9v???

[bengali548]

okay i did some research on this (even on the forums) but i couldnt find an answer to my question. okay everyone who attempts to do a 9volt setup ALWAYS DOES 2 9V why...why dont they just start off with one. well newayz i was thinking of doing a 1 9v setup to my evo car it has a 2x2 fet upgrade so TECHNICALLY it should handle it

i also read somewhere about amperage i have no idea what that means so sum1 shed some light please and lastly do you think my motors would over heat and blow and because i have a 2x2 board do you think any harm could be done to the board

Let us go back to the old water analogy. Picture a hose.... Voltage is the pressure of the water in the hose. The amount of water flowing through the hose is the current.

Now say you are trying to push around a big ball with this hose. You can have a ton of pressure, but without much volume of water, it's not going to move very well. Or, you coud have a ton of water flowing through the hose and not much pressure... same thing is going to happen, the ball is going to sit there.

The ball is like your motor. A 9v batter is made of 6 small cells hooked up in series in a sqaure case. In a series connection, only one current is allowed to flow, that current will be limited by the weakest of the 6 small cells.

With a 9V, you have tons of pressure, but not enough current to supply to the motor. This is why people try to run 2 9V batteries in parallel, effectively doubling the amount of current that can be supplied. Even in that case, it still isn't a whole lot.

You're trying to do too much with your cars. 6 cells with your FET upgrade will give you enough potential to make that thing faster than you can control with the right motor. Pushing 9V is trying to push more heat and power through the whole system, and it does put your motor at more risk.

My li-ion powered truck just burned up a motor. I took it out and there were chunks inside with a lot of broken wires from where some melted. That was a stage 2 RS. I even put on another big heat sink to try to help.... still didn't work.

[bengali548]

see the thing i dont get is i have an fet upgrade in my evo but whats it good for?? i mean i can only run 2 liths which is the same as 6 cells. sorry if im a bit blunt but wuts the big fuss over liths than other than its light. and if it produces the same amount of volts as 6 cells why would you need a fet upgrade. and to people who do have liths wouldnt getting a 7th cell utilise both your fet upgrade plus make it significantly faster than 2 liths

[Rez]

The only thing a FET upgrade does is let you run a hot motor.

A high RPM motor will draw a lot of current, which can blow the FETs. By stacking your fets, you double the current they can carry (each FET transfers half of the drawn current in a 2x2). The FETs in and of themselves will make no change what so ever in the performance of your xmod (maybe lower the heat from the PCB a little *shrug*). But if you are not putting a hot motor in the car, your FET upgrade is useless. That's really as simple as I can describe it.

[bengali548]

so i can add liths with no problem and no fet upgrade

edit: sorry ignorant post im just gunna assume liths have different chemistry which fets are needed mayb a EXTREMELY high discharge rate. correct me if im wrong

[Rez]

The FETs only care about two things, the voltage (function of the batteries) and the current (function of the motor). They don't care what's supplying the voltage or drawing the current. Same goes for the rest of the car, really.

The only thing lithium batteries do is supply a higher voltage than a NiMH, NiCd or Alk battery of about the same size. In other words, you can get the voltage of a fifth cell mod while only having the weight and space of two cells.

As long as you don't exceed the voltage tolerance of your circuit, you needn't change anything. If you do plan on exceeding this voltage, you have to do more than stack your FETs. The easiest way to do it is run a 5v regulator to the PCB and use external FETs that can tolerate a lot more V. Neruokinetic did a bang up job demonstrating this, and Atomic Mods has a plug in board to do the same thing.

Yeah yeah, there's a lot more detail that could be writen about FETs, about LiIon, etc, but let's keep it comprehensible for now.

[bengali548]

okay than..i opened up another thread for this dunno why lol guess i wasnt thinking straight (thx azimov) but on a gen 1/evo for two liths(7.2v) ppl get a fet upgrade and with 6 cells (7.2v) people dont need one thats the only part thats boggling me and how much voltage can 2 fets run im guessing 16.8 but that would mean that i could run 14 cells and thats like friggin star wars speed.

edit: kk i was wondering if i added 8 cells would it be fast cuz i read that 7 isnt enuff power for the weight so 8 shud bring it up to par again

[Rez]

A Gen1 with two Li batteries does not need a FET upgrade, unless it also has a hot motor. The batteries don't matter to the FETs as long as you're not exceeding the rated voltage.

If you exceed that voltage you can blow the whole car, not just the FETs for the drive H bridge, but the radio Rx, the steering, everything.

2x2 FETs can not take twice the voltage, they can take twice the current, and the amount of current depends on the load, in this case, the motor. NOT the batteries.

Where did you get the idea that 7 cells wasn't enough power for the weight? If each cell delivers the same amount of power and weighs the same, how can an 8th correct this? I would be more concerned about the voltage. Seven cells at 1.5v each is 10.5v, which is dangerous to the health of your car. You might get away with it for a while, but you're pushing your luck.

[bengali548]

kk i think i got it but they way you explained it im thinking that this is okay but i just want to know for shure is getting 3 liths at 3.6 volts each with a stage 1 or 2 motor alright

wow i feel so stupid srry rez i can sorta tell youre getting frustrated at me but im just being cautious

EDIT::: okay that whole 8.4 volts thing was that the limit for the WHOLE board or is it just for the fets meaning if i go lets say 10 volts would that f*** up the whole board

EDIT AGAIN::: OKAY i think i finally get it lol (hopefully i do) okay so is this what youre saying the whole board can handle 8.4 volts if you go above 8.4 volts the fets wont blow it will just send more electricity to the other components of the board which might blow, and the motor. if you have a hot motor that means its drawing more current from the batteries and the stock fets cant handle all the current coming in thus blowing up but with the fet upgrade the fets can handle all the current going through them and send that current towards the motor

EDIT LAST TIME:::: okay so if 2 liths are 7.2 volts i know this is a bad idea but could i add a rechargeable aaa cell to make it 8.4 volts this technically shouldnt blow but i heard mixing types is a bad idea but if this can werk is there a cell thats like 0.5 volts lol so i can keep my pcb safe

[Rez]

Now you're gettin it

One thing to remember, the battery voltage goes to the whole car, every electronic system. If you want more voltage you have to isolate these systems with a voltage regulator, so that the FETs are the only thing dealing with the high voltage. And those FETs need to be upgraded and rated for that voltage, not just stacked.

And you are correct, mixing battery types is a bad idea.