lipo C rating

[MAXAMUS]

hi

what do you think about C ratings on lipo's ?
i ask because i am looking to get some 3cell lipos to run in my BJ and have seen some at 4000 mah 15c
or some at 4000 mah 30-40c ????

[Blackjack-sven]

The "C Rating" is the batteries current rating. The higher the current rating the more the motor can show it's true potential. If the C rating is too low and the torque demand too high, it will seem like the boat is stuttering. This stuttering is very common to see on rc cars with poor quality batteries. When you punch the throttle the motor will demand a certain amount of current from the battery. If this demand is not met it will seem to stop and start very quickly.

Long story short the better the C rating and quality of battery, the better your performance will be.

On my BJ 26 I now use 4900 Mah 25c 2s Trak Power batteries but this is how my boat runs on a completely stock setup without ANY mods using 4600 Mah Intellect NI-MH batteries.
http://www.youtube.com/watch?v=4bxOv...e=channel_page

This on the other hand is what the boat can do with my Trak Power batteries.
http://www.youtube.com/watch?v=CRIR2...eature=channel

[bwells]

In you post you said you use 2s but in the video it says 11.1 which is 22 volts which is a little scary for me as I don't want to burn anything up. It seems that 2 2s in series is about my speed as that is 14.8. the 2s2p increases the mah but not the volts, correct? for instance, 2 2s2p in series would get you 14.8 but double the mah, add more weight but what about the c rating, can you go 20 and be safe? Thank you, Brian

[Blackjack-sven]

In you post you said you use 2s but in the video it says 11.1 which is 22 volts which is a little scary for me as I don't want to burn anything up. It seems that 2 2s in series is about my speed as that is 14.8. the 2s2p increases the mah but not the volts, correct? for instance, 2 2s2p in series would get you 14.8 but double the mah, add more weight but what about the c rating, can you go 20 and be safe? Thank you, Brian

Sorry the video must be wrong as the voltage was 14.8v. As for

can you go 20 and be safe?

you will be safe even if you went to a 30c because the motor will only pull the current it requires. Your controller is what decides weather or not you keep running, but if you keep the stock motor and esc then you will be fine. Just make sure you don't go to a too aggressive prop as that will increase the load on your controller and motor potentially damaging something. Stick with the stock prop, Octura x642 or any other prop in similarity to a 40x52/2.

[MAXAMUS]

hmmmm

look at these http://cgi.ebay.com/EC-POWER-10000mA...742.m153.l1262


sure would get long run times here

[bwells]

but if you run 2 you would have 22.2 volts which I assume would be over the limit of the electronics on the bj26 plus they are from hong kong and I haven't heard anything about hong kong batteries. 2 7.4 4000mah 20c 30c would make me happy if I could get them for under 100 a pair

[MAXAMUS]

but if you run 2 you would have 22.2 volts which I assume would be over the limit of the electronics on the bj26 plus they are from hong kong and I haven't heard anything about hong kong batteries. 2 7.4 4000 mah 20c 30c would make me happy if I could get them for under 100 a pair

my 20c 6600 mah lipo's are from hong kong and are fine most lipos originate from eastern countries and are just re branded but remember you will need to check what voltage your set up can handle and run the bats in series or parallel as required

series doubles the volts and the mah stays the same
IE 2x 7.4v 4000mah = in series 14.8v 4000mah

parallel doubles the mah and the volts stay the same
IE 2x 7.4v 4000mah = in parallel 14.8v 8000mah

[Blackjack-sven]

hmmmm

look at these http://cgi.ebay.com/EC-POWER-10000mA...742.m153.l1262


sure would get long run times here

If your going to go with something of this caliber then why not use the max amps 12,000mah lipo 2s3p? I know that maxamps batteries are of very high quality and you'll get the longest run times out there.

http://www.maxamps.com/Lipo-12000-74-Pack.htm

If you want the best bang for your buck from maxamps, use this battery. But try to find one on e-bay if you don't have the cash for a new one.

http://www.maxamps.com/Lipo-10000-111-Pack.htm

[kookie_guy]

another quick note is that you can destroy your batteries if your motor is trying to pull more current than your batteries can provide. They will get very hot, and pretty quick. With lipos, that's not something you wanna do.

I had this issue with my e-maxx when I swapped out to 700HO motors. My cheap NIMH packs just could not supply the juice, and they went for a poop.

In short, get the highest C rating you can afford. If you have no plans of upgrading your BJ any time soon, or running the packs in a high draw application, then a pack that can put down close to 100 amps is a VERY safe bet.

Personally, I will be running 4900mah, 2s rhinos in mine. They are rated 20C/30C burst, so 90 amps is plenty.

A good ref point is the rating of the ESC. If for example the ESC can only put out 60 amps before it goes for a crap, then you know the motor will not pull that (until you mod or load it obviously). So a 90 amp battery is again, very conservative.

[bwells]

maxamus: 2 7.4 4000 mah in parallel = 7.4 volts 8000 mah but the stock wiring for the bj26 is in series. It would be easy to change to parallel but I'm running 2 8.4 4500 nimh in series now and I like the 2 pack thing for weight distribution. I guess 2 11.1 volt lipos in parallel would double the mah, never crossed my mind, I have to think about that idea but then your only running 11.1 volts whereas with my 8.4 nimh in series I'm ramming in a whoopping 16.8 volts, yeah, as 2 7.4 volt lips in series would give me 14.8 which is good I guess cause they are lipos.

[Blackjack-sven]

These are the specs of the stock Blackjack 26's ESC.

Specs

* Forward:Yes
* Brake:Yes
* Continuous Maximum Current:45A
* Input Voltage:Minimum 10V, Maximum 21V
* Momentary Peak Current:55A
* BEC Voltage:5.8V

[bwells]

blackjack-sven:
45amp continuos and 55 max thanks, now if I can find " the rule of thumb" formula someone posted something like volts times mah divided by 1000 equals max amp or c rating, I forgot but it for picking lipos, Thanks again

[kookie_guy]

blackjack-sven:
45amp continuos and 55 max thanks, now if I can find " the rule of thumb" formula someone posted something like volts times mah divided by 1000 equals max amp or c rating, I forgot but it for picking lipos, Thanks again

you sure that's not for charging lipos? because with the above it's quite simple. If the esc peaks at 45 amps/55 amps momentary, then as long as your battery can provide 55 amps, you are fine. The most the ESC will provide is 55 before melting.

As a safety buffer, I would get packs that can spit out 50% more current, simply to make sure they have a nice long life. So, 55amps + 50% = 82.5amps.

Maybe the formula you are talking about is figuring out how many amps your lipo will sustain.

For example, 4000mah pack rated at 20c/30c burst
4000mah x 20c / 1000 = 80 amps continuous
4000mah x 30c / 1000 = 120 amps burst

[Blackjack-sven]

I got this info off of the horizon hobby web site here.

http://www.horizonhobby.com/Products...ProdID=PRB3309

[Chuck E Cheese]

do any of you know about running lipo's in parallel and series? i have plenty of rhino 4900 20c. i am looking to run a 8xl with 150 etti. i was thinking if i ran 4 packs, 2 in parallel then in series i would come up with 9800 mah at 14.4 volts. is this a problem to run them that way or is it the same to series them and then go parallel as it would be running 2 9800 mah 4 cell packs. i dont care about the run time, i'm looking for the batteries to put out more amps.
thanks

[Meniscus]

Someone correct me if I'm wrong, but that would be a 4s2p setup at 9800mah, assuming that the rhino packs you refer to are 2s1p.

[kookie_guy]

do any of you know about running lipo's in parallel and series? i have plenty of rhino 4900 20c. i am looking to run a 8xl with 150 etti. i was thinking if i ran 4 packs, 2 in parallel then in series i would come up with 9800 mah at 14.4 volts. is this a problem to run them that way or is it the same to series them and then go parallel as it would be running 2 9800 mah 4 cell packs. i dont care about the run time, i'm looking for the batteries to put out more amps.
thanks

you are correct, you would get 9800mah, at 14.8volts. I would be affraid of one of the packs getting out of balance or something, and I'm not sure how the stock cutoff would act, since theoretically if one pack blows up, the other would still indicate that it's good. So the packs would all have to discharge equally.

I may be way out to lunch with my way of thinking, but ya.

[Blackjack-sven]

I would be afraid of one of the packs getting out of balance or something, and I'm not sure how the stock cutoff would act, since theoretically if one pack blows up, the other would still indicate that it's good. So the packs would all have to discharge equally.

I may be way out to lunch with my way of thinking, but ya.

If you were to keep the cutoff at lets say 10 volts, then when 1 of the batteries were to blow the voltage would drop instantly, and if it went below the 10v cutoff the boat would suddenly stop temporarily. If you wanted to run 4 packs at once for power and endurance just make sure you have the batteries balanced at all times and make sure they start off all new and of high quality so you'll never need to worry about problems.

[MAXAMUS]

do any of you know about running lipo's in parallel and series? i have plenty of rhino 4900 20c. i am looking to run a 8xl with 150 etti. i was thinking if i ran 4 packs, 2 in parallel then in series i would come up with 9800 mah at 14.4 volts. is this a problem to run them that way or is it the same to series them and then go parallel as it would be running 2 9800 mah 4 cell packs. i dont care about the run time, i'm looking for the batteries to put out more amps.
thanks

I'd just run 2 in series to run 4 packs in any combination of series or parallel etc its going to be a huge weight and CofG issue not to mention as others have said pack over discharge and balancing hmmmm you may even consider selling the packs to go towards the packs you require with a high c rating well that's my 2 cents worth............

[bwells]

blackjack-sven: thats the formula I was thinking of thanks. 2 7.4 4000mah 20c 30c should be fine for stock bj26

[Chuck E Cheese]

i am going to try just 2 but im not sure that 4900mah is enough amp output. i will try it and see if they get hot. if not it is all go but otherwise i need to up the capacity to get 20c to represent a larger number. i think my set up is going to pull right around 80-90amps so it is boarderline.... thanks for the replies. also dont worry, if i do use 4 i will ballance them and they are all brand new. i have a pile of brand new ones. cg not an issue because im set up with 2 forward center and 2 side of the rails. i hace a df 29 with 4" rails and rear motor configuration.

[bwells]

you can change voltage and mah by series or parallel but amp ratings by going series is going to stay the same. what you want to do is make the last battery in the series do more than it was designed to do, the buck would stop there.1st battery 20c going to 2nd battery at 20c which would only deliver 20c, how would it spit out 40c, the amps still have to travel through that last battery before leaving and heading to the esc. you would be asking that last battery to cough up more amps than it was designed for. Electric guys, is this correct, I don't want to steer anyone wrong?

[bwells]

plenty? do you want to sell 2? I was looking at 4000 mah but 4900 sounds good to me

[Blackjack-sven]

I wouldn't mind a set of 4900 lipo's as well seeing as I only have one set to play with right now.

BWELLS your statement seems a bit confusing. in series you would bring the voltage up, and both batteries would stay at 20c without problems. In parallel you would get the mah to double, also without a problem. If Chuck E Cheese wants both doubled for longer run times as well as more power, he would need to go to 2 batteries rated at 9800mah 11.1v and 40c or use 4 of his batteries 2s 2p to get the same, but if he does use 4 batteries, not only will the weight of his boat go up, his cg will certainly get screwed up, causing a fair amount of performance problems.

I'll post some pics up with the 4 batt. setup and the 2 batt. setup to show how the cg will get affected.

Actually the cg won't get affected too badly. It only moves the cg forward by 1 inch.

[bwells]

I'll have to disect your post again but he wants to increase the amp by series and I don't see how that can happen no matter whether he does series or parallel. amps is draw and the last batt, the one with the red wire going to the esc is handle everthing whether it is 2s2p or 2s 1p in series. answer back as I see you are still online

[Chuck E Cheese]

keep in mind bwells, in parallel there are now 2 red wires going to the esc, one from each last pack.
i am pretty sure that running 2 packs in parallel will yeald a higher output because the 20c is based on the pack capacity. it doesn't mater anymore, i went with 2 x 2650 4 cell 30c packs that i am going to run in parallel. i think this should give me 5300 mah @ 159 amp output, i really only need around 100amps. it should work well because i use 4s2p 4000mah total in another boat and they work fine

also i am not interested in selling packs. i run a 2 cell boat and am building my girl a delta 26 to run on 4 cells (2s2p)

[Chuck E Cheese]

i do have a 25c 4500mah 4 cell pack that i would sell. it is brand new with 5.5mm bullets (female on positive, male on negitive). $65 plus shipping.

[kookie_guy]

I'll have to disect your post again but he wants to increase the amp by series and I don't see how that can happen no matter whether he does series or parallel. amps is draw and the last batt, the one with the red wire going to the esc is handle everthing whether it is 2s2p or 2s 1p in series. answer back as I see you are still online

not by series, by parallel. like chuck e cheese said, now you have 2 red wires, so essentially you have 2 supply circuits of 14.8volts (2 packs in series), connected to ONE red wire on the ESC. The ESC can pull power from both circuits, hence doubling the potential amp output.

[kookie_guy]

here, this should make it nice and clear......

[Blackjack-sven]

Answer back as I see you are still online

Sorry I didn't answer you back on the issue yesterday, but I actually fell asleep on my computer. Either way, Kookie_guy answered your question in a very similar manner I would have answered.

BTW: I enjoy it when people dissect my posts as it gives me the chance to defend my knowledge base, and if my knowledge base is wrong I'll be able to see why better.