eastcoast

well i wanted too know Approx how many Flights i could expect out of my 2700Mah Nimh Battery ,so i did a little test too get a idea,im still learning about Battery's ,so if anyone has any input,By all means feel free...

I did a test too kinda get a idea on Approx how many flights i would get out of a 2700mah and this is what i came up with.
Plane-GP Cherokee/Radio-DX6i/Servos- 7 Futaba 3004's/Sanyo2700mah 5C 6V battery/Engine-OS 46AX.
Radio is set for 12 minute flights.

-Battery fully charged @7.50V 2700mah
- ive been told its good Practice too recharge a Battery when i drops too around 6V

- First i checked the Voltage of the battery and it read 6.26...(I was using the battery off on on for the last few days while adjusting some settings in the TX,so it was dropped too 6.26).
- Powered up TX then RX and pulled my trainer Switch too start the timer and moved the servos as if were flying /taxing for the whole 12 mins. when 12 min was up shut off RX/TX.
- used a digital muti-meter and tested the voltage of battery,readings were 6.15
- .11 volts used on a 12 min flight

so if battery is full at 7.5V and recharge is at 6V that gives you
1.50Volts of flying time 1.50V/.11 =13.6
so in theory you should get Appox 13 flights on a fully charged 6volt battery.
that was yesterday and today i rechecked the voltage of the battery and the reading was 6.18 form 6.15 yeasteday after my first test,im planning on doing it 2-3 test ,jsut too see for consistency.

The Ghost

The only way to find out how many flights you will get out of an RX pack is to fully charge the pack and then fly as many filghts as you can measuring the pack between each filght as every filght is different (different servo use). You will have to do this with every plane and battery setup as they are all different Then you will know haow many flights or total flight time you can get. Doing the measurement on the ground will be a lot less than in the air as there is no vibration from engine or load on the flight surfaces.

Cheers

Korps

I can be wrong here, but 13 flights seems a bit too much. On one of my planes I have a 4.8v 2000/2200mah (can't remember now off the top of my head) battery running 5 servos on a ghz system. I check my battery before every flight and have never gone pass 5 flights and only did this once (when I was on mhz) - then the reading starts getting too low for my liking. I do not have the precise voltage since the load tester only has a low, two medium and two high reading lights. After 5 flights it usually loads to about the last medium light (just before low). My flying time is anywhere between 7 - 10 minutes.

I'm sure someone with more indepth knowledge will give a more correct and appropriate answer.

Korps

Yes what Ghost is saying is very true. Each flight is different since sometimes you will use more surface inputs etc etc.

TexasAirBoss

My Feedback: (22)

I fly 6 flights on a 600 mah battery. Your 2700 mah battery is huge !! I would think you could get 25 flights, in theory. I wouldn't try it. But I think 13 flights is well within reason.

el-John-o

There are two issues with this that I would caution you about.

1- There is a bit of a 'curve' where the battery discharges less at X charge, more at X charge, so as others have said, recharge it and see how many flights you get!

2- as your flying through the air it takes a heck of alot more power to move a control surface than if stationary on the ground.  And, of course, flights are different.  In theory, your servos will have more draw in the air than on the ground because of the greater amount of force they need to exert.

If you do still want to test it on the ground, my suggestion, if you have a simulator, use your DX6i transmitter, and leave the Rx on, that would be the most consistent and realistic test (jt would, in essence, be almost the same movements as a real flight.)

CGRetired

My Feedback: (1)

Easy solution. Install a Voltwatch II. Set it for 6 volt pack and fly. Look at it before and after each flight. When it starts to flicker down in to the yellow, charge it.

With 2700 mah that should last you pretty much all day of normal fying, but with the voltwatch II installed, and if you look at it before and after each flight, well, you are assured that your battery is performing and has an adequate charge for the next flight, OR if it is ready to recharge.

CGr.

bkdavy

My Feedback: (1)

A better way to determine your flight times.

Get an amp meter and connect it between the battery and the reciever, with the battery fully charged (most multimeters have this function anyway, and they can be found pretty inexpensively). Turn on the plane and measure the current draw with the servos at full deflection. Now multiply that number by 1.25 or 1.5 for a safety margin. This should closely approximate the full current draw from the plane in flight (yeah I know its not perfect, but its a good estimate).

Now hook up your battery to a loaded volt meter. This should put about a 200 ma drain on the battery. Now use graph paper to plot the voltage vs. time. Plot it about every 5 minutes until the voltage drops to about 1.15 volts/cell. That's approximately 5.75 volts for a 6 volt battery, or 4.6 volts for a 4.8 volt battery. Then plot it every minute. For 600 mah reciever pack, this should take about 2-3 hours.

With this plot, you'll see the "knee" where the voltage begins to drop off quickly. This is the fully discharged point. Select the mid point of that Knee. You know that the battery has been discharging at approximately 200 ma. You can even measure the rate while your discharging for better data.

Using the discharge rate for your plane, assume a 10 minute flight, determine the current needed for a single flight. (Current x Flight time= mah needed.) Use that figure and divide by the discharge rate used for your discharge curve. This will give you the amount of time before the knee that marks the "no fly voltage".

You'll probably be surprised where this voltage occurs. Many myths about battery voltage continue to be propagated. For NiMH and NiCd batteries, your fully discharged point is generally considered 1.1 volts/cell, or 4.4 and 5.5 volts for 4.8 and 6 volt batteries respectively. Nominal voltage is 1.2 volts/cell Flying to 1.15 volts/cell should give you about 80 percent discharge.

For our typical 40 size plane, on a 600 MAH pack, that equates to about 2 hours of flight time, or about 10-12 10 minute flights.

With 7 servos, you might be drawing 300-400 ma in flight, depending on your flying style. With a 2700 mah pack, that equates to 6 hours of flight, or over 30 flights.

Just for comparison, I have a 30 percent Yak-54 with 5 HS-7955 TG servos. I have a 2300 mah A123 battery that powers all servos and the ignition (an additional 400 ma load). This plane will easily fly 6 10-minute flights (60 minutes of flight time) and only draw 75% out of the battery flying the IMAC basic routine.

Brad

Rudolph Hart

When it comes to electronics i'm dazzled.Ghost rider has answered the question in the most meaningful way,onya mate!

KW_Counter

Eastcoast,
Your statement:
"- ive been told its good Practice too recharge a Battery when i drops too around 6V"
is false.
I assume you are talking about a 5 cell pack.
At 1.2 volts per cell nominal voltage at 6 volts you have a lot of power left.
When you go below that voltage it is time to think about stopping.
When I cycle my batteries I take them to .9 volts per cell.
For safety I don't fly below 1.0 volts per cell.
Others have their own safety threshold, 1.1 is very reasonable and safe,
but 1.2 is robbing you of a lot of flying.
With the size of batteries you are using you will probably be to tired to fly before
it runs out of energy.
Good Luck,
KW_Counter

eastcoast

yes KW i was wondering that as well,as you know on here everyone has different opinions on what/not too do...
I also cycle mine at 4.5V cut off.I knew that doing these test Static would kinda give me a idea,and with wing-load/air moving over the control surface's that it would draw more juice from the battery.
Im planning on doing it at the field as well too see what the voltage drop well be as well,and compare it.I know from reading pretty much every page on this forum ,theirs alot of questions on how much battery life can someone expect out of there battery.
I think this is a good starting point for beginners on the (How too) concept of it. with simple math.

You said "At 1.2 volts per cell nominal voltage at 6 volts you have a lot of power left.
When you go below that voltage it is time to think about stopping."
So why not Stop at 6V then and recharge? instead of thinking about it. But you are right,say i 10 flights (flying) instead of (13) static out of the 1.5Volts in my test.It well Prob be time too call it a day.

Cheers
Mike

pdm52956

My Feedback: (1)

Science.........what a wonderful invention. Problem I have with it is that no matter how much math you use, or how complicated you make it, something simple will come up and disprove what you spent all the time proving.

I figure that it's nice to know in theory how many flights you can get, but in reality I find a couple minutes checking the voltage of my battery between flights a lot less expensive in the long run.

Just my thoughts.

bkdavy

My Feedback: (1)

This thread is focused on NiMH batteries, but other battery chemistries aren't quite as forgiving. Checking the voltage before the flight works very well for batteries with a relatively linear sloped discharge curve. If you ever switch to A123 batteries, this paradigm goes out the window. These batteries have a very flat discharge curve at 3.3 volts/cell. From a fully charged condition at 3.6 volts'cell, they rapidly drop to 3.3 volts and stay there for 80-90% of the capacity. When they drop off, they drop off very quickly. Consequently, for the A123 batteries I've found that its more effective to keep track of the number of flights rather than rely on a battery voltage.

In reality, its probably worthwhile to do both. Know how many flights you should expect, keep track of the flights you've had, and check the voltage. If these two indicators diverge significantly, look for a problem.

Brad

eastcoast

LOL how does it cost your more buy doing a few Static test verses a test at the field during flights? I know there well be a more of a load on a battery while flying verse's doing a static voltage measurement. And i was saying i put it in the beginners forums on behalf of someone new too RC and would like a little insight.

gboulton

My Feedback: (15)

I wrote a piece of software to handle my battery capacity.  it's based on pdm's rules above...

pdm52956

My Feedback: (1)

Point was that taking a few idle minutes checking the battery, or batteries, between flights here and there would serve the beginner more than relying on the math required to calculate how much flight time that same battery will supply. With the choices available in battery technology, checking and charging if needed doesn't take all that long.

Like was said, each and every flight is different, draws different current and once you do hit that point where the discharge curve drops off the cliff, checking that battery before hand would save you the possilbe cost of that plane and gear. The beginner may just have enough on his mind in trying to fly the plane straight without being concerned if he is pressing the envelope on his battery or not.

I guess I just prefer to rely on actual flight testing rather than simulated static tests. You are only going to simulate that flight time to a certain degree while static, and there isn't a need to in this case.

Like I said, "just my thoughts". Happy flying!

pdm52956

My Feedback: (1)

Computer geek! LOL

CGRetired

My Feedback: (1)

Voltwatch II $10.99.

Done.

CGr

geeter

My Feedback: (110)

i wouldn't be so conserned about the amount of flights you get ,or don't get on a battery pack. charge you tx and rx batteries before flight and don't worry. also use a voltwatch as stated and your good to go.......my .02..............RON

gboulton

My Feedback: (15)

gboulton's handy dandy non-existant not_actually_usable software...

$0.00

Done.

*lol*

pdm52956

My Feedback: (1)

Taking a plane home in one piece............priceless!

koolkrabber47

My Feedback: (6)

keep in mind he's running seven servos.....even with the bigger battery, that's quite a drain.......it also depends on the style of plane..... a trainer type plane stays straight and level much of the time and that puts minimul drain on the servos because your not moving the control surfaces much.........a sport plane or a 3d'er would be switching directions all the time and put more strain on the servos and most likely use larger, faster, more powerful servos.......best way to test it would be to just fly it and keep checking the voltage........for the sake of safety, i alway's check my batteries before i leave the house, at the field and after every flight.......even if you charge and check your batteries the night before and the day of, there's always the possibility you might bump the switch, accidently, when loading your vehicle or in transport they might rub together, so it's a good idea to check your batteries "preflight"......you don't want any surprises, like the pictures below.......JMHO, after 25+ years of flying.......thanx for listening, hope this helps????........(KOOLKRABBER47).........

CGRetired

My Feedback: (1)

fatfreddy17

My Feedback: (43)

Immediately after each flight you need to check your battery voltage UNDERLOAD!!

"Voltwatch" has no load, which is great if you are going to fly your plane under NOLOAD. If you have a bad cell Voltwatch won't help you.

Try something like this ,, http://www.horizonhobby.com/Products...?ProdID=HAN171

It is $40, but when compared to the cost of your airplane,,,, it really sucks to lose an airplane because of batteries run too low.

Also very important to charge and maintain your battery PROPERLY.

koolkrabber47

My Feedback: (6)

[quote]ORIGINAL: fatfreddy17

Immediately after each flight you need to check your battery voltage UNDER LOAD!!

''Voltwatch'' has no load, which is great if you are going to fly your plane under NO LOAD. If you have a bad cell Voltwatch won't help you.

Try something like this ,, http://www.horizonhobby.com/Products...?ProdID=HAN171

It is $40, but when compared to the cost of your airplane,,,, it really sucks to lose an airplane because of batteries run too low.

Also very important to charge and maintain your battery PROPERLY.
[/quote

that is a really nice DIGITAL volt meter........if the OP wants to save a little money he can buy a hobbico scaled volt meter for around $9.00 on e-bay or $25.00 at tower hobbies.......i bought my last two on e-bay for less than $10.00 shipped.......FYI, the term scaled means there are two color bars on the voltmeter......one red and one green.....very simple, green means your alright to fly, red means you need to charge your batteries first.......i know most flyers already know this but, i have to mention it for somebody out there that didn't........sure hope this helped.......(KOOLKRABBER47)...........