trpastor

I'm just wondering how many flights you should be able to expect on a NITRO plane set up with the following

4 standard servos (2 hi tec 475hb, and 2 futaba s 3003)

6v 1100 Mah battery (sanyo 5 cell flat pack)
specktrum receiver (ar 6200 2.4ghz)

Flight time about 10min-12 min.

What is unsafe flight voltage? Once the battery reads below what?

Let me know if I'm forgetting any variables you would need to guess. I know it's appx but shoudl I safely be able to get 2 flights (40-50 minutes of flight)?

Thanks
Tim

P-40 DRIVER

Off the top of my head, you should be able to get a couple of hours out of that set up. Any thing below 6V, I would consider hanging it up for the day. That will give you a good safety margin.

j.duncker

My Feedback: (2)

KEY QUESTION

Is it a NiCad pack or a NiMH pack. The answer depends on which one you have.

w8ye

My Feedback: (16)

6V and I recharge

HighPlains

My Feedback: (1)

When you get the voltage down to 6 volts on a 5 cell pack, you have used about 1/3 of it's capacity.

trpastor

It's a Nicad.

So you guys are saying if it reads 6v or right around, then it's time to recharge. Is this WITH a load, or not load?

Thanks
Tim

w8ye

My Feedback: (16)

With load

The voltage will stay at 6V for some time but when it starts below 6V it will go fast

trpastor

The reason I'm asking is I just crashed my plane. I read the voltage after and it was showing 5.4 and near that. I only did 3 flights. Witha load of 1 amp, it was showing 4... and dropping!

I charged it using a Pirahna charger. I did a quick charge of 1amp, and a 8mv/c setting. I charged it once, and then I actually put it back on and charged it again just to be sure it was topped off for the day.

Again it was 1100mah battery

Is it possible for a servo to place an usually heavy draw on a battery, and drain it prematurly? this was a new battery, because the first one on this plane, was an old battery I had that I never took it off the ground with, because after charging it, it quickly started twitching and freaking out. This battery didn't seem to be holding a charge, and I tossed it. The second one was another battery I had - I flew the plane, it glitched on my once - I got it down, and the voltage was reading 5.9 with a load on it. Not horrible but marginal.

then I got this new one, and it again seemed to drain prematurely. So can a servo drain a battery quickly somehow?

Nathan King

A battery can be quickly drained by a stalled servo; a stalled servo can draw several amps. Have you cycled the battery to check what its actual capacity is? If you are reading just under 6V with a load, the battery is almost dead.

trpastor

How do you cycle it?

Sorry for my ignorance

w8ye

My Feedback: (16)

You need a cycling charger or you can do it manually

http://www3.towerhobbies.com/cgi-bin...&I=LXEYD4&P=ML

trpastor

http://www.duratrax.com/caraccys/dtxp4005.html
this is what I have


How would I do it manually

It just got done charging that battery (that was SUPPOSED to be an 1100 mah battery, and was reading 3.4 and falling under a 1.5amp load), and it only put 400mah back into it!! What the hell is up with that?
Shouldn't it have put about 1000 back into it after being that low?

how do I cycle my batteries manually. Do you do this nicads only or nimh too?
Thanks
Tim

w8ye

My Feedback: (16)

Manually you would have to drain the batteries at a known rate for a documented time to the minimum voltage

You seem to be able to know how much you are putting it the battery with your charger

Phoenixangel

My triton 2 will do the same thing if I have the peak sensitivity wrong, or forget to change the peak delay time. If I leave the delay set at 30 minutes it will read the unstable voltage changes at the beginning of a charge in some way that causes it to charge at a lower rate and only put about half capacity in the battery after a a several hour charge.

If i set it to 90 minutes it hits the mark almost perfect every time. I do not know why.

jrcaster

With the twitching you may have a bad receiver instead of the battery packs.

If that is a new battery, you really need to form charge the pack. Use your wall wart that came with the radio and do an overnight charge.

Get an expanded scale voltmeter to test your batteries. AA cell packs are not designed to run a 1A load. The expanded scale voltmeter uses a 250ma load across the leads to load the packs. I would suspect that your original pack is good too if you checked it with a 1A load.

trpastor

Sorry again - but what do you mean to "form" the pack.

Also, what do you mean they are not designed to run a 1a load? Don't your servos put more of a draw on it than 1amp?

TFF

I find that fast charging without true fast charge cells kills the pack. The 1/10C rate will give the best life for NiCAD and NiMH. I sometimes do a quick charge but I can tell that the charge is not as good. Forming the pack is like training the pack to take a charge. If you abuse the cells it kills the electrolyte or plates in the cells. You can pull more than the rated amps from the pack but if it gets too high for too long, you can get the same as incorrect charging.

HighPlains

My Feedback: (1)

This is complete nonsense. A battery cell just off the charger will start at about 1.35 to 1.4 Volts and falls down to the rated voltage of 1.2 Volts after the first 25% of the discharge time. It takes about twice as long to go from 1.2 Volts to 1.15 Volts where 75 to 80% of the capacity has been discharged. They tend to go over the "knee" at about 1.07 volts, though that transistion seems to be somewhat softer with todays cells.

It really sounds like your charger was not fully charging the pack.

bkdavy

My Feedback: (1)

Like many others on here, I have always subscribed to the 1.2 v/cell as the point at which the battery was only about 25% discharged, as this was true for the NiCd battery chemistry. So I went and looked up a sample data sheet. I found a datasheet for the ENERGIZER NH15-1700, a rechargable NIMH battery. The attached discharge curves clearly show that when the cell gets to 1.2 v/cell, its on its way down, and you've probably used about 80 percent of the capacity. This may not be the exact curve for every NIMH cell, but its probably representative. If you're really interested, find the datasheet for your cells. Sanyo is probably one of the largest makers of OEM batteries, so you can probably look there.

Brad

TCrafty

Just curious, several have said that 6v is the point at which a 6v battery will start to drop off. Others are saying 1.2v. My math isn't that great but aren't they saying the same thing? 1.2x5=6?

w8ye

My Feedback: (16)

yes but remember the NiCd - NMHd situation. They are slightly different

HighPlains

My Feedback: (1)

Graphs taken on actual 4 cell battery packs, not an obsolete marketing chart for both chemistries.

http://shdesigns.org/batts/battcyc.html

w8ye

My Feedback: (16)

that's a good link and the curve is one that every model flyer should have in his memory

HighPlains

My Feedback: (1)

I firmly believe that anyone using Nicads or NiMH batteries should test their flight packs and keep a history for each pack. The equipment needed is not very expensive, at least compared to the cost of a model.

I use a simple 20 Ohm power resistor rated at 25 Watts, a digital voltmeter, and digital clock. Just treat the battery like you were going to use it, in other words charge it up but wait an hour or a day before testing. Then hook up the resistor and voltmeter and take a reading every 5 minutes. Plot the data out on graph paper. After you do a few packs, you will see general trends of a healthy pack. At the field, after a flight, you can plug in your test load and see where you are at with reasonable accuracy.

After a flying session, you can go ahead and run the pack down and see what was left before it starts to drop over the knee. This will tell you how much of the pack is used under your normal flight conditions. There is no set number of flights you can safely make based on battery size alone. It depends of the model and flight loads placed on it. So test and measure to determine for each airplane.

The above testing is for normal sized sport packs that are generally supplied with radios. If running higher powered systems with much larger packs for big digital servos, I would do the same, except use a heavier load with a resistor in the 10 to 12 Ohm range.

The Nicad battery is a very mature, well developed technology. Give the flight pack an chance by protecting it from vibration and heat and it will last a very long time. Avoid fast charging as well as trickle charging for best results.

If using 5 cell packs, or packs much larger in capacity, make sure your charging system is up to the task. C/10 is the best charging rate. Large capacity packs will not properly charge on 50 mAh rates, and chargers made for 4 cell packs may not charge 5 cell packs. Study, and know your equipment.

jrcaster

Here are a couple of good reads for battery technology.

http://www.rcbatteryclinic.com/

http://www.batteryuniversity.com/

I can't remember where I read about form charging but basically it is done by slow charging the battery pack at 1/10C for at least 16 hours. This should be done for the first 3 to 5 cycles of the batteries life. From the factory the plates are not completely formed and the slow charge process completes the cell, otherwise the battery will have a shorter shelf life. So the batteries are manufactured and sold with partially formed cells so we the consumers can get the maximum life out of our batteries.