Power in Flux
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Thread: What stinks and sizzles?

              
   
   
  1. #11
    Empulse R #24 frodus's Avatar
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    Quote Originally Posted by Richard230 View Post
    I only discovered the bad cell when just for fun on a rainy day last month I took the fairing off the bike and started checking each cell with a volt meter.
    So you knew about it for a month and still rode it anyway?

    No wonder it vented.



    Here's a TS vent:

  2. #12
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    After I found out that I had a bad cell I rode my bike one time in order to reduce the voltage of the rest of the cells in the pack so that they would conform to the voltage of the replacement cell. I didn't think anything would happen, as I had been unknowingly riding with the dead cell since buying the bike new and after all that riding it seemed like one more ride wouldn't hurt anything. In any case, I don't think it was the dead cell that vented. I hope it was, but I fear that coincidentally, another cell went south on that last ride. What I am trying to determine is how I can locate a bad cell, should there be another one in my pack. When full charged, all the cells read about the same voltage, but it might be different under a load. I was hoping that by visually inspecting my batteries I could tell if one had vented. If that happened, would the vent cap have blown off?

  3. #13
    Senior Member seanece's Avatar
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    I would be flabbergasted if the one dead cell (that has been dead for eons) did not finally vent or crack.

    However, if another cell vented or went bad, check the voltage on allllll cells. Check for odd fluid streaks and definitely look for swollen cells. Those poor Hi-Powers are notorious for swelling before and during their death. Yell at me if you need more cells, I actually have a few good ones laying I would sell for a great price.

    Good luck
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  4. #14
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    Richard,

    I'm assuming you don't have a BMS. I would highly recommend one. It will tell you when a cell drops below minimum voltage while riding, as well as balancing and HVC functions for charging. If you get a centralized system, with wiring going from the BMS to each individual cell, you can simply unplug the harness and check your individual cell voltages manually without taking the whole bike apart.

    Mini BMS

    http://www.cleanpowerauto.com/MiniBMS.html

  5. #15
    Empulse R #24 frodus's Avatar
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    Walter,

    He's got a GPRS, its got a BMS onboard. Just doesn't seem to be doing its job.

  6. #16
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    Cycleguy, I do have a BMS, as shown in the attached photo. As near as I can tell, the BMS is working perfectly. It uses a board on top of each set of 4 batteries and indicates when each cell has reached its maximum cut-off voltage by showing a green light. When balancing is completed, all four lights turn green and the charger stops charging for a while but if a couple of lights go out it will start charging again. The balancing charge rate is around 1.5 amps, instead of the bulk charging of 7.5 amps. However, it took me a long time to understand how these lights worked - being as how they are not visible unless you remove all of the fairing covers and I was too busy riding to do that. However, once I finally checked the voltage of each cell, I noticed that the green light over the dead cell never came on, although all of the other three lights in that pack did. So, it appears that my BMS is working OK, as after charging cuts off and balancing is complete, all of the cells are close to the same voltage, between 3.4 and 3.35 volts.

    Having said that, I just returned from an easy 10-mile ride. When I started off I was seeing 80.2 volts (after the bike had sat around for 20 hours without being plugged in). Before replacing the bad cell I would have seen 76.8 volts. However, after a mile of riding, the voltage had dropped to 76.2 volts, where it stayed for 5 miles. It then dropped to 74. 3 volts until I arrived home. After stopping for a minute, the voltage rose to 75.2 volts. All of these readings were at rest with the throttle off, but with a 6 amp draw from the sepex motor, I assume. This leads me to think that there is at least another cell not pulling its weight. When I inspected the cells after the apparent venting episode, there seemed to be no obvious damage to any of the cells, but because they all fit tightly in their retaining boxes, swelling can't be seen unless they are pulled out. What I did not look for was to check if any of the vent holes had blown open (if that is what they do when they vent).

    Unlike yesterday, when my charger was acting intermittently, the pack is charging normally and the charger is operating the way it always has. All I need to do now is to try to determine which cell is not carrying its load, if that is what is happening. My question would be, how do you do that?

    Thanks seanece, I might take you up on your offer to sell one (or more) of your old batteries - as soon as I figure out what is going on and which cell is bad, if any.

    I really appreciate all of your comments and suggestions.
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  7. #17
    SMPS Engineer BaldBruce's Avatar
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    Two generic things to look for witha pack that has lower than expected voltage under load. One is increased resistance from a bad connection, the other is a cell that has less capacity than all the others. You initially reported going all the way down to 52V under load and that sounds like a bad connection. Your ride today however looked more like the second problem where everything is fine until you start getting one of your cells near it's cliff. I'd charge it up, check all cells,then drive it till the voltage starts to drop quickly. We are looking fo rthe point where one of the cells is causing a quick drop in pack voltage. Stop and measure the cells to see if one or more is giving up before the others. (A BMS that actually tracks and records voltage would save you a lot of grief in troubleshooting this one...)

    Good luck and keep us posted.
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  8. #18
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    Sorry for being ignorant of your setup Richard, I'll try to pay closer attention next time.
    One way of identifying a potentially weak cell is to monitor your BMS cell boards while the battery is being charged, to determine which cell is the first to reach a full charge or first to start shunting (if equipped). This assumes that all your cells are balanced to begin with.
    The basic idea is that the cell with the lowest capacity will reach a full charge first. It will also be the first to reach it's low voltage threshold as well.
    You may want to operate the bike until the battery nears it's minimum voltage and then check the cell voltages before recharging, a faulty or low capacity cell will most likely show a lower voltage than the rest.

  9. #19
    Empulse R #24 frodus's Avatar
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    Richard,

    Your BMS doesn't cut off if a cell voltage goes below a certain point? I realize it cuts off charging if the voltage gets to HVC, but it should cut off the load at some point if a cell goes too low.

    That IMHO is a MAJOR design flaw.

  10. #20
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    Frodus, my batteries have always had a limited power draw when the voltage drops to 51 volts under a load and then the controller (I assume) keeps it at that voltage while the current is reduced. It has operated this way since I bought the GPR-S. The only thing different is that the current draw under a load has dropped over time. Originally the CA would show 175 amps at the 52 V cutoff, and now it shows around 135 amps at the 52 V cutoff. The current bounces around and so does the performance when that happens. Since I have nothing to compare my bike's to (not knowing anyone nearby who has a similar machine), I do not know what performance and charging characteristics are to expected from the bike's equipment. So most of the time I am guessing.

    Cycleguy, my BMS, as has been reported by others, seems to be set up to balance one group of four batteries at a time, starting with the ones furthest away and ending up with the four cells just under the "tank". At least that is how the green lights seem to light up. The box directly under the tank is the one where the dead cell was located and is the last one to be balanced. I don't know what the BMS does when the bike is running, but it does seem to operate properly when it is charging - at least that is my feeling.

    I think I will give Bruce's idea a try. I'll ride the bike around then take it home, take off the fairings and check each battery's voltage in a partially discharged state. Perhaps that will uncover the tired battery. I'll also check for any vent that seems to have popped off and report back.

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