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#1
25-02-2011
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Lipo Charging
i have a 4000mah 2s 40c lipo. and a sigma 2 charger.
what would be the best amp to charge this as its variable? 
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#2
25-02-2011
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Do not exceed a 1C charge rate, so 4A maximum. Constant Voltage to be set at 8.40V
N
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#3
25-02-2011
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Recommended charge rate would be 4A, which is 1C. Depending on the type of Lipo you can charge at up to 2C or 8A safely but most clubs won't like it and might start getting huffy about it.
__________________
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#4
25-02-2011
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Quote:
__________________
MBModels - Schumacher Racing - Vapextech.co.uk - MRT - Savox - SMD
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#5
25-02-2011
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I'm new to lipos so i'm kinda clueless!
its set to 0.1A at the moment so i presume that will do jack all! so if i set it at 4.0A it should charge fine?
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#6
25-02-2011
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Quote:
0.1A will do nicely if you want to wait until next christmas to drive your car.  4A will do fine.
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#7
25-02-2011
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Hope this helps...
A Lithium polymer cell operates between 4.2V when fully charged at 3.0V when fully discharged. It has an average voltage of between 3.6V and 3.8V. You charge them under a regime called CVCC which is constant voltage/constant current. Your charger will be set to charge the cells at a maximum of 4.20V per cell (or 8.4V for a 2-series battery. The remaining advice here assumes a 2-series battery). It is advisable to limit the current to 1C (in your case 4A). Assuming your battery is discharged when you start the charger the charger will limit the current to 4A and you will notice that the charging voltage will steadily increase towards 8.4V. While the charge voltage is <8.4V you will see that the current is max'd out to the 4A value and this is the time when you are putting the most charge into your battery. Once 8.4V is reached the charger will hold that value and the current will start to taper down towards zero. Many people think that once 8.4V is reaches the cell is fully charged or 'peaked' because they are comparing the effect to NiCd or NiMH cells. This is not the case and the current should be allowed to taper down to at least 0.1C before the charge terminates. I don't know what current taper your charger uses and a charger may terminate any where between 0.1C and 0.025C. As the current is tapering you are putting less charge into the cell for any given unit of time. Overall with LiPo cells: *Never charge them over 4.2V/cell (8.4V for a 2-series battery) *Charge using a LiPo charger that has a balance function. *Use an ESC with a LiPo cut-off (or always stop your car before it runs slow) *Never leave them in your car connected - even if the car is switched OFF. *Charge them in a LiPo sack *Store them 40-50% charged (my advice is to charge them before your race and then store them with the capacity that remains following your race). *Stop using them if they swell. N
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#9
26-02-2011
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One thing I will add:
Many chargers have a 'soft start' to their charging regime, so although you may have set the charge current at 4A you will initially see a lower charger current until the charger kicks in with the current you have set, This is most likely so the charger can validate that the cell voltages are what it expects and there are no cell shorts or under voltage cells. Also, if you put a battery on charge this is already 90% charged you will see that the voltage goes straight to 8.4V and that the current is already tapering.. this is of course normal. Lastly, if your charger set set to balance the cells then (at the end of charge) you will see the current rising and falling as the charger attempts to equalize the voltage of each cell, again this is normal. Note that balance charging can take much longer than regular charging. N
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#10
26-02-2011
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Much appreciated! I'll go and have a play with my charger!
Another thing.... if i charge 4200mah 7.4 2s 40c @ 4.0amps how long would it normally take?
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#13
31-03-2011
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Quote:
20c is your max discharge rate, so discharge at 20 x 4A = 80A maximum.
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#14
19-04-2011
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sorry for bumping this thread; didn't think my question required a new thread.
Quote:
So charging at 1C is the "max allowed"; if your charger has max 5A rating, if you want to charge a 5400 mah LIPO, you can safely charge at a lower than 1C rating I presume? It would just take longer than charging at 1C ? thank you in advance for your answer.
__________________
Ansmann ARE-2 - 5.5T C4.1 Centro - 7.5T X-Factory SCX-60 - 10.5T Hyper 9e - MMM
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#15
19-04-2011
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Correct. Charging below 1c will never have a negative effect on lipo's (infact there are arguments to say life expectancy is increased - my IB4200 lipo's have always been charged at 4.2amps and are as good now as they were 2 years ago).
Charge time will be slightly longer, but TBH the difference between 5amps and 5.4amps you'll struggle to notice due to Neil's previously mentioned "soft start" setting (my charger also "soft finishes")
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#16
19-04-2011
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I agree with Col. The only think I would add is that charging at C/2 (0.5C) will aid life (so a 5400mAh battery would be charged at 2700mA). Most Lithium ion batteries have their rated cycle life based on C/2 charging. If you have all the time in the world to spare then try reducing the charge current.
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#17
27-04-2011
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Ive just bought myself a Core-Rc UAC40 charger and some Intellect 7.4V 5400Mah 60C saddle packs and need some help on how to charge and balance my batteries...........
 I know that my 1C charge rate will be 5.4amps Are my saddles basically "TWO" 1S packs (3.7v) in series to make a 2S pack (7.4v) ??? What would be the cutoff voltage needed to be set on my ESC ??? What would be the Maximium voltage setting needed to be set at on my charger ??? Anything else i need to know before charging them up ??? cheers 
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Linear Mode
