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  1. BatteryMooch

    Standardizing the measurement of internal resistance

    Good points and good advice Doc! A huge resistor is a great idea to keep temps (and drift) down. You can also look up its TCR (temperature coefficient of resistance) and power vs. temp graphs and calculate what the resistance drift will be at various current levels. Since I made a mistake...
  2. BatteryMooch

    Standardizing the measurement of internal resistance

    [Edit] I goofed on my accuracy numbers, now corrected. The results you got were worse than mine. With one of my CBAs and a discharge at 20A, it was off 1.0%. About -0.2% at the start and then drifting to -1.0% within a couple of minutes. At 10A I got about a 0.4% difference. About -0.2% off...
  3. BatteryMooch

    Standardizing the measurement of internal resistance

    Hi steveo, I think it's still a resistance problem, but with the IRFB4110 and not the wiring. Try the same 2.3A current setting in your CBA but with a higher battery voltage. At 3.3V there's barely enough voltage to push current through the 4110's very high resistance (when only driven at the...
  4. BatteryMooch

    Standardizing the measurement of internal resistance

    It's the MOSFET. :) It's made to be switched on and off hard at a much higher voltage (10V at least) than the CBA can deliver (3.9V max). When it's turned on hard, the on-state resistance drops to that nice and low 11mOhms that's in the datasheet. But, as the voltage that's turning it on gets...
  5. BatteryMooch

    Standardizing the measurement of internal resistance

    Yup, you're right. I just checked the datasheet for the P75NF75 and with a gate voltage of 3.9V (the max the CBA can rise to) and around 3.5V-4V for the cell, the current it will let pass is off the chart...in the wrong direction. I'm amazed you got 2A! :mrgreen: If you can wait a bit, your...
  6. BatteryMooch

    Standardizing the measurement of internal resistance

    I saw the pictures of your mods Doctorbass...nice! :) I also looked for a thermal sensor of one type or another and never found it. I'm guessing that they're using the change in voltage drop across the MOSFET as a temp sensor? Once calibrated, it can work pretty well though.
  7. BatteryMooch

    Standardizing the measurement of internal resistance

    steveo Thanks for sacrificing a MOSFET for the cause! According to my calculations that IRFB4110 probably wasn't running above its absolute maximum operating temperature. IMHO, it blew because it hates being operated as a load. :mrgreen: An 86W test with a 12V pack? IMO, it would still blow...
  8. BatteryMooch

    Standardizing the measurement of internal resistance

    That 24V test sounds good. The wattage will still be within the CBA's ratings but it will test the 4110's ability to be used as a load. 150W is the rated max for the CBA (for short periods), 100W continuous. Based on my tests though, you should never run it above 86W or so with the stock...
  9. BatteryMooch

    Standardizing the measurement of internal resistance

    Check out Fig. 3 on page 5 of the datasheet. You can see that when the MOSFET is biased with a gate voltage below approx. 5.2V that any increase in temperature will result in the MOSFET trying to pull more current. And since MOSFETs are rarely biased at a voltage that high when used as a load...
  10. BatteryMooch

    Standardizing the measurement of internal resistance

    Be careful though... The IRFB4110 has great thermal resistance specs (a Rjs of about 0.9 degrees-C/W vs. the IRL2910's 1.25 degrees-C/W) but the Maximum Safe Operating (SOA) graph from the data sheet is worrisome (http://www.irf.com/product-info/datasheets/data/irfb4110pbf.pdf, FIgure 8 on page...
  11. BatteryMooch

    Even Newer 4 to 24-cell Battery Management System (BMS)

    Not a great solution but I've used zero-ohm 1/8W through-hole resistors as jumpers. Just solder the lead ends down onto small bare pads. The resistor body holds everything a bit off the PCB.
  12. BatteryMooch

    Standardizing the measurement of internal resistance

    :shock: Ouch! :shock: I hope you get it back soon Andy. Thanks for the part numbers Doc and Andy! I wanted to compare the specs for the FETs in the Amp with the IRL2910's in the CBA II, especially to see if the Amp's FETs were rated for continuous use biased in their linear region (i.e...
  13. BatteryMooch

    E trail

    Very nicely done pacobike! :)
  14. BatteryMooch

    Standardizing the measurement of internal resistance

    I'm a little late to the thread but I just joined the forums. :) I wanted to say great work on those mods! I had my fuse/fuseholders drop out about 1Ah in to a 29A, 100W test a few weeks ago and ended up doing a few mods myself. I'll post them soon. The CBA is such a great device, but often...
  15. BatteryMooch

    Standardizing the measurement of internal resistance

    Thanks for taking those pictures! I've been dying to know how it was laid out for a long time. :) Could you confirm that the op-amps. e.g, U1, are TLC272C's and what the MOSFET's are? I couldn't quite make it out in the photos. The CBA uses the TLC272C so that was expected but it appears...
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