SMC LiPo Info

[Danny-SMC]

As a proud supporter and sponsor of HobbyTalk I’m pleased to start this new thread to provide important info regarding LiPo packs for RC use. My goal is to help the consumer better understand Lipos.

In the past 5 years Lipos have become the power of choice in RC surface vehicles. In this 5 year period I’ve noticed the C rate and milliamp hour claims increasing at a rapid pace. I was lead to believe that these higher C rates were true as I believed the data supplied by the Lipo factories. Recently I found a meter that can measure the Internal Resistance of each cell within a Lipo pack. While communicating with the designer/builder of this meter and getting some measurements on various packs I quickly found out that C rate claims are mostly false. That being said it’s hard to accuse factories or resellers of claiming false C rates as there is no official standard for C rate testing.

Since there is no official C rate testing standard this opens up the door for factories/resellers to come up with a claimed C rate using different testing method or simply invent the C rate they feel will help sell the most packs and make the most profit. Now that I have my own equipment to test for C rate I will come up with my own C rate testing standard and will use this to rate all future packs we release. The Internal Resistance will also be listed on the new models so the customer will know which packs have the best performance based on the IR rating. The IR meter will be on sale on our website so customers who want to be able to test their packs and make sure they have the proper IR will be able to do so. This will show how misleading C rate claims have become. C rate and IR are directly related as C rate is the ability of a cell to withstand a certain amp load. Amps equals voltage divided by resistance.

Hope everyone will like the info I will be providing in this thread.

[Benracin']

What about ratings for milliamps? I purchased one of your 6100mah one cell packs about a month ago and when cycling the pack all it will take is between 5600-5700 mah. That's what your 5600mah packs were taking. I used it one weekend and the numbers were worse than a pack I bought back in Oct. last year.

[Danny-SMC]

The typical range for mAh is 5% of what is claimed. It's impossible to have every cell be at the same mAh within every batch. The 6100s have been in the 5900 to 6100 range under discharge with a 4.22v charge.

[PRI_rc]

Good to see you taking on the task of a grading process for lipos. We been needing one!

[Danny-SMC]

Yes and I'm not sure if it will help or hurt SMC but I feel it needs to be done as way to many companies/factories are taking advantage of the lack of standard for C rate so I'm willing to be the one to start a standard.

I've had success in the past as I'm the one who pushed CE to come up with Actual IR instead of Relative IR. The first few months I was accused of trying to sell lower sub-c cells with the Actual IR but in the end everyone switched to it as they found out it was the accurate way to measure the cells IR.

I hope I can do the same with LiPo cells/packs as I don't believe in the C rate of the month labels and feel it needs to stop.

Hope I can pull this off and I'm ready for this new challenge.

[Danny-SMC]

Here is the standard that I have come up with to rate cells/packs.

All C rate testing will be done on the cells used to make a pack. For 2S2P packs testing will be done on a 1S1P cell. This allows me to be able to do higher rate discharges and keep the Watt Hour down so my testing loads don't need to support as much Watt Hour.

When taking a 1S1P cell and adding it to another cell in parallel to make a 2S2P cell the IR drops in half this means the cell will be able to withstand double the amp load if testing were to be done as 2S2P.

Cell temperature and ambient temperature is critical to get consistent and accurate results. In my testing an increase of 3 degrees Celsius resulted in a drop of 0.20milliohms.

The charge rate is also very important as this will have an impact on the cell temperature.

All cells will be tested at 22 degrees Celsius and will be charged at 2C.

For a cell to be claimed at a certain C rate it will need to be able to handle the full C rate discharge and have a linear drop in the voltage curve. This means the voltage can drop but not rise again due to excessive heat in the cell lowering the IR thus increasing the voltage.

You can see the first graph of a 3250mAh cell used in a 2S Hardcase pack. Using my standard this cell is very close to a 30C cell but there is a bit of drop in the voltage then rise. This cell is most likely a 25 to 28C cell. You can see that it can handle 40C but has a major drop in voltage then as it gets hot due to the excessive stress the voltage rises again. The capacity retention is only 70% at 40C.

The second graph is another 3250mAh at 25C. This is the graph of the cell tested in the video below.

Typically factories will claim C rate based on the capacity retention. I feel this is not an accurate method as I have seen cells stay above 90% but have the sag due to the amp load being to high.

As my testing is a work in progress I hope to post my results of each cell I test and also post the cells Internal Resistance value as once we know the IR value of a cell we can know it's C rate base on my standard.

This should help clean up the market and I hope factories and resellers will adopt my standard but I think this will be a big challenge as many know that C rates help sell packs.

Here is a video showing how I do C rate testing.

http://www.youtube.com/watch?v=rqdLC...ature=youtu.be

[PRI_rc]

I hear what your saying.... It won't hurt you in the long run. Smc's reputation will only get better!

[Danny-SMC]

I'm doing this new system as I don't want to be part of the C rate of the month club.

Based on the extensive testing I've been doing recently I've come to the conclusion that 30 to 35C is the highest possible C rate using my standard. I think the factories felt pressure to outdo the competition so they decided to increase the claimed C rates then you through in the resellers trying to have an edge and they increase the claims from the factory. This means we now have 60 to 75C rated cells/packs.

In one of my tests I purchased a 65C pack and to my surprise it failed at 20C using my standard. Based on my standard it would be a 15 to 17C. I wasn't surprised that it was not a 65C as I had already figured out that 35C was pretty much the max using my standard but I would of expected it to be around 25C.

I have allot of info to pass on and I hope this will be welcomed by the majority.

[EAMotorsports]

SMC has always been a leader in battery technology so this doesn't come as a surprise to me. Glad to see someone taking the time and spending the money to figure out a way to fully test and sell quality and high performance lipo's.

EA

[WIGMAN]

Danny just curious if you have tested any of those 90C packs that are out there and what you came up with if you did.
Great thread by the way, glad they made it a sticky.

[Danny-SMC]

I haven't but I can guarantee they will not be any better than 35C using my standard.

There simply is a maximum amount of amps a cell made to fit a ROAR legal case can provide. Another thing to note is mAh and C rate have an impact on each other. Typically to get higher mAh you need to lower the C rate.

My goal is to be able to come up with IR readings using the IR meter that will give the C rate of a cell just by testing them on the IR meter.

At this time I can tell you that a 6000 cell at 30-35C has 1.5mOhms on the meter at the end of a 2C charge. To get the C rate to be 60C I believe the IR would need to be around 0.5mOhms or possibly lower which really isn't possible.

[Danny-SMC]

Testing a cell/pack consists of C rate testing and Cycle life testing. This post is about the Cycle life testing that I use to determine how a pack will hold up throughout it's cycle life.

The packs we offer are built using the best materials that mainly come from Japan. This makes for a higher priced pack but will result in a pack that holds up better over it's cycle life.

The factory which we buy from has always told me that if they were to make cells using all Chinese materials that the packs would be cheaper but wouldn't hold up as well and to test this I should do some cycle life testing.

A few months ago I purchased some of the cheaper packs in the market to do some cycle life testing to see how these packs compare to what we offer. My goal is to try and figure out if a cheaper pack is worth purchasing based on the performance and cycle life.

I purchased a 5000/40C and a 5300/30C from one of the cheaper companies who sell online and have a decent reputation. I paid 36.00 for the 5000/40C and 33.00 for the 5300/30C.

My cycle life testing consists of doing back to back cycling on my GFX using a 12 amp charge and 35 amp discharge with a 10 minute delay in between the cycles. This allows me to do 15 to 18 cycles a day if I plan on staying home all day. This is very time consuming but very important to show how different formulations react over a certain amount of cycles. This is harsher then using a pack under normal use but since every pack is cycled using the same method the results will show how different packs will react.

I messed up with these two packs as I didn't graph the first cycle so this will not show the drop in voltage due to the drop in mAh. On all future tests I'm making sure to graph the first cycle then the last cycle. On these 2 packs I did 24 cycles and I was truly surprised at the results compared to what one of our packs did after 24 cycles.

5000/40C cycle 1: 5279mAh Cycle 24: 4608mAh 13.7% drop in mAh

5300/30C cycle 1: 5094mAh Cycle 24: 4618mAh 9.4% drop in mAh

SMC 5400 cycle 1: 5483mAh Cycle 24: 5425mAh 1.1% drop in mAh


I will do another 26 cycles on each pack to see what will happen but it does take allot of time to do cycle life testing and at this time I'm testing many different packs so results will only be available later on.

I do have results of a so called 6000/65C pack I purchased for 39.95 from Hong Kong. This is the pack I tested for C rate and was very surprised to see it was a 15 to 20C at best using my C rate testing standard.

Below is the graph of this pack after 25 cycles.

Cycle 1: 5774mAh Cycle 25: 5608mAh 2.9% drop in mAh

This pack expanded some over the course of the 25 cycles.

As you can see different packs will react differently to being cycled.

I'm not sure that we can claim that the SMC 5400 will have 10 times the cycle life of the 5000 and 5300 pack and 2 times the cycle life of the 6000/65C pack but I think this does show that our pack will hold up better over it's cycle life and will have a higher cycle life.

I will do another 25 cycle on each packs to see how the mAh will react over the next 25 cycles.

Hope this info is helpful.

[Danny-SMC]

We've added the Internal Resistance meter to our website.

The ESR meter is designed to test the IR of a pack and the IR of each cell within a pack.

To do accurate tests I've found that it's best to discharge a pack let it cool down for a few hours then fully charge it using the same amp rate for all packs. I personally use 12 amps. Pack temp and room temp is very important if your looking to get accurate results from different packs. In my testing I've noticed a change of 0.20mOhms from 22 to 25 degrees Celsius.

You can get the packs IR when the pack has some storage charge in it but this will only give you a rough idea of the packs true IR. The IR goes up a bit when the pack is stored for awhile and different formulations react differently to the charge. I suspect this is due to the heat build up while charging. This is why I recommend that the IR be measured immediately at the end of a full charge using the same charge rate for each pack.

The 2S-6S meter is selling for 84.95 and the 1S-6S meter is selling for 94.95 and it comes with a small pack ready to power the meter when testing 1S packs.

ESR Meter - YouTube

[WIGMAN]

Do you charge at 12 amps for racing too? I have a Hi-tec charger but it only goes to 6 amps, If you do is that for oval racing or off-road?

[Danny-SMC]

Higher charge rates will only improve performance if you run the pack as soon as it's off the charger as this will result in slightly higher cell temps which reduces the IR.

Hard to say the exact impact on lap times but warmer cells will have lower IR.