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  1. #1
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    Low-Voltage cutoff for LiPo

    I have a Rustler VXL that I purchased new a couple weeks ago. I was offered a good deal on LiPo batteries and a charger so I upgraded. Using the low voltage detection on the VXL-3 ESC the power is cut completely at 3.86V on my 3S. I am relatively new to the RC world but I find this somewhat impracticable. The battery has a suggested minimum discharge of 3.0V and a max of 4.2V, if the cutoff is at 3.86V then only 28% of the battery's potential is being used. Is there some way to lower the cutoff to say 3.24 or 80% of the potential? Is the stock VXL-3 programmable in such a way to lower these settings? The Battery itself is healthy according to my charger...

    Any other suggestions would be much appreciated.

    Thank You

    EDIT: In case its important: the battery is a HYPERION 3S/11.1V/25C/4000mAh

  2. #2
    RC Champion
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    the vxl-3s esc is known for an early LVC problem. If that is the case, buy a LVC off tower or hobby city.

    one thing to think about is that the LVC is for 3.0V under load when you let it sit for a minute the voltage should rise to somewhere around mid 3.6's

    How much mah does your pack take? Keep in mind the pack takes a few runs to "break in"



    Also, if it is under a month old, traxxas will give you a new ESC under warranty if you send it in

  3. #3
    RC poster
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    4000mAh,

    so it's a problem with my ESC? It isn't designed to cutoff at such high levels?

  4. #4
    RC Racer
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    I don't have a VXL-3. However, keep in mind that lipos go down in voltage differently than ni-mh. Lipos maintain their voltage until almost the very end, then suddenly go down fast. Once the lipo reaches the 3.86V it means even if you change it to 3.2 cutoff, it will not add much more running time.
    Last edited by DynoXG; 07-27-2010 at 04:07 PM.

  5. #5
    RC Turnbuckle Jr. CarGuy7a's Avatar
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    The VXL ESC's Low voltage cutoff is NOT adjustable. That 3.8V per cell you are seeing is the battery's resting point voltage. When under load (while you are on the throttle) will be much lower and to the point of tripping the LVC.

    Lipo's will also bounce back up in voltage after you hit lvc and remove it from the truck. So for example if the LVC is 3.3v per cell, more than likely the LVC will trip when the pack is under load (on the throttle), you stop running the truck and remove the pack and check the volts per cell a couple of minutes later, you'll notice that they will be higher than 3.3v per cell. That is normal for lipos. This is why lipo instruction sheets will warn you to never let the pack rest after hitting LVC and then continue to run the same pack as it will over discharge it.

    When the LVC on the VXL starts acting up it will most likely trip within the first 5 minutes of the run on a freshly charged pack. Then you'll know something isn't right. If you are not getting this symptom, then your LVC is working properly.

  6. #6
    RC Racer
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    I had a similar problem when using my new SPC 3S 8000MAH batteries. It seemed to have gone away, after the batteries were recycled about 5 times, and I lowered the gearing to 19/76. Not sure if these two items had anything to do with the problem, but it appears to be fixed now.

  7. #7
    RC Champion
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    Its taking 4000 or thats what it is rated for?

    how long are your run times? use the pack a few more times to be sure, they take a couple runs to break in

  8. #8
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    I'm getting approx. 15 min run times. That's fine with me, I just wanted to know if I could possibly extend it. The battery is 4000mAh, but when I charge it I get approx. 2200mAh back into it.

    Appreciate the info carguy and BB!

  9. #9
    RC Champion
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    it should take within a couple hundred of the rated mAh, but give it longer to break in and you might see 25+ minute run times

  10. #10
    RC Champion
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    If its only taking 2200 mah the lvc on your esc is quite bad. it should cut off at around 3500-3600mah. i would give traxxas a call or just get a low voltage alarm or something.
    Slash 4x4 MMP-HV 5.5
    Slash Sidewinder SC 3800kv

  11. #11
    RC Champion
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    before you run to traxxas with a defective lvc... run the battery a bit more... I have several lipo's that didn't run very well and went flat after about 10 minutes tops.. they are 5000mah... after about 8-10 cycles they will run about 20 -25 minutes and will cut off at around 3.3 volts under load with the MM esc.. I check the voltage under load with a react radio... they were cutting out around 3.7 or so under load for the first few cycles... most lipo's seem to need a break in period of some kind..

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