RCCrawler Forums

Dubs Chops · 03-19-2009, 07:23 AM

OKay guys, I was wondering how to tell how many c ratings a system can effectively pull. no need to get a 30c constant battery if i can only pull 20c constant. I am going to build a basher slash and I want to get the perfect batteries. It will be running the velenion system because I got one on the cheap.

also how do you tell the c rating on nimh cells? or the equivilent of if they do not have a c rating.

How would an 8 cell nimh pack compare to say a 2s 30c lipo? thanks guys!

Terranaut · 03-19-2009, 08:05 AM

I'll leave a detailed answer to a more competent member, but I will offer this much. The 'C' rating is usually maximum continuous discharge rating. When you pull that amount of current from your battery it is stressing the battery close to it's limit. Stressed batteries have short lives and sometimes violent deaths!

Make sure your battery has far more discharge capability than your motor requires.

Cheers.

JohnRobHolmes · 03-19-2009, 08:12 AM

Quote:

Originally Posted by Terranaut

I'll leave a detailed answer to a more competent member, but I will offer this much. The 'C' rating is usually maximum continuous discharge rating. When you pull that amount of current from your battery it is stressing the battery close to it's limit. Stressed batteries have short lives and sometimes violent deaths!

Make sure your battery has far more discharge capability than your motor requires.

Cheers.

Yep. Getting a battery with some overhead room makes sure it will last more than 30 cycles. I like to pick batteries with continuous discharge ratings equal to the burst that they might see.

Nice Nimh doesn't really have a C rating, but most can take 20c before getting too out of whack. Nimh just falls in voltage when you over amp it.

comparing 8 cell nimh to 2 cell lipo, lipo still wins if it is a big enough pack.

An example, I just bought some PolyRC 25c 5000mah cells for my savage Flux. I calculated that my burst amperage would be around 100 to 120ish amps based on other setups, plus the cells fit into the battery tray. I have 125 amps continuous rated packs that will burst 250a. I have some headroom if the factory rated them properly.

JAM MaxAmps.com · 03-19-2009, 08:16 AM

With the Traxxas VXL systems 20C or higher will work fine.The higher the better as mentioned. More cushion is always a good thing.

Jason

Dubs Chops · 03-19-2009, 08:16 AM

how do i tell what c rating my system will pull. I have looked and wondering if the c rating is a ratio you get from dividing the amperage or something the motor draws. thanks guys,

JohnRobHolmes · 03-19-2009, 08:18 AM

You need a data logger to really find out what is going on. In a slash a 25c 5000mah pack would work well for most setups.

Dubs Chops · 03-19-2009, 08:22 AM

okay thanks. I just want to get all i can out of it and i know having the right battery will help. Thanks guys, i will look for 20-25 c packs for the slash with the vxl. rob, did you see my other post 2 or 3 posts down??
don't want to touch that one for me? LOL

JAM MaxAmps.com · 03-19-2009, 08:26 AM

Quote:

Originally Posted by Dubs Chops

how do i tell what c rating my system will pull. I have looked and wondering if the c rating is a ratio you get from dividing the amperage or something the motor draws. thanks guys,

Just to get you on the right track the info you want to know is "What your trucks amp draw will be or is" not it's C rating. As john said the easiest way is a data logger. You can get such devices from Novak, Medusa, or Eagle Tree. I have a Novak system and two different Eagle Tree systems all work really well. Your VXl system under normal gearing will pull 80 to 100 amps. So look for a pack that can do 100 amps or better.

Jason

Dubs Chops · 03-19-2009, 08:29 AM

so 100 amps would be 10C?

JohnRobHolmes · 03-19-2009, 08:33 AM

No, amperage and C rating are not interchangable. C stands for capacity.

A 5 amp hour (5000mah) pack being discharged at 10C is being discharged at 50 amps.

A 4 amp hour pack discharged at 10c is 40 amps.

CreepyCrawl · 03-19-2009, 08:36 AM

John, I'm logged in on your site right now getting ready to purchase some of your 1300 Lipos, but I'm having a difficult time deciding between 2S and 3S.

Having the extra power on tap would be nice, but I'm not a throttle junky so I'm feeling like 2S would work fine with my FX-R and 45T Trinity/Epic Kreepy motor.

Any suggestions for me..I was also curious about the amp draw on that set up.

Dubs Chops · 03-19-2009, 08:54 AM

Quote:

Originally Posted by JAM MaxAmps.com

Just to get you on the right track the info you want to know is "What your trucks amp draw will be or is" not it's C rating. As john said the easiest way is a data logger. You can get such devices from Novak, Medusa, or Eagle Tree. I have a Novak system and two different Eagle Tree systems all work really well. Your VXl system under normal gearing will pull 80 to 100 amps. So look for a pack that can do 100 amps or better.

Jason

so now I am cinfused, If the c rating has nothing to do with the amps how do I know how many amps the pack will do? sorry for the ignorance.

JAM MaxAmps.com · 03-19-2009, 09:11 AM

The C rating refers to what the pack can sustain for a continuous amp draw. A 20C 5000 pack can handle 100 amps constant with out damage. C ratings apply to packs only.

Amp draw is what your vehicle will do. That amp draw can be changed with gearing changes. Load or binding will also increase the amp draw as well.

To find out what your set-up pulls for amps you need a data logger. You run the system then if it looks like you need more battery then you go up in pack size which is one way to get a higher C rate or you stay in same size range and go with a pack that has a higher C rating.

-J

JohnRobHolmes · 03-19-2009, 09:15 AM

Quote:

Originally Posted by CreepyCrawl

John, I'm logged in on your site right now getting ready to purchase some of your 1300 Lipos, but I'm having a difficult time deciding between 2S and 3S.

Having the extra power on tap would be nice, but I'm not a throttle junky so I'm feeling like 2S would work fine with my FX-R and 45T Trinity/Epic Kreepy motor.

Any suggestions for me..I was also curious about the amp draw on that set up.

You will be fine with either 3 or 2s with the 45t epic. It is the same base as my p-94 torquemaster without the handwound part. I can't find my amp draw charts off hand, but I know a 45t on my 1300 3 cell is a very stable combo.

CreepyCrawl · 03-19-2009, 09:43 AM

Thank you as always

Mic · 03-19-2009, 11:03 AM

To cover 80-1000 amps for you VXL system. You would need the equation c*mah= constant amperage. So if constant amperage is 100 you would need a 20c 5000mah pack, 25c 4000mah pack, 30c 3400mah pack, 10c 10000mah, 15c 7500 mah pack etc.

I would go with the 25c 4000mah pack as the higher mah packs will not be used to the max I have an 8000mah 20c pack but I can not run a full battery though the car because the speed control/wires/connectors/motor all get to hot before the pack runs down. The smaller pack is lighter and makes the car go faster.

Slowkrawl · 03-19-2009, 09:03 PM

So I am totally lost..My brain is trying to comprehend far too much at once LOL. Basically, I am going to be running a 45T warrior, and I need to know if a 20C lipo is going to work? I may buy 2 2400mah packs and wire them together to get 4800mah. Thanks guys, I just have no idea how many amps my truck draws?!

JohnRobHolmes · 03-19-2009, 11:41 PM

A 20c 2400 pack will be enough on both 2s and 3s. With crawling most any pack capable of 30a continuous will work on single motor 2.2 builds with 35t or slower. Mileage does vary however.

Terranaut · 03-20-2009, 02:27 PM

Wow! This could be a very informative thread, if we can just clarify exactly what 'C' rating means!

'C' is a mathematical constant. Constants are used in calculations to get a meaningfull, comparable result when there are variables present. In this case, the variables are the storage capacity of the pack, usually expressed in mAH, and how rapidly the particular battery (chemistry and construction) can deliver the stored charge. Note that one mA is 1/1000th of an Amp, 1000mAH = 1 AH.

Not all batteries are created equall. Some have better discharge capability than others, it depends to a large degree on the chemistry and the physical construction of the battery. Early LiPo's were only good for 5 'C', but nowadays 20 'C' continuous is common and 35 'C' is available.

To determine the actual discharge capability of a specific battery pack you have to multiply the 'C' rating by the capacity in Amps. For example, a 12 'C' 1000 mAH (1 AH) pack can give 12 Amps (12 x 1 = 12). A 20 'C' 2500 mAH (2.5A) pack can give 50 Amps (20 x 2.5 = 50). It doesn't matter if it's 2 cell, 3 cell or whatever, the number of cells only affects Voltage, not capacity or 'C' rating.

As a very rough guide a 540 brushed motor will pull around 20 to 25 Amps at full throttle and normal load. It will pull as much as 50 Amps or more when stalled, again at full throttle. As stated in other posts above, you need a Watt meter or data logger to measure the actual current draw on your own specific set-up. Also note that motors and ESC's are rated for maximum Voltages, ignore that at your own peril!

And don't forget, you should give yourself a healthy margin (approx. 150% should do it) if you want your batteries to last. 'C' rating is a maximum and LiPo's can only give that maximum for short periods, not all day every day.

Now, put all that together and you should be able to work out what battery capacity and 'C' rating you need. I'll invite the experts to take it from here, correct me if I'm wrong, and fill in the blanks. Thanks guys.

Cheers.

03-19-2009, 07:23 AM	#1
Dubs Chops Quarry Creeper Join Date: Jan 2007 Location: HAY CAPITOL OF THE WORLD!!!!! weeeeeeeeee Posts: 399	another lipo question about c ratings OKay guys, I was wondering how to tell how many c ratings a system can effectively pull. no need to get a 30c constant battery if i can only pull 20c constant. I am going to build a basher slash and I want to get the perfect batteries. It will be running the velenion system because I got one on the cheap. also how do you tell the c rating on nimh cells? or the equivilent of if they do not have a c rating. How would an 8 cell nimh pack compare to say a 2s 30c lipo? thanks guys!

03-19-2009, 11:41 PM	#18
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	A 20c 2400 pack will be enough on both 2s and 3s. With crawling most any pack capable of 30a continuous will work on single motor 2.2 builds with 35t or slower. Mileage does vary however. Last edited by JohnRobHolmes; 03-19-2009 at 11:44 PM.

03-19-2009, 08:05 AM	#2
Terranaut Quarry Creeper Join Date: Sep 2008 Location: Kuala Lumpur, Malaysia Posts: 372	I'll leave a detailed answer to a more competent member, but I will offer this much. The 'C' rating is usually maximum continuous discharge rating. When you pull that amount of current from your battery it is stressing the battery close to it's limit. Stressed batteries have short lives and sometimes violent deaths! Make sure your battery has far more discharge capability than your motor requires. Cheers.

03-19-2009, 08:16 AM	#4
JAM MaxAmps.com RCC Addict Join Date: Nov 2007 Location: Nine Mile Falls, WA Posts: 1,229	With the Traxxas VXL systems 20C or higher will work fine.The higher the better as mentioned. More cushion is always a good thing. Jason

03-19-2009, 08:18 AM	#6
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	You need a data logger to really find out what is going on. In a slash a 25c 5000mah pack would work well for most setups.

03-19-2009, 08:22 AM	#7
Dubs Chops Quarry Creeper Join Date: Jan 2007 Location: HAY CAPITOL OF THE WORLD!!!!! weeeeeeeeee Posts: 399	okay thanks. I just want to get all i can out of it and i know having the right battery will help. Thanks guys, i will look for 20-25 c packs for the slash with the vxl. rob, did you see my other post 2 or 3 posts down?? don't want to touch that one for me? LOL

03-19-2009, 08:29 AM	#9
Dubs Chops Quarry Creeper Join Date: Jan 2007 Location: HAY CAPITOL OF THE WORLD!!!!! weeeeeeeeee Posts: 399	so 100 amps would be 10C?

03-19-2009, 08:33 AM	#10
JohnRobHolmes owner, Holmes Hobbies LLC Join Date: Nov 2004 Location: Volt up! Gear down! Posts: 20,290	No, amperage and C rating are not interchangable. C stands for capacity. A 5 amp hour (5000mah) pack being discharged at 10C is being discharged at 50 amps. A 4 amp hour pack discharged at 10c is 40 amps.

03-19-2009, 08:36 AM	#11
CreepyCrawl I wanna be Dave Join Date: Oct 2006 Location: Centered Posts: 2,082	John, I'm logged in on your site right now getting ready to purchase some of your 1300 Lipos, but I'm having a difficult time deciding between 2S and 3S. Having the extra power on tap would be nice, but I'm not a throttle junky so I'm feeling like 2S would work fine with my FX-R and 45T Trinity/Epic Kreepy motor. Any suggestions for me..I was also curious about the amp draw on that set up.

03-19-2009, 09:11 AM	#13
JAM MaxAmps.com RCC Addict Join Date: Nov 2007 Location: Nine Mile Falls, WA Posts: 1,229	The C rating refers to what the pack can sustain for a continuous amp draw. A 20C 5000 pack can handle 100 amps constant with out damage. C ratings apply to packs only. Amp draw is what your vehicle will do. That amp draw can be changed with gearing changes. Load or binding will also increase the amp draw as well. To find out what your set-up pulls for amps you need a data logger. You run the system then if it looks like you need more battery then you go up in pack size which is one way to get a higher C rate or you stay in same size range and go with a pack that has a higher C rating. -J

03-19-2009, 09:43 AM	#15
CreepyCrawl I wanna be Dave Join Date: Oct 2006 Location: Centered Posts: 2,082	Thank you as always

03-19-2009, 11:03 AM	#16
Mic Rock Crawler Join Date: Mar 2008 Location: Arizona Posts: 578	To cover 80-1000 amps for you VXL system. You would need the equation c*mah= constant amperage. So if constant amperage is 100 you would need a 20c 5000mah pack, 25c 4000mah pack, 30c 3400mah pack, 10c 10000mah, 15c 7500 mah pack etc. I would go with the 25c 4000mah pack as the higher mah packs will not be used to the max I have an 8000mah 20c pack but I can not run a full battery though the car because the speed control/wires/connectors/motor all get to hot before the pack runs down. The smaller pack is lighter and makes the car go faster.

Sponsored Links

03-19-2009, 09:03 PM	#17
Slowkrawl Quarry Creeper Join Date: Nov 2007 Location: Alberta canada Posts: 386	So I am totally lost..My brain is trying to comprehend far too much at once LOL. Basically, I am going to be running a 45T warrior, and I need to know if a 20C lipo is going to work? I may buy 2 2400mah packs and wire them together to get 4800mah. Thanks guys, I just have no idea how many amps my truck draws?!

03-20-2009, 02:27 PM	#19
Terranaut Quarry Creeper Join Date: Sep 2008 Location: Kuala Lumpur, Malaysia Posts: 372	Wow! This could be a very informative thread, if we can just clarify exactly what 'C' rating means! 'C' is a mathematical constant. Constants are used in calculations to get a meaningfull, comparable result when there are variables present. In this case, the variables are the storage capacity of the pack, usually expressed in mAH, and how rapidly the particular battery (chemistry and construction) can deliver the stored charge. Note that one mA is 1/1000th of an Amp, 1000mAH = 1 AH. Not all batteries are created equall. Some have better discharge capability than others, it depends to a large degree on the chemistry and the physical construction of the battery. Early LiPo's were only good for 5 'C', but nowadays 20 'C' continuous is common and 35 'C' is available. To determine the actual discharge capability of a specific battery pack you have to multiply the 'C' rating by the capacity in Amps. For example, a 12 'C' 1000 mAH (1 AH) pack can give 12 Amps (12 x 1 = 12). A 20 'C' 2500 mAH (2.5A) pack can give 50 Amps (20 x 2.5 = 50). It doesn't matter if it's 2 cell, 3 cell or whatever, the number of cells only affects Voltage, not capacity or 'C' rating. As a very rough guide a 540 brushed motor will pull around 20 to 25 Amps at full throttle and normal load. It will pull as much as 50 Amps or more when stalled, again at full throttle. As stated in other posts above, you need a Watt meter or data logger to measure the actual current draw on your own specific set-up. Also note that motors and ESC's are rated for maximum Voltages, ignore that at your own peril! And don't forget, you should give yourself a healthy margin (approx. 150% should do it) if you want your batteries to last. 'C' rating is a maximum and LiPo's can only give that maximum for short periods, not all day every day. Now, put all that together and you should be able to work out what battery capacity and 'C' rating you need. I'll invite the experts to take it from here, correct me if I'm wrong, and fill in the blanks. Thanks guys. Cheers.

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