R/C Tech Forums

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

Reply
 
Thread Tools Search this Thread
Old 12-19-2008, 05:40 PM   #46
Tech Addict
 
Join Date: Feb 2007
Posts: 596
Default

I love using Lipos and am always wanting to learn more about how they work.


I have a few questions about these C ratings Danny..

If your pack is rated at 5000mah and 40C that means it is capable of discharging at 200amps right ?

Q1: how long (in seconds) can it discharge at that rate for ?

"the Capacity of the pack is determined by discharging the cells down at 1c"
Q2: How do you know what 1c is before you know the capacity of the pack ?


I'm sure I'll have other questions as I learn more..
__________________
CPD Racing
chris_dono is offline   Reply With Quote
Old 12-19-2008, 05:53 PM   #47
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

Yes a 40C/5000 means it can be discharged at 200 amps continous. So this means you can discharge it from a full charge down to it's cutoff at 200 amps. It will be the same time as the single cell which took 72 seconds to discharge at 100 amps.

That is a good question on the capacity. There is a way for the manufacturers to know the capacity when making the cells as the capacity is related to the size of the cell. You can increase capacity by making the cells longer , wider and higher. So 1C is used to confirm that the cells are really what they were suppose to be.
Danny/SMC is offline   Reply With Quote
Old 12-19-2008, 05:54 PM   #48
Tech Master
 
Join Date: Jan 2006
Location: Kansas City, MO
Posts: 1,260
Trader Rating: 13 (100%+)
Send a message via AIM to HenBeav
Default

50c for a 5000mah pack right? more than 50C for less than 5000mah?

if you had a 6000mah pack with a 250 amp capacity machine that would be up to 41.6667C right for the 6000 pack or 250 amps/6, just making sure i am thinking right
__________________
[URL]http://www.fastlanehobby.com[/URL]

Support your local Lowe's, Walmart and Layne Machine Works INC.
HenBeav is offline   Reply With Quote
Old 12-19-2008, 05:59 PM   #49
Tech Addict
 
Join Date: Feb 2007
Posts: 596
Default

ok, 72 seconds isn't much use in a 5/6/8 minute race

5000mah battery... 5 amp discharge = 1 hour ?
5000mah battery... 60 amp discharge = 5 minutes ?
__________________
CPD Racing
chris_dono is offline   Reply With Quote
Old 12-19-2008, 05:59 PM   #50
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

Yes the C rate is calculated with the mAh of the cell. So if you would discharge a 6000 at 250 amps it would be 42C discharge.
Danny/SMC is offline   Reply With Quote
Old 12-19-2008, 06:06 PM   #51
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by chris_dono View Post
ok, 72 seconds isn't much use in a 5/6/8 minute race

5000mah battery... 5 amp discharge = 1 hour ?
5000mah battery... 60 amp discharge = 5 minutes ?
Yes that is correct. The info I posted above was to show the new style 40C cells at full C rate discharge. Based on the graph that I did it seems like were not getting the same results as what our competitor got when they posted there graph. Maybe it's differences in the test equipment but based on our results it seems like they weren't pulling a full 200amps as there voltage seems higher and they claim 90% at full C rate discharge and we got 84% on there cell.
Danny/SMC is offline   Reply With Quote
Old 12-19-2008, 06:11 PM   #52
Tech Addict
 
Join Date: Feb 2007
Posts: 596
Default

Danny, Please don't take my questions as me in any way trying to discredit what you're doing !! I have one of your single cell Lipo's that I'm using in a 12th scale car at my local track and I love it !

You should be congratulated for being upfront and open about performance data as you have been

I'm just trying to learn how best to look at the minefield that is C ratings. I now know I can happily run a low turn modified motor with the battery from this example as it won't be able to pull a sustained 60amps (11c if my calculations are correct) from the battery and I won't dump at the end of a 5 minute run
__________________
CPD Racing
chris_dono is offline   Reply With Quote
Old 12-19-2008, 06:15 PM   #53
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

No problem with questions as I have learnt allot by asking questions to our supplier.

C rate can be a bit confusing and that is why I'm showing how this is tested.

I should have some more info in the coming weeks as I will ask for burst rate testing and cycle life testing. Real soon I will be able to do this on my own with my new equipment.
Danny/SMC is offline   Reply With Quote
Old 12-19-2008, 06:25 PM   #54
Tech Legend
 
Cain's Avatar
 
Join Date: May 2002
Location: West Fargo, North Dakota
Posts: 29,527
Trader Rating: 240 (100%+)
Default

Can you give some info on the machine you are planning to build to test the higher amps of the battery packs?

Also, who did you guys consider your closest competitor as far as battery pack goes that you mentioned in the beginning that this pack outperforms?
__________________
Member - Red River Radio/Control Car Club
< Tekno EB48SL / SCT410.3 | Tekno EB410 x 2 | Yokomo YZ-2 DTM x 2 | LC Racing EMB-1 Buggies and Truggies >
Cain is offline   Reply With Quote
Old 12-19-2008, 06:44 PM   #55
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

The system I will using to do up to 250A on a 2 cell pack will be CC-400 loads from Camlight. The GFX will be used to gather the data as it uses seperate voltage sensing for accurate results.

I have been buying and checking our competitors packs as to know what were up against. The cells we compared our new cell to is from TP as they are the only ones who currently offer 40C packs/cells if others release some we will be testing them as well.
Danny/SMC is offline   Reply With Quote
Old 12-19-2008, 06:48 PM   #56
Tech Legend
 
Cain's Avatar
 
Join Date: May 2002
Location: West Fargo, North Dakota
Posts: 29,527
Trader Rating: 240 (100%+)
Default

thanks for the info!
__________________
Member - Red River Radio/Control Car Club
< Tekno EB48SL / SCT410.3 | Tekno EB410 x 2 | Yokomo YZ-2 DTM x 2 | LC Racing EMB-1 Buggies and Truggies >
Cain is offline   Reply With Quote
Old 12-20-2008, 04:29 AM   #57
Tech Fanatic
 
Join Date: May 2006
Location: cincinnati ohio
Posts: 881
Trader Rating: 93 (100%+)
Default Testing

I would much rather see the numbers for an ampdraw that would be closer to the most you would see in mod racing. 20 c would be enough. That would be a better comparison. I bet the new 40c batteries would be pretty close in average voltage.
latemodel13 is offline   Reply With Quote
Old 12-20-2008, 06:36 AM   #58
Tech Master
 
TonysScrews's Avatar
 
Join Date: Jan 2006
Location: Central NJ
Posts: 1,660
Trader Rating: 13 (100%+)
Default

I look forward to your test data on the 2-cell packs. The whole 1S1P (single 2500mah cell) versus 1S2P (two 2500mah cells in parallel to get 5000mah) thing confuses me a bit with the performance numbers. In theory dumping a single cell at 100amps should yield the same numbers as a pair of cells in parallel dumped at 200 amps, but I'm curious if that will hold true when you get the newtest equipment.

From a balancing perspective I would think a 2S1P pack would be better than a 2S2P pack. The balance tap is charging two individual cells in a 2S1P pack rather than two "pairs" of cells (4 cells) in a 2S2P pack. In the 2S2P pack you're not really balancing the 4 cells individually (unless you have two pairs of 2S balance taps coming off the pack and charge the cells based on their individual capacity).
__________________
Tony P.

Tonys Screws LLC
http://www.tonysscrews.com
High Grade Alloy Steel Screws, Screw Kits and Mugen Parts
TonysScrews is offline   Reply With Quote
Old 12-20-2008, 08:00 AM   #59
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by latemodel13 View Post
I would much rather see the numbers for an ampdraw that would be closer to the most you would see in mod racing. 20 c would be enough. That would be a better comparison. I bet the new 40c batteries would be pretty close in average voltage.

Th data I posted was to show the cells at there full C rate. Not sure if your familiar with what I post on this site but I have said before that there are many claiming false C rates so I wanted to show graphs of the newest 40C cells.

20C on 5000 pack would be 100 amps which is still more than what we see on the track. I did test our the packs on a GFX at 35 amps.
Danny/SMC is offline   Reply With Quote
Old 12-20-2008, 08:06 AM   #60
Company Representative
 
Danny/SMC's Avatar
 
Join Date: Oct 2001
Location: Elkton, VA
Posts: 3,097
Trader Rating: 2 (100%+)
Default

Quote:
Originally Posted by TonysScrews View Post
I look forward to your test data on the 2-cell packs. The whole 1S1P (single 2500mah cell) versus 1S2P (two 2500mah cells in parallel to get 5000mah) thing confuses me a bit with the performance numbers. In theory dumping a single cell at 100amps should yield the same numbers as a pair of cells in parallel dumped at 200 amps, but I'm curious if that will hold true when you get the newtest equipment.

From a balancing perspective I would think a 2S1P pack would be better than a 2S2P pack. The balance tap is charging two individual cells in a 2S1P pack rather than two "pairs" of cells (4 cells) in a 2S2P pack. In the 2S2P pack you're not really balancing the 4 cells individually (unless you have two pairs of 2S balance taps coming off the pack and charge the cells based on their individual capacity).
I have asked our supplier before if testing a single cell is different than testing a 2 cells in paralell and or pack and he said that the temperature would be higher but the numbers would be very similar.

The current technology doesn't allow for a lipo cell to be higher than 9 or 10 mm not sure which one so to use two 5000 cells they would need to be the longer 5000s used in Airplane packs.
Danny/SMC 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 02:43 AM.


Powered By: vBulletin v3.9.2.1
Privacy Policy | Terms of Use | Advertise Content © 2001-2011 RCTech.net