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Got to be a better way to discharge batteries

Discussion in 'General Discussion' started by lawman0210, Nov 9, 2015.

  1. lawman0210

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    So the recommendation is to discharge to 8% every 20 cycles and the advice Is to leave it in your phantom and let stay on til it dies. It will take quite a bit of time if you have a lot of batteries. Isn't anyone concerned about wear and tear on computer chips, Leds, motors?

    Sent from my SM-G920V using Tapatalk
     
  2. LuvMyTJ

    LuvMyTJ ADMINISTRATOR
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    There is a thing sold on fleabay that is essentially a halogen bulb and some wires & connectors. Search Phantom battery discharge. It uses the halogen to drain it.
    I have also heard of people running their Phantom at idle with the props off.
     
  3. Ti22

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    Carbon Piles (Harbor Freight, JC Whitney, etc) are useful for Phantom voltage ranges and with some adaptive cabling/connectors can burn off a lot of energy in short amount of time.

    Another source for “load” is old toaster ovens or space heater elements. Bypass any control circuitry and connect RC Lipo directly to the heater element. These devices generally demand about 1200-1500W when operating on 120VAC.

    Not gonna pull anywhere near that amount from 12-16VDC Rc Lipo. Might see 20-30W or maybe 2A but that can often be enough to drain off a top charge.
     
  4. R2-D2

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    My 3 batteries only have 5 charges each on them and when I recharge them. On a full charge all I get out of them is 96% and dropping. Is this normal? How do you get them back to recharging at 100%?
     
  5. Ti22

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    What’s likely happening is that one cell in the series string of your battery pack is out of tolerance and during charge cycle reaching HVC (high voltage cutoff) before the other cells in the pack.

    Here’s a visual of a 20S battery pack with voltage graph of each cell.
    000001.jpg

    They’re pictured in close agreement but just imagine if one cell begins losing capacity which in turn would cause it to fill-up before the others?

    Now imagine charging this pack, the majority cells reaching 4V but that one compromised cell now hits 4.2V. The BMS will cutoff charging and the practical result is that you won’t have as much overall charge available from the pack.

    I dunno P2/P3 battery packs - in the regular RC Lipo world we would just use a balance charger to bring all the cells back into reasonable balance. But once cells start getting way out of balance, it’s gonna be a losing cause to keep up with ‘em. You need to be able to test IR and run true capacity tests to really know for certain.

    IMO, the best thing people can do to prevent this imbalance is to avoid deep discharging your battery pack. Once you reach around 50% indicated, bring it on in. Pushing it further into low voltage regions can really propagate cell imbalance. Just not worth the potential irreversible damage that can be caused to the battery pack.

    Buy an extra pack and between them fly as much as you do with one. But the difference is that they’ll last several years or more rather than being fubar within a few weeks/months.
     
    #6 Ti22, Nov 10, 2015
    Last edited: Nov 10, 2015
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  6. R2-D2

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    Thanks for the advice. Pretty much all of my flights I land around 55% since I'm breaking in the batteries. I hope this works it self out and I don't see these cells continue to drop. Weird how all 3 of them are doing this.
     
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  7. Ti22

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    In the world of commercial batteries there’s never been a design which increases capacity as it’s used and ages. Always net loss situation but keep an eye on it. I'm sure other users have more direct experience about expected capacity loss?

    Sorry I dunno those P2/P3 BMS systems and not sure if they’re using realtime voltage measurements or “predictive” time/use based logarithm? Or combination?
     
  8. yorlik

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    What is the common item to all 3?

    The dji 'charger' power supply. sounds like it may have an issue.

    Do you have a voltmeter? If so check it. No load, it will be above 12.6v; to go from 95 to 100% charge requires your voltage into battery to go to 12.6vdc and stay there for about 10 minutes.....

    You should try a known good battery, or send one of your batts to someone to test it for you on THEIR charger. I would do that if you want. PM me if interested.
     
  9. yorlik

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    Good thoughts.

    Main thing to remember is to put an ammeter in series with the unkown loads to make sure you do not pull more than about 10 amps from them to discharge so you do not stress them.

    As for 1500watt 120vac heater; the math is: 1500watt/120v=12.5amp. So R=V/I= 120/12.5=9.6 ohms. So use it on your 11.2v dji P2 batt and it will draw 11.2/9.6= 1.16amps. Just turning on your p2 and running assistant pulls .95 amps, so much simpler to do that than 1500watt electric 120v heater.
     
  10. yorlik

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    True but... My two P2 5200mah batts have been treated well; I charge them on hi tech charger that basically is a 12.6v power source in the end; but it shuts off BEFORE my dji smart battery does; not sure if this is why or other things I do, but BOTH my batteries show about 5400mah capacity now - after 30-ish charges each. :)
     
  11. yorlik

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    any other anomolies show up in assitant? maybe you should post screen shots of them? So we can see % life left and individual cell voltages?

    did you buy all 3 with the p2 new? Off brands? 5 recharges, but how old are they? Did you store them full each time for months on end?
     
  12. JB-I

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    I also have 3 new batteries with about 10 recharges on them. I have run them to about 45 - 50% each flight. I use the dji smart hub to charge them and have the auto discharge set to 2 days. I also have noticed that at full charge I'm only starting out at 98%. And also when I fly it drops quickly at first to around 80% and then slows down. I get about ~15 minutes till it hits 50% overall but the discharge rate is definitely not linear. Healthy drone reports also shows the first cell with deviations, but not into the danger zone. And this is on more than one battery. Would it be beneficial to do an 8% discharge now @10 charges to see if it's corrects the cell abnormality?
     
  13. yorlik

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    WHY???

    Let's see... you have batts that fly 15 minutes from 98-50%. that's great! why do something considered by many as detrimental to your batts??

    dji batt discharge curve is NOT linear; your doing potential harm to your GOOD batts will not make the curve linear.

    I vote don't do it, just fly and enjoy.
     
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  14. lawman0210

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    I did the 8% thing just recently because my batteries were going from 50% to 20% in just a few minutes and then to 10% or so quickly thereafter. It is so quick that I usually don't even get a low battery warning. Just straight to critical and phantom comes down quick. I have been asking how to change the parameters to 30% low and 20% critical but no one can answer this for me

    Sent from my SM-G920V using Tapatalk
     
  15. yorlik

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    So you did the 8% thing due to battery discharge issue, but you did not say if it helped you? Did it?

    You have received no replies to how to change low & critical batt set points I believe because they are not adjustable by us mere mortals: I believe in assistant we get to click USE low or don't click USE low but no value adjustment. Critical is purely built in and cannot be turned off I believe. THAT said, I CAN change my LOW setpoint % - in KenArgos's Ultrimate Flight program....
     
  16. lawman0210

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    It does not appear so. The battery flight time fluctuates so much I really am not very secure as to rely on it. I'll start off with 17-18 minutes then it can go almost to critical in just 3-4 minutes that it will start counting up 3, 4 5 then drop off again.

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  17. Fyod

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    There's no need to be afraid of discharging to 8%. Just don't leave the battery discharged. Let it cool down and then charge to 50-60%. Charge the rest before your next flight.
    The 96-98% full charge is nothing to worry about either.
     
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