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[old shrimper]

hi guys

I need some info on lypo batt, I assume they are rated in milly amp hours ?


How many MAH do you need to be equivalent  to a 7AH lead acid 12v battery ? and what would be the right, roughly.
 
I think 3 cells make 11.1 v is that right ?


Why do they have lots of wires hanging out of them other than the pos /neg leads.  Is it for charging and other things ????

Are chargers expensive for them ?


What do you do with the extra wires. ?  Do they go in to the ESC or just dangle.

 
thanks,

 Bob

[w3bby]

Yep LiPos rated in mAh so you would need a 7000mAh cell. They have 3,7V per cell so for 12V you are looking slightly under 11.1 (3S) or over at 14.4 (4s).

Here's one, weight 533g.

The extra wires are for balancing the individual cells in the pack, most Lipo chargers have this as standard. They connect to nothing when installed in a model.

Chargers are not that expensive, here is the one I use.

You may also want to consider the LiFePo batteries, these rate at 3.6V per cell but are less fussy to work with and safer.

[old shrimper]

hi mate
thanks for the good info 
can you tell me roughly  about how long they will run a model for compared to a SLA   on the same model with 540/1 motor
say 5ah 12v sla  to a 5ah 3s 11.1 ?
what is the basic diff between the lifepo and a lipo ?  price  size ect can you use the same charger ?
 cheers Bob

[malcolmfrary]

5AH = 5000mAH
7AH = 7000mAH
If you get 50 minutes from a 5AH battery, you get 70 minutes from a 7AH battery. 
Think of AH like litres of  fuel in a tank.  The more litres, the longer you get to go.
This assumes that both batteries are fully charged, and the same motor/prop combo is used.

[Timo2]

Hi Old Shrimper


   Ref LiPo info some basic at :   =    [size=78%]http://www.hobbyking.com/hobbyking/store/lipo_basics.asp[/size]


  Hope this will help


 Timo2

[old shrimper]

thanks guys that should get me started
 

[nick_75au]

I know its been a while but some info on Lipo compared to SLA, depending on the discharge rate a MUCH smaller Lipo can give the equivalent mAH of a gel cell, a gel cels AH rating is based on a 20 hour rate, for a 7 AH battery its about 350 mA, at


 When you get up to and over discharge rates of 1C or more the capacity available reduces considerably to the point where your 7 AH battery may only put out 3.5 amp/hour (3500 mAH) at a 1C rate where as a 3500 mAH Lipo will still have almost the same capacity even at a 10-20 C rate ie 35 amps discharge. even a 12 AH Gell battery will be lucky to put out 3000 mAH at those discharge rates.


the be all of this is if the current draw is over 50 % of the batteries capacity  the Li-po will have much longer run time compared to the gel cell.


Nick


The first image is a typical gel discharge
the second is a LiIon chart though Lipo displays very similar results, look at the difference in actual capacity at the 3C rate and its clear that the Li-po is far superior at maintaining its full capacity at high rateds of sischarge

[essex2visuvesi]

Be warned tho a fully charged Lipo will show a higher voltage than 11.1v usually nearer 12.5
Also you must use some kind of low voltage warning or cutoff as lipos are very fussy about being over discharged

[nick_75au]

Yep and a Gel will be 14.7 hot off the charger