Lipo charge question

[Jermo]

I read an article that spoke of charge rate being 85% of capacity. Capacity is the mAH rating of a pack right? so a 11.1v 2100mAH 3s pack has a max supply current of 2100mAH * 3s = 6.3A * 85% = 5.36A. Most chargers are supplying alot lower charge current???

or is it 85% of 2100mAH (2.1A * 85% = 1.79A) ?

The article also stated a Vt per cell of 3.7V then stated the charger supplies 3.6V to "top off" the pack.

that implies that when the pack reaches 3.7V per cell the pack is charged or does the pack never achieve 3.7v per cell again?

I really need some manf sheets on these darn things. They seem to be very different than anything I've learned about in the past. Their internal resistance must be whack.
Jermo

[Bayou Talker]

Do you have a link to that article? I am sure there are a lot of guys that would like to read it.

As for me, I usually charge at 1C which for a 2100mah would be 2.1 amp. That is what I have been told is a safe rate for the battery life. There are those that charge at 2C and above with the right charger/balancer combo but I don't know any details.

[Jermo]

http://www.rchobbies.org/lithium_battery_breakthrough.htm

that's why I'm confused. Capacity to me is how much energy the unit can deliver which would be mAH * nC. This would often result it charge rates well over 2 amps so that can't be right, however, if we use the mAH rating of the battery as the Capacity we end up with a charge rate of 2100mAH * 85% = 1.79A at ?? V.

I just havent' found a resource that speaks techno :)
Jermo

[Jermo]

bah..all this research just leads to more questions like Why don't we use Lithium Ion batteries instead of Lipo? They have a more forgiving cycle life, can be made smaller and apparently supply the power of lipo's if I read correctly..
http://www.batteryuniversity.com/partone-5.htm
Jermo

too many questions.. :roll:

edit: misread...many of the "advantages" of size and weight are on the Lipo batts.
Jermo

[Pinecone]

I think you got some things confused (or the article did).

Charge rate for lipos is nominally 1C (some packs with some chargers can be safely used at 2 - 3C). So for a 2100mAH pack = 2.1 AH x 1C = 2.1 amp charge rate.

The maximum you want to draw from a pack is about 80% of the capacity. So when your pack is recharged you want to see that your charger put back in no more than 80% of the 2100 mAH = 1680 mAH. 85% would be 1785 mAH. If you are putting more back in after flying you are drawing your packs too low and you are hurting your packs.

Lipos are nominally rated at 3.7 volts per cell. That is during use you can figure on about 3.7 volts average. Max voltage for a lipo cell is 4.2 volts per cell. And that is what you charge to. A 3S pack is nominally 11.1 votls (3.7 x 3) but right after charging they are 12.6 volts. The minimum you want to ever let your packs get is 3 volts per cell (9 volt for 3S). And lower and you are harming your pack.

Chargers work on constant current/constant voltage. That is at teh begining of the charge they charge at the max amp rate you set based on teh capacity of the pack, ie 2.1 amps for a 2100 pack. Once the voltage to charge at 2.1 amps hits 12.6 votls (for a 3S pack) the charger will switch to constant voltage and hold that 12.6 volts until the charge is complete. ANd since you are charging at a constant voltage, the charge rate continues to drop as the pack gets charged, so it will take an infinate amount of time to fully charge the pack. So we accept 90 - 95% as fully chargeed. For my Triton it stops when the charge rate drops to less than 0.1 amps and the voltage stays at 12.6. However, if I leave the pack on the charger for a while, the voltage readout will drop to about 12.56 - 12.58 volts.

C rates and capacity, and therefor charge rates, don't change for series connections.

[Jermo]

ahhhh...ok... that makes more sense. Thank you.
Jermo

[alexd]

I've got a Thunder Power 11.1v 3 cell 2100mAh lipo.
I also have the Align RCC-6sx intelligent digital multifunctional charger/discharger/balancer.
Thunder Power 40a ESC.

I let my lipo get to 9.8v. :roll:

The instructions with the Lipo say do not let it get below 9.9v.
There is no 'puffing' or heat.
Can I charge this battery as long as I do not let it get that low again or is that lipo gone/dead/bad? :(

Also, I thought the ESC would beep when the Lipo got too low.
It did not. :dontknow

[HeliDan]

I've got a Thunder Power 11.1v 3 cell 2100mAh lipo.
I also have the Align RCC-6sx intelligent digital multifunctional charger/discharger/balancer.
Thunder Power 40a ESC.

I let my lipo get to 9.8v. :roll:

The instructions with the Lipo say do not let it get below 9.9v.
There is no 'puffing' or heat.
Can I charge this battery as long as I do not let it get that low again or is that lipo gone/dead/bad? :(

Also, I thought the ESC would beep when the Lipo got too low.
It did not. :dontknow

You can continue to use it. Discharging a LiPo too low will generally shorten its lifespan.
I believe that puffing is caused by physical damage or overcharging. I could be wrong, but I dont think that over discharging will cause a puffed battery.....

[spork]

Jermo,

I think the basic confusion between capacity and charge rate stems from the language we use. When told to charge at 1C (C is for capacity of the cell), the implication is 1C per hour (or 2100 mAH/hr; therefore 2100 mA or 2.1 amps). I've always thought it was a little sloppy to mix units that way, but that's what's meant. So charging at 2C would nominally charge the cell in 1/2 hour, 3C in 1/3rd hour, etc. Make sense?

As far as multiplying the capacity by the number of cells, you would do that if you charged them in parallel. But remember, in series the cell has 2100 mAH capacity and the PACK also has 2100 mAH capacity (but it has 3 times the voltage). This too is confusing since we tend to think of capacity as total energy (mAH x voltage). So a 3S pack or a 3P pack does actually have 3 times the energy capacity of a single cell, but again we tend to be a little loose and talk about capacity in terms of mAH alone.


You can continue to use it. Discharging a LiPo too low will generally shorten its lifespan.
I believe that puffing is caused by physical damage or overcharging. I could be wrong, but I dont think that over discharging will cause a puffed battery.....

Discharging LiPo's too low will significantly shorten their life. I think you're just barely dipping into the danger zone in this case. Taking them too low also has a definite tendency to unbalance the packs. So balance charging becomes that much more critical for an abused pack. As far as I know the three things that will puff a pack are:

- Overcharge
- Charge at too high a rate
- Discharge at too high a rate (cells get above 140 deg-F).

HeliDan,
We gonna see you tomorrow at the Group-W fly-in?

EDIT:

If you read 9.8V on an unloaded pack after the flight you may well have over-discharged them significantly. Toward the end of the pack the load and no-load voltages are very different. In other words that pack may have read below 9V under load (which isn't so good).

By the way, I'm not aware of an ESC that beeps at you. Many have a throttle-cut feature, but it's typically set to go into affect at too low a voltage for our purposes, and most guys don't like this feature on helis. A timer and or a LiPo alarm is the typical answer.

[alexd]

Helps if I RTFM.

"To program esc via TX stick commands....."
"To program your gy401......"

If you dont set the low voltage warning in the ESC, then it won't beep for you when it gets low!

The Thunder Power 40A ESC does have a high, medium and low voltage values and beep alarm.

The Spektrum TX, as with most all these days, has built in multi-timer functions.

[spork]

The Thunder Power 40A ESC does have a high, medium and low voltage values and beep alarm.

That's a nice feature. I haven't seen one that does that. Two things you need to watch for:

- Are any of the thresholds appropriate for a LiPo?
- Are they absolute voltage thresholds, or are they proportional to the initial voltage? In the latter case you could be in trouble if you ever start a flight with less than a full charge.

[alexd]

absolute voltage.

Pretty slick.

There are some additional features supposedly since I'm using Thunder Power LiPo and ESC.

I'll have to read up on them.

[spork]

Sounds good. If you can set that threshold somewhere between 3.0 and 3.3 volts/cell you should have a good setup. The ticket is to find the point that has you putting 80% capacity back in a new pack.

[alexd]

:arggg:
Ok.
What am I doing wrong.
Can't seem to get my TP lipos to charge correctly.
I've got the Align RCC-6SX Intelligent Charger/Discharger/Balancer.
TP 2100mAh 11.1v 3S and a TP 2200 11.1v 3s Lipo
When I get the batteries, I charge them up to full.
I then go out and do my first run, not letting them get below 9.4v.
let them cool down.
Stick them on the charger.
They read around 9.1 - 9.2v.
They charge up to around 9.6v then the charging stops with no message or error.
Try again, they get up to round 9.75v and charging stops.

Wondering if I have my wiring on the lipo incorrect.
Had to re-wire balancer connector to Align compatible plug.

On old TP plug
1 = Black
2 = White
3 = Blue
4 = Orange

That is looking at the underside of the plug which has numbers on either end and you can see the metal through the plastic housing.

On the align plug
Arrow = Red
White
Brown
Black

Cant find any markings on the Balancer multi-port tap adapter circuit board which the lipo balancer plug inserts into.

[Hughes500Bob]

Has anyone used Air Thunder (http://www.airthunder.com/) Li-Pos?

No low-voltage cut-off limit.

Over-discharging has been a major issue with conventional Li-poly technology as it leads to over-heating, deformation, and degradation of the battery. Model aircraft owners are often advised to time their operation to avoid detrimental effects. Our proprietary formulation and packaging technology has circumvented such problems, allowing the battery to be safely discharged to zero volt. No low-voltage cut-off circuit is needed. This is an industrial-first; a true breakthrough in Li-poly technology. In addition, our battery maintains its voltage till the very end of the discharge cycle. This means you can fully enjoy your flying experience worry-free.

[spork]

It sounds to me like they've simply integrated a low-voltage cut-off directly into the packs. This would also explain how they maintain voltage to the very end of the discharge.

[alexd]

I figured it out.
I had my wiring wrong. :arggg:

:idea: Here is the Thunder Power LiPo to Align 4-pin plug color coding & wiring match up :

TP : Align
Black : Black
White : Brown
Blue : White
Orange : Red

My 2200mAh 11.1v 3-cell is now charging like a champ.
I think I might have toasted the other one because it charges for a little bit and tells me wiring disconnection. At least I have one.