7 or 8 cell battery packs

[mikeval]

I currently have a nicd / nimh charger that charges 4 -6 -or 8 cell rx packs. I notice lots of parkflyer kits come with 7 cell packs. Being an electric novice, would moving to an 8cell pack cause harm to the ESC or motor if not rated for the extra juice. In short... how do I ensure the correct setup between motor, ESC (5a, 10a, 30a, etc) and battery power... I appreciate any informed replies.

Mike

[supi7]

Most Brushed ESC's ( like GWS) count the number of cells based on 1.2V per cell. So there should not be a problem there.

The Amp draw can be a problem as with higher Voltage higher Amp draw follows.

Most park flyiers kits will include a 5A ESC which is sufficient for many 8cell packs and its highly unlikely that it will get burned up.

If you have some cash burning a hole in your wallet get a 15 or 30A ESC (its always safer for the ESC)



Dan

[aeajr]

I currently have a nicd / nimh charger that charges 4 -6 -or 8 cell rx packs. I notice lots of parkflyer kits come with 7 cell packs. Being an electric novice, would moving to an 8cell pack cause harm to the ESC or motor if not rated for the extra juice. In short... how do I ensure the correct setup between motor, ESC (5a, 10a, 30a, etc) and battery power... I appreciate any informed replies.

Mike

1) Receiver packs are used in glow planes, gliders, and electrics where the motor pack is separate. Receiver packs are normally 4-5 cells, or 4.8 to 6V. If you attach an 8 cell pack to your receiver you are likely to burn it up.

2) Motor packs are what you are asking about. A motor pack attaches to an ESC, electronics speed control, which delivers full voltage to the motor but a reduced voltage to the flight electronics through a circuit called a BEC, battery elimination circuit. This allows you to fly your plane with a single pack and not require a separate receiver pack.

3) Most ESC will tell you how many cells they are rated for. Older ones are based on 1.2V per cell which is based on NIMH or NICD cells. Many of the newer ESCs list the number of NIX cells ( NICD or NIMH ) and give another listing for Lithium cells which are 3.7V per cell.

4) your ESC may be able to handle more cells, that is more voltage, than your motor can handle safely. For example, your ESC might be rated for 10 cells, 12 V, but your speed 400 motor will have a very short life if you run it on 10 cells. Most brushed motors, such as speed 400s, typically want to be run under 10 V, and some of the smaller speed 280s and below want you to stay under 9V. They will run with the higher voltage, but will have a very short life span.

Hope that helps.

[Dave Robelen]

Hi,
There is one more consideration that affects the cell count or maximum voltage from the pack. The BEC circuit that feeds the servos and receiver must drop the voltage level from that of the pack to the 5V required by the flight controls. Depending on the BEC design, many have a limit as to how much voltage they can drop before overheating. This is what sets the voltage rating for the speed control, the motor is another matter.
Regards, Dave