Care of Lipo batteries for long life - Page 2 - RC Groups
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Apr 12, 2010, 09:59 AM
Novice RC pilot
u.rusty's Avatar
Quote:
Originally Posted by everydayflyer
...I charge at 3 to 6C routinely and this in itself results in a lower resting end voltage than a 1c charge rate would with most chargers.

I oftem use the Faster charge option on mnay of my chargers which causes them to end the CV stage sooner. This means that while my charger me be set to charge to 4.2 by charger at fater rates and using Faster Charge option the cells are really closer to 4.15 at end of charge.


Charles
I spent a couple hours yesterday reading through the thread concerning the Cellpro 10S, when it first came out. In one of your posts you mentioned, if I remember correctly, that as long as a LiPo battery pack temperature doesn't rise more than 10 degrees Farenhight during the charging process, the charge rate should be OK. This makes sense to me because a battery with higher internal resistance with show a higher temp increase at a given charge rate than a battery with lower internal resistance. So using this method to determine the max charge rate is basically adjusting the max charge rate to the internal resistance of the battery.

Do you still use this method to determine the max charge rate?
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Apr 12, 2010, 10:48 AM
Southern Pride
everydayflyer's Avatar
More or less, most of the ones I charge at 5 and 6C go on the charger at 120 to 125F and in fact cool down to 90 to 100 during the charge. Ones charged at 3C for the most part cool down perhaps 5F more.

Years ago a TP ProLite being charged at 3C would have a 10F increase if started at room temp. Newer lower IR Lipolys have less of an increase when started at room temp.

Charles
Apr 12, 2010, 11:57 AM
Novice RC pilot
u.rusty's Avatar
I like the idea of charging at a high rate (tuned to the IR of the battery) with a "faster charge" setting and having the battery voltage settle to a rested voltage between 4.15 and 4.2 volts per cell.

In the morning, when prepairing to fly, I will charge my LiPo batteries from a 50% storage charge to full charge with an FMA Cellpro 10S "Accurate charge" setting. (The A123 packs are stored at full charge.) Then use "faster charge" for field charging. I can see now that that isn't really nessasary, and that I would better serve my impatience to get to the air field before the wind comes up, by simply using the "faster charge" setting before I leave as well as at the airfield.

It's time for me to bust out the indoor/outdoor thermometer and record some temps while charging my LiPo batterys...
Apr 12, 2010, 12:11 PM
Southern Pride
everydayflyer's Avatar
Here you go. I posted this on another User's Group over a years ago. I have posted it here also a couple of times but no one ever comments.

Quote:
Efficient use of charging time:

This example based on charging 3S3300 at 12.5A (3.78C) and while not linear are representative of other rates. Each person will have to conduct their own equalization as chargers/balancers and LiPolys will vary.

Total charge time 18 min. capacity replaced 2896 for an average of 160.9 mAh per min..
During the first 12:30 while rate was holding at 12.5A
2600 mAh for an average of 208 mAh per minute.
Between 12:30 and 14 min . 200 mAh or 133.3 mAh per minute.

First 12:30 or 69.4% of total time 2600 mAh or 89.8% of capacity achieved.

This should make it clear that it is best to pull the battery at 95% statre of charge and fly it instead of wasting time waiting on that last little bit.


Charles
Apr 12, 2010, 12:17 PM
Novice RC pilot
u.rusty's Avatar
I take it that the 12:30 point in the charging process is where the algorithum switched from CC to CV.
Apr 12, 2010, 12:22 PM
Southern Pride
everydayflyer's Avatar
Yes
Apr 12, 2010, 12:32 PM
Novice RC pilot
u.rusty's Avatar
So, in the interest of maximizing my flight time at the air field, I would be better off using "Faster charge" in the morning before I leave for the airfield, and at the air field, considering the batteries full when they hit the CV charging stage. (So long as I don't discharge more than 80% of the LiPo batteries capacity.) As well as using a predetermined maximum charge rate.

Excellent. Minimum time charging, maximum time flying. [edit] Not maximum flight duration, just more time flying overall. [end edit]

Of course, there are those days at the air field that I spend most of my time chewing the fat with everyone else there...but that is a different story.
Apr 12, 2010, 03:47 PM
Expo is built into my thumbs
Hance's Avatar
Well I destroyed my fist lipo yesterday. Grabbed a pack that I thought was charged and it really wasn't. Threw the plane up for some fast full throttle passes and all at once hit LVC. This was only a few minutes into the flight. I brought the plane in and the lipo was smokin hot. Checked the voltage 2 cells were in the 2.9 to 3.0 volt range. One cell was 1.5 volts. The pack kept getting hotter for awhile after I landed no fire though. Guess I will be more careful about checking the pack voltage before putting it in the plane from now on.
Apr 12, 2010, 06:10 PM
Novice RC pilot
u.rusty's Avatar
OK, rain was falling and the wind was blowing so I decided to try a 2C LiPo charge test. I was planning a 3C charge test, depending upon these results, but it doesn't look like I'll be doing that, at least with this battery.

3S 1330mAh LiPo charged at 1C then discharged 1000mAh at 5A and allowed to cool for 1 hour.
Charged at 2.6A (2C) 965mAh in 29 minutes. (about 2A average current) with FMA Cellpro 10S using "Faster charge"
[edit] 89% of the charge delivered in 20 minutes, the point when all three cells reach 4.2V [end edit]
Internal resistance per cell 22.4 / 21.7 / 21.9 (milliohms)
Cell voltage settled to 4.175V/cell after 15 minutes.
Battery temp change during charge +10.8F
Ambient temp change during test +1.1F (including 10 minute cool down after charge)

1:57 PM 4/12/2010
charge start
batt 66.0F ambient 66.0F

2:02 PM 4/12/2010
5 minutes
batt 66.2 Ambient 66.2

2:07 PM 4/12/2010
10 minutes
batt 69.4 ambient 66.2

2:12 PM 4/12/2010
15 minutes
batt 72.5 ambient 66.2

2:17 PM 4/12/2010
20 minutes 4.2V/cell reached
batt 76.8 Ambient 66.4

2:22 PM 4/12/2010
25 minutes
batt 75.4 ambient 66.4

2:24 PM 4/12/2010
27 minutes balancing reached
batt 74.3 charger 66.6

2:27 PM 4/12/2010
29 minutes Charge complete
batt 73.6 ambient 66.6

2:37 PM 4/12/2010
10 minutes after complete
batt 70.5 ambient 67.1

Looks like this battery should be OK charging at 2.5A or about 2C
Last edited by u.rusty; Apr 13, 2010 at 10:39 AM. Reason: Added charge percentage when cells reached 4.2V
Apr 12, 2010, 06:45 PM
Registered User
Carlyle Harper's Avatar
Quote:
Originally Posted by Hellmut1956
Hi friends

My first contribution to this place. I want to relate you to an excellent article from Linear Technology about batteries. This article, focusing on the use of rechargeable batteries in Hybrid and electric cars, gives very interesting and I believe useful insights about the handling of batteries, the number of cycles they can provide their services in a pretty good readable way.

http://cds.linear.com/docs/LT%20Maga...ikeKultgen.pdf

Donīt worry about this relating to a specific component, but what they say about batteries is very valuables information. Effectively I am planning to build such a BMS, Battery Monitoring System, based on the device LTC6802-2.

I need to care about not spending too much money on my hobby, so the investment in the batteries for my class 1 Model sailship is pretty hefty. I plan to have in this sailboat LiFePO4 3,3V - Headway 38120 10Ah in a 12SP1 pack self build. These cells can be purchased with a screw connection attached, here the image:



Best regards

Hellmut
Don't expect much more than the 2C rating of these cells ( 20 amps). At 20 amps the voltage is already sagging. 10 amps would be a more accurate rating. I have six of these myself in a 4s and 2s packs that I use in low current applications.
Apr 12, 2010, 07:17 PM
Novice RC pilot
u.rusty's Avatar
Quote:
Originally Posted by Carlyle Harper
Don't expect much more than the 2C rating of these cells ( 20 amps). At 20 amps the voltage is already sagging. 10 amps would be a more accurate rating. I have six of these myself in a 4s and 2s packs that I use in low current applications.
I noticed that, but then I realized he is planning to use them to power a model sail boat. I have no idea how much power a model sail boat needs, but I would guess it wouldn't be much.
Apr 13, 2010, 03:11 AM
Registered User
ScotY's Avatar
Quote:
Originally Posted by everydayflyer
More or less, most of the ones I charge at 5 and 6C go on the charger at 120 to 125F and in fact cool down to 90 to 100 during the charge. Ones charged at 3C for the most part cool down perhaps 5F more.

Years ago a TP ProLite being charged at 3C would have a 10F increase if started at room temp. Newer lower IR Lipolys have less of an increase when started at room temp.

Charles
Hi Charles,

Why do the packs cool while charging? I never did understand the physics of what's happening here. Are they just getting cooler because they're simply given time to cool off or does the charging help cool them faster? I know, kinda dumb question, so I hope it makes sense to you what I'm asking.

Back in the old days, one would never consider charging a hot pack and I still have a battery cooler I used to use (computer fan attached to a piece of pipe). Do you feel charging a hot lipo packs shortens it's lifespan, or no change?

Thanks, Scot
Apr 13, 2010, 05:28 AM
Southern Pride
everydayflyer's Avatar
Quote:
Why do the packs cool while charging? I never did understand the physics of what's happening here. Are they just getting cooler because they're simply given time to cool off
Correct they are just not being heated nearly as much so cool down, not as quickly as the wopuld if noyt being charged at all perhaps but still fast enough in most cases.

I see no problem using a forced air type battery cooler. I have used them myself but do not most of the time. When the weather gets really hot I use more packs and do not fly as long or as hard. All of my aircraft will fly well with around 30% of available power so
keeping my LiPolys at around 125F max. is not an issue. Fact is that the newer higher C ,lower IR ones are more of an issue in cool weather as they do not warm up nearly as fast so down is down a little. .

LiPolys in fact perform better when they are warm. It seems to me they do best at around 125F to 135F. The problem is getting them that hot and no hotter. SOme who use LiPolys in competation use battery warmers to preheat them for increased performance,same has been done with Ni cells for years.

Charles


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