Lipo SAG

How much Voltage Sag is normal?

I'm going round and round with various batteries trying to find one that doesn't sag so bad. 

What I'm talking about is; in flight, it seems most batteries will get down to 10v or so, but once I land it's right back up to 11.7v+. It makes it really hard to guess if you still have time left or not by landing and checking the voltage. I have an amp reader on the OSD, and it says I'm pulling around 17-19 amps most the time. Batteries are 30c, 35c, and 60c. Don't see any difference between them really. 

The 35c had it's first flight today and I puffed it because I landed, checked the voltage (11v+), launched and about a minute later it sank to the ground. I checked my osd and it was below 10v already. Sux. (It was to windy for FPV).

I should probably stick with one brand.... Tried 6 different ones so far. None of them are giving me 100 flights before being useless.

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  • So I finally blew some cash on a Hyperion 4200Mah 35C battery. It's obviously a quality product. 

    One issue of note for anyone who stumbles in here: Apparently Hyperions use some other balance connector. I'm fishing around now to rewire it so I can charge it. *sigh*


    It's shockingly beautiful today in Florida. So I got to go out and try out my new battery alarm. That thing is LOUD. Oh yes. I can even fly in close and read the digits if I desire. It's awesome. It is either a Maxpro, or a copy of a Maxpro.
  • I have a puffed Hyperion LiPo at home that has had an easy and relatively short life so I would disagree, most of the LiPo batteries on the market are pretty much the same thing in my experience. You just need to take care of them properly. If you don't have it currently look at getting some form of telemetry that shows the battery voltage and setup an alarm based on that.

    The Aurora 9 radio has battery voltage telemetry out of the box which is what I use to monitor the battery voltage and it sounds an alarm on the transmitter when it gets low so I know when to land. There are various other telemetry products available that can be added to any radio setup. A cheaper alternative would be an onboard voltage alarm but they can be hard to hear at a distance.

  • Moderator

    One "should" only fly to 80% capacity to preserve LiPo's. On my 3 cell 5000's that means putting back 4000mAh which I get if I land at about 10.4V (3.4V per cell under load). Any lower and the danger comes from the probability of one cell in the pack being slightly weaker than the others and it will drop lower than the others under load, so you might have a situation where 2 cells are still at 3.1V (safe) and the weak cell is at 2.8V (damaging).

    This makes for really interesting reading if you want to know more:

  • I currently have 2 2200 3S packs and 4 2650 3S packs, all from Turnigy, and they've worked flawlessly for nearly a year and a half. In the end, you can make the cheap ones last for a long time if you're meticulous about charging and discharging regularly and completely, and take good care not to push them to their limits. If you don't want the extra caution and time to cycle them fairly regularly, then the higher quality ones will preform better for significantly longer, but you should take good care to cycle all your packs completely every once in a while.

  • What you are seeing is very normal and depends on the internal battery resistance. I also second the the quality of Hyperion cells. I use 4 year old 3300 mAh Hyperions and they are really good batteries. I use them in a number of sizes and everytime I tried switching, I regretted it. I also do not see anything unusualy in your results. You are measuring the voltage drop of some of your wiring as well so some of the sag is impossible to remove.
  • The brand of LiPo makes all the difference.

    It is sometimes hard to justify over $100 for a LiPo when HK might have it for $20, but I am still using the expensive Hyperion batteries looonnngggg after the cheaper ones I have tried have failed.

    An old 3300 3S I have is about 4 years old and gets used in everything, gliders, Hexa, whatever.
    I tried a Zippy 4000 3S recently and even new it did not give the output of my ageing Hyperion.
    It sags at about 3/4 the time the smaller Hyperion does.

    So, LiPo's aint LiPo's , to paraphrase and old oil add.

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