The future of lipo 12, 15 or 20c?

[Jev]

Hi guys n girls.

Just wanted to see what peoples thoughts on this subject. I know not many people on this board go down the 20c road. But I think in the end it will be better if we all moved over to them. The fact they can be totaly discharged in 5 minutes without too much trouble is why I think they are better for the hobby. Although you can get the same amps from a 12c pack of the same weight & size with similair strain on the pack, the potential for over discharge damage is higher.

2 hypothetical situation:

Racer X buys 12c 5000mah packs for 5 min racing. The the amp rating is just as good as the 20 for the same weight of pack but he gets more amp hours too. The cost is a bit more than the 20c 3ah packs

Racer Z buys 20c 3000mah packs also for 5 min racing. He think he will never need the extra run time and plans to use 90% of the packs capacity per race. He saves some money.

If both racers used 2800mah per race they should perform very similair. But Racer Z knows he is near to dumping the whole pack. Whereas Racer X has plenty of run time left and fancies a bit more speed down the straight, He goes to a wind lower on his motor but his pack is now getting much hotter than Racer Z's pack after the race. After 3 months of racing Racer X has to buy new packs, Racer Z's pack are still like new.

I'm not just talking about 12c vs 20 but 12c vs 15c, 15c vs 20c etc. The other aspect is the charge time. Would a 20c pack be ok to charge at 2c? Would only the first part of the charge be faster?

To use a real world example have a look at these:

polyquest 20c 2500(50amp) for $69.50 5.1oz
polyquest 12c 4000(48amp) for $78.50 6.6oz

I realise that for bashing the 4000 would seem more logical, but lets stick to racing for now.

[abiye]

for me, i would want the lightest battery that would last me the race... so i guess 20c since its lighter and lasts the whole race

[glassdoctor]

Racer X made the better choice.

1. Lipos don't like to be discharged to low levels. They will die sooner if they are always run down more, like a 3000 vs. 5000 would be. So the bigger capacity pack is much better, imo even if the rated current capacity (60A in this example) is the same.

2. Also, there are currently no 20C cells that can compare to 12C cells in performance... voltage and temps, etc. In other words a true 12C cell like TP's has better #'s at 12C than a 20C cell has at 20C. Technology is getting close but it's not there yet. The only cells that come close at 20C are very heavy... which is why you can go to a 12C cell and get at least 50% more capacity for the same weight.

The sweet part is though... that even the heavy lipoly cells are way lighter than Nimhs. You can still run the 20C cells....AND....have the 5000mah at the same time.

That's a win-win...

[e_lm_70]

actually there is not a big difference in price and weight between 12c and 20c lipo
a higher c lipo also tend to hold higher voltage at high amps (kokam 3200 20c is an impressive example)

I do agree that plan to discharge a pack for 90% is not a wise way to keep a good life of a lipo.

so I will say that a win win situation is the kokam 2s2p 6400mah

e_lm_70

ps: BTW I love the cheap Lipo from china between 8c to 12c ... very nice for longer then 5 minutes applications

[SpEEdyBL]

According to Optimaman's graphs, the 12c PQ 4400 cells drop to 3.1 volts under a 50 amp load. The kokam 20c 3200 cells drop to about 3.3 volts under an 80 amp load. Now both packs are about the same weight and the same price. I think racer Z made the best choice because he does not need to run the hotter motor to beat racer X.

[tcolesen]

I think the best choice (not listed) if it is possible (using the example), would be to get 2500mah 10C pack and run 2 in series, with a motor with half the kv compared to the motor that would run a single pack. This will net more watt hours, giving more total run time. This system would also run more efficiently, with high capabilities. It would be rather lightweight, and not too expensive (10C cells).

Assuming that both packs (racers x and y) were rated to the same amp draw, then Racer X would be a better pack. Tests have shown that the higher draw Lipos will heat up more (more stress). Comparing Polyquest 12C to Polyquest 20C, you can't really do that. It's like comparing apples and oranges. Naturally the 20C will be better because it is newer technololy, it is better thought out. But if you had a 12C developed at the same time as a 20C, the 12C should be just as good (for same total amp draw).

I think the future will continue to put out higher and higher C rated Lipos, but I think the best thing to do will be to get the larger capacities (not higher amp draw) into smaller and lighter amounts, still with something like 10C amp draw.

[Jev]

I know high V + High Wind = better efficiency, but this issue would still be relevant ;). The new UK 1/5th bike rules only allow 2s packs anyway. Personal I prefer the lower cog 2s pack and have not seen any cells thin enough except maybe the pq xp's that I'd be happy running.

I'm not convinced the so called 'latest generation cells' are a total improvement. I think the main difference is probably larger cathode and anode's which in turn lowers internal resistance. I'm sure the overall energy density will improve over time for all the c rating's. I think there will always be the choice between larger capacity, or better amp handling.

I've draw up a little list of some weight/max continuos amp comparisons. I realize that the cells are not rated exactly, but if we just use this as starting point.

TPower4000 12c 48amp 164g 293mA/g
PQuest2500 20c 50amp 140g 357mA/g
Pquest4000 12c 48amp 187g 257mA/g
Kokam3200 20c 64amp 200g 320Aa/g
Tanic 3650 20c 73amp 202g 365mA/g

mA/g = max continuos discharge per gram

I just run my tanic pack racing indoors on carpet, and I think the way they performed backs up these numbers. I know the weight of the pq 2500 xp's is 141g including wires and deans plug and the tanics are 202 with just wires, I cannot verify the weight of the others. PQ2500xp are very small compact packs, the tanic 3650's are very similar to nimh's but a bit lower and a bit longer(wires stick out a bit). 2500xp's in a 3s format would be an excellent fit as a nimh in just about anything.

[Jev]

One more pack. If anyone knows the weight of the packs inc wires let me know, as the TPowers might be heavier in the real world.

Pquest4000 12c 48amp 187g 257mA/g
TPower4000 12c 48amp 120g 400A/g
Kokam3200 20c 64amp 200g 320Aa/g
PQuest2500 20c 50amp 140g 357mA/g
Tanic 3650 20c 73amp 202g 365mA/g
TPower4200 15c 63amp 189g 333mA/g

According to this page the TP4200's are 120g

http://www.thunderpower-batteries.com/html/batteries.html

but 164g here:

http://www.maxamps.com/index.html?lang=en-us&target=d14.html&lmd=38645.687025

Can somebody weigh their prolite?

[GordonFreeman]

The best choice would be for ROAR to stop teabagging Trinity so we can get on with this. "Oh Mr. Trinity...you're so smart. You know what's best for us racers...please please take my money...oh God yes...".

[papapackard]

I thought I'd throw EVO 20 (http://www.flightpower.co.uk/proddetail.php?prod=4200012) packs into the mix and get a little feed back on your thoughts.

FlightPower Evolution20 2500mAh 2s1p 7.4V. 20C constant discharge(50A) 30C Bursts(75A). Fully compatible with FlightPower Balancers. Perfect for smaller lightweight models where extra punch is required. Dimensions - 14mm x 38mm x 123mm Weight - 125g

[Jev]

Rebadged pq xp's from what I can tell, all their packs are almost mirror images of the PQ's . Considering my 2500 packs are 140g including wire and deans connector, their 125g maybe the raw weight of the 2 cells? I don't know anyone that has bought them to confirm.

[glassdoctor]

actually there is not a big difference in price and weight between 12c and 20c lipo
a higher c lipo also tend to hold higher voltage at high amps (kokam 3200 20c is an impressive example)



The kokams are nice cells especially for cars.

But ThunderPower Prolite cells will out-perform the kokam and I think all other cells right now... when you compare watts gram for gram, and look at the discharge #'s.

The Prolite cells hold higher voltage and temps are lower than with other 12-15C brands, so they compare much better than these brands to the Kokam 20C.

Edit: here's a graph of the Prolite2100 cell which shows that it could easily be rated higher than 15C. No other cell looks this good at 15C... except maybe the kokam 20c. I'm trying to find a graph for that one. http://www.rcgroups.com/forums/attachment.php?attachmentid=586241

Everyone needs to remember that "c" ratings are not standardized and you can't believe everything you see. The people selling the batteries are the ones that decide what "c" rating to call them. If you look at actual discharge #'s many cells are overrated. They don't perform well at the advertized "c" rate. Some cells actually perform very well at the max "c" rate and really could be rated as a higher "c" cell when compared to the way other brands are labeled. Even among the same brand, some cells may be a bit overrated and others slightly underrated.

Then there is the whole weight issue. How big a weight penalty is being paid to get that higher "c" rating... and is it really worth it?

One last thing... if you compare a (50A) 2500 20c to a (48A) 4000 12C... even if the 2500 pack has equal or better voltage under the same load, the 4000 will never go much beyond 50% discharge curve while the 2500 will be dropping volts near the end of it's charge. In other words, the last minute of the race, which will be the better battery to have? Probably the higher capacity pack that's only half discharged and holding higher volts.

[SpEEdyBL]

You can find the graph of the kokam 3200 at www.fmadirect.com. So far, the kokam 3200 3s pack is the only 3s pack I can find that would fit in my car w/o mods.

[Jev]

You can find the graph of the kokam 3200 at www.fmadirect.com. So far, the kokam 3200 3s pack is the only 3s pack I can find that would fit in my car w/o mods.

That's a good point. The main reason I went with the Tanic 3650's is the shape, they fit excellently in both by tc4 and 1/5th bike. I've been using them in the bike today and have been so impressed I'm going to sell all my other lipo's.


But ThunderPower Prolite cells will out-perform the kokam and I think all other cells right now... when you compare watts gram for gram, and look at the discharge #'s.

The Prolite cells hold higher voltage and temps are lower than with other 12-15C brands, so they compare much better than these brands to the Kokam 20C.

While the TP's do look very good, the shape and the fact they are 2s2p is a no go for me. They don't fit in my bike or car, and I would rather avoid parallel packs if possible. I don't believe I will ever need more than 80% of the 3650mah that the tanics can provide. I was only using around 2000mah of the PQ's :D . That's the beauty of brushless.

I would like someone to test these packs at 40 amps:

PQ 3700XP - 74amp - $90
Tanic 3650 - 73amp - $93
Tunder Power 4200 Prolite - 63amp - $115 (84amp if Speedy is right)
Kokam 3200 - 64amp - $82

The Thunder Powers should be considerably lighter but you pay for that in $

[glassdoctor]

You're right about the size. Many of the new (best) cells just aren't a good fit. Airplane guys like the narrow cells, but they make for a lousy fit in cars.

TP 2100s for example are a stupid size for cars. But the TP 2000 cell works well. The 2000 cells don't perform quite as well as the 2100 but it's close. For comparing to toher packs, we probably should use TP 4000 Prolite instead of the 4200... since it actually fits a car.

Kokam has some of the best "car size" lipos which is nice.

I did find a 15C discharge graph for a "20C" Kokam. What was interesting is that it had about the exact same curve as a 15C graph of the TP Prolites. I think the TP cells would hold their own at 20C but TP chose not to label them as 20C. The TP 2000 cells may not look as good at 20C.

Also I found a thread where the latest Kokams and TPs are shown to have nearly identical energy density, if that's the right term... when a certain max temperature is considered. The Prolites are a lot lighter, but they will get hotter than a comparable Kokam which is heavier. By the time you increase the mah of the Prolites to get equal current and temps, the weight will be equal to a Kokam.

Now, the Prolites will have more capacity at this point. But it's interesting to see that they have identical "watt per gram" #'s basicly.

edit above list:
PQ 3700XP - 74amp - $90 200g
Tanic 3650 - 73amp - $93 200g
TP PL 4000 - 60amp - $95 175g (rated 12C but should be higher)
Kokam 3200 - 64amp - $82 200g

[tcolesen]

glassdoctor, you have brought up some very key pieces of information.

Kokam cells are considered very overrated by the airplane community, which is why they aren't brought up very often at all on RC Groups. Their price will also distract some people. IMO, the only application for the Kokam 3200 cells is for burst applications, which is what cars use. For me, though, I would never spend so much money on such a low capacity cell (like the airplane guys).

TPs will get hotter because they have less surface area to dissipate heat with. The nice thing is that they are capable of holding a high voltage. The Kokam's extra safety features like severe overcharge tolerance (up to 18v/cell :eek:) is where the extra weight comes in.

There are many factors to look at when comparing different LiPo cells. These include weight, capacity at .5C and 2C (to determine actual cell capacity), voltage at different C rates (based on actual C rate), temperature at different C rates, and burst rates (and the voltage the cells drop to). I realize, however, that this would get pretty complex for us *simple* car guys, but to do energy density comparisons aren't always valid when these other things aren't factored in when trying to determine cell performance.

[glassdoctor]

All true... it's a deep subject. That's why there are hundreds of threads about it on airplane forums.

The thread I mentioned above was about "lab testing" Kokam vs. TP Prolite cells for educational purposes. The calculations that showed nearly identical mass-to-watts ratio were interesting, but I also think they are badly flawed. The tread is about 600 posts long and I haven't followed it all the way. But I did read enough to see those #'s used are skewed, imo. and make the Kokam look better than it is.

They based the numbers on how many amps the battery could deliver while keeping the peak temperature under 140*F. The Kokam can dump it's load at very high "c" rates(20c)... without exceeding 140, while the Prolites will hit 140 at much lower "c" rates. The PROBLEM I found is that the kokams were only delivering half their capacity, and really bad voltage drop under these conditions. So even though they didn't "overheat", they really are unusable at those "c" rates anyway.

The Prolites delivered much higher capacity across the board, and although they get hot easier, they have a lot more energy and kill the Kokams given the same weight.

I pulled some numbers from their tests to see what all this means...

kokam 2100 179g = 1031watt/kg
27A current= 1800mah capacity, 6.79volts, 53*C

prolite 2100 95g = 1956watt/kg
27A current= 2060mah capacity, 6.76volts, 69*C

The prolite peaked at higher temp, but had better numbers otherwise at half the weight. And check this out...a Prolite 4000 pack weighs less than that kokam 2100. Guess how good the numbers would be at the same 27A current test? :eek: estimate based on graphs:

prolite 4000 175g =
@27A current= 3800 capacity, 55*C and volts should be right at 7.0

*see edit below about the kokams they tested*

Sorry for rambling... some might find it interesting.

Kokams have some strong points for sure, including the "safety" issues you mention... that they can tolerate some over/undercharge abuse.

Prolites still look the best to me.

Charlie from ThunderPower has hinted at possible new cells in the future that would be killer cells for us car guys. He said they were testing some large high-power cells... like 3000mah and bigger... and the size was car-friendly too.

Oh, one last comment on Kokams.. word is the 3200 20c cell is much better than the 2000 and 2100s used in the tests above. Sounds like the 3200 is very good, and would be a better match for TP and other new improved cells.

I think it's safe to say lipos will continue to improve...

[tcolesen]

I agree, the TPs are excellent batteries. BUT, they really need to come down in price! For me, weight is not so much of an issue as cost. I would rather buy something that would perform similarly to a TP but that would cost $30 less.

[glassdoctor]

The fire sale on the Polyquest packs sure looks good. Anyone buy some of these?

[Jev]

The fire sale on the Polyquest packs sure looks good. Anyone buy some of these?

For the money, this is a killer car pack, If I was running high voltages I would snap those up ;).
PX4S-2100 14.8 2100 15C (31.5A) N/A 228g 121 x 44 x 27 $75.95
www.rclipos.com

What we need is RCZONE to do a magazine artical comparing all the suitable sub'c replacement packs.

kokams 3200, tanic 3650's, tp4000 would make me happy. They could do the PQ 3700's too but would have trouble fitting them into most cars I think.

Rig up a pack tester with 50 amp continous discharge.

[glassdoctor]

I see maxamps.com has the TP 3200 packs. They aren't as cutting edge as the 2100 cells, but they are good enough. And they are sized like the Tanics, PQ, etc

TP3200 cell 130 x 45 x 6
So a 2s pack would be 12mm thick and 150g (5.2oz)

These would be great in 2s2p for cars... 6400mah, perfect fit and only 10.4oz.

How thick are the Tanic and Kokam cells?

[Jev]

If you was after runtime that would be a great solution, but at a high cost of $150, an extra 100g and no extra amps. More options has got to be better though. The fact that you can charge them at 6.4 amps might mean you could get away with less packs and keep costs down. Personaly it would always bug me that I was carrying 100g around in the car that I wasn't needing.

[Rtsbasic]

Where did you purchase your Tanic packs Jev?

[Jev]

Where did you purchase your Tanic packs Jev?

Tanicpacks.com

One thing I would say about the tanics. The wires are connected at the top and bottom of the pack at one end. As you can see in this picture. It's not been a problem for me as in my tc4 the wire is in one of the dips the sub's cell would of sat in. In the bike it makes no difference at all. If you had a flat chassis car it would be a bit akward.

http://us.a1.yahoofs.com/users/421a4c57zcb86101e/65e1/__sr_/4b00scd.jpg?phArhgDBB4l3EaKH

[glassdoctor]

I'm not sure the extra 100g is a bad thing.... for me at least. I race 1/10 offroad and we actually add weight to make our cars handle better most of the time. The lipos are so much lighter than nimhs that I wonder how the car will react.

A GP3300 pack weighs 400g so two of the Tanic 3650 or Kokam 3200 packs would be dead on for weight and the TP 6400 would be 100g less.

So how does a super light B4 really handle? Any serious racers here have experience with racing a buggy with a 5-7oz or less lipo?

With @ 6400mah lipo you only need one for racing.... since you probably only use @2500mah on average in a race, and you can charge at 6.4A. Turn around time would be really quick. With the Kokams you can charge at like 10 or 12 amps if your charger is capable. That would only take like 15 minutes to get the pack to +90% charged.

[OptimaMan]

When I used to race, being ultralight wasn't necessarily good. You had to have a totally different setup in terms of shock oil, springs, etc. which made it difficult to setup cuz I couldn't just copy somebody as a starting point. Once setup, the vehicle seemed much more aggressive, sharp, uh and quick etc. Generally better suited for even better drivers. I probably would get better lap times with a beater stock motor and 6 cells than 4slipo and the C4012s I was running. :)

With regards to 12, 15 or 20C. I think they're all here to stay. Different packs for different applications. For longer races, I'd take the higher energy density of 12C and for shorter races I'd take the 20C. For drag racing and 5 minute races, 20C. For enduro races, 20 minute races, bashing, I'd take the 12C. It's kind of nice to run until you're bored instead of running until the battery dumps.

[Jev]

When I used to race, being ultralight wasn't necessarily good. You had to have a totally different setup in terms of shock oil, springs, etc. which made it difficult to setup cuz I couldn't just copy somebody as a starting point. Once setup, the vehicle seemed much more aggressive, sharp, uh and quick etc. Generally better suited for even better drivers. I probably would get better lap times with a beater stock motor and 6 cells than 4slipo and the C4012s I was running. :)

With regards to 12, 15 or 20C. I think they're all here to stay. Different packs for different applications. For longer races, I'd take the higher energy density of 12C and for shorter races I'd take the 20C. For drag racing and 5 minute races, 20C. For enduro races, 20 minute races, bashing, I'd take the 12C. It's kind of nice to run until you're bored instead of running until the battery dumps.

As long as you set the car up to compensate, lighter will always be faster. There is another up side, if you crash you will do less damage. This is especialy important for the bikes because they have some of the most excruciating crashes I've seen.

The other thing to consider is the fact that the COG will be higher.