|
||
|
 |
|
||||||||||||||||||
|
#21
29-07-2008
|
||||
|
||||
I was worried as well at first whether 3200's would be sufficient, but after having run an entire race weekend with a single pack I must say I'm notworried at all anymore. 6 minutes on insanely grippy Astroturf with a 7.5 brushless pulled about 1200-1400mAh out of a pack in my B4.
They are well up to the task and didn't get hotter than 41°C at outside temperatures of 36°C. I have got rid of all my NiMh's and won't participate in races are not allowed! 
|
|
#22
29-07-2008
|
||||
|
||||
|
Quote:
Hi Codman, I understand that you trust your sources. I'll explain my own view point. Initially, the concept of Lipo on paper seems to good to be true and personally I won't be convinced by anything until I have proven it to myself. Around January/February Mark Christopher leant me a relatively well used 4900 stick pack which I used regular at Worksop. I was able to use one pack all day, without even balancing it, and my car was blisteringly quick - so much so that I had to go from a 5.5L to a 7.5R (Id have put an L in but I don't have one). The car is still verging on the too quick side of driveable. Around March/April I received a couple of packs of my own. I have been using the 3200 saddle in 2wd, the 3200 stick in 4wd and 4900 stick in truck. I have raced at many club meetings where I can use 1 pack of cells, and charge straight after race and contuously use. The most I have done is race 2 classes in a 7 heat schedule, both with Lipo and charging from 1 charger - I didn't miss a run and didn't once start a run with partially charged packs.  awesome.Recently at Belgium, I arrived on Thursday and proceeded to practice as regular as the speed of charging allowed with 3 classes, charging from 2 chargers and without a voltage cut off running them until I felt the punch drop (I WOULD NOT RECOMMEND THIS TO ANYONE, Please do use a Voltage cut off). I was able to do this over Thursday and Friday without any malfunctions or deterioration. Sunday I raced 2wd, and Saturday I raced 4wd and truck in a 7 heat schedule (bit of a rush getting pack straight on charger before marshalling). Furthermore, I was unable to balance charge on Sunday all day as somebody kindly removed my balancer from the pits. (  stolen  ) But I have managed all this, with 1 pack per car, no performance drop off, no cell faults, and am now convinced enough to propose Lipo to BRCA (which I did the week after the Belgium GP). From experience, I highly recommend trakpower Lipo. For similar performance to cells choose a 3200mah 20C pack. For anything more powerful you certainly will need to motor down.  Chris
|
|
#23
29-07-2008
|
||||
|
||||
|
Quote:
__________________
MBModels - Schumacher Racing - Vapextech.co.uk - MRT - Savox - SMD
|
|
#24
29-07-2008
|
||||
|
||||
|
Quote:
I'm so glad I didn't p::s away £££s on 5/6 packs of lame NIMH cells when I decided to get back into the hobby. it was pure luck that I stumbled upon some forums with real-world lipo experiences, just like in this thread. i've now gone a bit nuts and bought 4x trakpower 3200 saddle packs. but I could have easily gotten away with 2. we will look back on nimhs in a year or so and just laugh.... all this 'factory matched zapped' nonsense, up to £70 quid a pack, the soldering, the maintenance, the balance trays, the crazy heat after runs, the memory effect, the weight - utter crazyness.
|
|
#25
29-07-2008
|
||||
|
||||
|
After seeing other's trakpowers and getting feedback on here, I also took the plunge and went lipo.
They came off cold to the touch after 5 minutes racing last week, although I struggled to get the power down. I bought the 4800 saddles & 4900 stick and they have stupid levels of punch, if I hit full throttle in my B4 it just flips onto it's roof and that's with a 7.5.  I also have an Orion Platinum 4800 stick, even though that's 'only' 15c it's not much different to my trakpowers. Wish I'd bought them earlier, have just bought a 10.5 to try and get some steering back 
|
|
#26
31-07-2008
|
|||
|
|||
|
No problem guys. It clearly seems that you guys are getting the power you desire from those packs and that they are running cool (having no problems delivering). That's what's important!
I must admit, I was a bit surprised since I've read of several people (and as I've said seen first hand) using similar packs with similar motors, but the packs getting quite warm (to very hot). And as far as I get it (once again from what manufacturers have told me) that is a sign the packs are dishing out power near their limits (motors are demanding a lot) and is not good for the longevity of the packs.Also, and please correct me if I'm wrong, if a motor is "punchier" or "more powerfull" when using a higher capacity pack, isn't that a sign that the initial pack is/was holding it back from it's full capacity? Wouldn't it be better to have a better pack with a slower motor where you are getting it's full potential and not overstraining your batteries? In such a case, choosing a lower capacity pack to tone down a powerfull motor would be kind of like adding a slipper clutch and seems counter-intuitive to me. No? Anyways, as I said if it's working for you that's all that matters! On my side my 5500 mah packs are doing the job well with my 6900kv motor and I agree that there only seems to be advantages to this new technology in packs! God bless the Lipo!!!Oh and by the way, for a racer from accross the pond, I'd love to get a chance to race on a "Brit" style track like you have! The differences in track design and texture would be a really interesting experience for someone like me who has only raced on dirt before! I kept telling my local track, while they were building it, that it would be cool to haev a short grass section, just for a change in traction on the track! It would have been quite a challenge! Cheers everyone! Your friendly CODMAN
|
|
#27
31-07-2008
|
||||
|
||||
|
Quote:
Running 3200 20C Lipo with a 5.5R motor in a weighted up car, the car will be marginally quicker than a car with new Nimhs in. But you still won't need or use all the power available all of the time. The packs come off cool, no warmer than teppid..... is that a word? they'd get hotter left in direct sunlight anyway. Chris
|
|
#28
31-07-2008
|
||||
|
||||
|
Quote:
Quote:
I wonder whether these guys you know who are getting their cells that hot are either charging them correctly, discharging them too low or could it even be gearing issues?
|
|
#29
31-07-2008
|
|||
|
|||
|
Quote
'Oh and by the way, for a racer from accross the pond, I'd love to get a chance to race on a "Brit" style track like you have! The differences in track design and texture would be a really interesting experience for someone like me who has only raced on dirt before! I kept telling my local track, while they were building it, that it would be cool to haev a short grass section, just for a change in traction on the track! It would have been quite a challenge!' A by the same token, a lot of us Brits would like to try racing on your North American/Canadian style tracks. Truly a case of the grass (or dirt) being green on the other side.
|
|
#30
31-07-2008
|
|||
|
|||
|
Quote:
Honnestly, I'm pretty sure the over heating wasn't a case of poor charging since they're all using balance chargers... As for over gearing, that could be possible for some... But not all. Some I know are geared conservatively and watch out for running temps religiously (at least on their motor and ESC). Maybe the quality of their packs? Other than that, all I can think of is their motors are pulling too much current, too often, which is nearing the limits of the packs they are using. This I've been told (by manufacturers) is a definite cause for overheating and the main reason it's important to make sure the C rating of your packs combined with the capacity they have can dish out more than what is needed by the motor. But this is all heresay for me. As I've said, my packs are running nice and cool and have no problem dishing out the amps my motors need. And obviously, so are your 3200s!!! Thanks to everybody for giving your constructive detailed input to this! I've learned a lot, especially that I still have a lot to learn about these!  Cheers! CODMAN
|
|
#32
31-07-2008
|
||||
|
||||
|
Quote:
i.e. 10C 3200mah pack = 32amps 10C 5000mah pack = 50amps 10C 9000mah pack (unlikely) = 90amps
|
|
#34
31-07-2008
|
||||
|
||||
|
OK, so that is 40amp continuous.
I am using 3200mah 20C which is 62amp and slightly better than best Nimhs. So id suggest the 10C 4000mah is not enough, unless you are running mild motors. I can only estimate this, as I don't have experience of anything less than 64amp.
|
|
#35
31-07-2008
|
||||
|
||||
|
I'm glad I changed my mind about them, I went for the 4800 20c instead.
(Although my orion 4800 is 15c, so what's that continuous?) But, the fact that they are out there and being sold for use in RC Cars makes you wonder. Codman, looking at these calculations could that explain the heated cells you've seen?
|
|
#36
01-08-2008
|
|||
|
|||
|
Quote:
Well Peet, that's pretty much what I was arguing at the begining of my post. From what I had heard/read, the more powerfull motors could pull quite high amps at times, creating quite a strain even on a 20C 3200 mah Lipo (which can sustain 20c x 3.2 amps = 64 amps continuous). The data I saw was claiming quite high current demands at times which could strain a lower capacity battery and create overheating (and possibly even reducing the motors performance). But as I said, I've only read/ heard about this and haven't taken measurements of my own to back the numbers (don't have a logger of my own). Add to this, that most of you have been runing powerfull motors on these packs while they remain cool. This definetly would suggest, as Chris and others pointed out, that the real current strain is well within the capacity of the Trackpower packs 64 amps... So maybe the numbers I was reading about where wrong and there were other reasons for the heating of the packs? I honnestly haven't got a clue! Maybe the packs I've seen that were warm were poor quality and their C rating was overestimated???All I know is that my 5500 mah packs, which are only rated to 15C, should be able to dish out 82 amps continuous. And they gave me more than 12 minutes (I stopped counting) of practice using a mamba max 6900kv setup while remaining nice and cool to the touch. So I'm happy! And my Lipos are happy... I'm not sure that having chosen a smaller capacity pack, with the same C rating, would have given me the same thing. Cheers! CODMAN
|
|
#37
01-08-2008
|
||||
|
||||
|
Quote:
Just another perspective of it that I have been thinking about: A car will never run at such high ampage continuous. A motor under load will drain at (I estimate) no more than 20amps on average over a 5-6 minute race. i.e. If I discharge a pack of cells of any type at 20 amp continuous on my discharger, it doesn't take that long - so the motor will drain at that or less on average. (it should, in theory). So all the C ratings mentioned above are fine, on paper. But we all know, that the 20amp average above can range from 5amp through to 50amp depending on what the car is doing at any one time. Plotted on a graph it would look like the landscape of the alps. So the cells have got to be able to withstand the peaks - but they'll only be short bursts. My 3200mah 20C do that fine (64 amps).
|
|
#38
01-08-2008
|
||||
|
||||
|
Quote:
__________________
MBModels - Schumacher Racing - Vapextech.co.uk - MRT - Savox - SMD
|
|
#39
01-08-2008
|
|||
|
|||
|
If you were to dump a 4900mah pack in 6 minutes, you would be pulling 49 amps average.
On average I put about 1500mah in 2wd and 2200mah in 4wd back into my nimh's after a run, so thats 15amps and 22amps average consumption assuming the car is running for 6 minutes (warm-up lap ect). Saying that though the cars must pull significantly higher currents when accelerating hard, as I borrowed 3200 and 4900 (not sure of the C rating of each pack, but the 4900 was higher) lipo's from Jimmy at Southport recently and the 4900 had a lot more punch - even in a 2wd with a 7.5. As for them overheating, I wouldn't worry about it
|
|
#40
01-08-2008
|
||||
|
||||
|
Quote:
Now, if lipo sellers are being as creative with their labelling on their cheap lipos for the C rating!! Best stick with the decent makes I think.Sounds like you've got a decent pack though, what make is it?
|
 |
|
|
I sincerely do appreciate constructive explanations of why not all that is correct/ exact along with "over pond" hands on experience! There is a lot of good info on this forum and I enjoy soaking it up immensely! But I tend to not throw out my oppinions lightly. Good reasoning and credible explanations will always bring me around to changing my views on things (which is why I often invite people to correct me and explain why I'm wrong). But the classic "I use it and it works" just isn't "mind changing" material for me in general...
Linear Mode
