RC newbie, advice needed

[Fyathyrio]

11.1v is just the normal lowest voltage 3S cells are advertised at, they run between 12.6vdc max and 11.1 min during normal use. (You can run them lower than 11.1v, but they won't last as long.) Set your charger to the storage function and let it do it's thing.

 

[BodgeIt]

So I really need a low voltage alarm to tell me when its running low? Thanks again for the info guys, its incredibly helpful.

Edit: My ESC has a built in low voltage cut, so thats fine. I have downloaded the PDF, sorry for not searching harder first.

 

[Fyathyrio]

It's generally not a good thing to have the ESC warn you when the cell is low...by that point it's usually lower than the recommended 3.7v/cell, and the whole airplane in the air running out of power thing.

Best way to do it is use a timer if your radio as one, even a simple kitchen timer can work if you remember to start it. Fly for a set time, such as 5 minutes, check voltage, fly for 7 minutes, check voltage, ect. The goal is to set the timer to where you reliably land with the battery pack at about 3.7v per cell, or 11.1v on your 3S battery. The battery will be a little lower when you first land, they recover some as they sit and cool down after use, so don't worry if you see 3.65v at first, for example.

This website helped me learn all about proper care and feeding of my lipo batteries. Check out the other articles concerning charging, chargers, power supplies, and parallel charging if you have any other questions, very informative.

 

[rcspaceflight]

Do not be like Josh Bixler and ruin batteries by waiting for your ESC to tell you that your battery is low.

I don't really have any good advice for how long you use your batteries. I do not have a voltage alarm. Generally I fly for a short time, charge the battery, and then I know if I could have flown for a lot longer or just a little longer. I don't use a timer either. I go by how long I think the flight was and how long I think the flight can be. It works for me especially since I'm careful and I'd rather fly half of a battery than ruin it. But a low voltage alarm and/or a timer is a great idea. Just know that how you fly changes your flight time.

 

[BodgeIt]

Low voltage alarm it is! My ESC instructions say I can put a higher limit on there, so I will read up on that (hopefully it warns me before its genuinely low). I have put my battery on a 'storage mode' charge, so I know its safe. One thing I am a little confused with, (Its this battery) is that the battery specifies 1-3C charge, but what does that mean in amps?

I have just purchased a low voltage alarm, what should I set it to, 3.8V?

Edit again: I tried using DriveCalc, but I dont really know what I am looking at. Im just trying to work out what prop size suits my purchased electronics the best without demanding too much from the motor. Im off to read up more, my brain is being frazzled.

 

[Fyathyrio]

C = charge rate. Charge rate is battery capacity X advertised rate (three in this case).

2200mah = 2.2A = charge rate of 2.2A @ 1C, 4.4A @ 2C, 6.6A @ 3C (C is just the multiplier of battery capacity.)

Lipo batteries have a limited number of charge/discharge cycles, and heat can damage them, so most folks I know stick to around 1C or maybe a bit higher. A slower charge rate will get more energy back in the cell also. In order to save time, many will do what's called parallel charging, where more than one battery is charged at a time...the process is explained on the website I linked earlier.

 

[mjmccarron]

My ESC instructions say I can put a higher limit on there, so I will read up on that (hopefully it warns me before its genuinely low).

I had an issue with mine cutting out at full throttle when I set it high. The current load at full throttle on my setup was enough to momentarily drop the voltage to the ESC and trigger the low voltage shut off. The wires from the battery to the ESC were a bit light. The low voltage alarm is your best bet.

Mike

 

[BodgeIt]

I have so much respect for you guys, it seems simple on the face of it but there is a lot of math/thinking involved to get a good result. I also really do appreciate the constant advice and information, it really helps. Thank you. I have bought a low voltage alarm, and I will set it at 3.8V. I will charge my battery at 2.2A, I will only be flying once a day (itl take me more than a day to repair it after each flight!).

 

[Fyathyrio]

When the battery is under load, voltage becomes somewhat fluid throughout the system. For example, you may hit 3.8v right after takeoff while still under full throttle gaining altitude...but once you throttle back voltage will go back up. What this means is the alarm will start to beep briefly, but overall voltage after resting will be higher than the alarm set point. On my quads I set the alarm at 3.5v, and once I land and shut off the motors the cells are at about 3.7vdc. Starting conservative is good, just don't be surprised if your voltage is higher once you land.

 

[BodgeIt]

So if I were to set it around 3.6v and it goes off within the first minute or two I can ignore it as its probably just the motor drawing a lot of power gaining altitude. Thanks for the heads up, just got to figure out how to wire it now!

 

[Fyathyrio]

If you get one like this, all you have to do is plug it into the balance plug. Just look for one that has an adjustable range as some come fixed at low values like 3.3/cell. The one I linked is also a little large for these planes, just wanted to show you an idea and I know there's different options on ebay UK.

Just add a small bit of velcro and attach it to the plane. Also comes in handy for checking cell voltage at home or before you send the plane up...no accidental launches with low battery.