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drsmooth
2008.06.06, 05:33 PM
Is there any way to run a lipo pack in the F-1 Car? Not a big fan of nimh batteries.:rolleyes:

drsmooth
2008.06.06, 07:21 PM
My biggest concern was about the fets & board. Not sure what 8.4 volts would do to them.

dhamby123
2008.06.06, 08:25 PM
:eek:<<< ME TRYING TO CHANGE FETS

dhamby123
2008.06.07, 07:49 PM
wouldnt a fresh charged pack be more than 7.2 or 7.4 volts heck nimh cells freh charged are way over the 4.8 volts there rated ?

LBRC
2008.06.08, 02:07 AM
Only some Li-Ion cells are 3.1 volts, most are now a nominal 3.2 volts.

Lithium cells are charged to exactly 4.2 volts per cell, or 8.4 volts for a 2S pack, then discharged to not less than ~3 volts per cell (2.7 to 3.2 depending on the specific cells specifications), the 7.4 volt designation for a lithium 2S pack is it’s nominal value. The 1.2 volt designation for a NiMH cell is also a nominal value, the difference being that a full NiMH charge is determined by it’s current level where as a lithium’s is determined by it’s exact voltage level.

The 3010 FETs are rated at 60 volts for drain to source and 20 volts gate to source, the FETs ability to handle a 2S LiPo pack’s “voltage” is not the problem. The first problem is that by increasing the voltage you increase the servo motor’s speed and current drain, that’s where steering problems like jittering come from. The problem with the FETs is that by increasing the voltage you also increase the amount of current a motor can draw which depending on the motor can and occasionally does damage the FETs. But even that’s not the real danger, the problem lays with all of the other components on the circuit board, some rated for higher voltages and current levels but others not, the bottom line is that the circuit as a whole is intended/designed to operate off of 4xAAA’s whether 4.2v nominal NiMH or 6 volt alkaline, to put it poetically the candle that burns twice as bright burns half as long.

Many of us have used 2s LiPo packs with Mini-Z circuit boards, in Mini-Z’s as well as other vehicles.

http://lbspd.com/v-web/gallery/albums/album23/MVC_626X.jpg

http://lbspd.com/v-web/gallery/albums/album34/Jim_with_1200_pack.jpg

http://lbspd.com/v-web/gallery/albums/album113/1_24_lost.jpg

http://lbspd.com/v-web/gallery/albums/album132/Pumpkin.jpg

http://lbspd.com/v-web/gallery/albums/album67/b4.jpg

In my experience as long as you’re careful about your motor and Mosfet choices the CB can and will last for many-many hours. They can be a great deal of fun in a Mini-Z Monster Truck or modified Xmod that you want to drive up an down the street as fast as possible, but for the track and racing even in the most carefully prepared car there is that small loss of precision that gets in the way of a 2S LiPo as a choice for a Mini-Z that you seriously want to win races with.

Can be fun though, a few years ago I built a 7.4v 600mAh Li-Ion stealth pack that can fit in a MR-02 without any modifications. The ends of the cells are sealed so they can’t make contact with the tabs, unfortunately it wasn’t possible to completely conceal the wire and connector that was necessary to connect the two sides so they still look like Li-Ions.
http://lbspd.com/v-web/gallery/albums/album21/MVC_704X.jpg
Gives a stock motor the speed of a modified one, for a short time at least. Thing is that when a motor speeds up so does the battery drain and the motors life, and as mentioned there is that slight loss of precision and control that makes a modified motor my preferred choice for increasing a racers speed.

However there are other interesting possibilities; it’s hard enough as is to control a modified 2x2 FET stacked F1with a hot motor on even the largest of RCP tracks, and I haven’t worked up the courage to try an ASF Mini-Z CB with a 2S lithium pack, but I have built two ASF Mini-Z CB Epochs that use 3.7 volt 2P packs and they work well enough at the lower voltage levels to make the idea of an ASF CB, comparatively light 1400 mAh 3.7 volt LiPo, and 29 to 39 turn motor in an F1of possible interest.

dhamby123
2008.06.08, 11:10 AM
Great post really clears things up