I just purchased a Hangar 9 Load meter which is pretty nice! But what voltage should I stop flying at for 4.8v setups and 6.0v setups? I would assume I am supposed to throw a .5, 1, or 2 amp load and check the voltage! I have to admit the ones with pretty green lights are easier to read! But I like the accuracy of this one. Shoulda came with instructions!

I think 1.1v per cell is the bottom of the line rule. So, 1.1v X 8Cells = 8.8v + a margin for error would be 8.9v bare minimum.

Patrick

Edit: Doh! Note to self, read post before replying Anyhow, it is the same RX batteries, 1.1v per cell for . e.g 4cells x 1.1 = 4.4v for 4.8v, 5cell x 1.1 = 5.5 for 6v and then add a margin.

Hey Robi, yes, getting a voltmeter is a step in the right direction! Some of the guys I fly with like to have lots of margin, as Figment mentioned and stop flying when they get to 5V on a 4 cell pack! That means 2 flight with some models with lots of servos! I'd like to suggest a method which will take a little of the guess work out. But it will take a discharger that measures time. Futaba has one that is "only" $40.

First charge overnight or whatever you do normally then discharge making note of the time. Next, charge the same way and remember the number of flights you made, then when you get home discharge again. This will give you an idea of how much battery power that particular plane uses. If you make it a habit to voltage check before each flight you will get to know the charateristics of that pack/plane and will probably be able to catch a battery going bad before it does any damage. If you periodically discharge the packs with the discharger, this is also another good way to catch a pack going bad.

Seems like a bit of work, but gives me piece of mind, especially since a voltage check by itself is not a perfect indicator of charge.

Good luck!

On a 4.8 volt Rx pack I recharge when it drops to 4.7. On a 9.6 volt Tx pack I recharge at 9.5 volts.At 4.8 volts a pack is performing at it's rated capacity so it's good for several 10-12 minute flights. There is really no reason to charge them until it gets below that.
I used to have a phobia about batteries and overcharged them all the time. The battery life was significantly reduced. Since I have started running them down a little lower before charging they last a lot longer and hold their charge better. I don't use 6 volt packs so I won't comment on them.

WCB

Wow... too low for me...

1.2v per cell for the RX
1.1v per cell for the Tx

but thats just me...I like my planes

Okay, let me kick in my $.02. On a six volt pack, if the voltage under a 1 amp load is below 6.3 volts NiCad or 6.4 volts NiMH, I quick charge. I don't use 4.8's on much and the ones I run are in fun flies and are very small and light, so I always quick charge (smart charger) between every flight. The smart charger does not overcharge batteries like some other quick chargers. I use digital servos on almost everything anymore and they are known to suck amps, especially in aggressive 3D or aerobatic flying. I am just now starting into Lithium batteries, but doing so tenuously. Really trust the old reliable NiCads and NiMHs.

I cycle test my batteries once every two months with a Triton Charger, through three, charge/discharge cycles. If the pack isn't greater than 85% of rated capacity, the cord gets cut and the battery discarded. I have some NiCads and NiMH that are over 3 years old and still cycle over 95%. They are all Sanyo's.

You made a very smart investment in your meter. I have seen many planes lost, because of just one more flight for the day and the pilot didn't know his batteries charge condition.

This really isn't too hard to figure out. On a typical re-cycler, the battery is discharged down to 1.05 volts. Incidentally, if you store NiCds, you should discharge them.

Anyway for a RX pack 1.05 x 4 = 4.20 and for a TX pack, 1.05 X 8 = 8.4. As I recall, on my Futaba 9C, the warning for low voltage on the TX beeps at 8.5 volts and Futaba warns not fly below or at this voltage. On the RX, you're getting into dangerous territory at 4.5 volts.

Battery capacity is measured in mAh (milli-amp hours). Capacity is analogous to gallons of fuel in your gas tank. If you have a 1000 mAh battery then you have twice as many gallons of electrical fuel as a 500 mAh battery. Theoretically you should be able to fly twice as long.

If you have a recycler (Hobbico makes a couple), discharge your batteries (after they are fully charged) to see what their capacity is expressed in mAh. Most recyclers discharge at either the 250 or 500 mAh, and the typical radio use is around 250 mAh. Assuming a 250 discharge rate, Divide the capacity by 250 to find out the flying time of your batteries. If your recycler discharges at 500, then you'll have to double the times. BTW, my recycler has a minute readout saving me the computation.

Since I fly for long periods of time, I have switched over to NiMH batteries of 1650 mAhs in both RX and TX. Dividing 1650 by 250 = 6.6! Remember this is for continuous operation! Since I have to refuel every 15 minutes, I am never going to exceed 6.6 hours unless I do some night flying! Beside high capacity or a long operational period, another nice thing about NiMH is they don't require recycling, since they don't develop memory.

Ciao,

Mr Akimoto

I have seen from testing a number of packs from different manufacturers that simply the voltage alone doesn't tell the whole store. A pack with a high internal impedance might show a lower than expected voltage under load, where a pack with a low impedance will show a higher voltage until it is nearly discharged. Doing some testing on your batteries is time well spent.

Be sure you have more battery than fuel though. I was flying a friends Cub when the throttle servo linkage failed at a fairly low throttle setting soon after takeoff. It had a large tank. We took turns flying it for about 45 minutes before it ran out of fuel. The landing was uneventful, but it would have been different if we had only had 30 minutes of battery left.

LarryC

I stop at 1.1 volt on my TX and 1.2 volts on my RX

All great inputs. I keep it on the ground at about 4.9 for the 4 cells. The only planes I have ever lost were to squezing one more flight out of it. The "it's not in the red" in not good. If it is out of the green I'm swapping batteries. The price of an extra battery is cheaper than a whole new plane. There is always a fail safe for $40 if the plane can handle the extra battery.

I have fail safes in all my cars, if I lose signal or experience interference, the car just stops. In addition I have a return spring which is just strong enough to pull the throttle closed should I have battery problems and there is not enough power to move the servos. There are no fail safes on my planes in that I haven't figured out a safe setting and remember won't work if there is no power. An extra battery is not needed BTW.

http://www2.towerhobbies.com/cgi-bin...?&I=LXAFM9&P=0

This is what I meant, a battery backer. When reciever battery drops below a set level, second battery kicks in. Good insurance for those planes that took hundreds of hours to build.

The more I learn about batteries, the scarier they are. I was just reading an article that warned that ESV (expanded scale voltmeters) give us a false sense of security because NiCads have a long, flat discharge plateau. Think of a marble rolling along a chair fron the backrest. It drops fast, and then rolls a long time on the seat, and then drops off the edge. Same with NiCads. The voltage drops fast initially, and then is fairly flat until it again drops. If you are on the flat (the seat) it all looks about the same until it drops suddenly. The ESV won't tell you how far from that edge you are.

I've really come to love the timers on my Futaba 9C. I turn the receiver and transmitter on and off together and I can therefore tell how long I've been "on." I have an AccuCycler that I cycle the batteries on regularly so I can spot a failing pack, and I have my "wall-wart" chargers on a timer so after the full overnight recharge they spend an 75 minutes on trickle every day for all my batteries to float them until the next use.

And I still use the ESV just in case.

I think I may add one of those battery backers to my next build (a quarter scale) as added insurance. I'd use chicken blood and voodoo dolls if it would remove one more possibility from my list of flight stoppers.

I would eliminate the backer and use two packs, through two switches into the reciever.