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Old 01-30-2012, 11:30 AM   #16
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There is a standard to test for C rate but unfortunately it seems that most factories and resellers know it's very hard to test cells at high amp draw so they feel they can claim what they want.

I've been busy testing cells and packs for the last 6 weeks or so and I have come to the conclusion that the best possible true C rate is around 40 to 45C.

Yes even some of our packs are falsely labelled as I trusted the factories data for C rate claims.

I'm currently working a new rating system that will be base on the cells IR instead of C rate. We will still put down the C rate but it will be what I get off my own testing equipment and not what a factory claims.

The IR of a cell is directly related to the C rate of the cell. A cell with lower IR will be able to withstand a higher load thus giving higher C rate.

There's a relatively inexpensive meter that can be purchased that allows you to measure the IR of the cells in the pack. This meter will be used to determine the specs of our packs and each pack we ship out will be measured on this meter to make sure it's within the rated specs.
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Old 01-30-2012, 12:20 PM   #17
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Quote:
Originally Posted by Danny/SMC View Post
There is a standard to test for C rate but unfortunately it seems that most factories and resellers know it's very hard to test cells at high amp draw so they feel they can claim what they want.

I've been busy testing cells and packs for the last 6 weeks or so and I have come to the conclusion that the best possible true C rate is around 40 to 45C.

Yes even some of our packs are falsely labelled as I trusted the factories data for C rate claims.

I'm currently working a new rating system that will be base on the cells IR instead of C rate. We will still put down the C rate but it will be what I get off my own testing equipment and not what a factory claims.

The IR of a cell is directly related to the C rate of the cell. A cell with lower IR will be able to withstand a higher load thus giving higher C rate.

There's a relatively inexpensive meter that can be purchased that allows you to measure the IR of the cells in the pack. This meter will be used to determine the specs of our packs and each pack we ship out will be measured on this meter to make sure it's within the rated specs.
Besides the CE gfx, what meter can measure the IR of a cell. Just curious.

Thanks
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Old 01-30-2012, 01:00 PM   #18
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Yes there is a meter that can do this and we will offer it on our website. It will sell for 89.95 which is pretty cheap for the info it will provide.

Some of the good flight chargers also give IR readings but I have found there not as consistent as the meter.

At this time I'm working hard on our new rating system as it needs to be good and consistent. My goal is to sell packs based on IR ratings and true C rate ratings that are tested on my equipment and not the factories equipment.

As with any new system I need to make sure we can sell packs within the claimed specs. This requires that we use a factory that will sell us cells/packs at the required specs.
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Old 01-30-2012, 02:47 PM   #19
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Great, another vague measurement to compare packs...
Why on earth is it so difficult to hook up a battery to a known load (eg light bulbs) and measure the voltage sag?
IR of a pack depends on too many values to be used for comparison.
Apart from measurement method you have state of charge, temperature, gauge of the wires etc that have an impact on IR.
It seems that most car battery manufacturers do not want to use a proper measurement because they will lose their marketing advantage.
We are in the year 2011 where heli and plane guys charge at 5C without problems and car electronics manufacturers like Orion come out with a "high tech charger" that charges @ 5A discharges @ 1A and has a max power of 50W. Great I will use one to charge my remote control batteries...
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Old 01-30-2012, 02:54 PM   #20
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IR readings from a meter designed to measure IR of Lipos is allot easier than hooking up loads to the the pack.

State of charge , temperature and wire length will also have an impact when using a load as any change in IR will be reflected using a load.

The meter can measure the IR of the entire pack or each cell within the pack.
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Old 01-30-2012, 03:11 PM   #21
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Maybe I came out a little harsh.
My post was not directed at you and I really appreciate the fact that you are trying to find a way to accurately rate your packs.
Still I fail to see why a standardized method is not being used. IR measurement is easier than testing under load but this is not something you will have to do for each pack.
I am just sick of all the BS the RC car industry is putting out concerning batteries, chargers etc.
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Old 01-30-2012, 03:19 PM   #22
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Quote:
Originally Posted by taz00 View Post
We are in the year 2011 where heli and plane guys charge at 5C without problems and car electronics manufacturers like Orion come out with a "high tech charger" that charges @ 5A discharges @ 1A and has a max power of 50W.
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I am just sick of all the BS the RC car industry is putting out concerning batteries, chargers etc.
Some of the blame for the charging limits can be placed squarely on ROAR. Their rules state a charge limit of 1C.
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Old 01-30-2012, 03:23 PM   #23
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I am from Europe so ROAR means nothing to me.
EFRA rules state "It is advisable to restrict charge rates to 1C."
It is my understanding that advisable is different to mandatory.
Lack of knowledge concerning LiPo can be blamed in the late adoption of this technology in this hobby.
I find it amusing when some (not all) people with years in this hobby do not have a clue how to properly take care of a lipo pack and then whine when their pack has puffed after only a few cycles when they took so good care of it (storing it fully charged, fully discharging it every once in a while etc )
Still when you try to tell them this does not apply to lipo packs they do not listen.
Some of these people are part of federations.

I mean just check the tests ROAR performs for battery approval.
1. Impact/Drop test
2. Overcharge test
3. External short test

I understand that they are concerned only about the safety of the pack and not its performance.
Still this makes it easy to understand why a manufacturer can claim 150C and 10000mAh from a 300gr pack and say it has ROAR approval.
Most people will think that since it is approved it must be true. Great marketing.

Last edited by taz00; 01-30-2012 at 03:39 PM.
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Old 01-30-2012, 03:25 PM   #24
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Until recently I thought that 60C was possible but I now know for a fact that 40C is most likely the maximum C rate where you can discharge a cell and it will have a good looking voltage curve.

I invested in equipment to do my own C rate tests and I found this meter that gives the IR of cells and is very reliable. My goal is to change our ratings system and explain how we get the results we claim. I think this is a big step forward than just putting C rates on a sticker.

If someone wants to buy the meter we use and follow the way we test our cells/packs they will get the same results as we get. Basically this will be the standard which we use to rate our packs.

We use to be the largest cell matcher and we were able to be very successful at it because we would make sure our matching equipment and method was done properly. On the battery label you would see the runtime of the cells , IR of the cells and average voltage of the cells.

Basically we want to step it up with Lipos where we can sell our packs with a rating that means something,

By checking the IR of each cell in the pack we can make sure the pack is within the spec we claim so this means if you buy a pack now and one in 6 months it will be in the same spec range. This is a big improvement over just claiming 40C or 90C or whatever the reseller or factory feels like claiming.

Hope to have the first model for sale in early March as we need to work with a factory that will make sure they can deliver the cells/packs at the specs we claim.
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Old 01-30-2012, 03:32 PM   #25
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Thought some of you might like to see my C rate tester. I'm able to pull over 200 amps with this setup. All tests are done on one single cell.
Attached Thumbnails
LiPo Battery True C Rate !!-cratetester.jpg  
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Old 01-30-2012, 03:38 PM   #26
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Quote:
Originally Posted by Danny/SMC View Post
Thought some of you might like to see my C rate tester. I'm able to pull over 200 amps with this setup. All tests are done on one single cell.
I'd like to see the test setup to prove the 7200mAh/75C rating, or Orion's 90C rating. Welding cable, anyone?

And I'd like to see the standard 14ga wire /ESC/solder connection/Deans plug combo handle that current, especially for the standard "continuous" discharge.
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Old 01-30-2012, 03:44 PM   #27
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The biggest battery factory for lipos and lifep04's is based in china and uses material imported from japan it is also Government funded with an unlimited budget and some of the best chemical engineers in Asia.

The highest they have reached is 6000mah for a 7.4v 5200mah for a 14.8v and 5500 for a 3.7v and that is from november of last year and a cont racting of 60c

No more comments id let you figure out the rest about others who claim these rediculous ratings we see today .
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Old 01-30-2012, 03:45 PM   #28
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I edited my previous post so you will find some additional thoughts there.
@Danny/SMC : Cool, we have the same charger.

Here is a very crude but useful video for those that want to see some pack testing under load.
http://www.youtube.com/watch?v=KvIaL...ure=plpp_video
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Old 01-30-2012, 03:47 PM   #29
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just sold my ce gfx for pennies....now i will need it again....lol
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Old 01-30-2012, 03:57 PM   #30
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As far as connectors and wires go there is no way they can handle the full C rate. This why C rate testing should be done on a cell. My jig to put the cells in is made of 1/4 inch copper.

If there would be a C rate standard and every factory would follow this standard you would notice that higher C rate cells will provide more power even if the wires and connectors can't handle the full C rate loads. This all comes back to the IR of the cells. Lower IR cells don't drop under load as much as higher IR cells.
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