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Old Feb 12, 2009, 06:36 AM
Eggs @ Tea
Dover DE USA
Joined Feb 2007
506 Posts
Question
can the battery C-rating effect my charge rate? 1C is getting boring!!!

from what i gather, just waking up, the C of the battery looks like the higher it is, the more denser the cell, or thicker, heavier, right? well if this is so, can i bump up my charge times safely? I always wonder this as some of my charges as i cycle them with flights and such, have increased to my 80-min cutoff time and really annoys me..... Scott

charles if you are reading this, i have some batteries that are rated at 2150-2200 mah and whats weird is that they are 20C batteries but at different lengths like the cells in my zippy packs are longer than the other packs i used.....explain to me, is this a advantage in performance, or charge times....... Thanks guys
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Old Feb 12, 2009, 06:45 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,514 Posts
Charging at greater than 1C. I have been doing it for over three years. I have started a couple or three Threads on the subject. I have posted my charging results using different chargers such as TP1010C,Cell Pro 10,Hyperion DUO and 720i ,recently charging 3S and 4S 3300 mAh LiPolys and 3S 2P 4400 LiPolys.

A post by RC Man showing charge time at different rates.

Note date of post

http://www.rcgroups.com/forums/showp...&postcount=483

Capacity versus shape? There are NiMH AA cells ,all te same size from 600 to 2700 mAh capacity.

If you notice charging times increasing then also note how much longer the CV stage is taking and /or perhaps how much more balancing is going on. These are signs ot the battery wearing out or showing results of damage / abuse or just low quality cells dieing early as they most often do.

.


Charles
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Old Feb 12, 2009, 07:09 AM
Eggs @ Tea
Dover DE USA
Joined Feb 2007
506 Posts
i do notice this is more common with my packs as i put more cycles on them..... am i balancing them too much? my charger has the fast charge mode too. For some reason when i charge my batteries i like to see that they hit 12.60 on the meter (3 cell) and that the 2.1 charge (2100) rate slowly trickles down to about 0.1-0.3 and cuts off but this seems to be going past the 70 min and beyond mark thats why i thought of bumping up the charge rate too..... Scott
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Old Feb 12, 2009, 07:57 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,514 Posts
What can I say. All that care to disregard please feel free to do so.

There is not practical reason to charge a LiPoly cell past 95% full (4.195 volts) unless you are competing or doing capacity / performance testing.

There is no practical reason to balance a LiPoly battery any closer than 0.02 unless you are going to be connecting the packs in series or you are doing pack testing.

To save a major amount of charging / balancing time stop the charge at 90 to 95%. If charger has the option of Fast Charge such as Thunder Power 1010C / 210V .Cell Pro 10 and others then use it. If you are using a plane Jane LiPoly charger then stop the charge after the battery has reached 4.15 per cell in the CV stage and has settled there (goes higher but does not drop lower during the voltage check stages).

If you are waiting to fly and do not mind giving up just a little flight time then stop charge at 4.1 per cell.

You can avoid long charging / balancing times by using packs made from matched cells (higher quality ones) and by not discharging them over 80% of their capacity. Deep discharges cause more severe inbalance which causes some dumb balancer to fight the charger by trying to balance cells which should not be balanced while discharged in the first place.


Charles
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Old Feb 12, 2009, 07:57 AM
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gmohr's Avatar
New Jersey, USA
Joined Mar 2008
298 Posts
That Constant Voltage stage of charging will take longer when the cells internal resistance starts to go up.. usually a sign that they are getting tired, as Charles said above.

You can't balance "too much" in my opinion. That's just the charger working to overcome some weak cell(s).
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Old Feb 12, 2009, 08:22 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,514 Posts
Quote:
You can't balance "too much" in my opinion.
Just curious .How close do you fell they need to be?

I posted :


Quote:
There is no practical reason to balance a LiPoly battery any closer than 0.02 unless you are going to be connecting the packs in series or you are doing pack testing.
Asuming a 100% (4.2 per cell(?) charge level)that would mean a 2S could have one cell at 4.2 and the other at 4.18 (100% and 98%)or a3S could have as much as 0.00666 volts per cell spread.

I wonder if you have ever perfectly balanced a cross section of you packs, let them set for a few hours then rechecked their balance? Along the same lines I wonder if you have ever checked the inbalance of a discharge pack then charged it to say 4.1 per cell average without balancing then rechecked its' balance?

Again just curious.

Some may find this post from 4 years ago back when I first started checking pack balance interesting.

http://www.rcgroups.com/forums/showp...64&postcount=2

Snip

Quote:
Discharged pack to 8.76 @ 1.25 Ah on AF109.
Added taps and checked voltages.
3.67
3.45
3.67
Difference 0.22 volts

Charged at 0.9Ah (0.75C) on Triton to 12.3(Li Ion setting.
4.09 plus 0.42
4.05 plus 0.60
4.09 plus 0.42
Difference 0.04 volts.
Charles
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Old Feb 12, 2009, 08:30 AM
Eggs @ Tea
Dover DE USA
Joined Feb 2007
506 Posts
great advice charles, in the back of my mind, i had it when you hit the charge button, u leave it alone and let the beast do its thing to the end.... Here i thought it you stop a charge with a lipo that you cap off the total voltage for the rest of the lipo life, i guess meaning it begins to get a memory and will not go past there , for example 4.17 on a cell (ever again) u know? My normal charging process begins of me hooking a voltage meter on the balance connecter and watching the volts.... and you are right about 4.17 on the cells the Constant Voltage kicks in and recently ive seen my cells go all the way up to 4.23 but sag to 4.20 after the charging ends, and im thinking man this battery is going to be a winner..... but back to the C rating, it really has no effect on the charge rate then?
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Old Feb 12, 2009, 08:41 AM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
34,514 Posts
Quote:
but back to the C rating, it really has no effect on the charge rate then?
I believe it does and my testing says it does also. The real C rate (not the advertised one) for any give size(capacity) cell is determined by the cell's IR to a very large degree. Lower IR means the charge goes in easier as well as it comes out easier.

I have used the temp. rise of a cell to determine practical max. charge rate for many years. Yes I know that most say LiPolys do not increase in temp. during charging but most have not really checked,except perhaps by feel or other inaccurate means.

Charles
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Old Feb 12, 2009, 08:41 AM
Eggs @ Tea
Dover DE USA
Joined Feb 2007
506 Posts
Quote:
Originally Posted by everydayflyer
Just curious .How close do you fell they need to be?

I posted :




Asuming a 100% (4.2 per cell(?) charge level)that would mean a 2S could have one cell at 4.2 and the other at 4.18 (100% and 98%)or a3S could have as much as 0.00666 volts per cell spread.

I wonder if you have ever perfectly balanced a cross section of you packs, let them set for a few hours then rechecked their balance? Along the same lines I wonder if you have ever checked the inbalance of a discharge pack then charged it to say 4.1 per cell average without balancing then rechecked its' balance?

Again just curious.

Some may find this post from 4 years ago back when I first started checking pack balance interesting.

http://www.rcgroups.com/forums/showp...64&postcount=2

Snip

Charles

i would say i balance them after 3-4 cycles and usually if i see that when i bring them home and they sit for a couple hours after a flight, the balance is off say 3.56 - 3.67 - 3.75 something weird like that in different orders --- Scott
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Old Feb 12, 2009, 08:44 AM
Eggs @ Tea
Dover DE USA
Joined Feb 2007
506 Posts
Quote:
Originally Posted by everydayflyer
I believe it does and my testing says it does also. The real C rate (not the advertised one) for any give size(capacity) cell is determined by the cell's IR to a very large degree. Lower IR means the charge goes in easier as well as it comes out easier.

I have used the temp. rise of a cell to determine practical max. charge rate for many years. Yes I know that most say LiPolys do not increase in temp. during charging but most have not really checked,except perhaps by feel or other inaccurate means.

Charles
mine when they begin to charge honestly have a cool feel all the way up to the 50-60 min mark and where they get balanced by themselves u know.... they warm up slightly but never hot
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Old Feb 12, 2009, 08:48 AM
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New Jersey, USA
Joined Mar 2008
298 Posts
Hey Charles,

My BC610 tries to balance to the one hundredth of a volt, and so far is able to do so on all my packs. Whever I've checked them after some time goes by, they are off by at most .01, which seems great to me.

Since I use a balancing charger, I have no experience in trying to bring out of balance cells back into balance. Also, as far as what a realistic "acceptable" balance difference is, you have a much better feel for that than I do.
-G
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