R/C Tech Forums

Go Back   R/C Tech Forums > General Forums > Electric On-Road

Reply
 
Thread Tools Search this Thread
Old 05-03-2009, 08:00 PM   #1
Tech Master
 
CanyonCarverR1's Avatar
 
Join Date: Jan 2008
Location: NorCal
Posts: 1,340
Trader Rating: 13 (100%+)
Default LiPo C-Rating & 13.5

My basic question is this: When running 13.5 in a TC, is there a noticable increase in performance when using a higher C-Rated LiPo battery?
If a motor has a maximum current that it will demand, then forever increasing the current capacity of batteries will at some point have no effect, will it?
CanyonCarverR1 is offline   Reply With Quote
Old 05-03-2009, 11:19 PM   #2
Suspended
R/C Tech Elite Subscriber
 
Join Date: Jul 2007
Location: East Bay, CA
Posts: 703
Trader Rating: 17 (90%+)
Default

It might just be placebo effect on my part, but i SWEAR I notice and increase in punch AND top end now that I've switched to 40C batteries. The car just seems to have more power overall, especially for the first few min of the heat... JMO
StickyFingaz is offline   Reply With Quote
Old 05-03-2009, 11:56 PM   #3
Suspended
 
Join Date: Nov 2001
Location: SF Bay Area
Posts: 3,519
Trader Rating: 28 (100%+)
Default

not a figment of your imagination.Those booty ASS Orions you use to run are no match to a TP 40c or a C-max from SMC.And yes you are now faster for it!
Quote:
Originally Posted by StickyFingaz View Post
It might just be placebo effect on my part, but i SWEAR I notice and increase in punch AND top end now that I've switched to 40C batteries. The car just seems to have more power overall, especially for the first few min of the heat... JMO
racenut123 is offline   Reply With Quote
Old 05-04-2009, 01:46 AM   #4
Tech Addict
 
Skitee's Avatar
 
Join Date: Jul 2005
Location: Johannesburg, South Africa
Posts: 745
Default

I can't say I've noticed much difference in performance between my 5200 35c and 4000 25c packs in 13.5
__________________
Xray T4 2018 ~ HobbyWing Xerun XR10 Pro ~ Motiv RC 4.5
Xray X12 2018 ~ ORCA Vritra VX3 1S ~ Speedzone 4.5

POWERED BY SPEEDZONE USA
Skitee is offline   Reply With Quote
Old 05-04-2009, 02:34 AM   #5
Tech Master
 
Pablo Diablo's Avatar
 
Join Date: Dec 2008
Location: Sydney Australia
Posts: 1,005
Trader Rating: 2 (100%+)
Send a message via Skype™ to Pablo Diablo
Default

The C rating isn't what matters. Its all about voltage under load. In the case of a 13.5 an average of about 20 amps. The Thunder Power 40c cells would pump out much better voltage at a 20 amp discharge than most others. The real question is is there any between the Thunder Powers and the handful of other good cells on the market?
__________________
Paul H

Losi Type R | Xray T3 | CRC Gen XL | CRC Gen X 10 ME(Messiah Edition) | Black Diamond

www.FlyingFoxRC.com | Advanced Electronics | Team CRC | Factory Messiah
Pablo Diablo is offline   Reply With Quote
Old 05-04-2009, 03:00 AM   #6
Tech Elite
 
Drifting101's Avatar
 
Join Date: Oct 2007
Location: Melbourne, Aus
Posts: 2,199
Trader Rating: 8 (100%+)
Default

In 17.5 I was running a 20c changed to a 30c and made 15 seconds in 6 mins and then I bought a TP and made 20 secs from the 20c. Once I forgot to charge the TP and broke the track record for stock with out a top off What I am trying to say is get the Thunder power 5000 40c
__________________
::Mi4::17.5::::::M03R::HW 3000kv::::::T4::7.5::::::HB Cyclone D4::5.5::

"Why follow, when you can lead?"
Schumacher
Drifting101 is offline   Reply With Quote
Old 05-04-2009, 01:19 PM   #7
Suspended
R/C Tech Elite Subscriber
 
Join Date: Jul 2007
Location: East Bay, CA
Posts: 703
Trader Rating: 17 (90%+)
Default

Quote:
Originally Posted by racenut123 View Post
not a figment of your imagination.Those booty ASS Orions you use to run are no match to a TP 40c or a C-max from SMC.And yes you are now faster for it!
Well put. Those Orions were pretty damn booty...
StickyFingaz is offline   Reply With Quote
Old 05-04-2009, 06:06 PM   #8
Super Moderator
 
Grizzbob's Avatar
 
Join Date: Feb 2002
Location: Sand Springs, OK
Posts: 3,063
Trader Rating: 2 (100%+)
Default

To try to bottle the other responses, yes, it CAN make a difference, but how much depends on the packs you're talking about, since different battery manufacturers have different rating standards. When I started out with LiPos, it was an Orion 20C 3200 pack(bought for my Tamiya Mini), & naturally I was curious of how it would run in other cars, so I tried it in my 416(that I use a 13.5 in almost exclusively). It ran ok, but my best laps with it were about .2-.3 sec. slower than my best laps with a good NiMh pack(same track layout, conditions & car setup). Then not long after, once I had bought an SMC 28C 5000 pack, I tried it again, & found the SMC ran every bit as good as the NiMh(& again .2-.3 sec. better than with the Orion). Then recently, I picked up the Thunder Power 40C 5000, & if my car is faster with it(than the SMC pack), it's hard to tell, might be a tenth better, but I certainly can't tell by feel or by how competitive I've been compared to the guys I race with. So while yes, a higher C rating CAN make a difference sometimes, it really depends on which packs you're looking at, & above a certain point, you'll get diminishing returns. In your case, I'd just buy a decent pack from a reputable manufacturer(& I certainly think SMC & Thunder Power are about the best there is), & I think you'll be happy....
__________________
Bob Seay
Tamiya TRF417, TA05v.2, TRF211XM, M-05ver.2R, XRAY X12, Associated B5m Factory Lite

Go Pokes!!!
Grizzbob is offline   Reply With Quote
Old 05-04-2009, 08:59 PM   #9
Tech Elite
 
pakk's Avatar
 
Join Date: Mar 2009
Posts: 3,077
Trader Rating: 79 (100%+)
Default

I keep reading these posts and I keep going back and forth on this. It is amazing to me that some can say they have differences up to 20sec and some down to tenths. There has to be a science to this. A motor will only draw as many amps as it is designed to draw and a batter will only supply as much as it is able to supply.

I wish we knew how many amps max a motor would draw. Then we would know what batteries "should" be enough for it. If a 2000mah 20c is only a few tenths behind a 6000mah 40c, I'll run the cheaper 2000mah 20c. I don't think I'll be in a race that close any time soon. But if they are making 5,10, and 20sec difference, the higher dollar battery is money well spent.

--pakk
__________________
*Photon* *SC10 4x4*
RCRD
pakk is offline   Reply With Quote
Old 05-05-2009, 12:00 AM   #10
Tech Fanatic
 
Join Date: Jun 2006
Posts: 872
Trader Rating: 35 (100%+)
Default

Pablo you are contradicting yourself. The C rating IS what matters, because that is a direct rating of current capability.

Pakk, and you said that a motor will only draw as many amps as it is designed to, so lets review some #'s. Please refer to the Dyno thread. In my own testing, I have seen the Hacker and Novak 13.5 pulling over 100amps at takeoff (standard Novak sensor clamped). So, the battery that can deliver the most current will translate to a higher torque on the motors coils due to the relationship,

Torque = N (number of turns) x I (current) x A (area of loop) x B (magnitude of the magnetic field) sin O (orientation of the normal to the coil with respect to the direction of the field)

Describing torque created by an electromagnetic coil.

So, a battery that can deliver more current means more torque therefore more total power which also means more RPM. The reason we get more RPMs is because the back EMF (brushless motor acting like a generator) cancels out the current coming from the battery. So lets say a 13.5 motor creates 100amps of back EMF @ 24000 rpms, and a 25C battery can only produce 100A but a 30C battery can produce 120A, so at 24000 RPM the 25C battery can produce no more torque but the 30C battery can provide still another 20A and so gives more torque at the same RPM. The RPM would increase further until the back emf is 120A at which point the motor has reached max RPM.

I hope this makes sense.
__________________
High Desert Raceplace, Grand Jct CO, Sanwa Exzes Plus Stick Radio, Spektrum,Thunderpower 230g, Modified Tri-Nut Novak GTB2, Ballistic 4.5t 550, 5.83lb SCTE Ten, Novak Sentry Brushless Dyno, Crossweight Setup Station, Junsi 20A power supply Icharger 20A Charger,TP610C, 22B, Novak Edge, Novak 13.5, SC10, Havoc Pro SC XDrive, Ballistic 17.5 Matthew Joseph Cordova
mattnin is offline   Reply With Quote
Old 05-05-2009, 12:13 AM   #11
Tech Elite
 
pakk's Avatar
 
Join Date: Mar 2009
Posts: 3,077
Trader Rating: 79 (100%+)
Default

It does, have you tested any 17.5s?

--pakk
__________________
*Photon* *SC10 4x4*
RCRD
pakk is offline   Reply With Quote
Old 05-05-2009, 12:22 AM   #12
Tech Fanatic
 
Join Date: Jun 2006
Posts: 872
Trader Rating: 35 (100%+)
Default

No I have not, sorry. Maybe John Stranahan has.
__________________
High Desert Raceplace, Grand Jct CO, Sanwa Exzes Plus Stick Radio, Spektrum,Thunderpower 230g, Modified Tri-Nut Novak GTB2, Ballistic 4.5t 550, 5.83lb SCTE Ten, Novak Sentry Brushless Dyno, Crossweight Setup Station, Junsi 20A power supply Icharger 20A Charger,TP610C, 22B, Novak Edge, Novak 13.5, SC10, Havoc Pro SC XDrive, Ballistic 17.5 Matthew Joseph Cordova
mattnin is offline   Reply With Quote
Old 05-05-2009, 12:39 AM   #13
Tech Adept
 
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 237
Default

voltage causes current to flow into the motor, not the other way around. Back-EMF (or CEMF) is an induced voltage not a current.

The best battery is one that delivers the most current without reducing voltage, this is the definition of IR. The C rating is a measure of the maximum safe continuous discharge current, but it's no coincidence that higher C rated cells have lower IR since "safe" is usually defined by heat - a lower IR generates less heat inside the battery.
gameover is offline   Reply With Quote
Old 05-05-2009, 06:53 AM   #14
Tech Master
 
Pablo Diablo's Avatar
 
Join Date: Dec 2008
Location: Sydney Australia
Posts: 1,005
Trader Rating: 2 (100%+)
Send a message via Skype™ to Pablo Diablo
Default

Gameover I'm with you. My understanding is that the "C" rating is an indication of a batteries ability to retain its capacity at a high current draw ie. 30C,40C and not a measure of internal resistance. Does a Thunder Power 40C perform 33% than a Thunder Power 30C? Not in a rc car it doesn't. What really matters is the voltage curve under discharge.

The only way we can know what cells are the best and best value is if more of us do some back to back testing and post the results.
__________________
Paul H

Losi Type R | Xray T3 | CRC Gen XL | CRC Gen X 10 ME(Messiah Edition) | Black Diamond

www.FlyingFoxRC.com | Advanced Electronics | Team CRC | Factory Messiah
Pablo Diablo is offline   Reply With Quote
Old 05-05-2009, 07:39 AM   #15
Tech Master
 
CanyonCarverR1's Avatar
 
Join Date: Jan 2008
Location: NorCal
Posts: 1,340
Trader Rating: 13 (100%+)
Default

Exactly my point...I think? If a battery is supposedly restricting the current to a 13.5, then how come when I run a 4.5 on the same battery it clearly draws much more current? And don't tell me that a 4.5 is designed to have more power with the same ammount of current. They are designed to draw more current!

Quote:
Originally Posted by pakk View Post
I keep reading these posts and I keep going back and forth on this. It is amazing to me that some can say they have differences up to 20sec and some down to tenths. There has to be a science to this. A motor will only draw as many amps as it is designed to draw and a batter will only supply as much as it is able to supply.

I wish we knew how many amps max a motor would draw. Then we would know what batteries "should" be enough for it. If a 2000mah 20c is only a few tenths behind a 6000mah 40c, I'll run the cheaper 2000mah 20c. I don't think I'll be in a race that close any time soon. But if they are making 5,10, and 20sec difference, the higher dollar battery is money well spent.

--pakk
CanyonCarverR1 is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off



All times are GMT -7. It is currently 08:20 AM.


We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.
Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net