Is this a proper method to load test a module?

Discussion in 'Gen 2 Prius Technical Discussion' started by Kevin Cecchini, Jan 14, 2017.

  1. Kevin Cecchini

    Kevin Cecchini Junior Member

    Dec 28, 2016
    Clinton, Michigan, 49236
    2004 Prius
    Hello Prius brothers and sisters,

    I performed a little research on how to load test the modules from the HV battery pack. Unfortunately, I placed the cart before the horse (this will be covered in the 5th paragraph)

    So I load tested 3 modules, two out of three which I ordered blindly from amazon and 1 from the original HV battery pack, as it had a voltage reading of 6.14 - thus I replaced it, the other 27 modules read between 8.04 - 8.09 volts.

    I am using a car light bulb which is a "912 LL" bulb to perform the load tests. I simply taped wires to the bulb and gator clipped the other ends of the wires to the module's terminals.

    Here are my findings:

    Voltage before test: - after 2 minutes on "912 LL" bulb: = differences

    7.77 - 7.69 = .08

    7.36 - 1.04 = 1.04

    6.73 - 6.61 = .12

    What does the information in the above table suggest?
    To me it appears that the second module is shot and that the 3rd module is good, but for some reason it had low voltage. I plan on performing this test on the other 27 modules, however first I wanted to ask if this bulb is OK to use.

    Is this bulb to strong of a draw to properly perform a load test? I am following the instructions from Prolong™ Battery Module Load Tester – Hybrid Automotive Except I am not using the recommended light bulb (simply because I am using what I have on hand at home), other then that I am performing the rest of the suggested guidelines.

    Now, a bit of history, yesterday I removed the HV battery pack, checked all of the modules for their voltages and found the faulty one, as mentioned in the first paragraph above. However, I failed to check all of the modules for their individual load tests, lack of proper homework and attention to detail on my part.
    Also, I replaced the HV battery pack into the prius, powered up the vehicle, and test drove it. The "triangle of death" stayed off for 150 miles. An extra note, I have ordered a mini code reader so I can define what the issues are and properly correct them. Also note that I placed the middle temperature sensor onto the donor modules, as I read in another prius forum that this is safe practice, as it will help the computer keep an eye on the heat of the donor module.

    Question, I read capacity equilibrium is a huge deal for the modules. Does capacity refer to load testing? If not, How is capacity checked?

    Thank you in advance for all of your shared knowledge, suggestions, and replies.

  2. valde3

    valde3 Senior Member

    Jun 28, 2014
    2004 Prius
    No. Those numbers mean nothing. You need to test the internal resistance of the module. And you really should also measure the capacitance. Before you do anything else you need to charge all the modules to same charge level. Basically charge all of them to full.

    Just one method: Measure the voltage. Then measure the voltage under load. Then you can measure the capacitance by how long it takes for voltage to drop to curtain voltage. Of course those methods don’t give actual numbers but you do get numbers that you can compare to each other. Battery should be built with modules that are very close to each other.
  3. Kevin_Denver

    Kevin_Denver Active Member

    Mar 18, 2016
    Denver, CO
    2009 Prius
    I haven't needed to yet work on my pack, but here's what my EE degree, research on this, and thoughts tell me: Really the whole pack should be rebuilt all at once when you get it out of the car, testing the AH capacity of all modules individually after 3x charge-discharge cycles, and then replacing the low modules. Modules should be tested after being fully charged. Generally the load test is the last of 3 tests to confirm modules are okay:

    1. Fully charge module, if voltage isn't at least in the upper 7's replace it.
    2. Discharge module and record Ah capacity
    3. Repeat above 2 more times to restore balance between cells, if Ah capacity isn't sufficient compared with other cells, replace it.
    4. Test module using load test with battery fully charged, if voltage drop is too high compared with other modules, replace it.

    There's lots of details not included in the above. See the other rebuild threads on PC. I also don't think the bulb you're using is powerful enough, considering these modules can have loads of up to 100A. Also test equipment at home usually isn't very accurate, but is usually fairly precise. Therefore anything you check, you'll want to check for all 28 modules, then replace the low outliers.
    #3 Kevin_Denver, Jan 14, 2017
    Last edited: Jan 14, 2017
    valde3 likes this.