Dec 23, 2008, 05:16 PM
In search of RC nirvana
USA, MO, St Louis
Joined Jun 2007
1,115 Posts
Quote:
 Originally Posted by Thekid3418 Another key if you're going to abuse lipos is to not discharge them as much, a lipo will be much happier only discharging to 50% or 40% of its capacity. If you push every flight down to 20% (the recommended level), your batteries will start wearing out sooner. The further your batteries are drained the more likely they are to have differenent voltages in the cells, this will cause wear and tear
This has been my experience as well. I have several of the uber cheap Mystery 2400 mAh 15C packs with over 100 cycles on them and they are still going strong. But I only use about 60% of the total capacity each flight.
 Dec 23, 2008, 06:57 PM Spritual Pilot Silicon Valley, CA Joined May 2001 677 Posts How do you know the percentage of battery discharge? Let's say the battery capacity is 4s 2200mah. Could you explanin more what it means by only 50% of the capacity? Is there any good way to measure that the battery contains 1100mah at some point? Or, the voltage will tell the capacity? Last edited by jnyoun; Dec 23, 2008 at 07:36 PM.
Dec 23, 2008, 08:51 PM
United States, OH, Toledo
Joined Feb 2008
1,969 Posts
Quote:
 Originally Posted by jnyoun How do you know the percentage of battery discharge? Let's say the battery capacity is 4s 2200mah. Could you explanin more what it means by only 50% of the capacity? Is there any good way to measure that the battery contains 1100mah at some point? Or, the voltage will tell the capacity?

Time your flights and then see how many mah's go back into the battery to charge it full. Then adjust your flight times from there.

If you fly your 2200mah battery for 5 mins and then recharge and it takes 1100mah back in then you know a 5 min flight will take you down to approx 50% depending on throttle variations during each flight.
 Dec 23, 2008, 10:35 PM The Kid Detroit, MI Joined Dec 2007 2,587 Posts Yeah, you really just have to get a feel for it. It all depends on how much WOT you use, and how aggressive of a setup you are using. I would say if you kept a flight around 4 minutes you'd be fine. I usually fly my stuff for 5 minutes. And im either on throttle or off, not really inbetween. I just guess at it. You have to get a feel for how your batteries react too. If you fly them down to 50% and they are fine (no balance issues, warm to the touch) then you know you can fly a little longer. Its just if you push it in every way time in and time out, thats when they become unhappy
 Dec 23, 2008, 10:40 PM LOVE MAIDEN'S : > norfolk va Joined Aug 2007 1,480 Posts there should be a way to tell by the voltage..but im not that bright...pun intended
Dec 24, 2008, 12:52 AM
Crash - Rebuild - Repeat
Atlanta, GA
Joined Aug 2007
502 Posts
Quote:
 Originally Posted by jnyoun How do you know the percentage of battery discharge? Let's say the battery capacity is 4s 2200mah. Could you explanin more what it means by only 50% of the capacity? Is there any good way to measure that the battery contains 1100mah at some point? Or, the voltage will tell the capacity?
50% of capacity = 1/2 of the mAh rating of your pack. If you have a 2200 mAh pack...then 50% = 1100 mAh. Think of your mAh as Fuel. Voltage = power. If your pack drops below 3.0 volt per cell (12.0 for a 4S), you should be landing...regardless of how many theoretical mAh are left in the pack. I have some 3S2200 ThunderPower V2 packs that hit 9V with only 1600 mAh expended....theoretically, I still have 600 mAh to go...but reality says..."Land!"

As for how to tell when you're at 50%:

1. Time your flight and then charge your pack. Your charger will tell you how many mAh you used, and use some math from there.

2. Use an in-flight telemetry system that can report back to you. EagleTree makes one, and there are some out there that will even talk to you.

Personally, I use math. And I use it before I ever maiden a plane...

Flight time = Battery Capacity (Amps, not mAh) * 60 / Draw.

So, at 40 amps, using a battery with a capacity of 2200mah

Flight time = (2.2 * 60)/40
Flight time = 3.3 minutes or 3 minutes 18 seconds WOT

I hope this helps.

-Eric
Dec 24, 2008, 03:22 AM
Spritual Pilot
Silicon Valley, CA
Joined May 2001
677 Posts
Well, I am a little bit surprized that you are following all of these complicated procedures to figure out the discharge capacity. In my case, even until two weeks ago, my lipo charger did not have a LCD to show the charged capacity. Seems like it is going to be far beyond what I expected, hobby..

By the way, I have been using my home-made Lipo charger almost for 5 years. I have never had any problem so far. A few month ago, I started to use it with balancer. However, without balancer, it just worked fine.

Unfortunately, my DIY charger only supports 3s packs. Two weeks ago, because of the need of 4s packs, I purchased Turnigy ACC-6 charger. It worked good, but not that much better than my old charger.

The picture below was taken in 2003. I am still using it. Probably, I charged a couple hundred times so far. It is rather safer because the number of electric componet are small and the circuit is simple (less chance to broke)..and it can be immediately detected any problem if it has...(However, I don't recommend to use this kind of charger for your safety).

Images

Last edited by jnyoun; Dec 24, 2008 at 04:02 AM.
 Dec 24, 2008, 09:19 AM The Flying Herb Santa Barbara, California Joined Jul 2007 429 Posts a bit paranoid? i put my batteries in and run them until they stop. same lipos for over a year charging them everyday....i even balance them once in a while. just fly.
 Dec 24, 2008, 11:17 AM zoom zoom USA, NJ, Mt Laurel Joined Oct 2007 3,735 Posts yup i fly to 2.9 volts/cell everytime i get around 100 discharges
Dec 24, 2008, 03:32 PM
Crash - Rebuild - Repeat
Atlanta, GA
Joined Aug 2007
502 Posts
Quote:
 Originally Posted by rstein9 i put my batteries in and run them until they stop.
Yup...I do that with my slow stuff...like my Speedwing EX, or my foamies. But when I have a high wing loaded bullet flying around at 130+ MPH...I like to know when I'm low on gas and need to land.

If I fly until the pack is exhausted...I only get one shot at a landing...and sometimes I need 2 or 3 passes to bleed the speed enough for a touchdown where I want it. That...and the fact that I enjoy Math...it's not too hard for me to figure out when I'm running dry

-Eric
 Dec 24, 2008, 04:19 PM Suspended Account Joined Jan 2005 1,752 Posts Can you guys post the duration of your flights and when(if) you set your timer alarn. Thanks and please don't leave out details. My set-up with micro-dan 2505 2800kv on Fusion 3s 2200 lipo has been an exciting plane, but winter temps prevent concluding any real data. I limit flights to too cold fingers at 6 minutes, but the reality might be ~11 minutes which is more than enough flight time. Landings on snow have been smooth with one exception at 24 deg which did not appear to make the foam brittle. I am surprised that the heavier inrunner motors dominate, especially since the microdan 4800kv "velocity" motor is a 600 watt motor that should satisfy most speed freaks?
Dec 24, 2008, 04:35 PM
What smoke?
SoCal
Joined Feb 2008
279 Posts
Quote:
 Originally Posted by lammy1000 I am surprised that the heavier inrunner motors dominate, especially since the microdan 4800kv "velocity" motor is a 600 watt motor that should satisfy most speed freaks?
I use the Medusa in-runner and can say when running next to a microdan you can really see a power different, even when I see Arc motors next to the microdan.

The microdan is ok but doesn't have some speed or punch out like a good in-runner can do. Don't get me wrong they are good motors but it's like saying I'll have the store brand soda because they almost taste the same as a Pepsi or Coca Cola.
Dec 24, 2008, 06:24 PM
In search of RC nirvana
USA, MO, St Louis
Joined Jun 2007
1,115 Posts
Quote:
 Originally Posted by neiloneil there should be a way to tell by the voltage..but im not that bright...pun intended
There is clearly a correlation between pack voltage and % discharge, however I'm not sure how consistent this correlation is between different brands of batteries. However, I do know that 3.8V/cell (resting) is about 40% capacity for both Mystery packs as well as the silver Zippies.
Dec 24, 2008, 07:04 PM
In search of RC nirvana
USA, MO, St Louis
Joined Jun 2007
1,115 Posts
Quote:
 Originally Posted by lammy1000 Can you guys post the duration of your flights and when(if) you set your timer alarn. Thanks and please don't leave out details. My set-up with micro-dan 2505 2800kv on Fusion 3s 2200 lipo has been an exciting plane, but winter temps prevent concluding any real data. I limit flights to too cold fingers at 6 minutes, but the reality might be ~11 minutes which is more than enough flight time. Landings on snow have been smooth with one exception at 24 deg which did not appear to make the foam brittle.
With my Suppo 2212-06 (2200 kv) and APC 5.1x4.5E prop I'm averaging about 10 amps in flight, which should yield about 12 minutes of flight from my 2400 mAh Mystery packs without exceeding 80% capacity. This motor/prop combo pulls about 18 amps at WOT, which is probably about as low as it gets in this forum.
Quote:
 Originally Posted by lammy1000 I am surprised that the heavier inrunner motors dominate, especially since the microdan 4800kv "velocity" motor is a 600 watt motor that should satisfy most speed freaks?
Some of the 47 mm ARC motors (eg the 1.5T) can handle 1000 watts continuously and 2000 watts for short periods. When you have that much power behind you, an extra 3 ounces of AUW is negligible. At around 500 watts, when the MD 2505 starts to sweat, the big ARCs are still running efficiently. The MD 4800 is designed for a 4" prop (and even then you're up to 50-60 amps on 3s) that won't provide much thrust (20 ounces) for a FJ. I'm not dogging the MDs - they clearly have their place. But so do the big inrunners.
 Dec 25, 2008, 12:12 AM USA, NH Joined Sep 2004 293 Posts Merry Xmas