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Old 02-26-2009, 08:41 AM   #1
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Default High battery c-cell rating may not be so important?

Coming from R/C heli and airplane background (electric and nitro) and have been in Nitro buggy's for some years. I picked up on the electric side of cars and am thinking about the true need for a high C-rating battery in a Car or truck.
The electric heli's will chew up and spit out a low amp battery in no time because most are running at 80% motor power constant and bursting to 100%depending on the need to maintain rotor speed. Airplanes are alot easier on them because for the most part you are varying the power constantly. Usually when the batteries I have been using in the heli start to decay, I retire them to light duty in the airplanes.
So I am thinking that in general the need for anything higher than a 30C discharge cell kind of seems like a waste in an electric car or truck, but lower than 20C would be too taxing. I am running 24C constant batteries in my 1/10 buggy and after extensive runs on the track, they are barely hitting 90.
I think alot of this is due to fact that you have enough gearing selection to toy with to help keep the temps down and still get the performance you want from a lower C rated battery.

What are you guys finding?
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Old 02-26-2009, 10:14 AM   #2
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You're assumption is pretty much right.. Larger applications like 1/8 electric may benefit from 30-40C cells. Most electrics I think will be perfect with 20-25C packs.

I run 3 packs in 2WD electric, a 16C Trakpower, a 20C Orion Platinum, and a 35C Reedy. The 16/20C packs both work just fine and I have great power through the run, no complaints. However - the 35C pack allows me to clear a certain triple at the track I run at, and I cannot do that with the other two packs. My consistent laptimes are also a little faster. The 35C packs has a little more punch, everyone I've let run it thinks the same thing.

Even though the 35C has more rip to it I would still suggest saving a few bucks and running a 20-25C battery. The extra cost doesn't give that much benefit. But when the cost comes down there will be no reason not to buy 30+ C batteries.
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Old 02-26-2009, 11:13 AM   #3
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If your racing where you have high traction and speed makes a difference then higher C rate can help with performance as the cells have lower IR thus will drop less in voltage when coming off the turns and accelerating.

It all depends of the needs you may have in your particular racing applications.

Our 24C/5200 pack has very similar performance to our 5200/40C pack in low amp draw situations. In high amp draw situations you will have more performance out of the 40C pack.
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Old 02-26-2009, 12:27 PM   #4
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I have another question about higher C rated packs. Will they drain quicker in higher amp situations like 1/8 racing? I understand that they will have more punch than a lower rated cell, but it seems that extra punch should also be draining more mah.

An example would be:
1/8 E-Buggy with two batts
Batt 1 = 20C 5000 will not have as much punch 10min into a race, but may last longer.
Batt 2 = 30C 5000 will have more punch 10min into a race, but should drain the total mah faster due to being able to put out more power farther into a run.

I don't know if this is accurate, but I wonder.

Last edited by GO-RIDE.com; 02-26-2009 at 12:55 PM.
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Old 02-26-2009, 12:32 PM   #5
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Your theory is good but you must also consider that a higher C rate pack will not drop as much at higher loads.

Our 5200/40C for example will retain 90% of it's capacity at full C rate discharge where our 28C/5000 would retain allot less at 40C.

This would need to be tested on the track to get the exact results.
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Old 02-27-2009, 09:40 AM   #6
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Battery technology has gotten real good in the past 1.5 years. The new SMC packs I got can handle 2C charging even 3C [but they don't recommend it because it deteriorates the pack life]. Its hard to go from always charging at
1C and then when someone tells me 2C is OK, I end up staring at the pack thinking it is going to blow-up.
For sure I can see a benefit in the larger heavier 1/8 scale trucks. I am sure they can put a heavy load on a pack. I would think you would need both higher voltage and also a higher C rating.
I know in Airplanes and heli's we would put a load meter between the battery and speed control and at full power, we would make sure the chosen prop or gear ratio wasn't over taxing the battery. If it was, we would make the changes necessary to keep under the typical max burst amp for 15 sec. I have yet to see anyone checking this on a car, so I am sure their are plenty of batteries out there going over there discharge rating.

There is a bit of a rage with converting 1/8 scale to electric which I think will do better then when everyone got into converting larger Heli's and airplanes into electric. The airborne guys quickly figured out that nitro is still cheaper in the long run. Airplanes and Heli's have a lot less components then the there ground counterparts and the fuel is a lot cheaper, so the reality of electric making it cheaper didn't pan out. It did make small electrics boom.

Last edited by dhc8guru; 02-27-2009 at 02:28 PM.
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