which lipos- mmm combo

hello all...i have ordered a mmm combo 2200kv to use in an e-maxx 3906 i have two questions for castle staff.
id like to run 5s lipos around 4500 mah so is it best to buy 30c packs or will it run ok on 15c?
what is the difference between lithium,li-poly and lifepo4/a123 packs i see they differ in voltage but what else? which is best?
thanks, chris

[bdebde]

5s 4500 would be a good size, I wouldn't go much smaller mah wise. I would say 20c minimum, but myself would go no less than 25c minimum. Go with the 30c, it will stay cooler, give better run time, and last longer.

Plain lithium batteries are like watch, camera, calculator batteries, not rechargeable. Lithium-polymer, also called li-poly or li-po, is what most use. A123 are good too, some people like them better. They are probably more durable and can take more abuse than li-po, but the size/shape/weight, can make them less than ideal for some. The voltage difference can be adjusted for with gearing, or add another cell (6s lipo about the same voltage as 7s A123).

[himalaya]

A123s are great cells in abuse taking. but IMO its size is just stupid for RC use. I wish it was designed 23650 size instead of 26650.
Further more, the A123 is rated as 30C discharge capable, but this spec is only to describe how well it takes abuses, not how powerful. The voltage drop under load is much more significant compared to decent 25C LiPos. So it's not very likely to provide same output power as a good LiPo pack having similar capacity and steady-state unloaded voltage. You can tell this from its datasheet.

[lincpimp]

Personally I would go with a enerland based pack with 5s 5000 25c specs. You could also do the 4500 30c 5s pack. Anthing less and you may be overworking the lipos. 15c is too low unless you go up to 8000mah.

As for the 25c vs 30c debate, the 30c seem to run warmer, but do not seem to mind the heat.

[suicideneil]

Well, being in the Uk lipo options are limited, extremely limited infact unless you want to spend a small fortune in import fees (HMC&E can bite my ass).

Flightpower and Trakpower lipos are indigenous and can be found on most of the Heli and plane websites, and they have excellent specs; the prices are not so excellent though.

If you plan to import, anything Mike sells in his store is great if you just avoid the Maxamps lipos

I'd favour some 20-30c 5000mah lipos myself, but a 3906 chassis will limit your options, unless its kitted out with aftermarket parts- got some pics or a link to it some place?

Also worth bearing in mind a MMM system will eat a stock or fairly stock 3906 for breakfast...

hi neil/all...i found sum zippy lipos on line but they only 20c 5000mah so if i link two of them in parallel ill have 40c on tap yes and 10,000mah?
do customs charge alot for batt packs then?
no i have no pics of my maxx but its allready got a few upgrades proline wide kit, mip cdv's, ally bulkheads and maximizer baed locks on std tyres. so just a few more parts to go and it will be extended too im going to have a go at making some longer chassis rails on my mill so watch this space i will post pics
yes i wll have to do something about the packs being so big!!.
yer thanks neil errr but who's mike????

[bdebde]

Originally Posted by chrismechanic

...but who's mike????

RC-Monster Mike, owner of RC-Monster, check the store here.

[suicideneil]

Mike is our lord and master....

Zippy have some 25c and 30c lipos, check the hobbycity.com website. Customs will screw you over normally, but you can specify the value they state on the package before they send it to you, so customs are none the wiser (£15 is fine to dodge import tx and VAT). Most other places wont do that as its not exactly legal, but thats not something that bothers my conscience...

If you ran 2 zippy 5,000's in a parallel you will get 10,000mah, but you will still have a 20c discharge rate.

hi all...on with the stupid noobie questions ive seen a charger i like on hobby king and its a turnigy accucell-8150 bit it says:- lithium battery pack can be composed with parallel and series circuits mixed. we recommend you compose the lithium battery pack in series only.
does that mean that i cant charge 5s1p lipos with this charger ?
thanks all... chris

[suicideneil]

Its talking about charging more than one pack at once- meaning its better to charge 2 packs wired in series (say, 2x 2s 5000mah = 4s 5000mah) rather than wired in parallel to the charger (say, 2x 2s 5000mah = 2s 10,000mah). This is because both packs wont have exactly the same amount of juice left in them, so trying to charge them up in parallel will result in an over or under charge.

If the charger is rated for 6s and has a decent power output in the 100watts+ region, then that will be fine; just bear in mind most of the ones on hobbycity/hobbyking require a seperate powersupply.

[ren]

I snagged that turnigy 8150 charger from hobbycity and am pleased to say it is everything I hoped for. Charges up to 8s lipo, and stays cool doing it. I can charge a 6s 5000mAh zippy lipo at 5 amps with no problems. Highly recommended... my 2 cents.

hi all .thanks for your advice guys, lipos are new to me so id be lost without you're advice so thanks all . just one more thing this running 2 packs in parallel, is traxxasbasher right if i had 2 20c 5s 5000mah packs parallel id have 10,000mah but still 20c? i dont get it why not? twice the mah surley 20c x2???? thanks guys this is the only thing im not sure of now and nearly ready to order batts and charger yay bye...

[RC-Monster Mike]

20c means the discharge rate is 20 times the capacity. By doubling the capacity, you effectively double the discharge rate, but they are still 20c cells.
5000mah(capacity) = 5 amp/hours
5amp/hours X 20c(discharge rate) = 100 amps
5000mah X 20c = 100amps discharge
10000mah X 20c = 200 amps discharge

hi all...thanks for you time and advice worth its weight in gold.
so i am right just saying it wrong what i ment was it would be better for the packs to be sharing the draw from the mmm combo rather than risk using them individualy (because they are only 20c there is a chance lipo could be damaged with the current draw of the mmm combo).
so i will have approx 200 amps on draw with 2 rather than approx 100 amps with one pack. or would i be better off just paying more for 1 30c pack.
like the idea of the 10,000mah tho run time would be sweet