Voltage 16.8 to 14 in 30 sec flat?

Discussion in 'Cinestar Misc' started by Gary McCready, Oct 16, 2013.

  1. Gary McCready

    Gary McCready Active Member

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    Anybody ever seen this?
    My Cinestar 6 is about a year old. Went to do some photos this afternoon, and got a low voltage warning on my MX-20 as soon as I took off. Within 10 seconds I noticed my heli was coming down even at 3/4 throttle. Just before landing my Graupner told me the voltage was 9.0 = WOW. So after landing checked the battery, and it was pretty hot. Made sure I didn't have it hooked up backwards though it seems just about impossible to do with my connectors, and pulled the plug. Battery short??
    So I looked for crossed wires, smoke, sparks or smell and couldn't find anything. Hooked up another battery and saw it go from 16.7 to 14v in 20 seconds on my telemetry. Unplugged.
    Took it home, started MKTools, voltage reading on chart, and plugged in a fresh 16.8v battery. And nothing, stayed at 16.8, so I removed props, and plugged in again. Initialized and started motors = nothing! Never went below 16.2v
    I jiggle wires and nothing. Remove the FC and the Power Distribution ring and also checked the gimbal wires and only found one place were the wire was exposed on the LED wires, but it wasn't touching anything, or even near another wire.
    Next I cut off many zip ties and checked under them, and didn't find anything either.
    So I am a bit stuck. There are some wires I can't see because they are shrink wrapped, but if I have even a hint of trouble that is my next step.
    This just was so weird, and I couldn't duplicate it. Got to be a short in a small wire, right?
    Any other ideas, guys?
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Gary:
    It sounds as though the first battery is telegraphing that it's not a happy camper.

    Have you, by chance, been taking it down to Storage voltage in between flying days, or keeping it fully charged? It's exhibiting all the symptoms that it's about to become an ex-battery: immediate voltage sag under load and getting unusually hot when discharging....

    Andy.
     
  3. Gary McCready

    Gary McCready Active Member

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    The first two batteries lost voltage fast. The first went from 16.8 to 9 in about 90 seconds. It came back to about 14v when I unplugged. The second one went from 16.8 to 14 in 30 seconds. Had to be a short in the system, right?
     
  4. Shaun Stanton

    Shaun Stanton Active Member

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    Had the same exact happen, did not go that low though. I had a battery that had been used the day prior and charged to reasonable rate then I got immediate under voltage warning as well as the LED light trigger for MK 10 seconds after t/o Yours sound like it is having issues, like Andy said time to bench that battery. I had another battery do the same thing a few days later.

    good way to test your battery is to throttle to almost takeoff power or anchor it down good to a heavy weight were it wont takeoff an goto what would be normal hover/climb power. The thing to do is throttle up until your system is pulling about 60 to 70 Amps with the props on and see how much sag there is. The bench test without props wont yield the same results because the motor is not under load from the Aerodymic drag from the propeller.

    Shaun
     
  5. Shaun Stanton

    Shaun Stanton Active Member

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    Couple questions. Do you have GPX from a flight that was nominal and the files from these recent flights?

    Also could the batteries have been exposed to cold temps prior to the flight?

    Shaun
     
  6. Gary McCready

    Gary McCready Active Member

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    I had the GPX data, and looked at it. The flights on both batteries showed a sudden drop in voltage, to 14v, even before liftoff. The first one went from 9v back 14v as soon as I landed, after about 30 seconds of flight. Not cold either, just about 75 f. Looked at data from two days ago and it was perfect, as was the data today with my tests, on the 3rd battery. Just not sure which batteries I was flying two days ago. Both batteries I used today are about a year old, one is the Quadrocopter battery, the other is a Zippy. Guess it could have been the batteries, I can test them tomorrow if it doesn't rain. Sure freaked me out though!
    And Thanks for your relies!
     
  7. Shaun Stanton

    Shaun Stanton Active Member

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    Sometime these batteries "cry uncle." That's why as a technique I hold it in reasonable hover, about ten feet or so for a few seconds and see what the sag is after takeoff. If it has a real low drop and starts getting a warning on a slow climb to about 20feet I decide to land and the battery becomes a bench battery.

    I cant wait until a new battery technology comes out. There is some progress, I believe Stanford University has discovered a Lithium Sulfide Battery that will have more capacity and be much more stable then lipo's. Who knows when this will hit the market, but if their research it will be almost be the holy grail for us, so to speak.
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I don't think it's a short....if it was, you would have seen smoke, flames, fire, etc. A LiPo's internal resistance is sooo low you'd pull 150 Amps or more out of it with a short....

    Still sounds like a LiPo about to fail.

    Andy
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    My testing showed that the LiPo's under test all dropped about a volt under a 60 Amp load and recovered about a volt when the load is removed.

    Let us know what you find when next you fly.
    Andy.
     
  10. Gary McCready

    Gary McCready Active Member

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    Yea, I learned alot today! lol Never seen that before. Since it was two in row I figured it must be a short, but go figure? I do date all my batteries, and realized about a week ago all my 5800mah batteries were a year old, I ordered 6 new ones. Already on the way!
    I did see the Amps go up to 80 on the first flight today, and two days ago I looked and they never went above 40?
     
  11. Gary McCready

    Gary McCready Active Member

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    I "tested" my two batteries. Both batteries charged to 16.6v, which I found odd. But they appeared to be charged fine when they lost voltage fast too.
    The only thing I found was that my first battery, that voltage crashed so bad, had m ohm readings of 6,5 3, and 11! My other battery had 4,5,3,4, so I can't really see anything wrong with it. I did parallel charge them? Not sure what this "11" means but my new batteries were at 2-3 m ohms per cell (4S = 4 cells).
    Both batteries also showed Voltage of 4.18v to 4.2v per cell, so that seems fine.
    I would still like to determine, ahead of time, which batteries have gone "bad".
    Don't think I'll fly the Qaudrocopter battery till I find what the 11 m Ohms means??
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    It means milli-ohms. How were you measuring this please Gary?

    EDIT: Oh....sorry....were you meaning "what is the significance of a reading of 11 milliOhms?" I maybe misunderstood.

    Generally speaking, LiPo's internal resistances seem to vary from one vendor to another and from one LiPo battery to another. I'm not sure I'd put too much stock in the fact that one cell is 11 milliOhms.

    What you might want to try is a flight with these batteries but stay in a low hover about three to four feet above the ground and just get a sense of the discharge curve. That way, you can land at the first sign of problems.

    Andy.
     
  13. Gary McCready

    Gary McCready Active Member

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    Thanks Andy, I'll give the low hover a very careful try... I'm just concerned about these batteries and wondering why they failed even though they really show no signs of it. My battery charger measures the milli-ohms, each cell and total. My battery charger manual suggested testing all new batteries, and then keeping track of the changes. Also found out one of my new Zippy 3S 500 mah batteries only has 2 cells. The third showed "0" volts...but at $6 hardly worth returning.
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    A 3S battery that only has two cells? How many wires are there coming out of the battery to the balance connector? (There should be four.)

    I would avoid parallel charging these batteries until you've established what condition they are in.

    Andy.
     
  15. Gary McCready

    Gary McCready Active Member

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    The 500 mah 3S is one I use for the Video Tx, but it does have 4 wires coming out of the balance port. It only shows 7.5 v on the main leads too, so there is only 2 of the 3 cells connected inside the battery. Zippy, made in China, go figure? I did charge the "bad" batteries and all the new ones individually to start, and checked all the m-Ohms too.

    I'm still not convinced I didn't have a hot side (red) wire on the small LED lights ground to the CF frame? I assume CF carries electricity? There are carbon arc lamps, and carbon/graphite motor brushes? The reason is that it happened with two batteries in a row. Then after a ride home it disappeared. And I did find a small bare area on a LED wire, but it wasn't anywhere near a black, but was near the frame. I've now covered it with liquid tape.
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Zippy?
    Say no more. Nudge, nudge, know what I mean? I invoke the fifth law of thermodynamics: youse gets what youse pays for. :)

    The carbon that's in lamps and motor brushes is solid carbon/graphite -- not carbon fiber. CF is certainly conductive but it a patchy sort of way -- if you put an ohmeter on each end of a boom, you can see resistances around 200 ohms (if I'm remembering correctly), but it's high variable depending on whether the meter probes are touching CF itself or the binding resin used (which is an insulator).

    However, I'm still not convinced that the entire Cinestar frame is connected to the -ve side of the LiPo. That's certainly something that you can check though. I just checked on mine and there is no conductivity.

    Andy.
     
  17. Steven Flynn

    Steven Flynn Member

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    Just wondering ... could someone tell me what parallel charging is? And what would it gain me? I fly two batteries (4 Cell 8K) lipos on an octo frame, but I've always used "solo" charge on my Hyperion. Do I gain something by charging/running them in pairs? I've found my batteries are going from 16.9 to high 15's very quickly, and just wondering how I can prolong their demise? Also, is there a good place to go for a battery primer? I'm looking at upgrading motors/batteries etc... and I'm sure there is much I need to learn. Thanks. Steve
     
  18. Steve Maller

    Steve Maller UAV Grief Counselor

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    There have been several discussions here. Use the search to look for “paracharging” or “parallel”.
    Basically, using parallel LiPos is a little complicated, and not 2x as good. There are tradeoffs for flying and charging.
    It’s best to completely understand what goes on.
    In particular, you should have perfectly-matched batteries, because it’s not clear whether you can consistently (or even safely) charge or fly with a pair of batteries that may not match.
    In order to charge, you’ll need a Y-adapter for the mains, and one for the balance connectors, too.
    ProgressiveRC sells a good parallel charging adapter that combines both. That’s what I use.
     
  19. Shaun Stanton

    Shaun Stanton Active Member

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    Everything Steve says correct. Ill just add to some of it. I find that having a dual charger with sync mode helps like a Hyperion 720I Duo charger. You can both in in solo or put it in sync mode to do exactly as Steve mentioned.
     
  20. Gary Haynes

    Gary Haynes Administrator
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    Steve

    With the proper equipment it works fine. Part of the answer lies in how big your packs are in mah. Charging 3000 mah packs in parallel works with smaller chargers than say a 9000 mah pack. Reason is that there aren't to many chargers that have the oomph to do multiple large packs at a reasonable charge rate. Here's an example.

    The popular Hyperion 720iDuo3 only does a 20 amp charge rate per port. To get 20 amps per port you would need a 40amp power supply and most of us don't have something that big. With the 3000mah packs, assuming that you want a 2C charge rate you could only charge 2 per port (3000 x 2c x 2batt = 12000mah). So better than charging one at a time. But if you want to do a 9000mah setup you can charge 1 at 2C or 2 at a 1C charge rate since the port can't handle more. It would take just about the same amount of time either way to get two batteries charged. So your pack size has an impact on what you will be able to do with your charger.

    Now switch chargers to something like the PowerLab 8 from Revolectrix which can do 40amps out of the port and you can charge 2 9000mah at 2C with no problem. That's why I switched. Power supply I am using is an eFuel 1200 which is rated in the 50-60amp range at 24v.

    I also use the FMA MPA parallel adapter board. Used a couple of lesser boards and unless you are absolutely positively meticulous in how you plug in the balance connectors it was easy to burn up the circuit board traces. With the MPA board all circuits are fused. It is built like a tank. Well worth the investment from a safety standpoint.

    Here's a couple of articles that I found while doing the research. Only real caveat seems that the packs must be the same size and cell count and not be grossly different in voltage. If you fly dual packs and charge them at the same time it should be non issue regardless.

    http://www.icharger.co.nz/articles/ArticleId/7/What-is-Parallel-Charging-and-why-is-it-for-me.aspx
    https://sites.google.com/site/tjinguytech/charging-how-tos/parallel-charging

    Another benefit is that after flying if you want to discharge your batteries down to storage level that can be done parallel also.
     

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