RE: RC Surfer
If your DC charger has the large crocodile clips that connect to a 12V car battery then yes you can. However, a car battery is only about 7000mah, so if you try and charge a second battery, your car will probably not start ; )
If your charger takes an AC adaptor, then spend the 20 bucks and buy one off eBay, much less hassle.
There are lots of cheap lipochargers with balancing on eBay from China. They are fine. I have bought two and they have lasted years and charge up to 5A which is normal as you DO NOT charge your lipos more than the amps. For those who do not understand amps or currents, I will explain below with what i have learnt online. I hold no responsibility for any false information, i'm just passing on what I have read.
7.4v 20C 4000mah.
When a battery says it is a 4000mah battery, it means it is 4amps.
The 20C means the current. is times 20. A battery at 1C will discharge in one hour at full throttle.2C will discharge in 30 minutes, 3C in 20 minutes.Dividethe #C into an hour.
So a 20C battery is able to be discharged in 3 minutes. No this is where it gets confusing..
The battery above is 20C, to work out itscontinuousdischarge rate, we times 20C X 4000mah (4000mah = 4Amp. Mah ismilliamp) So we get a 20C x 4Amps = 80Ampcontinuousdischarge. If your motor is rated at 80A and your battery is 80A, at 20C you will discharge the battery in 3 minutes at full throttle. If the motor only draws 40A (half the amps) then it will last approximately 6 minutes. You all get longer than 3 minutes at the beach as you do not go full throttle for the entire time.
Now the 7.4v has no impact on the aboveequation, it is just the rotation power of the battery. But this is where volts come in to play.
A motor will rotate 33% more with a 11.1v than to a 7.4v at full throttle. So in effect, you use 33% less power to do the same speed as a 7.4v would using a 11.1 battery or at full throttle you will go 33% faster. However, 11.1v batteries ate also 33% bigger...
Us RC Surfers (excluding those who make their own and require much bigger motors and ESC with greater capacities) will use a motor that spins at approximately 3000rpm/v motor. This motor can draw 54A max.
Now we all use an 60A ESC, which is appropriate for our needs.
Our choice ofbatteriesdiffer, however, those on lipos will probably be using around 7.4v 25C 4000mah batteries as they will fit in the space for the battery without cutting out the battery area.
The motor will rotate at around 21,500 time per minute and draw at a maximum rate of 54A at full throttle.
The battery has acontinuousdischarge of 100A
The ESC can handle only 60A, but this is ok as the motor will not draw more than 54A and your ESC will not blow up. If you were to run a motor which draws 100A on a 60A ESC, then your ESC will heat up and go pop and a small puff of smoke will come out and you will have to buy another ESC.
A prop with a higher pitch will put more strain on the motor. We all use around 30mm props with a pitch of around 1.4". This is good as the motor can spin the prop effectively without over heating, or spinning too easily which will waste power and push our surfers that weigh around 1.7-2kg. A motor loses efficiency the hotter it gets. If you have a good cooling system, your motor will perform better, if you do not the motor will heat up and become less effective. If your motor is running hot after a surf, then i suggest either installing a better water cooling system, reducing the size of your prop, of reducing the weight of the surfer.
Electric RC is complicated. You always need to take into account the motor Amps and rotations, the ESC amps, the battery Amps, the size and the pitch of the prop and the weight of the object you are moving. While there is no straightequation, it is best to use what is recommended by those who have trieddifferentconfiguration.
People will often recommend to have a motor and battery that draws and discharges an ampage rate lower than the ESC rating, but as we all use batteries that are rated higher than 60A and we all use ESCs that are rated for up to 60A, this is not a problem. Just always make sure the maximum rate at which a motor will draw amps is below the Amps of the ESC.
Now with charging your lipo battery, always charge it at the same rate as the amps. So if your battery is 4000mah, charge it at a rate no higher than 4amps. For a 5000mah battery, no higher than 5. Now remember lipos lose their punch after a while so when you battery starts to charge to 3500mah, lower your charge rate to 3.5A. I always charge mine .5 below the rated level to make sure i do not damage any of the lipo cells.
I know a lot of you out there reading this already know this, but i wanted to know this a couple of years ago and i really had to search elsewhere to find the answers, so those RC Surfers who were not sure will now know.
Hope this was helpful.
PS. I don't write too often here so i think this long explanation gives me a week or two off from adding material ; )