the basics of lipo batteries
06-15-2006, 07:07 PM
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the basics of lipo batteries
Hello i am getting a brushless setup for my mini supersportster and here what im going with.
Motor: E-Flite Park 400 Brushless Outrunner Motor, 920Kv
ESC: E-Flite 20-Amp Brushless ESC (V2)
Battery: Thunder Power 1320 mah 3s 11.1 volt pack. 13c constant, 20c burst. PROLITE SERIES
On this lipo battiery i am planning on using a triton charger and i was wondering do i really need to get a balancer or should i go with one of the E-Flite batteries that have the balancer built in?
Im a noob when it comes to any electric stuff so tell me as much as you can about it. The only batteries i have ever used are nicads.
Motor: E-Flite Park 400 Brushless Outrunner Motor, 920Kv
ESC: E-Flite 20-Amp Brushless ESC (V2)
Battery: Thunder Power 1320 mah 3s 11.1 volt pack. 13c constant, 20c burst. PROLITE SERIES
On this lipo battiery i am planning on using a triton charger and i was wondering do i really need to get a balancer or should i go with one of the E-Flite batteries that have the balancer built in?
Im a noob when it comes to any electric stuff so tell me as much as you can about it. The only batteries i have ever used are nicads.
06-16-2006, 02:31 PM
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RE: the basics of lipo batteries
If you don't know anything about lipos, buy the cellpro 4s from FMA...or they are now available from horizon hobby(stocker of your LHS)
This charger is perfect for you if you don't understand batteries yet. Now settings to know on this charger and it has enough safety features to keep you from burning down the house. They are out of stock now, but will be available in July. Only $70 bucks too! You will need an adapter for the TP battery. They sell those too.
The next best option is the 3s 800mah eflight combo balance charger/and lipo used in the blade cp pro, probably need 2 of the batteries in series to equal the 3s TP 1320 PL.
This charger is perfect for you if you don't understand batteries yet. Now settings to know on this charger and it has enough safety features to keep you from burning down the house. They are out of stock now, but will be available in July. Only $70 bucks too! You will need an adapter for the TP battery. They sell those too.
The next best option is the 3s 800mah eflight combo balance charger/and lipo used in the blade cp pro, probably need 2 of the batteries in series to equal the 3s TP 1320 PL.
06-16-2006, 02:48 PM
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RE: the basics of lipo batteries
I dont know that much about lipos but what ive heard i think ill just use some packs of nimh batteries. do u all think ill b able to get close to the same performance with nimh batteries. I also just bought this tritan and i dont want to go and have to buy a lipo balancer also now. Tell me any suggestions. Thx
06-18-2006, 07:06 PM
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RE: the basics of lipo batteries
I have been using a Triton charger to charge my ThunderPower 2C; 7.4V; 910Mah lithium batteries at 1C without a balancer and so far no problems. I am not sure about balancers myslef and would like to ask why I "need" one. There may be a valid reason and suspect it has something to do with uniform charging and discharging. So, does anyone (other than an vendor) have any test results on lithium batteries charged and discharged with and without the use of a balancer?
06-18-2006, 11:56 PM
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RE: the basics of lipo batteries
Balancing lipos is not a matter of performance so much as it is a matter of safety and battery longevity.
A lipo pack consists of 2 or more cells. You want each cell in the pack to be charged to the same voltage, which is 4.2V for each cell when the pack is fully charged. Thus, a fully charged 2-cell lipo pack will measure 8.4V (2 x 4.2) and a fully charged 3-cell lipo pack will measure 12.6V.
Due to small differences between cells, sometimes the voltage of the cells in a pack will not increase at quite the same rate while charging. But the charger will still try to charge the pack to full voltage (8.4V for a 2-cell, 12.6V for a 3-cell).
As a result, the cells in the pack may be at different volages when the charge is completed. For example, you may end up with a 3-cell pack that has two cells at 4.0V, and one cell at 4.6V. The total pack voltage is correct at 12.6V, but the pack is out of balance because its cells are at different voltages. The typical low-tech lipo charger can monitor only the total pack voltage, not the individual cells, so the charger does not know the pack is out of balance.
When a lipo is charged to a voltage greater than 4.2V, even by a few tenths of a volt, damage can occur. This can lead to "puffed" or swollen cells and a ruined battery pack.
Balancing a pack means using some method to make sure each cell is charged to the same voltage. You can do this by charging each cell separately (if the pack has taps that allow this) or by using packs and chargers designed to keep the cells in balance while charging. That's why you now see some battery packs with separate "charge" and "discharge" leads. Charging through the "charge" lead with the correct charger will charge the pack and make sure it is in balance.
Keeping lipo packs in balance simply reduces the chances of battery failure. You "need" to balance your lipo packs only if you want to minimize the chances of safety and reliability problems. Many people never balance their lipos and never have any problems. And unless your packs already have taps that allow access to the individual cells, there is no easy way to balance them, anyway.
- Jeff
A lipo pack consists of 2 or more cells. You want each cell in the pack to be charged to the same voltage, which is 4.2V for each cell when the pack is fully charged. Thus, a fully charged 2-cell lipo pack will measure 8.4V (2 x 4.2) and a fully charged 3-cell lipo pack will measure 12.6V.
Due to small differences between cells, sometimes the voltage of the cells in a pack will not increase at quite the same rate while charging. But the charger will still try to charge the pack to full voltage (8.4V for a 2-cell, 12.6V for a 3-cell).
As a result, the cells in the pack may be at different volages when the charge is completed. For example, you may end up with a 3-cell pack that has two cells at 4.0V, and one cell at 4.6V. The total pack voltage is correct at 12.6V, but the pack is out of balance because its cells are at different voltages. The typical low-tech lipo charger can monitor only the total pack voltage, not the individual cells, so the charger does not know the pack is out of balance.
When a lipo is charged to a voltage greater than 4.2V, even by a few tenths of a volt, damage can occur. This can lead to "puffed" or swollen cells and a ruined battery pack.
Balancing a pack means using some method to make sure each cell is charged to the same voltage. You can do this by charging each cell separately (if the pack has taps that allow this) or by using packs and chargers designed to keep the cells in balance while charging. That's why you now see some battery packs with separate "charge" and "discharge" leads. Charging through the "charge" lead with the correct charger will charge the pack and make sure it is in balance.
Keeping lipo packs in balance simply reduces the chances of battery failure. You "need" to balance your lipo packs only if you want to minimize the chances of safety and reliability problems. Many people never balance their lipos and never have any problems. And unless your packs already have taps that allow access to the individual cells, there is no easy way to balance them, anyway.
- Jeff
06-20-2006, 12:06 AM
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RE: the basics of lipo batteries
Thank you jdetray, excellent job!
That explains things very nicely.
OK, now I understand the "need" for balancing, but I am bit confused with 8.4 volts max.
I have two Thunder Power 910 mah lithium polymer battery packs. Each pack has two cells (2C) and the voltage for each pack is 7.4 volts. This means each cell is 3.7 volts (3.7 x 2) not 4.2 as you noted, but 4.2 may be the max. So...I pulled out my Platinum Polymer 7.4 volt 1200 mah battery and in parenthesis I find (8.4 volts max) AHA! Now I suspect voltage as a variable in the equation of this battery game and thus the need for balancing! OK so next to test things out further, I try to charge my lithium batteries at 8.4 volts with my Triton charger but there is not an 8.4 volt option, however there IS a 7.4 volt option. Deductive reasoning now suggests 8.4 volts is the maximum of a 2 cell lithium cell pack and my Triton charges a 2 cell pack at a conservative/safer 7.4 volts...correct?
When things are complicated they are so much more fun!!!
That explains things very nicely.
OK, now I understand the "need" for balancing, but I am bit confused with 8.4 volts max.
I have two Thunder Power 910 mah lithium polymer battery packs. Each pack has two cells (2C) and the voltage for each pack is 7.4 volts. This means each cell is 3.7 volts (3.7 x 2) not 4.2 as you noted, but 4.2 may be the max. So...I pulled out my Platinum Polymer 7.4 volt 1200 mah battery and in parenthesis I find (8.4 volts max) AHA! Now I suspect voltage as a variable in the equation of this battery game and thus the need for balancing! OK so next to test things out further, I try to charge my lithium batteries at 8.4 volts with my Triton charger but there is not an 8.4 volt option, however there IS a 7.4 volt option. Deductive reasoning now suggests 8.4 volts is the maximum of a 2 cell lithium cell pack and my Triton charges a 2 cell pack at a conservative/safer 7.4 volts...correct?
When things are complicated they are so much more fun!!!
06-20-2006, 12:27 AM
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RE: the basics of lipo batteries
If your 2-cell lipo comes off the charger at much less than 8.4 volts, there is something wrong.
The "nominal" voltage of a lipo is 3.7V per cell. That is 7.4V for a 2-cell lipo and 11.1V for a 3-cell lipo. This "nominal" voltage is how lipos are usually specified. However, the actual voltage of a fully charged lipo is greater than its nominal voltage -- it's 4.2V per cell.
A fully charged 2-cell lipo should measure very close to 8.4V, and a fully charged 3-cell lipo should measure very close to 12.6V.
Chargers usually refer to lipos by their nominal voltage, either 7.4V (2-cell) or 11.1V (3-cell). But when you actually charge your lipos, they should measure 8.4V (2-cell) or 12.6V (3-cell).
Some convervative chargers may not charge all the way to 4.2V per cell, but they will be close -- perhaps 4.1V per cell.
Here's a handy chart that shows a lipo's percentage of charge for different measured voltages.
4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%
As you can see, a lipo that measures 3.7V per cell has only 11% of its capacity remaining. Or stated a different way, a lipo that measures 3.7V per cell is 89% discharged.
The most important thing to remember from all of this is that a fully charged lipo should measure very close to 4.2V per cell. It should never be more than that but with some chargers may be slightly less.
I hope this is not too confusing.
- Jeff
The "nominal" voltage of a lipo is 3.7V per cell. That is 7.4V for a 2-cell lipo and 11.1V for a 3-cell lipo. This "nominal" voltage is how lipos are usually specified. However, the actual voltage of a fully charged lipo is greater than its nominal voltage -- it's 4.2V per cell.
A fully charged 2-cell lipo should measure very close to 8.4V, and a fully charged 3-cell lipo should measure very close to 12.6V.
Chargers usually refer to lipos by their nominal voltage, either 7.4V (2-cell) or 11.1V (3-cell). But when you actually charge your lipos, they should measure 8.4V (2-cell) or 12.6V (3-cell).
Some convervative chargers may not charge all the way to 4.2V per cell, but they will be close -- perhaps 4.1V per cell.
Here's a handy chart that shows a lipo's percentage of charge for different measured voltages.
4.20v = 100%
4.03v = 76%
3.86v = 52%
3.83v = 42%
3.79v = 30%
3.70v = 11%
3.6?v = 0%
As you can see, a lipo that measures 3.7V per cell has only 11% of its capacity remaining. Or stated a different way, a lipo that measures 3.7V per cell is 89% discharged.
The most important thing to remember from all of this is that a fully charged lipo should measure very close to 4.2V per cell. It should never be more than that but with some chargers may be slightly less.
I hope this is not too confusing.
- Jeff
