Why 7.2 volts ??

[SRBaja]

Why do the Rc motors run 7.2 volts ? Saw a radio shack car with 9.6 volts ?? Also confused about the 1400, 2000 #'s etc. Do you get longer run times only or more power ??
Thanks
SR(learning)Baja

[hpiguy]

I think they came to 7.2 volts based on an evening out of runtime and speed.

As well as for durability on the motors, and the size of the cars suits six cell packs well. For awhile the 7cell packs (8.4volts) were popular, but then 7.2 regained it's standing as most popular due to the lack of runtime with 7cells and the high power mod motors.

It's like the BETA and VHS. BETA was smaller, but people just preferred the "feel" of VHS tapes. It's an odd comparison, but I hope you understand it.

[Aylien]

I think it has something to do with the way 9.6 super mega power volts! sounds better than 7.2 volts.

Kinda like when someone wants to sell you computer speakers that are "1200" watts, but only cost 9.95 and are the size of a box of pop tarts http://www.rccaraction.com/ubb/tongue.gif

[This message has been edited by Aylien (edited 12-01-2000).]

[ZenLosi]

Well, 7.2 volts came from the fact that 6 NiCd sub C cells are rated at 1.2 volts a piece. 1.2 x 6 = 7.2 volts, the radio shack 9.6 volt packs are NiCd AA cell batteries and are also rated at 1.2 volts each, but the packs come with 8 cells, so 1.2 x 8 = 9.6 volts. I believe the regular alkaline batteries (Duracell, Energizer and so on) are rated a bit higher at like 1.5 volts or
so.

1700's provide more punch than 2000's, but 2000's last longer. 3000's last forever, but I'm not sure if they have less punch than 2000's or not. You really only need 3000's if you run mod. I think 1700's are the best for stock racing, but 2000's work good, too.

-Zen

[This message has been edited by ZenLosi (edited 12-01-2000).]

[This message has been edited by ZenLosi (edited 12-01-2000).]

[JP]

[QUOTE]Originally posted by ZenLosi:
[B]Well, 7.2 volts came from the fact that 6 NiCd sub C cells are rated at 1.2 volts a piece. 1.2 x 6 = 7.2 volts, the radio shack 9.6 volt packs are NiCd AA cell batteries and are also rated at 1.2 volts each, but the packs come with 8 cells, so 1.2 x 8 = 9.6 volts. I believe the regular alkaline batteries (Duracell, Energizer and so on) are rated a bit higher at like 1.5 volts or
so.

1700's provide more punch than 2000's, but 2000's last longer. 3000's last forever, but I'm not sure if they have less punch than 2000's or not. You really only need 3000's if you run mod. I think 1700's are the best for stock racing, but 2000's work good, too.

-Zen

You got that kinda backwords. 1700's dont last as long or have more punch as 2000's. 2000's are better in every way except price. NiMh cells last longer but have less punch.

[sarujin]

I agree with ZenLosi

I find the lower the mah rating on the battery, the more punch.

For example when my mini has 1300s in it, it can take off faster then the other cars, and has a speed advantage for maybe 1/4 of a lap, then the loose their peak and slow down heaps.

Now I run 2000s in mini the speed always stays the same, but it doesn't have as much punch!!
Even though overall now it goes better as they keep there power.

sarujin

[SRBaja]

Where does watts come into play ? People were saying thay discharge batteries with a tray of ten - 1157 turn signal lights. Why couldn't you just use an old headlight and get the same affect. Headlights are about 55watts.

[ou812]

Just to add to what others have said...

R/C motors can run on whatever voltage you send to them. The R/C Boat guys run on anywhere from 4 to 18 cells. Now, usually they also run dual motors with their mega-cell setups, but that's not much different than running a Clod/E-Maxx/Jugg.

The best way to visualize how more cells affects your car is to use Ohm's Law from basic electronics ... V=I*R, or I=V/R.

This second form of the equation says that if voltage (V) goes up, and resistance (R) stays basically the same, then current (I) will have to go up. If your current goes up, your batteries won't last as long.

We can work this out in rough numbers too...

I=V/R ... use 20 amps current and 7.2 volts ... this means that our Resistance is about 0.36 ohm.

Now, use a 7 cell pack and plug 8.4V and 0.36 ohm into the equation and we see that I jumps up to 26 amps.

Probably more technical than what you wanted... but it backs up what hpiguy says above ... it's a balance between run time and speed.

[BadRacer]

LOL SR.....I know your new and these are not dumb questions. Just listen to these guys and you will not have any problems. Trust me, i have learned alot since i have been on here from most of these guys. Im kind of a newbie myself....well 2 years and im still learning more each day. Just sit back and don't let this stuff confuse you, and if you ever get pizzed off cuz you don't understand your car/truck just walk away from it and cool down. Iv busted some stuff on an old MRC i had cuz i got pizzed at it!

[SirSpeedy]

OK.

Your headlight is 55 watts. Let's say 60 watts to make this easy. Since modern autos operate @ 12volts, that is what we must use to derive the amperage.

60watts @ 12volts = 5Amps

An 1157 is rated @ 25 watts.

25watts @ 12 volts = ~2Amps

So, to get 20Amps, you can either use 10 1157 bulbs = ~20 Amps, or four headlight bulbs to get the recomended discharge current.

I think the 1157's fit in most peoples pit boxes a little better!!

See ya.....

[malici]

All these guys are trying to help they're all giving good information, but all out of context. I mean they;re confusing me and I know what they're talking about. I think the best thing for you to do is to go to the nearest library, and checkout a book of basic eletricity. This will help you learn more about volts, amps, and resistance than most any other way (Omh's Law is a good place to start).

The one thing I have't heard is how each cell gets its voltage. Each cells voltage comes from the acidity of the liquuid/gell in it. The stonger the acid the more voltage the cell will have.

Malici

[Barrff]

Originally posted by hpiguy:
It's like the BETA and VHS. BETA was smaller, but people just preferred the "feel" of VHS tapes. It's an odd comparison, but I hope you understand it.
I doubt that %90 of the people on here are old enough to know what a BETA tape is!!!

You just dated yourself bad! http://www.rccaraction.com/ubb/rolleyes.gif

[hpiguy]

My top loading Beta machine is on top of my orange shag carpeting, and next to my 8 track stereo.

[BrianCio]

Good stuff buried in a Oooooold post.

[ViciousKnives]

hey, i have a beta max. those things are great. i still have some stuff on it too, like Conan the Barbarian... hehehe