resistor help.please

[max]

Hi peeps just a fast question about a resistor i need.
Im running my RC car on a standard 6vpack but im going to upgrade to a lipo pack. 7.4v.
Im not a electronic freek and i have done a little research on the colors and there meaning.
Iv just come out of hospital and i cannot do anything to strenuous so i put my bike build to 1 side and sat with my sons Rc cars moding there tyres off .(soon i will be well thow )

What resistor to use to drop the v's from 7.4v800mah to 6v.?
I see resistor gagets that plug inline with the power on ebay but i cannot see why wast £££ on them when there just resistor's.?
And if i add a second pack 2x7.4???mah will i be able to use the same resistor/?
Any help will help me help my sons help themselves to learn..Feed the collective and she will eat.

Thanks all for reading my post.

max

 

[Link]

Resistors drop voltage in proportion to the amount of current flowing through them. The less amperage, they less voltage they drop.

http://en.wikipedia.org/wiki/Electrical_resistance

If I were you, I'd see if the thing can just handle the extra 1.4V. It might not, but I think it should...

 

[gmouchawar]

Most 6V RC controllers should handle 7.4V without an issue. A resistor wont work because the voltage drop will be proportional to the current demand.
A diode would work but it will get very hot. Try to connect it straing.
For the second battery, I assume you mean connecting it in parallel to get more run time and not in series to get more speed.
If in parallel, you should be able to connect them directly again.
For a 6V system, I would connect the in series. Most likely you will end up with melted Silicon devices.

 

[317537]

Upgrade the power fet for best results. You should be fine in some cases with the overvolt. Source to gate break down voltage and gate max is all important so you may need to upgrade the power fet on your controller or increase the gate resistance a touch. A single 3 amp rectifier diod should give you a .7 drop in volts 6.7. Not too much heat loss as its only .7 of a volt. Buy a few diodes as the voltage drop varies a little from diode to diode depending on the size and tolerance and luck. Ive had some big diodes read a full volt drop under load. Resistor is not a solution as mentioned above.