Calculating Battery Run Time

[LCHelilover]

I remember seeing a post (from Chris I think) regarding how to calculate safe battery run times......it involved peaking your packs, flying a timed 5 minute flight and then recharging the packs to see how many electrons you flew out, then calculating a safe 80% level. I can' t seem to find that post again...could someone please direct me to it?

Thanks,
G

[MinAirChris]

Don't know where that was but...

Fly your five minutes, the way you want to.

Let the batts cool and recharge them, retaining the highest number of mAHr's put back in.

Take your battery capacity and divide it by that highest number.

Multiply that number times the 5 minutes and that result times the 0.8 safety margin.

By way of example:

Lets say I flew for 5 minutes and after recharging my batteries took in 3400 and 3700 mAHrs. My batteries are 8000mAHr packs so...

(8000/3400)*5*0.8=9.412 minutes
-OR-
(8000/3700)*5*0.8=8.649 minutes

Obviously, to be safe I would want to fly for no more than 8.649 minutes.

Some other things to ponder...

-Do you really know what the true capacity of your packs is?
-How is this capacity affected by different charge/discharge rates?
-Do you think that the capacity does not change as a pack ages?

After testing a number of batteries over the last few years, I have determined that rarely is a battery what you think it is. This is mainly due to the fact that capacity ratings are based upon a very low discharge rate...like .5 or 1C...NOT where we use them, which is typically at an average of 30 to 40 amps discharge which would be 3.75 to 5C for an 8000mAHr pack. Batteries will exhibit LOWER capacities at higher discharge rates...this makes sense as we already knew the battery heated up when used. That heat has to come from somewhere, yup, those precious mAHrs.

I have also found, through repeated testing of batteries over a long term usage (say every 10 to 20 flights), that they do indeed loose capacity as they are used. This is of course accelerated with abuse.

What this means is that if you really want to be sure about how long you can fly, you need to know a little more about your packs, the ACTUAL CAPACITY, not that printed on the label. I would highly recommend the periodic testing of your packs with either a charger/discharger capable of doing so or one of the commercially available analyzers that are being sold now.

'nuff said

Chris

[LCHelilover]

I just found it -- it's in a reply to the "A Few Words of Caution" Thread

Thanks :arggg:

[misskimo]

Thanks Chris , YOUR'E THE MAN!!

HUH! lipos are like us then , breaken in a pack of lipos is like growing up , so like 12 flights , the batteries are grown up " nice and strong" till , around 40 flights , like Im 40 now , and going down hill, or over the hill , but Im not swelled up
huh? something to chew on huh? :smokin: