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need lipo education

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Old 02-24-2013, 07:21 PM
  #1
cflchurch
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Default need lipo education

I'm starting to get into lipo's and need some schooling on the subject. I have jumped around a few sites but nothing is compiled for what I'm curious about. Caution this will be lengthy. I want to know what the breakdown of the battery info is and what it does and means.
I'll use this as an example...
4200 mah 2s1p 25c 7.4v
1. 4200 mah- is this for power, run time or something else?
2. 2s1p and 2s2p- which one is better and what do they do ? I think 2s refers to 2 cells but the 1p 2p and why they differ is beyond me.
3. 25c 30c 40c-?
4. I believe each cell is 3.7v , correct? but what is it for ? runtime or power ?
Thank you guys for being patient for a 38 y.o. lipo newbie. trying to get my 4 and 6 y.o into the game and my oldest had so much fun with an old stampede , so I need some education on lipo's for some new trucks. Thanks again. Brian
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Old 02-24-2013, 09:04 PM
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Quote:
ORIGINAL: cflchurch

I'm starting to get into lipo's and need some schooling on the subject. I have jumped around a few sites but nothing is compiled for what I'm curious about. Caution this will be lengthy. I want to know what the breakdown of the battery info is and what it does and means.
I'll use this as an example...
4200 mah 2s1p 25c 7.4v
1. 4200 mah- is this for power, run time or something else?
2. 2s1p and 2s2p- which one is better and what do they do ? I think 2s refers to 2 cells but the 1p 2p and why they differ is beyond me.
3. 25c 30c 40c-?
4. I believe each cell is 3.7v , correct? but what is it for ? runtime or power ?
Thank you guys for being patient for a 38 y.o. lipo newbie. trying to get my 4 and 6 y.o into the game and my oldest had so much fun with an old stampede , so I need some education on lipo's for some new trucks. Thanks again. Brian

G'day Brian,
OK, Question 1, 4200Mah is Milli Amp Hours, that is how much current the battery will supply in 1 hour, 4200Milli amps or 4.2 amps for 1 hour, this is 1C or 2.1 amps for 2 hours this is 1/2C & so on. or 8.4 amps for 1/2 hour this 2C.
Question 2, 2s1p is 2 cells in series, & 1 in parallel, so in series the voltage is added together, so 3.7 + 3.7= 7.4 volts. And parallel the voltage stays the same & the current output is added.
so 2s2p is 2 cells in series, double voltage, & 2 cells in parallel, double the current output. or 3.7+3.7=7.4volts & if they were 1000Mah or 1 amp cells that would be 2000Mah or 2 amps for 1 hour.
Question 3, Power is voltage x current = watts, that is power.

The batteries supply a motor, through a speed controller, the load on that motor determines how much current it draws, so if you use a motor or speed controller, that is too small for the job, it will draw more than it is rated for & usually burn out.
So the idea is to use a motor & speed controller, that are rated a bit higher than the maximum load, then the battery capacity in Mah, determines how long the motor will run per charge.
Most motors also have a voltage range, so don't exceed that & all is well.
C ratings are capacity, some cells are 20C, 30C, so it follows that a 10C battery can supply 10 times it's capacity for a short time, & so on.
So our 1000Mah battery if it was 30C could happily supply 30 amps, but only for a short time before it went flat, but it would not hurt the battery.

I hope this is helpful

Cheers
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Old 02-24-2013, 10:29 PM
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cflchurch
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Default RE: need lipo education

Alan, it helped a lot, Thank you. still trying to wrap my brain around all of this. so the higher the mah the longer the run time? The higher the c rating (20c 30c 40c) the more power it will have but for limited time? So these are the specs for the speed control , what would be the max or safe working battery 2s and 3s?
Continuous current: 200A
Peak current: 320A
thses are my motor specs- 65A constant; 100A peak/burst
The system is a traxxas velineon .
last thing, I hope. If I'm charging a 3000 mah lipo, is the rule of thumb to charge 1amp per 1000mah? I.E. 3amp on my charger? Thanks again Alan and to all who help. Brian
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Old 02-25-2013, 12:28 AM
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Default RE: need lipo education

Multiply the capacity (mah) of the pack by the C rating to determine its maximum amp output. A 3000mah pack 5C can put out 15amps. A 3000mah pack 20C can put out 60amps. most manufacturers exaggerate their claims and it is not good to run a battery (?anything!?) close to its max so have at least 15% error of margin.

By definition higher power use uses more power so run times will reduce.

Make sure your battery can provide the amps your motor draws and make sure your ESC can handle the amps.

NoBS hangtime hobbies has good information on lipos.

All the best
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Old 02-25-2013, 07:02 AM
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Very good information guys for lurkers like me
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Old 02-25-2013, 08:15 AM
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Default RE: need lipo education

Take a look at Ken's newsletter.
http://www.theampeer.org

He has tons of newbie information as well as extensive battery and motor testing.
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Old 02-25-2013, 11:11 AM
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Default RE: need lipo education

The definitive source for battery information of all types www.hangtimes.com
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Old 02-25-2013, 11:19 AM
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Default RE: need lipo education


Quote:
ORIGINAL: Goldenduff


Make sure your battery can provide the amps your motor draws and make sure your ESC can handle the amps.


Are you sure this is correct?

My understanding is that the motor will only use what you feed it. A 25C won't harm anything that could use the current of a 40C (assume same cell count and mah). Whether the ESC and motor can handle the higher current is a different story, but the lower C should be fine.
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Old 02-25-2013, 11:30 AM
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Default RE: need lipo education

If the motor demands too much from the battery the battery will not cope and it could fail. Same as the esc. 

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Old 02-25-2013, 12:05 PM
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Default RE: need lipo education

thank you guys so much for this, I kept searching and was getting frustrated. again thank you. Brian
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Old 02-25-2013, 01:04 PM
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Default RE: need lipo education

Depending on the prop te motor will demand a certain current. If the demand exceeds the battery and or esc ability one of them will pop. 

If the prop is too large and the battery an esc are capable of supplying the amps and or volts the motor could go too. 

Prop within the motors specs and make sure the battery AND esc can deliver say 20% more amps than being demanded. Rough figures.
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Old 03-01-2013, 03:13 AM
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Default RE: need lipo education

Here are a few MANDATORY guidelines for charging/using LiPos (Lithium Polymer Batteries).


1. Use only a charger approved for lithium batteries.[/b] The charger may be designed for Li-Ion or Li-Poly. Both batteries are charged in exactly the same. Some older cell phone chargers may charge the batteries .1 volt to low (4.1 vs 4.2), but that will not harm the battery. However, inexpensive lithium chargers are widely available and the use of cellphone chargers is highly discouraged. 
2. Make certain that the correct cell count is set on your charger.[/b] Watch the charger very closely for the first few minutes to ensure that the correct cell count continues to be displayed. If you don't know how to do that, get a charger that you do know how or don't charge the batteries.
3. Use the Taps.[/b] Before you charge a new Lithium pack, check the voltage of each cell individually. Then do this after every tenth cycle there after. This is absolutely critical in that an unbalanced pack can explode while charging even if the correct cell count is chosen. If the cells are not within 0.1 volts of each other then charge each cell individually to 4.2 volts so that they are all equal. If after every discharge the pack is unbalanced you have a faulty cell and that pack must be replaced.
Taps are provided on most new lithium packs. Taps give you the ability to check individual cell voltages and charge one cell at a time. Make sure and get the appropriate connector to go into your taps. Don't try to stick you volt meter probes in the taps to measure voltage. They could slip and short your cells. Don't try to charge more than one cell at a time from the taps. Unless you have an isolated ground charging system, you'll short your batteries out. Refer to your individual cell maker for tap pin-outs. 
4. NEVER charge the batteries unattended.[/b] This is the number one reason for houses and cars being burned to a crisp by lithium fires.
5. Use a safe surface to charge your batteries[/b] on so that if they burst into flame no damage will occur. Vented fire safes, pyrex dishes with sand in the bottom, fireplaces, plant pots, are all good options.
6. DO NOT CHARGE AT MORE THAN 1C unless specifically authorized by the pack vendor.[/b] I have personally had a fire in my home because of violating this rule. Todays highest discharge batteries can supposedly be safely charged at greater than 1C, however so far in all cases doing so shortens the life of the pack. Better to buy 3 packs than to try to charge 1 pack 3 times quickly. This may change in the future but as of Winter 2005 1C is still the recommended charge rate. 
7. DO NOT puncture the cell, ever.[/b] If a cell balloons quickly place it in a fire safe place, especially if you were charging it when it ballooned. After you have let the cell sit in the fire safe place for at least 2 hours. Discharge the cell/pack slowly. This can be done by wiring a flashlight bulb of appropriate voltage (higher is voltage is ok, lower voltage is no) up to your batteries connector type and attaching the bulb to the battery. Wait until the light is completely off, then throw the battery away.
8. If you crash with your lithium cells they may be damaged[/b] such that they are shorted inside. The cells may look just fine. If you crash in ANY way carefully remove the battery pack from the aircraft and watch it carefully for at least the next 20 min. Several fires have been caused by damaged cells being thrown in the car and then the cells catch fire later and destroys the car completely. 
9. Charge your batteries in a open ventilated area.[/b] If a battery does rupture or explode hazardous fumes and material will spew from the battery. 
10. Keep a bucket of sand nearby[/b] when you are flying or charging batteries. This is a cost effective way to extinguish fires. This is very cheap and absolutly necessary.
11. It can happen to you[/b], do not think to yourself that “it won't happen to me” as soon as you do that it you'll be trying to rescue your kids from your burning house or car. I'm very serious about this.
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