Phev Kit, and using torque app to monitor hv battery amps help

Discussion in 'Prius PHEV Plug-In Modifications' started by glyndwr, Jan 8, 2014.

  1. glyndwr

    glyndwr Member

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    Hi all

    I have a self buld pis kit and a 7kwh lifepo4 battery.

    On the phev battery i have a jld404 ah counter / monitor display.

    Ok, i am abit baffled with the readings i am getting.

    Using torque app and samsung phone i am monitoring the hv battery amps whilst driving, i have used this alot even before i fitted the phev kit and was confident of the readings.

    Anyhow, today whilst driving at 30mph, the torque app hvbattery amps was reading 25 amps, my jld404 was reading 50 amps, i also had a DC clampmeter on the phev cables and the clampmeter was reading 49 amps, basically the same as the jld404, so i can assure myself that the jld404 is reading correct.

    With the phev kit in parallel, i would have thought that my jld404 would always read lower and approx 1/2 of what the hvbattery amps is reading as the packs are in parallel.

    I`m scrqtcing my head here, and can only conclude that the prius pid for hv battery amps reading is not correct or calculating properly.

    Can any other phev owners maybe read what amps they are pulling from their packs whilst driving on a flat road at 30mph please, I can compqre to my readings then. Thanks.

    Any input very much appreciated.

    Thanks.
     
  2. pjc

    pjc Member

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    From my experience, if you are on a flat at 30 mph and just maintaining speed, 25A is closer to the right amount. 50A would produce some noticeable acceleration. Are you sure you didn't have 25A going to the inverter and 25A into the OEM HV battery?
     
  3. glyndwr

    glyndwr Member

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    Hi pjc,

    from what i observed, the reported amps in the torque app is nigh on always 1/2 of waht my pack is reporting. I have noticed this on a few test drives now, i checked my jld404 settings with a clampmeter i own, but i borrowed another one from a friend just to make sure my clampmeter was reading ok. So both clampmeters match what the jld404 is reading.

    I am a mechanical trained engineer thats trying to get thoughts around electics, and these readings confuse me alittle.

    Lets say, for instance, the cars motor is demanding 30 amps, and i have 2 packs in parallel, then if the packs were the same chemistry and resistance, then i would asume each pack would output the same 15 amps.

    Now, with my pack being lifepo4 and having less resistance (from what i have read) then the lifepo4 pack would carry more of the load than the nimh.

    from what i am reading on my guages, it would seem that the prius battery isnt doing much at all, and the phev pack is carrying nigh on all the load, something i wasnt calculating for to be honest.

    The batteries i have a are 33ah capacity and have a max constant discharge of 2C, so the way i am looking at it now, the phev battery is running at max load most if not all the time.

    I was hoping they would be running more to 1C most of the time.

    Any suggestions?

    Thanks
     
  4. Britprius

    Britprius Senior Member

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    If the battery voltage in the lifepo4 is higher than the nimh and is also lower internal resistance then the lifepo4 pack would carry all the current unless it's voltage sagged below or down to that of the nimh.

    John (Britprius)
     
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  5. glyndwr

    glyndwr Member

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    Hi John,

    well at rest the phev pack is 250v fully charged. i have got 76 cells is series and fully charged the rest at approx 3.31v, some alittle higher, some alittle lower depending on how well i have manually balanced, but they are all within 10mV.

    The instant the phev contactor opens, the pack voltage settles to the oem voltage under sag. The way the pis system is working the ocntactor is coming in and out frequently as and when requiring additinal power. That to me though doesnt explain the currnt rate of 2 times the recorded oem rate unless the current from the phev is doing 1, all the work to power the cars motor, and 2 at the same type adding capacity into the oem battery.

    maybe this is why i am seeing this load differential, if it is the case then i maybe need to nurse the batteries to stop workjing them too hard.


     
  6. mrbigh

    mrbigh Prius Absolutum Dominium

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    I have the same experience in my PHEV conversion. Tried secondary packs with NiMH and LiFepo4.
     
  7. Britprius

    Britprius Senior Member

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    Yes effectively whenever you put two batteries in parallel, the higher voltage battery will charge the lower voltage battery unless you have a blocking diode to stop this happening. A diode only conducts in one direction. Unfortunately no use where you wish to capture regen to charge the battery.
    The only way to reduce the current flow is to reduce the voltage so that the batteries are more evenly matched.

    John (Britprius)
     
  8. planetaire

    planetaire Plug in 20 kWh 85 km/h or > 208km range

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    Glyndwr.

    In summer you need about 4kW on a flat road with tires well inflated.
    If your voltage is 230v then the amperage is between 17 and 18 Amp.

    kw_kmh_mph.PNG

    Because of the boost converter, current is not constant. There are important and quick variations.
    They can be seen reading passive pid on the can bus.
    The 17-18 Amp is an average value.


    :)
     
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  9. glyndwr

    glyndwr Member

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    Hi John,

    i did try that approach too, i fitted 70 cells as a test and run it. Because of the voltage sag at those current levels, the sag dropped too low to influence the pis kit to keep the oem battery in the green range, hence i went back to 76 cells, basically the extra cells are counter effecting the voltage sag under load.
    maybe there is a halfway house i can try, 72 or 74 cells. Its something that maybe i can try to see if it has a beneficial effect on the current draw from the phev pack

    Thanks for the input.

     
  10. Britprius

    Britprius Senior Member

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    I think that is the way to go. I should point out here that I have know experience with with PHV conversions but I was an EE specializing in servo motor control systems (industrial robots), so the Prius drives are not very different in operation.
    As I have said before I may give this a go myself if I can pull some bits together at a good price "being retired". Time is also a problem now I've retired I do not know how I found the time to work.

    John (Britprius)
     
  11. glyndwr

    glyndwr Member

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    Hi John,

    I myself am a mech eng, (49yr old) used to work for sony in south wales making tvs in a fully automated production line, specialise in equipment installation, facilities and maintenance. Had done some plc programming too.

    I am now a full time carer, i have a 16yr old disabled lad that was brain damaged from birth. Had to give up work when he was 5 to be his full time carer, i too sometimes wonder how i had time to work.

    This type of project keeps my mind occupied as well as keeping my hand into techie stuff.

    I got my equipment quite cheap, all used, batteries are 33ah lifepo4, and have good capacity, i was lucky enough to pick up 120 of them for a bargain to be honest. Tested 3 random cells last week using an 8 amp load from a resting voltage of 3.32v. They all gave up 30ah capacity and i stopped the load when the cell was at 2.7v, so there was still alittle to come out of them. I was pleased with that to be honest.
    If i could have afforded it i would have prefered a larger ah capacity cell, but my budget for these types of hobbies is tight.
    Grumpyb had a great deal the other day on 200ah thuderskys, i wish i had the monet for them, i would have had a set and converted a car to ev, those batteries were a bargain.

    Thanks for the help and advice.

     
  12. Britprius

    Britprius Senior Member

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    Done some very rough basic calculations:- At 0.025 ohms, average resistance of a pair of Prius modules, the battery would have a resistance of 0.35 ohms. A voltage of 8 volts across this resistance the possible difference between the two batteries would give a current of:- 8 divided 0.35 = 22 amps. This would be the charge current into the nimh battery assuming no other losses.

    John (Britprius)
     
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  13. Britprius

    Britprius Senior Member

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    I did some work in the Sony plant. Cannot remember much about it though. I have done work in most of the major production plants in this country from the Royal Mint, car production, north sea oil, and nuclear also many other places across the world.
    I am quickly approaching 70, but like to keep the brain ticking over even if little else works.

    John (Britprius)
     
  14. glyndwr

    glyndwr Member

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    thanks john,

    i hope i am as enthusiastic with hobbies when i am fast approaching 70 as you are, this is a way for me to keep my mind off other worrying things, so i try to keep as busy as possible.
    My missus is always having a go, nag nag why you spending so much time on the car, jsu go and buy an elecgtric one in the first place.
    1. if i could afford a leaf i`d have one tomorrow
    2. i couldnt sit and watch kyle all day, id go stir crazy
    3. she wouldnt want me in the house all day messing it up for her

    so best place for is working on my hobbies
     
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  15. Britprius

    Britprius Senior Member

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    I know exactly where your coming from.

    John (Britprius)
     
  16. mrbigh

    mrbigh Prius Absolutum Dominium

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    Dear people, you'r suffering from the mismatch battery chemistry and properties. You would have to voltage balance both pack in order NOT to have one pack discharging more that the other.
     
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  17. glyndwr

    glyndwr Member

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    Ok small update,

    Warmed the car up with the phev kit off, the oem battery was showing 230v after a short warm up run.

    Done a test this morning using 70 batteries, fully charged was 231v, and indeed due to the match in voltage, did see a more even current draw from the oem and phev batteries when the kit was turned on.

    I took the car for a test un, However, due to the voltage sag I am experiencing only managed to do 3 miles before the oem voltage dropped to 3 bars approx 45% charge.

    I can conclude that I have not got a sufficient budget to do a better job. Lol.

    In reality, I assume a 60 ah battery set running at 1c continuous will have a far less voltage sag under operation, therefore 70 cells in series will work mighty fine.
    But, in my situation, where the current draw at 1.5 c and sometimes 2c means that the extra voltage is required to counter the effect of the sag.

    From what I have read from the earlier types of lifepo4, sag of whic I am experiencing is expected and indeed common.
    The later newer lifepo4 from what I have read are much better and do not sag as much.

    I shall continue to run with 76 cells until such a time where a set of 60or higher ah batteries become available at a price I can afford, I will then upgrade and sell mine on.

    I and a few of my friends so have solar panel systems so we may even utilise these batteries as a recovery system (if better batteries come my way)

    Thanks for reading, hope it helps someone, I for sure have learned and continue to learn this technology, I am for sure glad to have had the experience to fit the kit and learn new stuff along the way.

    Anthony.
     
  18. mrbigh

    mrbigh Prius Absolutum Dominium

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    (y).....
     
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