DJI S800 - know your weight....

[hazardpro]

Well this may be useful to someone so I will post it anyway.

Just weighed all the parts of our S800 set up, they are as follows:

6 x arms (complete) = 1860g
Nex7 with 16mm = 440g
2 x Zippy 5000mah & battery tray = 1553g
Frame: Wookong | OSD | Datalink | Optima 9 | Wiring = 821g
DJI Retractable Legs | Zenmuse | Optima 9 | DJI Transmitter | Wiring = 2324g

Total weight.... 6998g 8-|

That's about as close as your going to get to the limit! That helps explain why we are only seeing 8.5mins flight time!

 

[Zzr]

How many c rating for your zippy? It can't be possible for 8.5 mins? Your S-800 is too heavy weight.
A few month ago flown my S-800 with old LG abt 12 mins of flight time, less 6g but two months ago I added RLG on my S-800. will result later. I recently ordered ACE 10000Mah 25C which weight is 1.35g It will arrive here abt 2 weeks. I think maybe about between 14 to 15 mins flight time.

My S-800 weight
2.6Kg S800
1.25Kg Zen
118g WKM
50g bracket gps not sure
56g iosd Mark II
60g data link
875g RLG -400g from old LG removed
269g Nex 5
70g pancake lens 16mm
100g Spektrum receiver and Telemetry
39g FPV
1220g zippy 8000mAh
Total
6707g-400g = 6307g

 

[hazardpro]

Hi Zzr

Would the C rating effect flight time? They are 20C

We actually flew for 9mins & 9.5mins but the batteries were down to 14%..... not wanting to go below 20% Im estimating the 8.5mins.

Problem is, because we are so close to the 7KG limit any other battery (which are heavier) would push us over the 7KG mark (we need to stay under that to fly here.)

Doug

 

[hazardpro]

Pretty much the only diff in our set ups in the retractable legs and camera. I know high torque servers can be power hungry, but cant see them making that much difference.

Hmmmm

Did you actually weight your stuff or take figures from DJI? Some of your figures dont match mine.... I actually weighed mine on scales..

Anyway, the Ace batteries look pretty good... light.... (actually says 1.214KG on their website).

 

[hazardpro]

Only other slightly odd thing... which makes me wonder if my battery checker is faulty....

After our flights we checked the batteries, each cell was reading 14% but with a cell voltage of 3.76-3.78v

If my understanding is correct, that voltage per cell would be something more like 28%?


Also after flight as above they were reading 14%, then when we got back home and put them on charge they were reading 34% (I know this would raise slightly if you let the battery sit for a while)...

hmmmm

 

[Zzr]

how much a cell or pack can discharge in amps. C always equals the capacity of a cell or pack. For Example Let use your 2x5000mAh pack rated for 20C. C=10000mah, The number before the "C" is the multiplier. so 20X10000 = 200000mAh, to get amps divide by 1000mAh = 1 amp. 200000/1000 = (200amps)
IF 1x10000mAh pack rated for 25C equal is 250amps.
IF 2x5000mAh 35C for 350amps is best but bit more weight
1 x Zippy 8000mAh 30C (240amp) is lighter weight/high discharge than 2x5000mAh 20C (200amp).

Hi Zzr

Would the C rating effect flight time? They are 20C

We actually flew for 9mins & 9.5mins but the batteries were down to 14%..... not wanting to go below 20% Im estimating the 8.5mins.

Problem is, because we are so close to the 7KG limit any other battery (which are heavier) would push us over the 7KG mark (we need to stay under that to fly here.)

Doug

 

[Zzr]

I just figured from DJI. I cant find scale weight damn it! I ordered it from
http://www.soodohobby.com/ACE-22-2V...S800-Hexa-Multicopter-1345g-Soodohobby_g.html

Pretty much the only diff in our set ups in the retractable legs and camera. I know high torque servers can be power hungry, but cant see them making that much difference.

Hmmmm

Did you actually weight your stuff or take figures from DJI? Some of your figures dont match mine.... I actually weighed mine on scales..

Anyway, the Ace batteries look pretty good... light.... (actually says 1.214KG on their website).

 

[Zzr]

That's normal I used telemary voltage down to 22.2v from 25v about 10 mins of flight time. I stopped fly while go up to 22.5v by itself. I charged my zippy upload about 5800mAh of 8000mAh. I used one zippy 8000mAh 30c.

Only other slightly odd thing... which makes me wonder if my battery checker is faulty....

After our flights we checked the batteries, each cell was reading 14% but with a cell voltage of 3.76-3.78v

If my understanding is correct, that voltage per cell would be something more like 28%?


Also after flight as above they were reading 14%, then when we got back home and put them on charge they were reading 34% (I know this would raise slightly if you let the battery sit for a while)...

hmmmm

 

[Zzr]

I don't see anyone fly the S800 with TP 7700mAh 65C
TP 7700mAh 65C is (500 Amp) 1211g $350
65C is real C rating?
http://store.batteryspecialists.com/tp77006spp65.html

 

[hazardpro]

Ok, so is anyone able to confirm the following points:

After use each cell was reading 3.76-3.78v = this should mean 28% left no? (not 14% as per my reader)

Also perhaps the low C rating is a problem? I didnt think the C rating would actually effect the flight time, (10000mAh is 10000mAh).... I thopugh the C rating was just how many Amps can be drawn from battery at once?


Thanks

Doug

 

[FerdinandK]

@hazardpro,

it is not important what voltage you have after the flight, the voltage during the flight is important. I would not go below 3,5V (a cell) during the flight. This you can only see with some telemetry, or OSD. I am not sure about the outside temperature at your side, but the Zippys are pretty sensible with that point, so preheating them (and isolate them) in Wintertime is a good thing to do. If you get 12min with 6kg, 8min with 7kg is ok. Eventually you mistreated your batteries already some times, this you also notice immediately in the flighttime. It is also a difference if you hover around or you really "fly".


best regards

Ferdinand

 

[hazardpro]

Thanks although that doesn't answer the Q's.

I'm trying to establish if 3.76-3.78v per cell = 14% or 28%

The DJI OSD only gives total voltage, and I cant get the calculator out whilst Im flying. :nevreness:

I normally fly, then check battery - get close to say 25% after a flight... and that = the average flying time I can safely run.

At the moment Im (according to my battery checker) only going to get 8.5mins..... HOWEVER, my battery checker was displaying a % of 14.... this doesn't tally up with the cell voltage it was showing (or at least that is what I believe / am trying to establish)..

Thanks

Doug

 

[FerdinandK]

3,5x6 = 21V so if you get close to 21V-> land the copter.

How much is left in the battery (with a given voltage) depends on the temperature, the condition of the battery, how many cycles, cells already damaged or not ... I would not count on the quantitative message of your battery checker.

best regards

Ferdinand

 

[hazardpro]

Hi thanks for the reply.

So you reckon safest thing it to be guided by OSD voltage display? Fly until (lets say 21.5V) for safe flight.... time it (eg 10mins) and that should be a 'safe' flight time.

Doug

 

[FerdinandK]

There is no "save" flight time, if something goes wrong (a motor draws more than ususal, ...) the voltage will drop more rapidly ... . My experience is, you should monitor the voltage of your battery during flight and learn how it behaves. In my experience I learned, that 3,7V (a Cell) so 22,2 Volt on 6S is the "point of no return" (voltage under load). At 3,6V (a Cell) so 21,6V for 6S you should think of coming close to the point where you want to land (should be reachable within short time) . If you are at 3,5Volt (a Cell) 21V for 6S you should land the copter with seconds. How long the flight-time is at the end, depends on your flight (hover, fast forward, ...), on the conditions (weather, temperature, battery, ...). If you have telemetry, use it, react on the numbers displayed. Telemetry is great if it uses a "free channel to your brain", e.g. acoustic message on the voltage (alarm beep at a certain level is not sufficient).

Here an example that something unexpected can happen:
During this flight, I noticed, that the voltage of the battery was dropping "too fast", so faster as I would have expected, which forced me to return, and not rely on the "usual" airtime this copter typically has:

Just as a summary:
There is no save flighttime!
If you have telemetry, use it!

best regards

Ferdinand

 

[hazardpro]

Thanks for your help.

So I guess running DJI battery failsafe is not such a bad idea?

I have been unable to find/work out the optimal failsafe settings for our set up. We have it turned off at present.

Our telemetry only gives total voltage, I don't think that is sufficient?

Thanks

Doug

 

[FerdinandK]

DJI-Failsave, takes over at some point, that is always bad, you should be in control, always.

You only get the total voltage, but you can monitor it over time (at every moment), if you take that serious, you will learn to know what is "normal", and when voltage is dropping "rapidly" or when "something is wrong". Lipo-Batteries do not age "over night", if you have a look at them at the end of every flight (at the cell voltages) and at the end of recharging, you will notice very early when a cell is going to die.

If total voltage is not sufficient, what do you want more?

best regards

Ferdinand

 

[r44heli]

Hi Guys,

I had a long chat with Charlie Wang, the CEO of ThunderPower a few years ago, and, If I remember correctly, he said that 3.3v per cell was a good voltage to set the
alarm at. He advised that if you go under this voltage its actually not that critical, but it does reduce the useful cycle life of the pack. I also seem to remember that he
mentioned NEVER go below 3v per cell.

On our S800 we use 22v as the first protection alarm and land with at least 21v showing on the Telemetry readout. Using this method with 2 x 5000/6S/30C packs in parallel
we get a consistent 15 minute flight with Z15 and Sony NEX5R.

 

[FerdinandK]

If you would monitor the single cell voltage on a multicopter with a sensitive Voltmeter, you would be surprised what you see. Our ESCs are not running at 30% when hovering, They run bursts of 100% for 30% of the time. Since we have a lot of ESCs on our multicopter, the peak loads on the battery are dramatic. You will not see this peaks in our telemetry / OSD displays/logs, but if you attach a sensitive Voltmeter, it will show that even if you are above 3,5V on average (what you see in the telemetry), during this load peaks your go close or even below 3,0V (just for milliseconds or even less time, but the LiPo-Batteries will "remember").

best regards

Ferdinand

 

[hazardpro]

Hi Guys,

I had a long chat with Charlie Wang, the CEO of ThunderPower a few years ago, and, If I remember correctly, he said that 3.3v per cell was a good voltage to set the
alarm at. He advised that if you go under this voltage its actually not that critical, but it does reduce the useful cycle life of the pack. I also seem to remember that he
mentioned NEVER go below 3v per cell.

On our S800 we use 22v as the first protection alarm and land with at least 21v showing on the Telemetry readout. Using this method with 2 x 5000/6S/30C packs in parallel
we get a consistent 15 minute flight with Z15 and Sony NEX5R.

Hi thanks this is really helpful... Can I ask which batteries you run? It's odd that ours were reading 14% at 3.77v.... It has to be more than 14%....