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Old 03-21-2008, 04:18 PM   #61
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Questions?? DOD

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Originally Posted by TeamTekin View Post

Also consider DOD depth of discharge and the huge effect this has on life.


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What effect does DOD have on the life/performance of a Lipo? And how should they be handled?
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Old 03-22-2008, 10:35 AM   #62
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Lipo batteries are very different than Nimh in many ways. Nimh likes to be used completely for best performace. In fact we discharge what is left after we use them and always try to do a continuous full charge.

Lipo prefers to be used partially and it is not recomended that they are discharged at all. Lipo manufacturers typically reduce the expected life cycles significantly if you use 100% of the capacity. If you know the battery will run for 20min before hitting the voltage cuttoff you really should only run them for 15min or less for best life.

Especially in our applications this can be important because of the pulse drive. Most lipos cutoffs do not activate unless the voltage is below 6v for some period of time, seconds on some products. Remember we are switching thousands of times per second and can actually be drawing the lipo well below 6v during the on time pretty early in the run.

On most average quality lipos a 3t mod will hit 6v right from the beginning under load. Our system reacts fast enough to low voltage that it will act like a throttle limit..... A true voltage cutoff. Some cells handle these short term low voltages better than others. Even with light constant loads manufacturers do not recomend using 100% DOD.

Moral to the story is do not run them all the way to the voltage cutoff for best life.... and do not cycle your batteries on a GFX just to see how they are looking anymore than you have to. Really we should only be cycling them to about 7v since below that is pretty meaningless.

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Old 03-22-2008, 10:42 AM   #63
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Information on DOD and cycle life from the Kokam website.

http://www.kokam.com/english/product/kokam_Lipo_01.html

Our results are far worse because like everything in RC we push the limits and really abuse things. However the relationship between DOD and cycle life is still valid. We need to think different with Lipo. Cycling packs at 35amps to 6v may be a decent relative comparison, but not really a good thing to do very often...

How many people have had packs go soft and drop to 70% capacity after only weeks or a few months of use? Probably less than 50 cycles. I have a pile of them. DOD, balance, marginal voltage cutoffs and general abuse have an exponential effect.

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Old 03-22-2008, 10:53 AM   #64
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This provides a higher top speed with a nimh because they hold a higher voltage under the lighter load at spool out and why all the Amain guys at the carpet nats ran Nimh... and a brushed motor.
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And this is why, despite what some want to believe, Ni-MH is far from dead. As they say, the proof is in the pudding.
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Old 03-22-2008, 11:14 AM   #65
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The ease, consistency and life of lipos will still rule for the mass market and average racers. Our problem is scrubbing speed in the corners and bouncing off walls. A few tenths of voltage are not going to make us national champs. The lipo does provide the grunt for recovering from a mistake. It is a trade off and the straight away and full spool out is only a small part of the track. It only adds up to anything real in the very competitive world of stock TC. I for one have gotten completely lazy and love them.

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Old 03-22-2008, 12:23 PM   #66
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Places that sell lipos that have all this claims should get one of those CBA and do their own testing to provide some real results. Run the pack through some cycles and post the results on here or their website. A company could be trusted more if they do this and don't rely just on manufacturers claims. That's what I'm going to do when I start bringing my lipos to the market. I'm currently just using a BNP Products DPR-150 to get real life datas.
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Old 03-23-2008, 07:58 AM   #67
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Quote:
Originally Posted by TeamTekin View Post
The ease, consistency and life of lipos will still rule for the mass market and average racers. Our problem is scrubbing speed in the corners and bouncing off walls. A few tenths of voltage are not going to make us national champs. The lipo does provide the grunt for recovering from a mistake. It is a trade off and the straight away and full spool out is only a small part of the track. It only adds up to anything real in the very competitive world of stock TC. I for one have gotten completely lazy and love them.

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Haha, I totally agree on those points! Who can argue with them?
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Old 03-23-2008, 08:57 AM   #68
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Thanks Tekin Prez - some good info!


Quote:
Originally Posted by TeamTekin View Post
Lipo batteries are very different than Nimh in many ways. Nimh likes to be used completely for best performace. In fact we discharge what is left after we use them and always try to do a continuous full charge.

Lipo prefers to be used partially and it is not recomended that they are discharged at all. Lipo manufacturers typically reduce the expected life cycles significantly if you use 100% of the capacity. If you know the battery will run for 20min before hitting the voltage cuttoff you really should only run them for 15min or less for best life.

Especially in our applications this can be important because of the pulse drive. Most lipos cutoffs do not activate unless the voltage is below 6v for some period of time, seconds on some products. Remember we are switching thousands of times per second and can actually be drawing the lipo well below 6v during the on time pretty early in the run.

On most average quality lipos a 3t mod will hit 6v right from the beginning under load. Our system reacts fast enough to low voltage that it will act like a throttle limit..... A true voltage cutoff. Some cells handle these short term low voltages better than others. Even with light constant loads manufacturers do not recomend using 100% DOD.

Moral to the story is do not run them all the way to the voltage cutoff for best life.... and do not cycle your batteries on a GFX just to see how they are looking anymore than you have to. Really we should only be cycling them to about 7v since below that is pretty meaningless.

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Old 03-23-2008, 05:23 PM   #69
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Quote:
Originally Posted by TeamTekin View Post
Lipo batteries are very different than Nimh in many ways. Nimh likes to be used completely for best performace. In fact we discharge what is left after we use them and always try to do a continuous full charge.

Lipo prefers to be used partially and it is not recomended that they are discharged at all. Lipo manufacturers typically reduce the expected life cycles significantly if you use 100% of the capacity. If you know the battery will run for 20min before hitting the voltage cuttoff you really should only run them for 15min or less for best life.

Especially in our applications this can be important because of the pulse drive. Most lipos cutoffs do not activate unless the voltage is below 6v for some period of time, seconds on some products. Remember we are switching thousands of times per second and can actually be drawing the lipo well below 6v during the on time pretty early in the run.

On most average quality lipos a 3t mod will hit 6v right from the beginning under load. Our system reacts fast enough to low voltage that it will act like a throttle limit..... A true voltage cutoff. Some cells handle these short term low voltages better than others. Even with light constant loads manufacturers do not recomend using 100% DOD.

Moral to the story is do not run them all the way to the voltage cutoff for best life.... and do not cycle your batteries on a GFX just to see how they are looking anymore than you have to. Really we should only be cycling them to about 7v since below that is pretty meaningless.

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Hey are we ever going to see an updated charger from Tekin? I'd love to see something more along the lines of a GFX from Tekin. That'd be awesome!!
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Old 03-24-2008, 03:19 AM   #70
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From some NiMh VS LiPo forum I read,

The Lipo must keep in 40% of its total charge capacity to ensure life expectancy. It could last for very long time and takes many cycles without degrading in a well control environment.

Over Charge or Over Discharge LiPo overheats the Lipo cell, is also dangerous. The Heat damages the cell and shorten its Life Expectancy greatly. Many LiPo reaches it's point which are no longer safe to use. !!It can Really Blow your RC into pieces!! Those Extreme Heats it can produce can even catch metal into fire. check out youtube for lipo.

Lipo cell are fragile, it needs protection in High G Environment. An internal shortage of a damaged cell could cause Heat and destroy your RC car completely!

We are still in the drak age of LiPo. Higher output cell, the more active chemistry, the high risk. Be a Wise Careful person when using LiPo.
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Old 03-24-2008, 07:55 AM   #71
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Default dark ages of lipo

All lipo batteries are compared to the orion packs, why, because kokam is the only lipo cell MANUFACTURER (not reseller, or company that slaps on labels)that has ever provided any data of any kind. Other r/c companies even point to kokam data when making the case for lipo's or when making a case about lipo's. I have a question-> why doesn't orion or kokam come on these threads and push their agenda? Answer-> because when you are regarded as the gold standard (rightfully), you don't have to.

As for discharge rates, I look at it this way. At our club, 1/2 the guys (maybe more) are running brushless, and more and more are running lipo. A brushless equivalent is considerably more efficient than a brushed motor, draws less power, and wastes less power as heat; which is why my 13.5 sedan draws about 1600 or 1800mah during a 5 minute race. Since 13.5 and 17.5 are by far the most popular on road classes (stock and super stock), in my opnion, this is where the issue of discharge rates should focus. Not on the 3.5 motor that is more motor than 99% of racers can handle.

Usually, rules regarding a certain wire guage for a certain level of amps are designed for continuous duty at that current, and are also designed for a considerable wire run, not 1/2 second of high current pull over 6 inches. If you doubt that, open your speed control and look at the size of the circuit board copper connections. If you took those out and rolled them up, what guage would they be?

Lastly, and this is not meant to offend anybody, but it seems to me that pretty close to everything "some" battery matchers have said about lipo is proving to be incorrect. I don't know whether this is from ignorance about the technology, pushing an agenda, or whatever, but when your profits are based on your ability to fudge and guess at information about a product (including your own product,) I guess you will say anything, and assume that your "facts" and "impressions" will soon be forgotten, when you are proven wrong.
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Old 03-24-2008, 09:45 AM   #72
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Personally I don't think the whole "C" rating thing is very good for how we use the cells. For the powertool industry it's probably fine because their tools are built around a set motor and load/gear. They use the C rating of the cell to make shure that they're not going to kill the cell with normal/extreme use. In RC, we run different motors and loads/gears all the time. This means we're really only concerned that the pack will handle the current that we need for our class and motor. This includes the current spikes that a "C" rating doesn't take into account.

For some reason we seem to compare C rating with performance and that may not always be the case. The cells ability to take the large current spikes that we have is probably more important than the C rating in most cases. I don't care if my pack can handle a 75 amp discharge if it can't handle a 100 amp spike in mod (or a crash). What we need really hasn't changed much. Runtime, IR, and voltage are the most important things in RC racing.

So, I think we need to have a company come up with an RC standard (just like what happened with NiCd). All of the normal runtime, IR, and voltage info should be included at a standard discharge rate. What they would need to add is a test that would show how well the cells can take high current spikes.
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Old 03-24-2008, 10:33 AM   #73
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What you refer to is Burst C rating. Unfortunately as per one of the issues this thread was started, some manufacturers list (most notable from the air portion of the hobby). Others (especially Vehicle packs) use the burst as the C rating versus listing both.
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Old 03-24-2008, 10:35 AM   #74
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C rate does have an impact on the Lipos performance. I asked our Lipo manufacturer to send us a 20C/5000 pack to test out as it costs less than our 28C/5000 pack. The 20C pack has .10 less in average voltage at 35 amps and is 3 milliohms higer in IR. That equates to less power on the track.
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Old 03-24-2008, 11:10 AM   #75
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C rate does have an impact on the Lipos performance. I asked our Lipo manufacturer to send us a 20C/5000 pack to test out as it costs less than our 28C/5000 pack. The 20C pack has .10 less in average voltage at 35 amps and is 3 milliohms higer in IR. That equates to less power on the track.
Yes, for a given mAh pack, the C rating can give a good direction for performance but if you start comparing packs of different mAh ratings the C rating is not likely the best way to compare the packs. 28C at 3200 may not be as good as 20C at 5000.

You're the first company to actually cycle the packs that you sell and provide useful numbers that the RC car guys can easily identify. For me, that's much more important than some crummy C rating. All we need to do is standardize what we do (more standardized than NiMh)
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