YAPiP - recreating pEEf's approach

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

  1. miscrms

    miscrms Plug Envious Member

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    I don't think its accurate to say that the the Prius controllers tries to cycle the range from 40 to 80%. Not sure you were trying to say that, but wasn't sure. In general the controller tries to maintain 60%, and takes aggressive action to keep it within 40-80%. The irony of the (non-PHEV or CS PHEV) Prius is that its most efficient when the battery is used as little as possible. The battery is basically just there to compensate for inefficient driving :)

    I believe this is part of the reason why most all of the PHEV packs I've seen use a higher voltage than the stock pack. That way when they are fairly full the Prius is in a mode where it tries to use more electric power to bring SOC down (increasing use of electric drive), and when getting toward empty the Prius will just try to maintain SOC. As the Prius tracks SOC by Wh not Volts, the actual amount of energy it will try to draw and replace in this mode is very small compared to the capacity of the PHEV pack.

    Taking for example the Realforce pack that jdh is using, with (I believe) 72 cells it should have a full resting voltage of about 252 Volts. At ~80% DOD it should be getting down to ~215-220V. This is right about where the stock pack would have been sitting at 60% anyway. Basing this on data from the Enginer spec sheet * 4.5 packs.
    http://www.enginer.us/img/48V80AHBatterySpecification.pdf

    Now of course this is all kind of moot in the peef/jdh approach as not only is the stock pack taken out but so is the stock battery controller, which is the box that tells the hybrid ECU to send power to the battery when its low. So in this approach, the charge/discharge/SOC messages can be tailored to match the desired behavior for the single large pack at any given actual SOC.

    or something like that ;)

    Rob
     
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  2. vertex

    vertex Active Member

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    I think we were saying the same thing about the battery charge range. And you are correct about the peef approach. The point that I was trying to make is that the algorithm can be tricky when you switch from EV only to normal Prius operation, which may need to occur at any state of charge. You then need to stay at that nominal SOC and operate around it. Certainly doable. WE really don't know exactly what PEEF did about this do we?
     
  3. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Hi Vertex,

    Yes, you're right about the existing contactors - however, they're controlled directly from the Hybrid ECU and their operation is checked at the beginning of the drive and then don't change. The contactor's to separate pack A from pack B wouldn't necessarily get checked at the beginning of the drive (without more software and more complexity) and they would have to operate during the drive (as the switch from A to B has to occur while driving).

    Remember that we will be spoofing the SOC that the Hybrid ECU sees - call that sSOC. I will be tracking real SOC separately (by counting Ah) - call this one rSOC. So, when I need to switch from EV only to "blended mode" then I can make sSOC look like it would in a normal Prius. This might be as easy as basing sSOC as if it were attached to a 6Ah battery pack (which I believe is the size of the original NiMH pack). For example if I need to enter blended mode at the end of a run and I know that the Prius likes no less than 40% sSOC of the real pack and no more than 80% sSOC. For the NiMH pack this equates to 2.4Ah and 4.8Ah and a usable range of 2.4Ah. Now, I want to run my pack no lower than 80%DOD (20% rSOC) - which for the real pack is 8Ah. I know I need 2.4Ah more capacity than that for the existing algo's to keep from going below that - so, if I switch on blended mode when I'm at 10.4Ah (or 26% rSOC) I should be good. If I want to switch on blended mode earlier (for more HP) then I simply add an offset to account for that. In the case of switching on blended mode for more HP then if I want to get fancy my sSOC spoofing algo can allow for the rSOC to drift downwards towards 26% rSOC before "really" switching to blended mode. Or it maybe better to have the blended algo attempt to maintain rSOC as well as sSOC and thus "save" the electrical energy for use at the end of the journey (because a typical journey pattern might be slow at the beginning - fast in the middle - slow at the end).

    Does that make any sense? It almost makes sense to me... ;)

    Let's try summarizing:

    rSOC > 26% and power request < 20kW = use EV only
    rSOC < 26% = use blended mode and have algo's attempt to maintain 23% rSOC (60% sSOC)
    rSOC > 26% and power request > 20kW = use blended mode and have algo's allow rSOC to fall towards 26% by favoring EV more than original blended algo.

    Yup - I'm making this up as I go along - but, hey, that's what makes it fun!:D
     
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  4. miscrms

    miscrms Plug Envious Member

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    IMHO once the stock pack is gone, you really only need to approximate the stock Prius operation under a few pretty clearly definable conditions, and I'm not sure it needs to "copy" the Prius mode very closely. Part of the advantage of removing the stock pack/battery ECU is to free yourself from those constraints.

    Charge Sustain mode would be desirable either when PHEV battery reaches some predefined real SOC level, or when manually called (like HV mode on PiP) to save charge for later. This could look pretty much just like the Prius stock operation, but doesn't have to be that exact. As I think jdh indicated, you'd just want some trigger value of rSOC where this mode starts, and then a lower limit and upper limit where CDL/CCL/sSOC values are used to keep the rSOC value in that window. That could look like the used capacity range of the stock pack, but I'm not sure the actual capacity range is that critical. DOE testing on the first Prius found little impact on effective mpgs with a 50% degraded stock pack capacity in their accelerated end-of-life tests. Similarly early experimenters doubled the size of the stock battery and also found not much difference in effective mpg in standard hybrid mode, besides perhaps the more efficient capture of regen energy due to the reduced series resistance.

    More important likely is to design this range to protect the Li pack, so you're not trying to draw to many Amps from a highly discharged pack affecting cycle life and introducing inefficiencies due to voltage sag once the phev battery falls off the Voltage vs. SOC cliff. In that case something analogous to the SOC Drift recalibrartion of the stock ECU could be useful, though in a PHEV which should always start from a known SOC level it may not really be necessary as there is effectively a reset of the coulomb counter after every re-charge.

    Other non-standard Prius modes will also be important, but again should be tailored to the health of the Li pack rather then simply mimicking the stock Prius operation. Such modes would include using CDL/CCL/sSOC to protect the PHEV pack at very low and high battery temperatures for example, and controlling the ventilation fan as appropriate. There would also ideally be some protection against overcharging, say in an event where the phev battery is freshly charged and then a big regen event occurs for those who live/recharge at the top of mountains ;)

    In some ways that may be the most challenging part of this type of conversion, understanding your Li pack well enough to know how to set the software limits to protect it adequately without unduly sacrificing range or efficiency.

    Rob
     
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  5. roflwaffle

    roflwaffle Member

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    I think that's the advantage of keeping and isolating the stock pack. Instead of tailoring the new ECU to compensate for the different characteristics of the add-on pack, the owner can just remove it from operation once it's SOC reaches some value and the car will behave like a normal hybrid. I'm not sure if pEEf's approach, intercepting and modifying CAN bus communication, is easier than creating a new battery ECU, but it seems like it would be. That said, I'm pretty sure jdh's work will allow someone to take either approach, so it's not like these options are exclusive.

    Either way, I think that the add-on pack alone would need to be babied relative to the stock pack because it can't take high discharges at low SOCs as well when operating alone, and if it's in parallel with the stock pack there's the risk of the stock pack dragging it below what it can safely handle, so it would need to be isolated past a certain SOC in that case.
     
  6. miscrms

    miscrms Plug Envious Member

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    Just to clarify peef pioneered the complete pack/ecu removal for diy conversions, jdh is building on that work. There are other conversions that do as you say and intercept messages between the stock ecu and the rest of the CAN bus, I believe the BMS+ approach and some commercial conversions such as PIS use variations of this method.

    Certainly both approaches have their pros and cons. At least Toyota does seem to think there is a solution, as this is essentially the approach they have taken in the PiP (Li only with custom controller/software).

    FWIW the datasheet for the A123 20Ah pouch cells that a number of people on the board are looking at or using seems to indicate there are Li cells that are up to taking the regen load at low SOC.
    http://info.a123systems.com/Portals/133376/docs/a123%20systems%20amp20%20data%20sheet.pdf
    At 10% SOC, the battery still supports 600W or >182A of current for 10s. In an 8kW pack it would be double that. So at least for these batteries it doesn't seem like 100A regen even at 10% SOC would be very stressful. Its a little more of an unknown how cheaper Chinese cells will hold up, but that's part of the experiment ;)
     
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  7. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Yup & Yup.

    As far as cell choice goes - two very important things to remember about me: I'm cheap and I'm lazy*.

    I got the RF cells from Enginer at a good price *including* packaging them and wiring them.

    I am not aware of anyone else who sells cells by the seashore that are pre-packaged and ready to use. (Pouch cells that is).

    * actually "impatient" would be more accurate - but I'm always up for poking fun at myself because I am such an EASY target!
     
  8. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Yup.

    I think my way/peef's way is "mo' better" than what you suggested but your way may be slightly less work.

    Dang, I guess I'm not lazy enough...
     
  9. NortTexSalv04Prius

    NortTexSalv04Prius Active Member

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    JDH/Lopez
    The OEM pansonic HV pack is (consist of) 28(7.2vdc nimh 6-7 ah cells) for a overal 201 vdc....
    Based on the above I have the following quest/question.....Could I or someone make a custom battery pack to replace the above oem replaced with(for example) 3.2vdc Lifepo4 10-7ah cells until you have 201vdc.(say 64 to 66 cells 8ah) 204 to 211 vdc for example.......then check to if works on vehicle until you get no DTC....
     
  10. Flying White Dutchman

    Flying White Dutchman Senior Member

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    you will get a DTC because the OEM got 14 cell monitor sensors and things like that.
    you need a new BMS board te replace or fake the OEM one.
     
  11. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Yup - I agree with FWD.

    However, I'm curious - what would you gain by replacing the OEM pack with a LiFePO4 pack of the same specs?

    IMO, unless you're going to significantly increase capacity and implement some sort of additional control to take advantage of the extra capacity then it's really not worth the headache of changing away from stock.

    If you have a dead OEM pack you'd be better off refurbishing it yourself or buying a refurbished one.
     
  12. lopezjm2001

    lopezjm2001 Senior Member

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    The only thing you would gain is a higher power density. The battery would be a fraction of the size of the OEM. It would need be protected against high charge and discharge currents over the rated (discharge - 5C = 32.5 amps, charge - 2C = 13 amps) by an additional BMS and it would be very ineffective to assist the ICE. Limited regenerative braking. Next to useless. It could take higher charge and discharge currents but only for a short period of time. You would still need to fool the OEM BMS by using a voltage divider network connected to the cell voltage sensors, spoof SoC otherwise the usable SOC is limited to 40% = 2.6 AH. It would just not be worth the effort.
     
  13. NortTexSalv04Prius

    NortTexSalv04Prius Active Member

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    Thanks
    I kinda did not consider the OEM BMS .........what do the oem cell monitors do???... I have seen an image of a modify oem pack using the blue round headways and was curious..........
     
  14. NortTexSalv04Prius

    NortTexSalv04Prius Active Member

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    Thanks
    Probably be alot of effort for poor results.......
     
  15. roflwaffle

    roflwaffle Member

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    I'm not seeing where A123 is showing how stressful the effects of high +/- C rates is... The only thing they show is the degradation at +1C/-2C, not at a mix of +1C to +8C/-1C to -4C, which seems to be what a 5+kWh Li pack would see in a Prius. If A123/Winston/etc cells can handle that and still manage to only degrade to 80% of capacity after 3000 cycles, great! If it turns out that the stock pack can handle certain things without additional degradation, like high +/- C rates better, then I think it would be advantageous if users could optimize pack use instead of having to replace the Li pack earlier than they would if they kept the NiMH pack and used the Li pack in different ways.

    For that matter, it could be that A123 cells will handle everything with minimal changes in degradation, but maybe Winston cells won't. Otoh, a Winston/NiMH pack that was managed properly might be able to perform almost as well as the A123 pack for a lot less. All I'm talking about is optimizing for lifespan/cost depending on the battery pack configuration/type. I'd say we're a long way off from that since no one has so far determined what the different Li cells will take and what that will cost in terms of cycle life, but it still seems like a worthy objective.


    I'm not sure if optimizing performance depending on different characteristics of different battery packs counts as less work. If someone can't afford or doesn't need a a 6.5kWh A123 system, then designing a controller that can not only handle, but optimize, the use of both the stock pack and a 4kWh Winston pack, if need be, would be useful, and I would think harder. Course it's your project. If you think it's "mo' better" to design something that can only be used with an A123 pack, then that's your call. :p
     
  16. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    Errr, I hope not. Because if I did then I'd definitely be wrong. I'm not using an A123 pack. I'm using RF pouch cells.

    Also, AFAIK, what I design will be able to be used with any single pack - LiFe, LiPo, NiMH, Mr Fusion, Hamsters on a wheel. Each different energy storage source will be able to provide a different amount of power density - this will affect how suitable they are for propelling a Prius and for gathering regen energy (I think the hamsters will get just as tired if their wheel is turned into a high-powered treadmill during regen!). My design (thanks to Toyota's already present control strategies) can be adapted for many different power profiles.

    What it won't be able to do is switch between two separate packs. And that's because I think switching between two packs is sub-optimal for the following reasons:
    - adds a more substantial failure mode
    - requires more hardware (and thus more cost)
    - the OEM pack is big and heavy and not suited for a PHEV (because it was designed for a HEV)

    OK - that's the last I'll type on this particular subject. Onwards and upwards. Or round-and-round in a downwards death spiral. It's all fun to me! :)
     
  17. roflwaffle

    roflwaffle Member

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  18. usnavystgc

    usnavystgc Die Hard DIYer and Ebike enthusiast.

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    Let's not flush it out and hijack JDH's thread. If you want to flush it out, start a new thread. This is a dead horse to me (and I'm sure many others). If you want to do it your way, do it and let JDH do it his way. I'm baffled as to why you're constantly trying to convince him to change his course???? I really don't want you to answer that question though.
     
  19. jdh2550

    jdh2550 Co-Founder, Current Motor Company

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    OK - as some of you know I've been "sidetracked" and working on CAN commands for the DuinoMite Mega development board. I've put that in quotes because on the one hand it's not getting me closer to YaPIP. However, with a bigger picture view the more knowledge about CAN I gain and the more tools I create the better the overall product (oh, and did I tell you all about my plans to replace the MFD after I've got YaPIP working? - that'll require CAN and LIN and GPIOs and SBC and LCDs and oh what fun!).

    However, I really need to get some momentum back on the "main line" for this project. I have a second bECU that I bought of e-bay. My plan is to re-purpose this as a pack monitor. I hope to start working on this sub-project next.

    And in other news - I'm also job-hunting. Paying the mortgage comes first.
     
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  20. roflwaffle

    roflwaffle Member

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    I'm not trying to convince him to change his course, I'm just following up on what other people were talking about and responding to some incorrect conclusions about my assertions. And while the OP did ask for the discussion to be moved to another thread, they also seemed to be OK with a page of discussion about it after they asked for it to be moved, so I figured they were ultimately OK with it, since someone who wasn't probably would have responded to more than just my post on the subject, but either way, you're correct that we should start a new thread on this.