G'day DIY Drones,

I have a question about batteries, yes, I know this has been done to death, but I would like some real world experiences rather than the math.  

I have used the search bar but I guess I am not using the right keywords, hence the reason for this post.

I am considering using 1 10000mah 4s instead of 2 5000mah 4s batteries to get more flight time from my 690mm photography rig.

A bigger battery of the same C rating or close to it.

Here is the math (feel free to correct me if I'm wrong)

2 x 5000mah 4s at 25 C = 125 max amp draw and has 10000mah. Weight, approx 1300g

1 x 10000mah 4s at 25 C = 250 max amp draw and has 10000mah. Weight, approx 800-850g

I only need about 115 max amps so both will do the job.

My question is about flight time and battery voltage sag.

I don't want theory but real world experience please.

Will the 10A, lighter battery give me more flight time because of the weight saving or will the voltage drop off sooner because it is only a single battery?

Another way to put it would be, would the 2 5A batteries hold the voltage longer than the 1 10A battery given the same flight situations?

Another way to put it is, are two batteries that equal the one in MAh, better?

I hope I am making sense here 

Cheers

Aussie

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The persons who made the statement that parallel packs do not increase the available current was from one of the more legit sounding websites, but as a vendor all advice given is suspect.  I think the truth is that the 25C packs that I have produce a serious voltage lag when passing 50% of that C rating, and if you use packs with a much higher C rating than the calculated max load then the voltage lag should be minimized.  I plan on upgrading to 60C packs, when the funds make that possible. 

This leads to a different discussion of vendors and brand names that would probably be more appropriate for another site.  I would be happy to copy all my communications with my battery supplier, but I believe this venue is more focused on the technical isues and is not meant for that type of conversation.

Joe,

I agree that my failsafe values need to be adjusted down to avoid triggering the failsafe to soon.  I am currently set for failsafe at 16v, after a flight ending in battery failsafe, with no load, the packs are usually around 18.5v, and that seems to high, OR, my 25C batterys are so shy of adequate current capacity that when under load the voltage is dropping from 18.5v to below 16v at 90-102A.

I have stated that I have been flying my drone for 3-4 months,  I'm ready to fly farther and higher, but without confidence in the power, I need to stay close

iskess,

I don't have a battery brand preference at the moment.  I am using Zippy Flightmax from Hobby King presently.  What I was asking the community for was their real world experience and not so much a technical explanation.  

Although I must add that all of the info I have received from everyone here is great, and lets face it, the more knowledge you have the better you are at making an informed decision, but I was more after a "this is what I use and this is why and these are my results" type answer with a little bit of technical thrown in to back up the answer.

Cheers

Aussie

Alasdair,

My Hexa setup consists of a (genuine) Pixhawk with the 3DR battery monitor connected.  My batteries are 5000mah 30C Zippy Flightmax (x2).  The Pixhawk sends the battery voltage information via the 3DR telemetry to my iPad.

I always bring her home when the voltage reaches 13.7v total of both packs and get about 13 minutes before I bring her in.

My 1st question to you is, if i were to connect the balance leads, how would the Pixhawk differentiate the cell voltage of each?  Maybe that is asking too much of my current setup.

My 2nd question to you, (per the title of the post) is,do you recommend 1 or two batteries?

I would like your opinion

Cheers

Aussie

I do not understand why you do not tell me / us the AUW of your copter and Watt/Amperes needed to hover.

With this information we could help you more.

If your batteries get warm/hot because of very high Ampere drain , two batteries might get better heat dissipation and have more predictable behavior in time.

Pixhawk will continue to show you the average voltage even if you connect the balance leads.

With Pixhawk and 3Dr battery monitor you do not see each cell value.

Luc,
I haven't provided the info you ask for because it was the middle of the week when I posted my question and didn't know it was going to be such a topic.  All I asked for originally was what people have and why and an opinion for 1 or 2 batteries.  Please don't get me wrong, however, I am VERY appreciative for all the help this community is giving me.

HA! I thought it was going to be a simple question when I penned it.  Boy was I wrong!

It is piddling down rain right now and has been very windy the last few days, but I will try to get you the info today......weather permitting.

Thanks for taking an interest in my question mate

Cheers

Aussie

I am assuming you have a 4s setup.  

The voltage value for battery life you should pay attention to is the no load voltage which is a indicator of amount left in the battery.  About 3.6 per corresponds to 20 percent of capacity is left.  This is generally considered a safe value.  If you are coming down at 18.5 and you have another .5 Volts drop in battery voltage that would probably be acceptable.

You should also look at how many mah you are putting back into the battery after a charge. You want to be using about 80% of the available mah so for a 5000 pack this should be 4000mah.  Most good chargers will show you this value.  If you put back in 3000 you can probably lower the voltage a bit - if you put back in 5000 increase the cutoff voltage.

Batteries also degrade over time and abuse so keeping track of battery capacity is a good idea and adjust accordingly.

Being cautious is the best path - last thing you want is to kill expensive batteries or crash your craft so building confidence is in order. I always do test flights to confirm battery performance and flight time and make sure all is OK before going on longer flights that might come close to using battery capacity. I also usually do a close in flight to full capacity where i can land quickly of a issue arise before longer missions.

If you lose one cell in parallel batteries, the good battery is going to try to charge the bad battery, the overall voltage will drop to whatever the the lowest charge voltage the bad bad battery can develop under that charge, in any case the voltage will be lower and the good battery will discharge quickly,

In the case of series batteries the result is the max current will be limited to whatever the dead cell can pass, and overall voltage will be down by 1 cell.

So when using 2 batteries, you would have some redundancy and be able to get home in the case of a cell failure.  With only one battery, it would drop like a stone.  Correct?

Aussie

So really, there is a choice between redundancy and max flight time and a bit of a trade off.

1 battery (should) = more flight time due to weight saving

2 batteries (should) = slightly less flight time but redundancy in case of a cell failure

Yes?

Aussie

Luc:

I have a Y6 with pixhawk controller and six 700KV motors with 60A esc's.  Three 5S 25C 5000mah batterys.  I have very stable flights after the auto tune was complete.  flights consistently around 15 min that end in voltage dipping below 16v during flight.  after the flight the voltage with no load is 18 to 18.5v.

Each of the three battery packs have independent 10ga wires to the distribution board.  One battery has a 180A Ottopilot battery monitor.  In the pixhawk parameters I have calibrated Amps per volt to  result in a current reading that is consistent with motors listed no load current, and also, be in line with the hover current predicted by ecalc.  The results give me confidence that this is providing a close reading.

Sorry typo above I meant 5S

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