook up the known good CAN source to the Prius OBD2 connector. This will confirm connection parameters and isolate the problem in the dev board (either hardware or more likely the software)

    So, I've a long ways to go yet. But that's fine - I'm more interested in the learning and doing than the using (otherwise I'd purchase an Enginer or PIS kit -- or I'd buy pEEf's car).

    In the meantime - does anyone know how the standard Prius handles warmup? Does anyone know how Volt handles warmup?

    Thanks.
     
  20. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    jd,
    I think I have the perfect solution for the warm up issue. It is an ECT spoofer designed by ccdisce. Here are the details of it (A Prius ECT Spoofer MCU Controlled | PriusChat). In summary, it allows normal op to 104 deg F and then spoofs the ICE temp to 168. Come to a stop, do an idle check and transition to S4. You can be in S4 in less than a minute in the summer and about 2 minutes in winter. It works flawlessly. I have been using it for 3 months with no issues, others have been using it longer. cc is a great guy but, I'm not sure he is willing to mass produce them for us but, according to his last post, he is going to etch some more boards.

    Let me know what you think.