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Old 12-17-2007, 11:05 PM   #151
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Originally Posted by linger View Post
I disagree - see below



answer - the memory effect of lipos is almost not measureable (see below)



Danny, I think you might be interpreting the data incorrectly.

I've tested for the memory effect on Lipos and it almost doesn't exist. See the attached plot of a pulse discharge on a Kokam battery. The pulse is over a 30C discharge rate.
The battery was given exactly 500 partial discharges (3.1V cutoff at a 35C rate which is approx 50% discharge depth). The dark blue line represents the plot of the last partial cycle.
The battery was then subject to a series of full discharges. The pink line is the first full discharge (2.8V cutoff) after all those partial discharges, and the green line is the 2nd full discharge (also 2.8V cutoff).

All plots pretty much fall on top of each other.

There is no difference between the last of the 500 partial discharges and the first couple of full discharges. There is no memory effect going on here.

Cycling a lipo battery all the way down does pretty much nothing other than take away cycle life.

I think the main reason that you are seeing such a difference in results is that the first cycle is on a cold battery. After the first cycle, the heat is retained and there is tons of data showing that a Lipo battery discharges much better with higher temperature. Per your quote, the other cycles were started immediately after the first and a 35amp discharge generate a lot of heat.

This can all be confirmed by all the racers currently using lipos out there. With NIMH, all of us felt that NIMH batteries felt "flat" when charged the day before or if we didn't discharge them all the way down. I don't know the actual difference in discharge numbers, but it was enough to be easily felt.

With lipo, I have never experience a "flat" run. They feel the same all the time. Whether it's been through a bunch of partial discharges, the punch is incredibly consistent.

I've also never seen any data to suggest a difference in discharge whether the previous discharge was a high or low rate. Cycling a lipo is not needed.

It's a matter of time until everyone comes out with lipo warmers

Anyways, this isn't an arguement, I just wanted to make as much data availiable for all the lipo users.

-ling
So Ling, master of the black art of lipo, what IS the proper temp to preheat a lipo, hard case?
Got an extra set of wrap tire warmers laying around.
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Old 12-18-2007, 02:41 AM   #152
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Originally Posted by C_O_jones View Post
So Ling, master of the black art of lipo, what IS the proper temp to preheat a lipo, hard case?
Got an extra set of wrap tire warmers laying around.
as far as i know, 55 degrees C .


i did alot of research :P
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Old 12-18-2007, 03:35 AM   #153
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I hope NiMH market die sooner.
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Old 12-18-2007, 08:31 AM   #154
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Originally Posted by joe of loath View Post
as far as i know, 55 degrees C .


i did alot of research :P
Thanks Joe
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Old 12-18-2007, 09:23 AM   #155
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Originally Posted by C_O_jones View Post
Thanks Joe
you might want someone slightly more knowldgeable to back you up before you try it, or at least heat in a lipo sack!

one of the first, proposed applications was for server centres, where the batteries would be heated to 55 degrees with the hot air from the servers, so if there was a power cut they would carry on working for longer than they would if they carried on using lead acids. of course, they still use lead acics because they're cheaper
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Old 12-18-2007, 10:02 AM   #156
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Quote:
Originally Posted by linger View Post
I disagree - see below



answer - the memory effect of lipos is almost not measureable (see below)



Danny, I think you might be interpreting the data incorrectly.

I've tested for the memory effect on Lipos and it almost doesn't exist. See the attached plot of a pulse discharge on a Kokam battery. The pulse is over a 30C discharge rate.
The battery was given exactly 500 partial discharges (3.1V cutoff at a 35C rate which is approx 50% discharge depth). The dark blue line represents the plot of the last partial cycle.
The battery was then subject to a series of full discharges. The pink line is the first full discharge (2.8V cutoff) after all those partial discharges, and the green line is the 2nd full discharge (also 2.8V cutoff).

All plots pretty much fall on top of each other.

There is no difference between the last of the 500 partial discharges and the first couple of full discharges. There is no memory effect going on here.

Cycling a lipo battery all the way down does pretty much nothing other than take away cycle life.

I think the main reason that you are seeing such a difference in results is that the first cycle is on a cold battery. After the first cycle, the heat is retained and there is tons of data showing that a Lipo battery discharges much better with higher temperature. Per your quote, the other cycles were started immediately after the first and a 35amp discharge generate a lot of heat.

This can all be confirmed by all the racers currently using lipos out there. With NIMH, all of us felt that NIMH batteries felt "flat" when charged the day before or if we didn't discharge them all the way down. I don't know the actual difference in discharge numbers, but it was enough to be easily felt.

With lipo, I have never experience a "flat" run. They feel the same all the time. Whether it's been through a bunch of partial discharges, the punch is incredibly consistent.

I've also never seen any data to suggest a difference in discharge whether the previous discharge was a high or low rate. Cycling a lipo is not needed.

It's a matter of time until everyone comes out with lipo warmers

Anyways, this isn't an arguement, I just wanted to make as much data availiable for all the lipo users.

-ling
Ling,

He was talking about Low C rate partial discharges, i.e. stock. Your testing is High C rate partial dischages.

Art
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Old 12-18-2007, 10:17 AM   #157
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Originally Posted by linger View Post

I've also never seen any data to suggest a difference in discharge whether the previous discharge was a high or low rate. Cycling a lipo is not needed.
Quote:
Originally Posted by Advil View Post
Ling,

He was talking about Low C rate partial discharges, i.e. stock. Your testing is High C rate partial dischages.

Art
Art D.- Read the whole post - I've addressed that. I've done tons of high and low discharging and the next cycle is always the same. The previous discharge has no effect on the next one.

Next time I see you, I'm going to kick you in the nutz because you failed to read the whole post.
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Old 12-18-2007, 10:40 AM   #158
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Art D.- Read the whole post - I've addressed that. I've done tons of high and low discharging and the next cycle is always the same. The previous discharge has no effect on the next one.

Next time I see you, I'm going to kick you in the nutz because you failed to read the whole post.
What nutz? You know I'm married just like you are. LOL

P.S. We'll have to talk about Pulse discharge vs. Linear at the track some time.
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Last edited by Advil; 12-18-2007 at 10:47 AM. Reason: Just poking at ling again....LOL
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Old 12-18-2007, 12:35 PM   #159
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Preheat temp for those of you who are non-metric: 100degF

This, and more lipo info I've written based on long-term actual use and real world experience in cars here:
http://www.secureonlineshopping.biz/...&pagewidth=550

(All Linger approved info... LOL)
Sup Linger!
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Old 12-18-2007, 12:58 PM   #160
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And now it is said again that you don't have to discharge the battery because of a memory effect. Will someone please make up my mind. It seems that pushing for a majority acceptance of lipo has created a lot of information and disinformation. So who do I believe? Do I accept the answers from those who are pushing lipo as truth, cause they surely have nothing to deceive about, or do I accept the truth from those who say lipo are just as bad as nimh and still require additional maintenance for full performance?
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Old 12-18-2007, 02:06 PM   #161
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Originally Posted by trilerian View Post
And now it is said again that you don't have to discharge the battery because of a memory effect. Will someone please make up my mind. It seems that pushing for a majority acceptance of lipo has created a lot of information and disinformation. So who do I believe? Do I accept the answers from those who are pushing lipo as truth, cause they surely have nothing to deceive about, or do I accept the truth from those who say lipo are just as bad as nimh and still require additional maintenance for full performance?
there is NO memory effect. the first time i heard of one from a proffesional ni-mh matcher on this site. so no, you don't have to discharge.
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Old 12-18-2007, 05:17 PM   #162
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And now it is said again that you don't have to discharge the battery because of a memory effect. Will someone please make up my mind. It seems that pushing for a majority acceptance of lipo has created a lot of information and disinformation. So who do I believe? Do I accept the answers from those who are pushing lipo as truth, cause they surely have nothing to deceive about, or do I accept the truth from those who say lipo are just as bad as nimh and still require additional maintenance for full performance?
What were the words from days gone by? Ah, yes, "Follow the money." Having been beaten back on the lipo safety FUD (Fear Uncertainty Doubt) front, we are now told that well, after all, lipo's will need just as much maintenance and will require the same premium services as NiMH, so get ready to pay. Your lipo cells will have to be "matched" just like NiMH's. Really? And if so, how hard is it to match TWO cells? Just how much of a premium are we going to pay for that favor?

I wouldn't bother with a single word Mr. SMC writes. He/they should have been the first ones posting advice and warning as it became obvious that the IB 4200's were temperamental at best, and outright dangerous at worst. (See J&J, Tylenol tampering: the best example of corporate crisis management in history.) Instead, it was all "User Error," and "More Perfect Idiot." So then, when they do bring out a lipo but don't put it in a hard case, they insist that it's perfectly safe--imagine that! They use these in airplanes? Whodathunk?--and in fact, hard case lipos heat up too much! Really? Haven't heard that one. I wonder, having missed the market and in their scramble to catch up, whether SMC will be so kind as to tell us how to manage the heat their new hard case lipos will generate. Honestly, we can't see their back soon enough.

Lipo tech is solid, evolved, and applied. While more expensive than NiMH up front, they are more economical over time, require less maintenance, and have a much more durable window of high performance. Some will choose to run NiMH's for awhile yet, especially as there are few really optimized chassis for lightweight lipos. Those will come. But it's all over, now it's just shouting.
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Old 12-18-2007, 06:08 PM   #163
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What were the words from days gone by? Ah, yes, "Follow the money." Having been beaten back on the lipo safety FUD (Fear Uncertainty Doubt) front
Exactly, and I think the TRINITY/I.B. deal just adds to that theory...The NiMh matchers don't want to watch the demise of their business anymore than Oil Companies want 'Alternative Fuels' to shut them down...and will plan to SPEND a fortune to keep their positions.
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Old 12-18-2007, 08:02 PM   #164
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Exactly, and I think the TRINITY/I.B. deal just adds to that theory...The NiMh matchers don't want to watch the demise of their business anymore than Oil Companies want 'Alternative Fuels' to shut them down...and will plan to SPEND a fortune to keep their positions.
There would have to actually _be_ an alternative fuel for the oil companies to be worried.
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Old 12-18-2007, 08:22 PM   #165
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You guys know that trinity has hard case lipo out already right? If you guys like running Lipo great I'm getting some also since my club is allowing it as long as our cars make the legal min weight limit.... I just don't get all the bashing... I'll be running lipo for club racing and practice and NIMH for non club races since I feel that NIMH still has a noticable performance advantage in 19 turn class....
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