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Parallel Battery Packs

Discussion in 'Gen II Prius Technical Discussion' started by ServoScanMan, Jul 30, 2006.

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  1. ServoScanMan

    ServoScanMan New Member

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    I had some time to kill the other day and noticed a used 2006 Prius HV battery pack on Ebay sold for less than $600 USD. It apparently came out of a car that had less than 6,000 miles. That got me to thinking...uh, oh....not again. :eek: Anyway, if I put 2, 3, or 4 battery packs in parallel, would the ECU know the difference? I'm only dreaming about installing multiple packs and building my own HV plug in charger for the batteries. Thoughts? Is it possible?
  2. efusco

    efusco Troll Slayer Staff Member

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    Yes, it would know the difference, in most situations. It's possible to connect additional battery capacity without triggering error codes however.

    This is no easy job, it is dangerous, and the battery has no means of being cooled, no means of monitoring the temp, and is not protected should you be in an accident....but it can and has been done.
  3. Cheap!

    Cheap! New Member

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    <div class='quotetop'>QUOTE(ServoScanMan @ Jul 30 2006, 07:51 PM) [snapback]294800[/snapback]</div>


    Bwahhh, haaa, haa. Another madman in Texas!

    How far is Lorena from Houston?

    Should we try to conquer the world?
  4. ServoScanMan

    ServoScanMan New Member

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    <div class='quotetop'>QUOTE(Cheap! @ Jul 30 2006, 08:36 PM) [snapback]294819[/snapback]</div>

    Don't you mean, "How far is Houston from Lorena'? :rolleyes: I'm kidding. I'm about 4 hours from Houston, give or take a traffic jam or two.
  5. 200Volts

    200Volts Member

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    What about a second 12V battery?
    Now hear me out before you laugh.... The A/C is driven off the 12V system (from what I've read) so having more 12V amp hours in reserve (or a slower voltage drop in the 12V battery-s) will mean less ICE running to help cool down the car after sitting a while in hot weather.

    or should I move to Texas also?
  6. donee

    donee New Member

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    <div class='quotetop'>QUOTE(200Volts @ Jul 31 2006, 05:08 PM) [snapback]295276[/snapback]</div>

    Hi 200Volts,

    Nope, the AC is run off the 200 volt battery. You should know that Mr. 200Volts! Don't you feel kinda dragged out when its hot outside ? :lol:
  7. hobbit

    hobbit Senior Member

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    Go read Wayne Brown's site ... http://privatenrg.com/
    Go catch up on the earlier archives of http://calcars.org/ to see
    some of the early problems they ran into...
    .
    Parallel packs are doable and rumor has it that the Prius BMS
    can learn about the larger capacity but you'd better have SOC and
    temp control just as rigid as the Prius ECU itself and all the
    appropriate safety stuff in place.
    .
    _H*
  8. ken1784

    ken1784 SuperMID designer

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    Parallelling NiMH battery is not a good idea.
    I've never seen any good professional application using parallelling NiMH batteries.
    Does anyone see any?

    Ken@Japan
  9. c4

    c4 Active Member

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    The problem with paralleling battery packs is that the two packs must be exactly matched in capacity and charge level.. The problem is mainly with the charging of the packs- you can make things work for a while, but as soon as the two packs show any significant difference in charge level, the whole thing goes unbalanced and you end up cooking one battery while chronically undercharging the other until both batteries are dead.. This is why, except for early testing, all the EV mods have gone with complete battery replacements, or only allowing discharge in parallel and preventing parallel recharging via a diode (the aux pack would then be mains charged, creating a PHEV)..

    Even the 12V systems are not true parallel systems, because they have an isolator in between and the charging paths are independent to prevent battery damage.
  10. ekpolk

    ekpolk The Regenerator

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    At the outset, please forgive my ignorance -- I'm brand new to the Prius thing (just got mine on Saturday), and I'm at best an armchair engineer. All that admitted, what would be advantage to the parallel battery? I certainly have not explored all the dark corners of the "envelope" with my car yet (I've put ~350 miles on it so far, 75/25 highway/city), but I have not seen the HV battery either completely full or completely drained. Since, of course, the battery merely stores energy, rather than generating more of it, how would more capacity help when one battery does not seem to "fill up" by itself?
  11. ServoScanMan

    ServoScanMan New Member

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    <div class='quotetop'>QUOTE(ekpolk @ Aug 1 2006, 12:20 PM) [snapback]295720[/snapback]</div>

    Congrats on the new car.

    It was a pipe dream. I live 10 miles from work. Going to work and coming home there are seperate legs of my route I can go 1.5 miles on battery power alone. I even showed this to my 17yr old son with the AC going. He was impressed. The first 5 minutes of my trip leaving my house and work is the worst mileage because the ICE has to run to warm up. If I had more storage capacity, I could re-charge at night and take advantage of a couple of hills I go down. If I'm going to plug in a charger for the HV batteries I might as well plug in a temperature controlled block heater. This would reduce ICE warmup time.

    Well at least when someone at work tells me it's going to cost me $3,000USD to replace my batteries, I can tell them I saw one on eBay for less than $600USD. Hopefully by then, there will be a Lithium Polymer replacement pack I can buy with a plug-in option. :)
  12. ekpolk

    ekpolk The Regenerator

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    SSM:

    Thanks very much. Actually, mine is "merely" new-to-me (best yet euphemism for "used"?). Previous owner in an eccentric who bought mine two years ago, did her maintenance at the dealership, and walked in last week, checkbook in hand, and said, "I want a red one" (mine's black). So I ended up with a loaded car that has only 15k miles, and looks nearly new. Alas, my 17 year old son is not impressed -- he was enjoying showing up in my last car, a G35 :rolleyes: .

    I've already heard the battery thing a couple times. Judging from the way it's coming across, I think it represents "hybrid mileage envy" and a desire on the part of the speaker to affirm a phony belief that you're not really getting around for that much less than they are. Whatever -- I love the car so far!

    Sure will be interesting to see where the battery technology goes. The more research I do, the less it looks like I'll ever need a replacement, but who knows. :)
  13. mwbueno

    mwbueno New Member

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    <div class='quotetop'>QUOTE(ken1784 @ Jul 31 2006, 08:31 PM) [snapback]295446[/snapback]</div>

    Greetings Master Ken-San,

    I have 120,000+ miles on my 2004 Prius with 90,000 of those miles on my 18Ah parallel system. Both the OEM HV Battery & the parallel auxiliary array test with internal resistances that are well within new specs. I would wager that most Prius with 120,000 miles do not have an OEM internal resistance that is as healthy as mine is.

    I know that my installation is not 'Professional' but, I can attest to the viability of such installations if done correctly. Cooling is a 'BIG' deal however, all this fuss about matching parallel packs & etc is nonsense. I knew it was nonsense before I installed the system because of the testing I did with my 2002 Prius. The reason matching does not have to be worried about is we are never running above 80% SOC nor below 40% SOC. I was careful about matching the voltages within each 'D-Pack' & then I set them up with a nominal of 208.8 Volts DC rather than 201.6 VDC like the OEM system.

    This summer is the first time that I have done a lot of 'City' driving & without even trying, I am gettin 75+ MPG during my 'City' drives & that is in HOT TEXAS with the 'Auto AC' set to 77 F. Out of interest, I have unhooked my 18Ah array & run the same 'City' routes with the same driving style on the OEM and my mileage falls to about 53 MPG. That indicates a 40+% improvement in 'City' mileage.

    I only get about a 5% improvement on the highway but, that could change if I could better control how the extra Ah are used.

    Best Regards,
    Wayne -- http://privatenrg.com
  14. ken1784

    ken1784 SuperMID designer

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    <div class='quotetop'>QUOTE(mwbueno @ Aug 6 2006, 04:32 AM) [snapback]298307[/snapback]</div>

    Hi Master Wayne-san,

    Thank you for the great experimental data.
    The 40+% improvement is huge I think. But, I've heard that Dan did not get any significant improvement with the same batteries as yours, and he is now enjoying 1992 Honda Civic driving. :)
    I would like to know any reason of Dan's case if you know.

    If everybody gets 75+MPG, why doesn't Toyota offer such simple options?

    Best Regards,
    Ken@Japan
  15. ServoScanMan

    ServoScanMan New Member

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    Wayne,

    You're brillant! That's exactly what I was thinking about. I'm impressed with the install and the amount of research you did to accomplish this. Where in Texas do you live?
  16. 1davide

    1davide New Member

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    <div class='quotetop'>QUOTE(ekpolk @ Aug 1 2006, 11:20 AM) [snapback]295720[/snapback]</div>

    The advantage is if you can charge the battery from an outlet: a Plug-in.
    This page goes into more detail why you'd want to do that:
    Hybrids Plus - about PHEVs
    Davide
  17. mwbueno

    mwbueno New Member

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    <div class='quotetop'>QUOTE(ken1784 @ Aug 7 2006, 09:40 PM) [snapback]299411[/snapback]</div>

    Master Ken-San,

    Dan did not add 18Ah like I did. I believe he added 6Ah, he did not have the kind of cooling I set up for mine & because he lives in hilly or mountainous country, we believe that he very likely got his batteries too hot early in the game & may have greatly diminished their functionality or overall usefulness.

    These batteries have much higher internal resistance than the OEM HV Battery does. I determined that I had to add 18Ah to just begin matching the internal resistance that the Prius OEM has with its 6Ah. In other words, my 18Ah array only takes half the charge available even though it is 3 times as large as the OEM. However, if I travel on the highway at normal speeds for 12-20 minutes both the arrays are able to charge up to the 65-67% SOC that the Toyota BMS (Battery Management System) tries to keep our systems at. Then when I come into 'City' traffic again, I have very long EV modes that the Prius 'naturally' (I do not have to use the EV Button) leaves the Prius operating in.

    I have also added a large array of Capacitors that buffer the I/O that catch and/or deliver most of the high voltage pulsing that both arrays would normally turn into heat instead of capturing or delivering so, I am getting a more efficient system all the way around via the following:

    1) I have half the internal resistance of an OEM system in the battery arrays alone.
    2) I have a large capacitor array that drops the overall system resistance even further by buffering the I/O which lessen heat build, captures & or delivers more energy & further reduces the equivalent of internal resistances.
    3) Both battery arrays pretty much share the duty cycle that most OEM systems have to experience so, my system will have greatly extended longevity.

    Toyota, in my opinion, has not done this for the following reasons:

    1) NiMH battery manufacturing is a very large bottleneck for them already. When they started building the Camry Hybrid, they had to reduce the Prius assembly line speeds for a while because NiMH production could not keep up with both Prius & Camry Hybrid assembly lines running at full production.

    2) A Prius with 24Ah of battery would likely cost much more than their market research tells them the market will support. At $3,000 for 6.5Ah, 24Ah might cost somewhere around $10,000-11,000; not to mention much added weight for their kind of design vs. how I have done it. Mine is not superior to theirs at all; mine is 'Garage Hack' without all the safety housing & structural integrity they build into their system.

    3) Toyota has some agreements with Cobasys (via lawsuit settlements) that limit the size & quantity of NiMH sales in the US & many other parts of the world. It is heavily rumored that these 'lawsuits turned to settlements' or agreements are why we don't see the RAV EV vehicle in production right now. Much of the current limitations will begin a gradual reduction starting sometime in 2008 & that is very likely why we are hearing about PHEV & other upcoming improvements to the Prius that all involve more Ah. When Toyota adds these improvements they will far exceed what I have done to my Prius & I will be buying one of those immediately & begin a whole new world of 'Garage Hacking Fun.'

    Best Regards,
    Wayne -- http://privatenrg.com
  18. saechaka

    saechaka Member

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    or how about using the bigger batteries in the HyCam or HiHY. just a thought. thats if they even use a bigger battery.
  19. kammssss

    kammssss Member

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    hey wayne,

    i just started my research on parallel packs, again, and i ran into your set-up. it sure does look good. was it expensive? why aren't more people doing what you're doing? 40% increase is phenomenon! if this is just a direct parallel, without CAN, INVERTERS, and etc., it sounds very doable for regular DIY people like myself. also, do you have any specific directions? i am going to follow you steps. i will be aggressively pursuing this in the following months. i will keep everyone posted. thanks.
  20. drees

    drees Senior Member

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    I know this is a really old thread, but this statement is backwards:

    It's serial battery packs that you have to worry about maintaining an even charge and make sure the packs are matched. This is why on the Tesla's battery pack they have the ability to individually bypass and monitor cells - if one gets weak and no longer matches the performance of the rest of the cells, they bypass it.

    With parallel packs the risk of damage is much lower because the cells will inherently stay matched - if one packs voltage drops lower, the other will top it off.
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