|Apr 25, 2011, 08:43 PM|
Joined Apr 2011
Clear some things up for me? (Batts & Motors)
Hey everyone I have a huge topic that I don't understand... BATTERIES AND MOTORS.
I did read the complete guide on Li-Pos but I still need some clearing up.
Where do I start?
1) Does increasing voltage increase your vehicle's top speed? Is this a good idea?
2) If "C" means discharge rate of a Li-Po, Would a lower "C" last longer during drives or did I misunderstand?
3) "S" represents the number of cells in a Li-Po?
4) The higher the mAh, the longer run time?
5) What are Kv in a motor?
6) What does say "20T" mean in a motor?
(I drive RC buggies)
Any explanations would be greatly appreciated. Thank you all so much.
|Apr 25, 2011, 10:45 PM|
1) Does increasing voltage increase your vehicle's top speed? Is this a good idea?It increases the power going to the motor. Make sure both the motor and ESC can handle the increased voltage
2) If "C" means discharge rate of a Li-Po, Would a lower "C" last longer during drives or did I misunderstand? No, the C rating is how much theoretically the battery could handle, ie : 1000mah lipo with a 30C rating can be expected to deliver up to 30amps...but these C ratings are rarely completely accurate, so always get a little higher then you need
3) "S" represents the number of cells in a Li-Po? Represents the number of cells in series, as opposed to parallel (determines the voltage of a cell, 1s=3.7v 2s=7.4v, etc
4) The higher the mAh, the longer run time? Yes, but increased weight
5) What are Kv in a motor? Determines rpm of motor
6) What does say "20T" mean in a motor? No idea
|Apr 25, 2011, 11:55 PM|
1. in general motors have "kv" ratings. For instance, a motor with a "kv" of 1000 will (with no load, i.e. just the shaft turning and nothing attached to the shaft) will turn at 1000 rpm for each volt of electric that gets to the motor. If 2 volts get to the motor then 1000 X 2 = 2000 rpm. When you add more voltage you get more rpm. There is however, a limit as to how much "power" a motor can take in and put out AND still be efficient (say 80% efficiency or better). A good electric setup is all about matching the components to the job. I am not a rc car person however there must be some good set up info in the car section.
2. Lets say you drive your car for 10 minutes and the battery is completly discharged, what is that average discharge rate? LiPo's are rated in Ah (Amp Hours) and there are 60 minutes in an hour. 60 / 10 = 6 or the avg disch rate is 6C. With 2 batts of the same capacity but different "C" ratings, they should last about the same amount of time however as they are getting low on power the higher C rated battery may heatup less since it probably has lower internal resistance and since it will loose less power due to lower internal resistance, it may run a little bit longer and hold/output a higher voltage towards the end as compared to the lower C rated batt. WARNING! just because a mfgr says their batt is a "25C" rated batt does NOT guarantee that it is! Check for reviews of the batts that you are interested in!!!!!
3. See post #4.
4. Think of amp/hours as gallons of gasoline. 1 Ah, 1 gallon. 2 Ah's, 2 gallons. The more gallons you have the longer you can run and as posted above more amp hours means a bigger battery that will weigh more and may or may not fit in the space available!
5. See #1, above!
6. no comment!
Sorry for being long winded! Hope I helped!
Michael (if your not fryin, your not tryin!)
|Apr 26, 2011, 12:31 AM|
The last buggy I had got upgraded to a 15T double motor. I belive it was a 550 size and was brushed. That means there is 2 wires instead of 3(brush less). It was pretty quick off the line and had a decent top speed. If you want all out top speed you could go for a 12Turn double but make sure your speed control can handle the higher rpm. You also don't want to run a lipo on a speed control that is supposed to have a nicad or nimah battery. You can but risk not only frying your speed control but toasting your lipo. You don't want to take a lipo under 3.0v per cell(that's the S.) If you discharge the lipo to low it will stop working. Not sure how much you know about this stuff so hope I am not being presumptuous. If you want a buggy that is going to do 70mph+ you want a brushless motor, brushless speed controll, and a 3s1p 11.1v 4000mah 30c lipo. You also need a lipo charger to be able to charge the lipos. Hobby king has some realy good deals if you don't mind paying a little bit for shipping.
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