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Old 11-19-2008, 03:29 PM   #16
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Originally Posted by Trips View Post
Danny,

How about instead of worrying about a standardized C rating, why don't you take the lead here and rate your LiPOs on average voltage and internal resistance, numbers that are actually meaningful to us?

I never cared how much amperage I could dump my Nicad or NIMH cells at, and I don't much care how much amoerage I can dump my LiPOs at, but if the manufacturers would lable them with runtime, average voltage and internal resistance, I could comparison shop with some useful data...

Thanks
In one of the threads I did a few months back I explained the benefits of higher C rate packs. Typically they use better materials plus they will have better cycle life. Voltage recovery and burst power will be better with higher C rate packs.


On our 28C packs we do print the specs as we cycle each pack. Some companies will not do this as either there packs don't have good specs or they don't want to spend the extra time/money to do this.

I know this thread will stir things up but my goal is to let the consumer be aware that just because a pack has a certain rating on it doesn't mean it's true.
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Old 11-19-2008, 03:31 PM   #17
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I totally agree, average voltage, runtime and IR seem to be what matters to most racers.
So if you pay for more for a pack that should be able to provide a certain C rate you don't matter if it isn't as long as it has good IR and voltage ?

Does this mean we should call our 24C/5200 a 40C pack since it has good cycle numbers ?
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Old 11-19-2008, 03:33 PM   #18
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Originally Posted by trailranger View Post
Average Peak wattage would be a more simple number to look at

like 500W @ 135A

The test should be the average continous wattage for at least 60 seconds

you can't fake work not being done, At some point less power is outputted becuase the increased load will severly drop the voltage.

Watts = Work Done = V x A

I'm pretty sure what you saying is similar to the capacity retention of a pack under a high C rate discharge.
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Old 11-19-2008, 03:49 PM   #19
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I'm pretty sure what you saying is similar to the capacity retention of a pack under a high C rate discharge.
Similar, but that would be rated in W seconds or hours if you want to compare capacity renention in the from of watts.

I was more leaning towards instantous wattage averaged for 60 seconds

As a just peaked pack may be putting out 1050watts and then drop to 950watts after 60 seconds with linear votage drop so the average for 60 seconds would be 1000W. I don't expect the voltage drop to be linear, but who knows.

Yes this would require some new software in the load testers, but the algorithems are already in use with SolarPanel Battery chargers and the controllers used to track the Maximum Power Point of the Panel throughout the day as sunlight conditions change.

But a simple solution could be predict a max load to produce the max continous wattage and using a WattMeter connect the load to the batter for 60S. Adjust the load should predicted figures be off. If too low, reduce load. If slightly higher than predicted becuase of higher average voltage, increase load.
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Old 11-19-2008, 03:50 PM   #20
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I have been running a non smc lipo battery that claimed 28c and recently bought a backup smc 5000 pack at 28c and have noticed a Huge difference in punch and mah usage i have tested both at full capacity in two different vehicles with diff esc and motors and the SMC pack just Flat out performs my non smc pack
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Old 11-19-2008, 03:51 PM   #21
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Originally Posted by Danny/SMC View Post
Does this mean we should call our 24C/5200 a 40C pack since it has good cycle numbers ?
Call it a chocolate souffle or a yak sphincter for that matter, I'm just saying it doesn't matter to me what the C rating is, I'd rather know the average voltage, runtime, and internal resistance.

When I raced Nicad and NIMH I never asked a manufacturer how much current I could continually draw and still maintain 90% capacity, I looked for average voltage and IR for stock racing, and runtime was the primary factor I looked at for mod racing. Nicad and NIMH cells have C ratings too, but no one ever advertised them or even cared about them.
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Old 11-19-2008, 03:53 PM   #22
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This is good to know since I am buying a new battery very soon.
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Old 11-19-2008, 04:09 PM   #23
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i think those who understand lipos will say that the c rating is as important as mah. there was a big difference when i switched from my orion to an smc5000 ... as far as nimh batts. i dont know much about batteries but i thought that the discharge rate (20amps 30 amps etc.) is similar to a lipo c rating i think dont kill me if im wrong
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Old 11-19-2008, 04:09 PM   #24
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I dont want to cause trouble , but there will be alot of 5000 35c batterys, 5200 35c, and 3800 35c lipos. I hope for your sake Danny these other batterys dont beat the SMC packs on the track. Cause then who do we believe? A superior product gets beat on the track by what you are telling us as a 20c lipo.

I do thank you for the warnings, but i hope it doesnt come back to bite you. I barrowed a SMC 5000 from a buddy for a race 2 weekends ago and did very well with it, so i hope you are correct in calling out these other batterys for what they are.
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Old 11-19-2008, 04:11 PM   #25
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After you draw a Li-Po down to 90% , what do you do with the pack ?
Chuck it ?
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Old 11-19-2008, 04:19 PM   #26
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Correct me if I'm wrong:

3T 540-size sensored brushless is less than 900W. LRP says its X12 3T is 797W but at what voltage? So lets say it is maximum 900W which at 7.4V makes 121A. When we consider ESC's internal resistance we can say that the MAXIMUM current can go up to 125A.

For 5Ah battery it has to be 25C to give out the 125A. So we don't need more than 25C capable 5Ah battery. Newer hardcase LiPos go up to 5300-5400mAh capacity. To get 125Amps from 5400mAh LiPo it has to be only rated at 23C.


When you run 5-minute races you can't use more than avg 12C without completely discharging the battery
(60min / 5min = 12)

When you run 8-minute races you can't use more than avg 7.5C without completely discharging the battery.

I admit that the C-rating is quite weird and we just have to trust the manufacturer. Only stating C-rating doesn't really say anything. I've taken it as the maximum amperage the battery can handle without blowing up

To make the C-rating count as a real value we should have more information on how it has been measured.

- How many % of capacity do you get when discharging with the C-rated amperage?
- Down to what voltage do you dischage the cell?

I hope ROAR will test the rated C-value and publish the results or not accept the battery if it fails. Of course we need to know what the limits are ie 80% of rated capacity, under +30 delta degrees temperature rise, discharged down to 3.0V
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Old 11-19-2008, 04:21 PM   #27
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Originally Posted by Trips View Post
Call it a chocolate souffle or a yak sphincter for that matter, I'm just saying it doesn't matter to me what the C rating is, I'd rather know the average voltage, runtime, and internal resistance.

When I raced Nicad and NIMH I never asked a manufacturer how much current I could continually draw and still maintain 90% capacity, I looked for average voltage and IR for stock racing, and runtime was the primary factor I looked at for mod racing. Nicad and NIMH cells have C ratings too, but no one ever advertised them or even cared about them.

So you don't mind paying for something your not getting as long as it has good IR and voltage ?
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Old 11-19-2008, 04:27 PM   #28
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Originally Posted by wallstreet View Post
I dont want to cause trouble , but there will be alot of 5000 35c batterys, 5200 35c, and 3800 35c lipos. I hope for your sake Danny these other batterys dont beat the SMC packs on the track. Cause then who do we believe? A superior product gets beat on the track by what you are telling us as a 20c lipo.

I do thank you for the warnings, but i hope it doesnt come back to bite you. I barrowed a SMC 5000 from a buddy for a race 2 weekends ago and did very well with it, so i hope you are correct in calling out these other batterys for what they are.

Winning on the track doesn't mean a pack is better. It means the driver and car setup was better and in some cases the battery can make the difference but very rarely. In fact our 24C pack will run as well on the track as our 28C pack but we didn't call it 45C we called it 24C as this is what it ruly is.

This thread is all about getting what you paid for. I just thought some should know as it has gottent out of hand.
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Old 11-19-2008, 04:28 PM   #29
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Originally Posted by Wild Cherry View Post
After you draw a Li-Po down to 90% , what do you do with the pack ?
Chuck it ?
Not sure what kind of packs your use to but ours can be discharged down to 5.6volts under it's full C rate and the pack will be fine. In fact after 50 full C rate cycles the pack will still have 80% of it's rated capacity.
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Old 11-19-2008, 04:31 PM   #30
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Originally Posted by sonic31 View Post
i think those who understand lipos will say that the c rating is as important as mah. there was a big difference when i switched from my orion to an smc5000 ...
Are you sure the C rating was the reason the SMC pack performed better?

Quote:
as far as nimh batts. i dont know much about batteries but i thought that the discharge rate (20amps 30 amps etc.) is similar to a lipo c rating i think dont kill me if im wrong
You're wrong, but don't worry, I don't want to kill you... C rating is not a very meaningful thing for racers, the C rating is basically a rating of how much current we can safely pull with a LiPO pack. In the typical racing application a LiPO pack is doing very light duty... It's the high powered aircraft guys who really have to worry about C ratings, they fry LiPos on a regular basis. When I was flying 3D aerobatic planes, I'd be running a 10C 600mah battery (600mah at 10C means the battery could safely be discharged at 6 amps} in a plane that could draw ten amps at full throttle... I knew I had to limit my throttle use or risk toasting the pack... When I put a 5000mah 20C pack in a car I don't worry about it, I'\ know I'm nowhere near drawing 100 amps continuous. The difference between a 5000mah 20C pack and a 5000mah 30C pack is that the 20C is safe to run at 100 amps the 30C is safe to run at 150 amps. My car is pulling maybe 25 amps average, so the C rating doesn't really matter to me. What does matter is higher average voltage and lower internal resistance. Those numbers tell me how much punch I'll get from the pack.

All that being said, I'll go on to say that higher C rated packs should tend to have lower internal resistance, but I'd still want to see those numbers on the packs I buy.
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