lipo charge question

lipo charge question
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lipo charge question - 3/20/2008 1:51:29 AM

keithn4

Posts: 29
Joined: 11/4/2007
From: mayo, IRELAND
Status: offline

hey lads,

ive a quick question about charging lipo, i want to make sure ive got this right,

ive got 2 of these batterys,

Polyquest 1800mAh 3S 20C - 30C Lipoly

http://www.islandmodels.ie/component/page,shop.product_details/flypage,shop.flypage_new/product_id,304/category_id,14/manufacturer_id,0/option,com_virtuemart/Itemid,27/

http://www.islandmodels.ie/component/page,shop.product_details/flypage,shop.flypage_new/product_id,304/category_id,14/manufacturer_id,0/option,com_virtuemart/Itemid,27/

i just want to make sure i charge these at the right rate ive been reading a lot about them, and been hearing some mad stuff about them, i just want to make 100% sure

would 1.8amp be the max rate i cud charge at? or what rate would you reccomend?

do i need to cycle thse a few times before i use them?

do i cycle them by chargen them to the max then run them about half way down?

plus anthing else i would need 2 do?

i have my ammo box.

cheers guys for any help

keith

Post #: 1

RE: lipo charge question - 3/20/2008 3:54:59 PM

ozrcboy

Posts: 1751
Joined: 10/5/2006
From: CanberraACT, AUSTRALIA
Status: offline

Hi Keith,

Max charge 1.8A correct.

They don't need to be cycled. Never discharge a LiPo past about 90% of its rated capacity (below 2.7v/cell).

Cheers,
Oz.

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(in reply to keithn4)

Post #: 2

RE: lipo charge question - 3/20/2008 6:12:53 PM

Swift427

Posts: 482
Joined: 3/15/2007
From: Minneapolis, MN, USA
Status: offline

quote:

ozrcboy
They don't need to be cycled. Never discharge a LiPo past about 90% of its rated capacity (below 2.7v/cell)

I think he meant to say "70%" of its full/peak charge or 9 volts. Seventy-two percent of 12.6 volts is 9.1 volts or 2.66v/cell.

quote:

keith
do i need to cycle thse a few times before i use them?
do i cycle them by chargen them to the max then run them about half way down?
plus anthing else i would need 2 do?
i have my ammo box.

you can effectively cycle them the first few times with a conservative flying pattern
running them half way down to 6.3 volts could cause overheating. overdischarging drastically shortens its life.
do you have a lipo charger with built-in balancer to charge thru smaller 4-pin connector or a blinky balancer if you are charging by way of larger discharge connector.

_____________________________

Never Give Up, Never Slow Down, Never Grow Old, and Never Ever Die Young

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Post #: 3

RE: lipo charge question - 3/20/2008 6:33:20 PM

weeweeboi

Posts: 402
Joined: 1/14/2007
From: Seattle, WA, USA
Status: offline

1amp=1000mah so 1.8amp=1800mah.so you are correct

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Post #: 4

RE: lipo charge question - 3/20/2008 9:32:07 PM

ozrcboy

Posts: 1751
Joined: 10/5/2006
From: CanberraACT, AUSTRALIA
Status: offline

quote:

ORIGINAL: Swift427

I think he meant to say "70%" of its full/peak charge or 9 volts. Seventy-two percent of 12.6 volts is 9.1 volts or 2.66v/cell.

Actually swift I did mean exactly what I said. As the voltage drop on a LiPo is non linear (it starts at 4.2v/cell, rapidly loses current till about 3.7v/cell, then gradually loses current towards 3v/cell, at which point the battery is more of less fully discharged. The voltage then crashes. If the cells fall below 2.7v the battery will be irreparably damaged) what you can reliably do is discharge about 90% of the battery capacity (not voltage). At 90% you wont have quite hit the 3.0v /cell, but there is a general consensus that using the last 5% of the battery can shorten the number of cycles you get from the cell..

quote:

quote:

keith
do i need to cycle thse a few times before i use them?
do i cycle them by chargen them to the max then run them about half way down?
plus anthing else i would need 2 do?
i have my ammo box.

you can effectively cycle them the first few times with a conservative flying pattern
running them half way down to 6.3 volts could cause overheating. overdischarging drastically shortens its life.
do you have a lipo charger with built-in balancer to charge thru smaller 4-pin connector or a blinky balancer if you are charging by way of larger discharge connector.

6.3 volts being "half" discharged is not really an accurate way of thinking about it. Yes you only have half the voltage left (although your LiPo is already ruined) but voltage is not capacity. Capacity is how much current you can draw from the battery for how long. A 2000mAh battery can have 2A drawn from it for 1 hour, or 20A drawn from it for 1/10 of an hour (6 minutes), 40A drawn from it for 3 minutes etc. We say the battery is half discharged when it has use 1/2 of this Ah capacity, not when it reachs half its initial voltage.

To give you a way to think about this we often describe electricity as being like water. Voltage is electrical pressure, current is flow rate (measured in litres or gallons per minute). A battery's capacity is how much water it holds. So, imagine a large water tank on a hill behind your house. The bottom of the water tank is 20 metres above your house. The top of the water tank is 22 metres above your house. When the tank is full you have 22metres of water pressure. When the tank is half full you have 21 metres of water pressure, and when the tank is empty you have 20 metres of water pressure. By the time the water pressure gets to 11m (swift's "way" of thinking of half discharged) the water tank is already empty and the water is half way down the pipe to the house.

Charging inside the ammo box is a good idea. Provided you follow the rules a LiPo fire is very unlikely. However, if it does happen having the flames contained will help you control the situation far easier. If you can close the lid of the container, and have it so it is fastened, but not clamped down. If a fire does occur the LiPo will produce a lot of gas. If the gas can't vent from the box you will turn it into a bomb.

Here's what I charge in:

http://www.ozrcflying.com/2007/04/managing-risk-when-charging-lipos.html

All the best.

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http://www.ozrcflying.com

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Post #: 5

RE: lipo charge question - 3/21/2008 6:01:40 PM

Swift427

Posts: 482
Joined: 3/15/2007
From: Minneapolis, MN, USA
Status: offline

Ozrcboy - Thanks for the clarification.

Keith,

This may seem rather confusing so I hope this helps. Most ElectronicSpeedControls(ESCs) have a 3S(11.1v) cut-off of power to the motor based on the dropping voltage of the LiPo. Some have a 70% soft cut-off assuming the Lipo is fully charged so as not to overdischarge the LiPo below 9 volts. As soon as the voltage drawdown to the motor is cutoff at 9volts the LiPo voltage will immediately start rising again above the 9 volt cutoff and stabilize at oh, let's say 9.5v. If you were flying aggressively the voltage will rebound a little higher than if you were flying slowly and gradually depleting the voltage. Anyway, that is why you are able to restart the motor again, but only for a very short time--the lower the throttle(less amps being used) the more time until the LiPo will again cutoff at 9v. Usually, there is enough rebound capacity to land the plane with minimum throttle.

As far as 90% of capacity another consideration is the rate of discharge. Let's say a LiPo is rated at 12C, but the plane and pilot fly very aggressively. Then a more realistic rating for this LiPo might be 10C, and on the other hand if the plane and pilot fly a conservative pattern than a rating of 12C by the manufacturer should not be viewed as overrated. If your plane has a very aggressive flying pattern its even more important to take the best tender loving care possible with your LiPo to get maximum performance and the most number of recharge/discharge cycle life. If you and your plane have a conservative flying pattern it stands to reason that the LiPo should last longer. If both planes use a 11.1 volt 1800mAh 12C LiPo, but one is designed to be flown aggressively the battery in this plane may get rather warm and effectively have a shorter life. A 20C battery may have been a better choice. If the other plane were a slow flyer, with a very conservative pilot. who never flew for more than 10-12 minutes than a 1000mAh 10C LiPo would do just fine.

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Post #: 6

RE: lipo charge question - 3/25/2008 3:11:07 PM

keithn4

Posts: 29
Joined: 11/4/2007
From: mayo, IRELAND
Status: offline

THANKS GUYS FOR ALL THE GREAT INFO.

I DONT HAVE A BALANCER, WHAT RATE WOULD YOU RECCOMEN4D CHARGING THE BATTERY AT?

IVE BEEN CAHRGING IT AT 1.4, SHOULD I CHARGE IT LOWER THAN
THAT

I
HAVE ONLY DISCHARGED IT TO 11.5 SO I COULD DISCHARGE IT TO 10.5 AND STILL BE SAFE? AM I CORRECT?

THANKS AGAIN

Polyquest 1800mAh 3S 20C - 30C

(in reply to Swift427)

Post #: 7

RE: lipo charge question - 3/25/2008 6:00:14 PM

Swift427

Posts: 482
Joined: 3/15/2007
From: Minneapolis, MN, USA
Status: offline

quote:

ORIGINAL: keithn4

I DONT HAVE A BALANCER, WHAT RATE WOULD YOU RECCOMEN4D CHARGING THE BATTERY AT?

You need to buy a LiPo charger. Here is one that comes with the RTF Stryker 27C.
http://secure.hobbyzone.com/catalog/HZ/parkzone_f27c/parkzone_f27cparts/PKZ1040.html
Your local hobby store may have it in stock or can order one for you. You have an expensive LiPo that costs twice as much as a LiPo charger. Buy a LiPo charger=keep the 3 cells balanced for top performance, safety=minimize danger, and extend life for your money. Here are some other Lipo chargers and your hobby store should have various brands. http://secure.hobbyzone.com/catalog/HZ/catalog/catalog_chargerslipo/

quote:

IVE BEEN CAHRGING IT AT 1.4, SHOULD I CHARGE IT LOWER THAN
THAT

GET A LIPO CHARGER and charge at battery’s rating (1800mAh = 1.8amp charge). The first few cycles charge to 12 volts instead of 12.6 volts, and fly conservatively the first few flights.

quote:

I HAVE ONLY DISCHARGED IT TO 11.5 SO I COULD DISCHARGE IT TO 10.5 AND STILL BE SAFE? AM I CORRECT?

Just fly conservatively(half throttle) after the initial launch/climb the first few flights until the 9v cut-off. Thereafter, fully charge to 12.6 volts and fly as plane is designed to fly until 9v cut-off. Give your LiPo a catnap to cool down and rest before recharging.

The following link has some good information-
http://www.batteryuniversity.com/parttwo-34.htm

< Message edited by Swift427 -- 3/25/2008 6:10:37 PM >

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Never Give Up, Never Slow Down, Never Grow Old, and Never Ever Die Young

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Post #: 8

RE: lipo charge question - 4/6/2008 10:11:11 PM

casey_lamm

Posts: 137
Joined: 3/16/2008
From: Lancaster, PA, USA
Status: offline

what irks me is that companies know about the danger, yet they provide a charger that has a cigarette lighter adapter and the cord is 6 inches long. So how exactly do you charge that outside the vehicle?

go figure.

(in reply to Swift427)

Post #: 9

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