Batteries How far to discharge a battery

[Slobberdog]

Guys this might sound dull but how much can I use my batteries.

I had approx 6 mins of flight today and that left me with 3.8v per cell, I know the low level for charge is 9v and I don't want to get to there again, lol, but am I right when you say 80% discharge would be 3.4v per cell left or 10.2v total

What do you guys leave in your cells after a flight,

 

[breeze400]

I have my low voltage alarm set for 3.6. Gives you a little time to land.

 

[coolgabsi]

I think the 80 percent discharge percent applies to the mah's.

So a 2200mah battery, you wouldn't wanna discharge more than 1760maj out of it

The only way to tell is charge and see how much you put in.

Fly safe!! have fun!

 

[RandyDSok]

The 80% ( some say 70% ) is for either voltage or current ( mah ) since both are directly related to each other. So you can quickly check where you are with a voltmeter... and then later verify it with what mah your charger puts back into the batter. I slightly favor using the capacity I put back into the battery since it doesn't rely on whether it is under load or not like voltage does.

 

[Lee]

Its good to keep an i on both the Amps and the Volts. I tend to set my alarms for 3.5V under load, which means once i land and the battery comes to rest, it will rise to about 3.7V which is a good voltage to end at.
The 80% of capacity is good to. As Gaba said for a 2200 battery 1760 is the most you will want to see the charger put back in. When this comes unstuck, is when the battery gets older. It will lose some of its capacity, so if you rely on the 80% rule, 1760 back into the battery will be something more like 90%.

 

[Ken Jackson]

I'm still some what confused on this issue. Maybe my charge is cheap?

I know I have put more mAh back in then the mAh rating on the battery. That's bad right?

For example;
4/2/13
Flight time set at 5:45
Starting charge volts 3.56 end 4.20 volts
76.5 Minute Charge Time
2648 mAh

This is a 2650 mAh battery. If that's what went back into it shouldn't that battery have been ruined? I took everything out of it but 2 mAh?

Here's a different battery, different day;
4-4-13
Flight time set at 5:50
Starting charge 3.74 V
120 Minute Charge Timed Out did not complete
2736 mAh

Any help would be appreciated

Ken

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Both batteries are about a month and a half old, both have under 8 flights

 

[wolfman76]

THIS IS ALSO SOMETHING I WOULD LIKE TO KNOW AND HAVE NO CLUE ON... sorry bout caps did not realize they were on

 

[coolgabsi]

I'm still some what confused on this issue. Maybe my charge is cheap?

I know I have put more mAh back in then the mAh rating on the battery. That's bad right?

For example;
4/2/13
Flight time set at 5:45
Starting charge volts 3.56 end 4.20 volts
76.5 Minute Charge Time
2648 mAh

This is a 2650 mAh battery. If that's what went back into it shouldn't that battery have been ruined? I took everything out of it but 2 mAh?

Here's a different battery, different day;
4-4-13
Flight time set at 5:50
Starting charge 3.74 V
120 Minute Charge Timed Out did not complete
2736 mAh

Any help would be appreciated

Ken

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Both batteries are about a month and a half old, both have under 8 flights

Yeah that seems to be a battery or a charger issue .. A battery that low wouldn't even charge.

What charger?

Fly safe!! have fun!

 

[RandyDSok]

Most of the time, a battery will have slightly more than their rated MAH capacity... but I don't believe that is this issue at all.

I suspect a bad or weak cell in the pack... the charger is trying to balance the pack and in doing so, it must remove extra power from the high cells in order to bring them back down the value the low cell or cells have... and then it replaces that current. One with a really bad or weak cell will repeat this process a lot of times to finally get all cells up to power.

This type of issue is usually caused by how the battery was treated durning it's life span or by the battery just getting old. Cheap batteries will also do this much sooner than a quality one will.

 

[pvolcko]

For example;
4/2/13
Flight time set at 5:45
Starting charge volts 3.56 end 4.20 volts
76.5 Minute Charge Time
2648 mAh

This is a 2650 mAh battery. If that's what went back into it shouldn't that battery have been ruined? I took everything out of it but 2 mAh?

I'd say you drained that battery too much. Bump your flight timer down to maybe 5min, or even 4m30s. If you do this once or twice it isn't the end of the world (particularly with a quality battery), but if you consistently drain the battery like this it will end up damaging it and shortening its life significantly.

Here's a different battery, different day;
4-4-13
Flight time set at 5:50
Starting charge 3.74 V
120 Minute Charge Timed Out did not complete
2736 mAh

This start voltage is a little low, again indicating you need to shorten your flight times. I agree with Randy, you probably have a cell way out of balance. Use the balance charge mode and if needed put it through a few balance charge cycles. The charger will recognize the overall charge condition and switch into balancing mode fairly quickly, so you aren't in danger of ruining anything by doing this. Your balancing charger should have a mode that displays the cell voltages, could help us if you report back those per cell voltages before you hook up for another balance cycle.

 

[Ken Jackson]

Took me forever to find this thread again, damn. Anyway I only charge balanced and I always look at the individual cell voltages. That 3.56 was crazy low and I was lucky because the ESC was shutting down as I landed. Normally I see 3.76 - 3.78 volts at start. And that is all six cells. I have never seen a cell more then a 10th or 2 away from the others. I had always just looked at voltage, a friend recently told me about the mAh method but as you can see it makes no sense based on what I am seeing.

Battery performance is consistent. I wouldn't call these expensive batteries but they are decent. Buy these from hobby king for $52.



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Flight time set at 5:45
Starting charge 3.76 v
66.49 Minute Charge Time
2369 mAh

Start charge 3.99 volts
28.5 Minute Charge Time
786 mAh

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the start charge voltage I list is the average of the six cells

 

[Ken Jackson]

So is my charger just too cheap??

 

[Lee]

The higher priced chargers will give you more info about the battery. like the internal resistance. And will have a better balancer. I have 4 batteries that will not balance after a charger damaged them. I'm waiting for a new charger that has the ability to balance them again.
I have those same batteries as you but the 5000mah ones. If you fly too long then one cell will start to drop of quickly. I had one that was at 3.65 on all cells but one that dropped to 3.45

 

[breeze400]

I'm still not getting this when I do the math 80% of 4.2v is 3.36. So I figure 3.4 to be on the safe side. Now that is loaded volts not idle volts. Now I have my loaded volts set to 3.8 my warning lights start to flash. At 3.6 volts my NAZA lands. Now remember this is loaded volts. Once the motors stop, the volts will come up some. I'm I right on this or off bace?

 

[Lee]

The 80% is for Mah not the voltage. I have my voltage set to 3.5 under load, which normally raises back up to 3.7 at rest.

 

[breeze400]

I'm still confused? In post 7 he says that he put in more mah then the battery was rated for?

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If I can figure out how to use skipe, then we should talk ths weekend! Lol.

 

[Lee]

Yes, if you look at Craigs post on the first page, he says, a lot of batteries have more Mahs than they actually state on the battery.

 

[breeze400]

Ok so on my 4s nano teck's, 5000's I can take them down to 1000 mah? And put back 4000mah?

 

[pvolcko]

Yeah, that's the idea. As a quick stand in, take a look at what your battery at 1000mAh left reads as a voltage under load and at idle. It will be in that same voltage area at that capacity so you can then use that voltage as a means of knowing what the remaining capacity is. And, the capacity rating is just a rating. A 5000mAh battery may well take 5500mAh of charge from a "complete" drain. Another might only take 4800mAh. Different vendors are more honest about their capacity ratings than others.

 

[RandyDSok]

I'm still confused? In post 7 he says that he put in more mah then the battery was rated for?

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If I can figure out how to use skipe, then we should talk ths weekend! Lol.

Also remember that if the charger is balancing the batteries... it has to remove power from the cells that are high and then it replaces that power across all cells... If a cell is weak, it won't take as much charge as the good cells will and the process repeats until the weak cell finally has caught up to the good ones.

You could say... two steps forward followed by a step back... then two forward again and one back...