Hv battery voltage check

Discussion in 'Gen 2 Prius Main Forum' started by Ewhitaker0020, Mar 19, 2021.

  1. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    How do I check the voltage of the traction battery with it out of the car? I wanted to check the voltage of a used battery I just got for $100, but when I install the circuit breaker and check between the 2 studs on the left side of the battery I read zero volts. The meter doesn't even move, so that must not be the correct place to read it.

    I pulled the orange circuit breaker and checked between the 2 contacts there and I read 28v so I'm thinking that's not the correct place either. So where can I check the voltage before I install the battery? Otherwise I'm just going to install it and hope for the best.

    Posted via the PriusChat mobile app.
     
  2. bisco

    bisco cookie crumbler

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    that sounds like a bad plan. how old is it, and how many miles?

    it might be worth reconditioning before installation.
     
  3. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    Checking the voltage of a battery sounds like a bad plan? What makes it a bad plan? I'm an electrician and have to check the voltage on 480v ac all the time. But I'm not sure where to check the voltage at on this battery and I'm not sure why the 2 screw terminals aren't showing anything. I guess I'll have to pull the cover off and check each module individually. I just hoped I could check the entire battery to see how close to 201v it was.

    If you're saying that just putting the battery in and seeing if it'll start the car is a bad plan then I have no idea. I don't have a way to recondition it myself.

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  4. ChapmanF

    ChapmanF Senior Member

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    The relays at the battery's output are normally off. If you are probing at the relays' output connections, it is no surprise that you see zero volts.

    With the service plug in place, have you tried just measuring between the two most distant battery module terminals, where the + and − cables attach?

    Carefully, of course....
     
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  5. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    Thanks! I was wondering if something was off. Because the chances of a battery (even an extremely dead one) reading 0 were slim. Would I remove the top cover to do this reading? Or is there a point where I can do it on the outside?
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  6. edthefox5

    edthefox5 Senior Member

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    Look at my picture.

    See the 2 red lugs that the wires have been cut off.With the orange safety plug installed carefully measure across those red lug positions. You can clearly see where I have marked the positive + wire and the other side is the negative. That's the input to the battery relay from the battery. The other set of relay connections are of course the relay outputs which will measure zero if the relay is off.
     

    Attached Files:

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  7. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    Thank you. I'm about to go out and take a look, but before I do I was wondering if I have to remove the metal cover to get to the point in the picture you showed me.

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  8. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    I went out and found the places you were talking about. Unfortunately the battery seems to only have 85v in it right now. Now I have no way to charge this battery and cannot find anybody locally to do it for me. I would really like to get my car up and running. I'm an electrician so I understand the hazards of 200v ac or dc electricity and I have a question.

    Would I be able to install the low battery that won't actually start the vehicle. Then take my battery that can start the car just fine and hook it up in parallel to start the vehicle, then immediately unhook it? I don't see a reason why I couldn't, but I'm not sure if this is something that's possible to do. I would hook it up from the "line" side of relays of the old battery to the normal attachment points of the new battery. On normal lead acid batteries (which I know these aren't) this would allow the batteries to be in parallel and increase the capacity which not providing too much voltage. All I need is for the car to start and it'll charge the battery. I can let it idle for a while then drive it. I know it's not a perfect solution, if it works at all, but without wanting to spend a bunch of money, I don't have much other options right now.

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  9. ChapmanF

    ChapmanF Senior Member

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    Putting a well-charged traction battery in parallel with an 85 volt traction battery would create a substantial charging current into the 85 volt one, quite possibly leading to this kind of situation:

    [​IMG]

    Low-current power supplies of adequate voltage to charge the battery can be not very much money on ebay, etc., if you look for small electrophoresis supplies or the like, which could allow you to put a charge on the battery.

    I'd be concerned, though, that an overall voltage of 85 V for a 168-cell battery means that it has been discharged down to an average of half a volt per cell. That isn't good, or it could mean that a bunch of cells are closer to nominal voltage while a bunch of other cells are shorted, which also isn't good. It doesn't, in other words, look very much like a healthy battery.
     
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  10. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    Man, talk about hitting the nail on the head. So far I'm taking off the bus bars and 16 cells have exactly zero volts. So shorted internally? And the 2 others I've checked have 7.3 volts. So looks like I might just rob a module out of here.

    According to my Dr Prius app modules 3 and 4 are going bad. But mostly module 3. Which of the battery cells are modules 3 and 4? I think I'll just swap over 2 modules for now and plan on doing something else in the near future

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  11. ChapmanF

    ChapmanF Senior Member

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    As far as nomenclature, you can't get to the cells. There are six of those in every module, and the modules don't come apart. There are two modules in a block, and the voltage and resistance measurements are per block.
     
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  12. davecook89t

    davecook89t Senior Member

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  13. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    Thanks. I had a hard time keeping that straight in my head.

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  14. dolj

    dolj Senior Member

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    BTW, those zero volt modules are not necessarily bad – NiMH is quite happy to be stored in a zero state of charge. All you can say at this point is they are fully discharged. If you can find a charger that can supply 325 mA and get the voltage up to around 8.2 to 8.4 V you might have a usable module. The trick here is low and slow bringing them up from zero. Keep an eye on the temperature as you charge and make sure to have the module clamped between 2 pieces of 2x6 if you have them removed from the battery. If they are still clamped together in the battery's tension bars, that will be ok too.

    The decider will be load testing for 5 minutes after they have been charged. To do this you need a load like a 12 V 55/66W auto headlamp with the high and low filament connected in parallel. Measure and record the OCV (start voltage) then attach to the headlamp for 5 mins. Right at the 5-minute mark (before disconnecting the load), measure and record the loaded voltage (ending voltage). Subtract the ending voltage from the starting voltage and record this difference. For the modules to play well together the difference needs to be very similar. Any outliers can be considered bad.
     
    #14 dolj, Mar 21, 2021
    Last edited by a moderator: Mar 23, 2021
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  15. ChapmanF

    ChapmanF Senior Member

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    It has long been my understanding that "zero state of charge" is not synonymous with zero volts; that there is generally a nonzero voltage that will be seen on a cell of chemistry X when it is at nominal full discharge, and an actual reading of zero would indicate that a cell has developed a short.

    Someone who keeps up more avidly than I do on battery chemistry details might know something I don't there, but this understanding has kept me out of trouble for a good while.
     
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  16. dolj

    dolj Senior Member

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    Yes, you are, of course correct, a poor choice of words on my part. What I meant and should have said – NiMH is quite happy to be stored at zero volts.
     
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  17. Ewhitaker0020

    Ewhitaker0020 Junior Member

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    I'm hoping to eventually learn how to recharge a weak battery confidently so I can give mine a refresh. Hopefully all the cells will settle down into a more uniform voltage.

    If I measure resistance in the zero volt batteries and get zero ohms then the battery is shorted and therefore junk, right?

    I managed to swap out 3 modules from that bad pack to my own, somewhat decent pack. I just picked the 3 modules in mine with the lowest outlier voltages compared to the rest and swapped in 3 of the highest voltage modules from the donor pack.

    I doubt this was the best way to do it, but I didn't have any way handy to charge and test the modules to find the actual best ones. All of mine read 7.8v consistently except the 3 I changed out. One was as low as 6.4 volts. That was in my bank 3 modules.

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  18. gdanner

    gdanner Member

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    First, about me and my Prius: I did a partial restoration on my 2005 Prius HV pack 5 years ago. After barely driving the car at all during 2020 because of the COVID19 pandemic, I recently had a POA80 fault. After clearing the code the car is again behaving well. I have reconnected my OBDII Bluetooth adapter and the Torque Pro Android app that I used 5 years ago. Once again I’m monitoring the HV pack in order to determine if more modules are failing. I have logs and data from 5 years ago to compare with. That way I expect to be able to tell how much my HV pack has degraded. Perhaps I simply didn’t drive the car frequently enough to keep the HV pack properly charged and cycled?

    Next, some recommendations for you:

    You should emove the top cover from the HV pack and perform a detailed physical inspection.

    My procedure is to remove the bus bars from both ends of the 28 individual NiMH modules. Check for loose fixing nuts, corrosion, and for any signs of overheating or of electrolyte leaking out of individual battery modules. Note: With all the bus bars removed there is no “high voltage” present anywhere.

    Each individual NiMH module should measure 7.0 to 7.5 volts in resting condition. It is safe to try charging each module at about 300 to 400mA from an adjustable charger. If a given module does not rise to >7.5V after several hours of charging at 300/400mA then it is faulty and should be discarded.

    I have several spare modules which I acquired (but didn’t use) back when I repaired my HV pack 5 years ago. I’ll check them to see if they are still holding any charge. They’ve been stored indoors but haven’t been charged or tested for 5 years. I’ll report what I find.

    -Greg
     
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  19. gdanner

    gdanner Member

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    Please check all 28 modules in your recently acquired HV pack. Modules that currently have >7.0 volts are likely to be good and could be used as replacements for failed modules inside your other HV pack.

    Did you say the total voltage from your $100 HV pack was about 85 volts? If so it’s likely that 10 or 11 of the individual modules in this pack are good. Again, there are 28 modules in a Prius HV pack. The Prius battery management system monitors them in pairs. That’s why the Dr. Prius app or Torque Pro show 14V per “block.” There are 14 such blocks, each containing two 7.5V modules wired in series.

    As for those modules in your $100 HV pack which individually read 0V, it is useful to try individually charging each of those with a low current (300 to 400mA). The charging current must be limited. Do not connect a 0V module directly in parallel with a charged module. That could permanently damage both modules, as shown in the photo of an “exploded” HV pack.

    -Greg
     
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  20. gdanner

    gdanner Member

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    Well, that doesn’t look good at all!
     
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