I am getting ready to do a little testing and experimenting with LiPo batteries and brushless motors. My goal is to be able to have at least 20 minutes of run time at "modified" speeds... ideally it will be 30 minutes. This would put electric racing in the same class as the vast majority of nitro racing done at the local level.

For these tests I will be using my Associated T4, a Novak 5800 motor and two Poly-Quest 4400 LiPo packs wired in parallel... that will give me 8800mAh of battery. I know the Novak 5800 motor will be less powerful then a nitro engine but I already have one so it's a good place to start. Once we figure out how much run time this setup gives us, we can adjust from there.

The two Poly-Quest batteries stacked on top of each other are about 1/4 thicker then a normal NiMh pack. This will require a custom battery strap to be constructed. It shouldn't be hard to do and if easily done I will get additional straps made for anyone that may want to do the same thing.

Once I get the packs I'll post some pics and updates as we get into it.

I've got zero experiance in Nitro racing... be it off road or on road... and I've also got zero experiance with LiPo use in RC... So, if I don't understand some fundimental thing, please enlighten me...

Anyway... My understanding is that Nitro guys have to re-fuel to run for 30 minutes.. is that correct? If so, then couldn't a racer who wants to run electric have a quick change battery that might help a racer with say NiMh cells run for 30 minutes with a few packs charged and ready to run?

I guess the reason I ask the above is... LiPo seems very impractical for a few differnt reasons... Primarly is the expense of the packs to start with... If I'm not mistaken, Hank is proposing using two $95 packs to get one 30 minute run... You could get nearly the same run time out of two 3600 packs, but clearly could get even more time from three... I think it's failry safe to assume you could buy 3 reasonably good quality 3600mAh NiMh packs for $190... (perticularly if they were these new IBC packs, since they are realtively cheap and suposedly of pretty good quality)...So, in some ways the up front costs are not that differnt but what really concerns me about LiPo is there proformance drop over time... Apparently LiPo packs have a natural and farily significant voltage drop with many charges over time... At high discharge rates they can loose maybe 8% of their voltage in just 100 cycles and drop by nearly 20% in 500 cycles... I could be wrong, but I don't think we see anywhere near this kind of voltage loss with NiMH or did we with NiCd packs.

So... It makes me wonder, just how practicle is the use of LiPo cells in RC racing... Now, in off road, maybe you won't notice the loss of voltage so much... but I would think that in road racing where traction is good, the voltage loss of LiPo packs over time would have racers buying new packs very frequently in a effort to maintain the highest voltage they could get... this sounds very expensive.

So, while I see the fun in testing and/or playing with LiPo packs for things like Hank is doing... but just how practicle is it really? Are there alternitives, such as the changing of packs like I suggest?

I personally think that LiPo is going to be the next big thing in battery technology for R/C cars. They have been using them for R/C airplanes for years. (as well as brushless motors). I don't know if the voltage loss will be a big deal or not. That is a "time will tell thing". But, they start out with higher voltage - a 2 cell LiPo pack 7.4 volts. They weigh roughly half that of a sub-c pack. Runtime is reportedly up to 5 times that of 3300's.
I don't think they are really that expensive. It seems to me that I saw an ad where you could get a 3000mah pack and the special charger for about $100. And if the runtime issue proves true than you may only need a couple packs for a day of racing.

THE DOWN SIDE -
- They are dangerous in the hands of someone who is... let's say somewhat undisciplined in common sense. They catch fire/explode without the proper safety precautions when charging and discharging.
- It takes upwards of 90 minutes to charge. Not really a bad thing if you plan properly for race day.

******
Like brushless, I believe race organizers would have to have a special class for vehicles with batterys that weigh half that of sub-c's. That would be a very significant weight advantage.

At the Michigan State Carpet Oval Championship in Lansing a couple weeks ago the Truck classes had a weight rule of 60 oz. I had to add 6 oz. to my truck. With LiPo's I would have to add about a pound!

As far as running with Nitro guys goes.... I don't think you can change batteries as fast as they can refuel. They usually have access to the tank from outside the body. They just pull on a zip-tie attached to the tank stopper and squirt some fuel in.
They probably rival Nextel Cup pitstops minus tire changes! LOL!!

Dyno... that is what I am trying to find out. Anyways, with any quick change system for packs it's not really suited for everyday use... besides buying the quick change modification (chassis and battery holders) will add quite a bit to the cost of the vehicle.

I think part of the bad rap that LiPo's were getting was from older cells that really couldn't handle the high discharge rates like the newer cells. The 4400 cells are rated from the factory at 12C or 65 amp constant discharge rate... when was the last time we have seen a NiMh rated at that high of a rate?

I also think the price will come down as production ramps up. This is all very new technology so it is fairly expensive. In theory, if races are held to 5 minutes, you could use one pack changed one time for the day and run for the whole day.

Yes, nitro refueling stops take about 5 seconds. But if I can run 30 minutes on a single pack then I could run a complete normal "main" event without stopping while the nitro trucks will have to stop 5 times to refuel.

Anyways, this all just to see what this new technology is all about. Just like brushless motors, it took a couple years for it to really come into it's own. I suspect that in a year or two LiPo will be where brushless is now.

Down south here there has been several guys running what is now called Pro Truck. The 2005 Carolina Points Chase has included these guys in with the nitro gas trucks.

They are running 8400 mah LiPo packs, not sure who's running what motor, they are different, but they are capable of running between 20-25 minutes on a pack. From what we discussed this week, pushing them much farther than that is risky. They will go thermal. These guys are very much equal in speed to the nitro trucks.

Cost for these packs was quoted around $190. But you could run NimH in the heats and save the LiPo for the mains. You will also require a charger that is specifically designed to handle LiPo packs as well.

You do need to be careful, they are a little bit more volatile than any other batteries we run.

Hank, if want a bunch of info on the subject, go to www.carolinasrc.com forum board and look up a guy that goes by the handle CRAPS. He's been at this for more than a year now. Probably has more knowlegde on Lipo/brushless than anyone I know.

OvalTrucker... I've yet to see any LiPo packs that are 5 times the capacity of 3300mAh NiMH packs... They would have to be 16500mAh capacity since this is rated the same regardless of battery construction material. That is 3300mAh is the same run time wether it is NiCd, NiMH, or LiPo...

I can see advantage to the cells being lighter... (and I'm sure that's why the plane guys like them)... but I'm not sure there is any other advantage to using LiPo. Given that we do have minimum weight rules in RC cars... lighter batteries would only mean you could move ballest weight around to more strategic locations, unless of course weight restrictions were lowered along with any aproval of LiPo cells...

Based on the info that this forum's sponser PureHobby has on their LiPo cells... the dicharge curve of a Lipo pack is not that much differnt then a NiMh pack would have. That is, the voltage drops as the pack gets further discharged, so I don't think your going to be able to run a full days worth of 5 minute heats on one charge, unless you can put up with having lower and lower voltage though out the day... So I don't see this that as a option...

I have heard from my uncle-in-law who's into planes and operates a wholesale RC business(mostly planes) out of Taiwan, that the top level flyers are constantly using new cells to keep the preformance levels up... Now just how much differnt this is from what we tend to see with RC cars and NiMH, I don't really know, because clearly top level RC car racers also get new packs quite freqently.

Here is the PureHobby spec page presumably for the cells they are currently selling... notice also the voltage over number of cycles data as well as the dischrge curves and take note that they are differnt depending on how much current your pulling out of them...

http://www.purehobby.com/polyquest%20lithium%20polymer%20common%20Specifica tions.htm

That is an interesting throught... just how many times do we use our NiMh packs before we replace them. I bought new packs last year. I went to 5 MARS races and 3 local races last summer. During practice I used old practice packs for the most part and used my 4 "new" packs for racing.

My normal race day starts by running my practice packs in practice. This is to make sure my setup is pretty close. Once I'm sure my setup is decent I'll switch to a "good" pack for a last practice or two. The difference in power between my practice packs and my good packs makes a difference in how I have to take jumps and rythem sections.

So lets say each race day I used each new pack three times... that would equal 12 total runs per day (2 classes, 3 heats and a main + practice)... that's about about right for 2 classes including practice.

So over 8 race days with three runs per pack, I used each of my "new" packs 24 times. Know what? I'm buying new packs this year. I might be able to get away with last years packs but I'm not taking a chance. My guess is that the difference between a LiPo pack rated at 500 cycles and a NiMh pack rated at 1000 cycles don't mean squat. We stop using them long before we ever get to that point.

If we compare costs, those 4 NiMh packs cost about $260 street price. If (and that is a big IF as I don't know) we can get away with 2 (or even 3) LiPo packs the price is very comparable ($260 compared with $275 for 3 LiPo packs).

On the weight... my truck, even with graphite, is still about 4 oz heavy running NiMh packs... I could benefit from the lower weight of the LiPo packs.

On the discharge curves... it is the same with NiMH packs too. Below is an example comparing curves at 19 amps and 40 amps. While this is data from when we ran 2400 packs (I don't have data from 3300) we can suspect the same issues are there.
http://www.hobbytalk.com/images/sections/s2401bas.gif

On cost... lets take the price of a 3300 pack and increase the cost 1/3 to match the 1/3 more capacity the LiPo has... that $70 NiMh pack now becomes $91... comparable to the price of a LiPo pack. It has been a few years since racing was increased to 5 minutes... the higher capacity could allow for 6, 7 or even 8 minute races.... BUT, once we start increasing the race time it becomes very hard on brushed motors.

From what I can see just by looking at numbers (as I haven't had any real world experence with them yet) is that for racers, the cost performance ratio is just about break even. The problems are the unknowns with the main reason being durability and there is no way to find out unless we try them. We have to remember, NiMh cells were not very durable when they first came out... now we wouldn't think of going back to NiCd (and we heard many of the same arguements ;) ).

Now Craig....I taught Craps everything he knows (LOL)!

GP3300s have been known to start degrading after only 25 cycles. You have to deal with memory retention and cycling as well. More cells to get the voltage also leads to more resistance. One of the big benefits to lipoly is the punch you get. You can run the same pack all day and keep topping it off between heats. About the only downside is packaging. Lithium Ion hard cased cells may prove to regain popularity with new built in safety circuits, especially as they are introduced to the power tool market this year........which brings to mind the best benefit of all to me. Every grab that electric screwdriver to find the battery died while it was sitting in the toolbox for a month? That's the reason I use corded tools. With lipoly, self discharge is extremely low meaning you can turn around and use that screwdriver one year later and the battery still have most of its charge.

Can't lipoly packs explode or catch fire if they are dented? A crash and burn could be kinda cool, LOL

Every grab that electric screwdriver to find the battery died while it was sitting in the toolbox for a month? That's the reason I use corded tools. With lipoly, self discharge is extremely low meaning you can turn around and use that screwdriver one year later and the battery still have most of its charge.

I have a craftsman drill with a NiCad pack that hasn't been charged in over a year I just used to drill a hole the other day. However if I dont use my laptop (with lipoly) in a month the battery is dead, go figure.

Strange......my black and decker won't hold a charge for a week. Explosions and fire are overated. The pack has to be really charged up and punctured for the contents to mix with oxygen. Dented a few with no ill effects. Exploded some for the sake of experimentation......but never not intentionally.

STARLUCKRC: Sorry man for not giving credit where credit was due. Geez I thougth CRAPS invented Lipo's. LOL

Yeah Hank, I realise that we often replace NiMh packs with far less then a hundered cycles on them. I also don't know for sure how much NiMh does degrade over a period of cycles. I'm partialy just playing devil's advocate with regard to this issue, but then I do also have real concerns about it and other issues.

Typicaly I only race indoors in the winter and for about 6 months a year, charge a pack no more then twice in a week... This would put me at about 48 cycles per pack with maybe 3 race packs total in my pit box. I pretty much do replace my race packs once a year... but then this year my new packs actualy are no better then my year old packs, this must have something to do with a new generation of cell that in my opion isn't quite as good as the previous generation for my needs.However, I am also pretty sure my year old packs haven't lost 4% of their original voltage, which LiPo packs used this many times apparently would have.

I have heard that there are better packs then the new ones I have, but I already spent my wad of cash on those packs and don't really have the luxury of buying another pack or two of new ones to see if they are any better then my year old packs... All these issues are probably going to still be there with LiPo however...

So for me, in many ways it comes down to not wanting to be the first to jump on a band waggon that may never get anywhere... but also in wanting to be sure those that do play with that new wagon to consider both the good points and bad points of the new wagon...

I also question what it would take for a orginization like ROAR to allow the use of LiPo. While many of us have personal concerns about the saftey issues involved with LiPo, ROAR would really have to be concerned. I do have concerns about saftey, and while they may not be as bad as what I think they could be, they clearly have more saftey issues then our current batteries do. Now I'm a very capable guy when it comes to electronics and such, I mean it is my profession, so I'm not concerned for my own safe use of these things... however many of the people in this hobby are childern... and well we all were kids once so we know how stupid a kid can be... This leads me to my opinion that is... I belive ROAR or simmilar orginization would almost have to demand that any legal LiPo cells would have to have built in safety protection of some sort. I think at a minimum a pack would have to have a built in shutdown mechinism that would prevent it from being discharge so far that it would catch on fire. I don't think ROAR would ever aprove such a power source that could catch on fire if someone could accedently discharge it too a point that it would catch fire... I could be wrong, but I just don't think they'd want to get into that kind of a saftey issue for racing that they sanction.

Obviously the use of LiPo in power tools would also require extremely safe packs as well... so maybe if the power tools do start using LiPo, they may also drive saftey aspects as well and maybe the saftey issues will soon be a thing of the past.

Can't lipoly packs explode or catch fire if they are dented? A crash and burn could be kinda cool, LOL

I have dented my packs, (not majorly) but this is why you need to make sure there in a safe protective area.. not dangling off the back of the car.

As far as fire, I saw a NiCd powered car short and catch fire.

And kids racing Lipo. Only if they have a parent or responsible guardian present. Tracks are not nurseries, parents that just drop kids off for someone else to take care of at the track are ____________ (fill in the blank with the adjective of your choice)

how many cell phone fires do you know of?? Most newer quality phones are powered by li-poly batterys. remember you keep you phone in you your pocket and does it cach fire?? NO!

how many cell phone fires do you know of?? Most newer quality phones are powered by li-poly batterys. remember you keep you phone in you your pocket and does it cach fire?? NO!

Well for one peoples cell phones are not raced against each other, therefore they are not banged up against a wall at 40 mph, they have a minimal discharge load and minimal charge current.

And yes cell phones have been known to explode when people are using them, do a google search.

I'm here!!!!

Jamie and Craig has been talking about me and I had to make the trip!

As they have told you, I have been testing and racing li-pos and brushless motors for about 1 1/2 years. I don't even own a set of nickel batteries except what is in my TX. I have used 8000 and 6000 mah Thunder Power batteries until last weekend when Jamie sent me 2 PolyQuest 4400 mah 7.5 volt li-pos I hooked together to get 8800 mahs. In the T-4 you will need to get longer battery bar screws and raise it up a little for both batteries. The PolyQuest fills up the entire tray and has pads built in them. The Thunder Power TP8000-2S4P needs 3 pads in front and at least 1 pad in the rear to protect wires in the rear of the battery pack.

I am currently using the best motor/esc combination I have found to date for the 2wd 1/10th scale T-4 stadium truck that is the one Jamie sells. The Schulze U-Force 75 esc and the Plettenberg Extreme motor. This is the smoothest throttle control with a huge amounts of torque and top end to push a gas truck down the straight a way.

I have tested numerous battery, motor and ESC configurations. From Thunder Power I have tested 7.4 volt and 11.1 volt packs to also pairing up 2 11.1 volt packs for 22.2 volts in my electric 1/8th scale project I don't have anymore due to maintence issues. From Hacker Master Comp to the Schulze 18.61, 40.160 and U-Force 75 ESCs. From Hacker C40 8 turn and C50 10XL motors to the Lehner 4200 and 5300 motors to the Feigao 540 7 turn motor and my favorite 4 pole brushless motors the Plettenberg Extreme and Shadow.

Feel free to ask questions about race track testing, but I will have to leave the real technical questions to my mentor Jamie at www.starluckrc.com

Thanks for the info. I'm using the Novak 5800 because I already have one. With my limited driving skills ;) I think it will provide more then enough power. I also am looking into molding some custom battery staps for the T4, T3 and XXX-T once I get my packs and see what is needed.

The T-4 Pro Truck racers either get longer screws with the holes in the top for the clip to raise the battery bar up or they put longer screws with big washers to hold down the battery bar, but this is not a fast way to take out battery that really doesn't matter anyway.

The XXX-T racers go to the local hobby shop and get a brass strip like the airplane guys use that is the width of the Losi battery bar and bend it to go over the top of the battery with some pading attached to it.

These will work with both the Thunder Power TP8000-2S4P and the hooking together of the 2 PolyQuest 2S 4400 mah batteries stacked together.

Pro Truck 20 minute mains!

Argggg.... I got the cells today and they will not lay flat in the T4s chassis. The specs say the packs are 49mm wide but mine are 51mm at the widest point. If they were 49mm they most likely would have layed flat in the chassis.

Craps... how are you guys mounting the PolyQuest 4400 cells in your chassis?

That is the padding in the ends and it is a tight fit that is good. Don't ever use the wires to pull it out of the tray. The actual cell is a little narrower than the padding on both ends.

You'll love the run time and performance of the 2 4400 mah li-po batteries together.

I raced mine Sunday and loved the punch they had!

The lenght isn't the problem, they are too wide to fit in the battery tray.

Welcome to the forum Tim. Glad to have the race experience aboard.

OvalTrucker... I've yet to see any LiPo packs that are 5 times the capacity of 3300mAh NiMH packs... They would have to be 16500mAh capacity since this is rated the same regardless of battery construction material. That is 3300mAh is the same run time wether it is NiCd, NiMH, or LiPo...


I didn't say capacity. I said runtime.
I have read of instances where people are getting enormous runtimes out of LiPo packs of the same capacity of NiMH's. That's all I am saying.

scott

The lenght isn't the problem, they are too wide to fit in the battery tray.

They are tight fit on the width and you may need to force them on the padded ends, but they will fit and they are not as fragile as the internet rumor mill has made them out. They are pretty tough batteries as long as you follow the manufacturers instructions to handling and charging them. Please use the correct charger for them.

Note: Do not use the MRC 969 Smart Brain charger no matter what anybody has read about them. The charging method MRC recommends is using alot of questimating of discharging and charging used a measured charge you set yourself.

Astro Flight 109 is the preffered charger, the Duratrax ICE is good along with Schulze chargers and the Triton charger. With big batteries of 8000+ mahs you need a charger that will charge at 8 amps or it will take alot longer to charge. 8000 mahs at 8 amps will take around 1 hour to 1 1/4 hour to peak charge, where a 4 amp charger will take twice as long. The manufacturers recommend to charge at 1C rate of the battery, example: 8000 mahs = 8 amps or 4400 mahs = 4.4 amps the 1C rating.

It isn't the ends that are the problem but the width along the whole side of them. I would have to force them in so hard that I would be afraid of breaking the chassis. Yes, it is that tight. I have removed the shrink from one of the packs and it looks like if I replace the 12g wire with 14g wire that will reduce the width enough to fit.

Scott...

If people are getting longer run times out of Lipo then they are out of NiMH packs with the same capacity, then there are only a couple logical explinations... one is that the packs capacity isn't measured the same way and/or is differnt in some way regardless of the lables say... or the vehicles using the lipo packs are not consuming as much current as they do with the other batteries...

One reason could be that the LiPo batteries have far less IR then NiMh packs. According to the review in RC Driver magazine, when they used LiPo pack there was so much punch that they really had to change their driving style to compensate... they explained it as massive wheel spin.

This would mean two things (at least). One is the batteries are much more efficient so there is less loss to heat. Second is that since you have be easier on the throttle it naturally uses less battery.

Now, I'm not sure how much this adds up to... one of my tests will be to compare run time between LiPo and NiMh packs.

I don't think you have the same packs I do, because the PolyQuest 4400s Jamie sent me are just slightly narrower (1 MM) than the Thunder Power TP8000-2S4P we have been using. The TP and PQ are both tight fits which is good, because you don't want that battery to come out. Maybe use the dremel with a sanding wheel to polish the sides of the battery tray and make more room?

I have not put the PQs in a XXX-T yet, but it is the same as a T-4 on the width of the tray?

Scott...

If people are getting longer run times out of Lipo then they are out of NiMH packs with the same capacity, then there are only a couple logical explinations... one is that the packs capacity isn't measured the same way and/or is differnt in some way regardless of the lables say... or the vehicles using the lipo packs are not consuming as much current as they do with the other batteries...

Where is this coming from about packs the of the same capacity?

I thought it is about comparing 8000+ mah li-pos to 3300 mah Ni-Mh batteries that is close to 2 1/2 times the capacity.

After a 20 minute race, my 8000 mah li-po is mildly warm versus 3300 Ni-Mh batteries are hot after a 5 minute race.

What is really neat is the TP8000 li-po is 5 ozs lighter than most 6 cell Ni-Mh packs!

What size wire do your packs have? Mine have 12g wire and I am thinking that some of the packs may have 14g wire... I believe that would be enough to make a difference. My packs measure 51mm down the sides and the specs for them say 49mm. Can't polish down the sides of the tray as they won't really fit between the bosses that hold the screws for the hold down.

I'll take a few pics and post them before I take the shrink off of the second pack I have.

Sounds like your packs are bigger than mine from some manufacturing error or something that has them wider than 49mm. The TPs are 50mm and fit tighter than the PQs.

Be a good question for the supplier or manufacturer? I would let them know! Maybe Jamie or somebody from Pure Hobby can find out or explain why they are wider than speced?

I'm attaching a couple of pics. One is a top down view and you can see the battery barely fits between the clamp hold down screw heads much less fit in the tray.

The second picture is of the pack with one side laying down in the tray with the other side already hard against the boss that holds the clamp screw. Further pushing of the pack into place would really crush the pack.

Hope the pictures are clear enough to understand what I have.

Factory used a Fat 12g wire where on the last batch i think it was 14g which may have been what Craps received. I pulled the 12g off mine and went with 14g. The other problem on the T3 anyways is with the wiring still coming out the side of the circuit board it will not fit so I am going to rewire coming off the top of the pack no wiring out the side.

Wow! 2 thicker size wires makes the packs 2 mm larger and not being able to fit.

Well did the packs fit in the trays after the wires were downsized to 14g wire?

Does this mess up any kind of warranty the batteries have by cutting open the packs?

I know Thunder Power has done a 50% off swap of upgrading batteries to newer Generations of batteries or if you over discharge one. My Electric 1/8th scale was rough on the TP batteries.

I had to order in some 14g wire and "pack" shrink wrap as I don't have any. Won't know until I get it in.

Craps... my comments about run time and/or capacity go back to one of the first few posts... Scott and I were having a sidebar sort of discussion about the differances between LiPo and NiMH... Early on Scott had said LiPo users were reportedly getting up to five times the run time of NiMH users... But anyway...


How much is a 8000mAh lipo pack, and where do you get them? What's the cost per mAh and how's that compare to NiMH packs? etc...

I hope to work on it tonight and I will let you know what I find.

As for Hank having to cut open the packs he has my ok on warranty. Hopefully future production of the 2s 4400mah packs will go back to the maximum of 49mm width so this is not an issue.

Robert
www.purehobby.com

How much is a 8000mAh lipo pack, and where do you get them? What's the cost per mAh and how's that compare to NiMH packs? etc...

I don't even own a Ni-Mh pack to compare, but maybe the thread sponsor "Pure Hobby" can answer the questions about cost comparision or maybe even Jamie with Starluck can jump in, but if you are considering cost per mah, you better consider runtime times cycles of both brands and you will see you will get 18 times more useage out of the Li-pos (300+ cycles)versuses the Ni-mh (50 cycles) batteries. In the long run you are alot cheaper with li-pos than Ni-Mh and the FUN Factor that is the most important thing to me is so much greater than chasing the old battery charger swap out of batteries every 5 to 10 minutes.

It is bad when the gas truck guys envy your truck for run times and not having to stand down by the track all the time with the bottle of fuel, screw driver, glow plug ignitor, starter box and temp gun constantly checking or re-cranking the truck when you just run on and on and on and on.....

Life is GOOD!!!

Other questions... What's the standard charge rate for LiPo packs? (that is how long does it take to charge a 8000mAh pack?) Are there any problems with charging them multiple times per day/week, etc?(If so, please describe what the issues are...) Do you have to wait for them to cool before re-charging? etc...

Where did the figure of 50 cycle life span of a NiMH come from?

Dyno, Info from the web on cost... we have to remember that LiPo tech is a new tech and that most likely the price will drop as production numbers increase.

SMC GP3300 packs from Tower Hobbies for $70 = $0.0212 per mAh
PolyQuest 4400 packs from Pure Hobby for $96 = $0.0218 per mAh
That would mean the costs per mAh are almost exactly the same.

The 50 cycle life for NiMh comes from me. That is how many times I used mine last year and I am buying new packs this year.... I can tell the difference in the new packs. It's pretty well known that GP packs start to drop off pretty quickly (at about 25 runs or so).

Standard charge rates for LiPo's is 1C (4.4 amps on a 4400 pack - 8.8 amps on a 8800 pack) so a full charge should take somewhere around 1 hour. Two things I have read is that there is a very low self discharge rate so you could charge the day before you race... no need to discharge after a race so you just repeak them and use them again. Because of the very low IR, they don't get anywhere near as hot as NiMh during use. Also I have read, if you charge to 90% you can't tell a performance difference on the track.

Now, with that said, there is not a ton of testing done. I don't think anyone is "matching" LiPo packs yet and they haven't been used in serious competition so we don't have any data yet like we do on NiMh packs (such as the effects on using more then once day, storage, etc.).

There are several of us Pro Truck racers that use the same battery all day long at the race track. Just re peak it every time you run. Sort of like topping off the fuel tank while you make changes to the truck. I hook it up right off the race track on to the charger. Even after a 5 minute qualifier I hook up the battery to the charger while I go turn marshal and it is almost peaked by the time I get through TMing the next race after I raced.

After 20 minutes of hard racing, the battery is mildly warm. So battery heat with li-pos is not a concern for at least the 8000+ mah ones.

I have used batteries that were a year old until I traded them in for the newer Gen 2 ones TP offered me.

Great batteries!

So are the 8000+ mAh packs Craps is speaking of really that much capacity, or are these two 4000+ packs in paralell?

If you can top off LiPo packs and still get voltage like you get with a pack that had been charged from near zero, then that is indeed a good thing.

Yeah Hank, I looked up the pricing on the packs your using and I see the cost per mAh is very simmilar to a high grade 3300mAh NiMH pack.. I guess it's just sticker shock that gets me, when I see $95.95 for a single 4400mAH pack... I'm used to buying 4 cell NiMH packs for about $40... The thought of buying two packs for $96 each, and having to run two at the same time is kinda scary still. It'd sure be a bummer to have something happend where you'd have to replace a pack unexpectedly during a season do to damage or whatever... It's also still kinda scary to think that this is indeed still developing technology, and what may be top of the line today, could be a mediocre pack tomorrow.

Bottom line is that this is interesting stuff, but I don't see it putting an end to replacing packs every season or more often to stay on top. You off road guys have it made in this area, loosing a few underdths of a volt is not that big of a deal... Us carpet oval guys like to have every extra 100th of a volt we can get, but then we only buy 4 cell packs, insted of 6 cells so are packs are cheaper... but then if we should ever go LiPo, we're either going to have to go down in voltage or up... Not sure going down to 3.7 volts would be doable, since ESC's and such tend to want at least 4.8 volts...

I don't think anyone has claimed it will put an end to buying cells every year. You also have to consider that these packs are 2-cell packs which is equal to a 6-cell NiMh pack.

With 3.7 volts and the lower IR I wonder how well it would perform? Of course you'd need to use a receiver pack but then a large number of people already do. But just think about never having to worry about your pack going out of match.

what may be top of the line today, could be a mediocre pack tomorrow
Not any different then now... you now have IB cells, new GP cells and the Sanyo cells. The only think stopping your need to spend big bucks is ROAR.

Off road is probably more about driver than on road or oval where equipment makes a huge difference, but I have never done either of those. I can tell you this, I got 1 racer that has been around electric and gas racing for 10+ years to go to li-pos and brushless. He was so happy he sold his comm cutter, Turbo 35 and all of his nickel batteries and brushed motors. He is even talking about selling his gas monster trucks due to the huge maintence problem they are if the Pro Truck class takes off and that being said from the East Coast Unlimited Monster Truck Champion in the Pro Series who finished 3rd overall in the nation.

Once you go li-po, you will never go back to nickel batteries!

The reason I bring up that you will likely be buying LiPo Packs every year, just like you would with Nickle based packs, is related to the comments about Lipo packs lasting 300+ cycles compared to 50 with NiMH... First I think 50 for NiMh is a very conservitive number and I think it shoudld be made more clear that this is really more reflective of a typical racers season, rather then some actual number of charges before the packs are no good. However 300+ cycles for LiPo is a bit of a stretch by almost any means of counting I think... Again if you go to PureHobby's statatisitcs with regard to LiPo, they clearly fall off in voltage with every use... and acording to purehobby's data, it looks to me like they fall off by nearly 5% after just 50 cycles when used at 10C rates, even something close to a 2% drop in voltage even at 1C discharge rates after just 50 cycles.

I know for sure no RC racer making the A-Main would ever consider runing a pack that was 5% less power then a new pack would be, so they will replace the packs if they even close to that point. Even at 2% loss of voltage we are talking about almost 15 hunderdths of a volt loss on a 7.4 volt pack, most carpet racers I know wouldn't put up with even that much voltage loss. To my knowlege I don't loose 2% voltage after 50 cycles with a NiMH or a NiCd pack, unless I was abusing them big time. (and this is at 10C discharge and 2C charge rates, which I don't consider abusive)

Nope, I don't see any evidence that would make it fair to claim LiPo packs will have any better longevity then Nickle based packs.

I guess I never argued that LiPo packs would have better longevity. The charts on the Pure Hobby site do show they do degrade with use, but it doesn't say if it's voltage, capacity or both that degrades... and how do they degrade? Is just a loss, does IR increase or ???? Until that is a known it would be hard to make any knowledgable comment on that.

If you don't charge a pack more then twice a week how many packs do you have? On a race weekend I may run at least 6 practice runs and then 3 heats and a main in two classes. That is 14 runs minimum... if I held to the not more then twice a week scheme I would need at least 7 packs. 7 packs x $60 (conservitive) is $420.

Capacity is usually degraded first as cycles on the packs are performed. Many of us have put a volt meter on a pack that appeared to have very high voltage yet under load couldn't deliver a thing.

Over time peak charged voltage will degrade as well but nowhere as quick as the capacity does. As the capacity is degraded over time the voltage, under load, tends to drop off quicker due to the fact that the capacity is degraded.

IR does change some in all batteries. In polymer IR is more stable then most type chemistries but will change some. The change = higher IR.

Robert
www.purehobby.com