Li Po batteries, C ratings?

hecells say 6 c on that site. Tunder Power says 16 amps on the 2100 cells. The others you could email them and ask or look on other sites. The new Kokams have a high discharge rate but i don't remember what it is off the top of my head. What exactly are you looking for?

remove my-wife to reply :-)

Kokam 340s will do 20C, but whats teh pint - a battery that flattens in

Most LiPoly will dop 5C, E-techs about 6C. Kokams similar, Irate and Tanics 10C. Thunderpower about 6C but,. being Thunderpower 'they have world beating cells coming real soon now' Yeah.

Right.

Icrashrc,

This is what I'm looking for. Tried to order but they were sold out. Good price when they re-stock. They don't specify any C rating though and they don't have a number I could call. Email, I was told they will re-stock. Could you help on the C rating? Or if I connect 2 in parallel could they discharge in short intervals at 20 to 25 Amps?

SOLD OUT KKM-1500SHD-3S 1500 mAh 11.1V 3 Cell in Series  $50.00 Sale $46.99

Thanks, Wan

I logged into the ezonemag site and it's quite interesting. Very thorough articles. Book marked it so I can explore later. Thanks.

world beating cells coming real soon now'

Not doubting you but if true, I'm lucky to have missed the Kokam sale. What do you think the new Thunderpower Li Po batteries, 11.1 V may cost?

Wan

Specs can be found at

remove my-wife to reply :-)

| Kokam 340s will do 20C, but whats teh pint - a battery that flattens in | 3 minutes is of marginal interest.

It's of more than marginal interest.

If it'll do 20C, then it'll do 10C without even breaking a sweat. Your batteries (of any sort) will last longer if you don't push them all the way to the breaking point.

And 20C may be full throttle, where using 4C is enough for normal flight -- letting you fly 15 minutes if you want, but you can also go hog-crazy for a minute or two if you want.

Maybe it's for a powered glider, where being able to climb 1000 ft/minute is a very good thing.

And maybe somebody's interested in a 4 minute pylon race :)

I recently made the plunge into Li-Poly cells and bought two of them. So far they seem quite nice, but my Triton will not charge them properly (the voltage display is about 11-15% too high -- but only when charging Li-poly and Lead-acid cells. I checked it against a multi-meter -- when charging NiMH and NiCd cells, the display is accurate to within 1%, but when doing Lead-acid and Li-Poly cells, the displayed voltage is too high, so it cuts off before it does any charging. I've emailed GP's technical support and we'll see what they say ...

The two best currently available high dischrge cells are Tanics and Irate.

Mike at

I have some of these cells, and they are very good indeed so far. Mine are 3s2p 1100 cells, designed for really up to 20A, so you need the bigger cells to get 25A. DO watch out for teh physical dimensin. Irate cells are large abnd thin, to get the high current, and they may not fot teh way you want em.

Mike will make up whatever size you want, at a slight premium over bare cells, if soldering aluminium tabs is not your thing.

world beating cells coming real soon now'

Dunno. Thunderpower ofer easy fit and forget packs at a slight premium over everyone else. Chequebook modelling. I am running with Irates now as they seem to be the best price performance cells around.

I have a Triton charger as well. Learning how to use it. Be interested in what GP says.

The was my complaint, I was unable to find the C ratings before I buy.

Wan

| I have a Triton charger as well. Learning how to use it. Be interested | in what GP says.

They said it sounds faulty, send it in. Which I will do, I guess. I was hoping they could tell me how to calibrate it myself, but they did not.

The charger is 14 months old, with a 12 month warranty. (I got it when they were brand-spankin' new.) We'll see how much this costs me ... probably not too much.

| A friend of mine gave me the above web site on batteries. I have to | admit, this group does give specs including C ratings.

Well, C ratings are just another way of giving maximum discharge rates. So if they say `maximum 10 amp discharge rate', it's just a matter of some math to get the C rate. Of course, most Li-poly cells don't seem to list a maximum discharge rate of any sort.

I replaced the 8 cell 4/5 A NiCd pack in my XE2 flying with with a 2 cell Tanic Li-poly battery that can handle 22 amps continuous. With my Astroflight 020 it now draws about 16 amps and it definately has less power, but climbs better due to the much lower weight.

(Of course, it's now also way tail heavy and I can't push the battery any further forward. I hate adding weight to an electric, but may have to. Still, it's kind of fun -- it's the first plane I've flown that will spontaneously go into a spin and not get out by simply letting go of the sticks. Of course, without rudder, it's hard to get out of any spin -- but the plane is all foam so a flat-spin crash landing is quite alright.)

Doug, isn't it the way warranties always work? Runs out just before a fault shows up. I hope it won't cost much for you.

I'm lucky to have a friend they called "Mr. Electric" who has just about everything electronic. He programmed my Triton and watch me as I did it myself.

That was my original complaint. I looked all over my battery and could not find any discharge rates on it and the first web site didn't specify. But the second site does.

I found 2 Li Po batteries (3S-2P) 11.1 V, rated at 8 C and can be discharged continuously at 12 amps. I would like to know what happens if I gave bursts of 20 t0 25 Amps?

I believe you could extend the nose section by cutting and splicing. This way you need not add weight to balance. I've done this on my E3D. The splicing added about 2 - 3 oz, but more than made up for it by the much lighter Li Po batteries (Lighter by 14 oz), compared to the NiMH battery.

Still, it's kind of fun -- it's the first plane I've flown

My E3Ds (2 of them) have very large rudders and I still get into trouble. Too quick, too snappy. Fun? exhilarating!

I had not flown my outdoor E3Ds with Li Po batteries yet as it's bitter cold here.

Wan

If they are rated at 8C and discharge at 12A in 2p config, that sounds like a 700mA/h cell?

For 25A you really need to parallel up something bigger - 1300 or 1500 cells.

What happens if you burst to high currents is teh voltage drops way down, the cells get hot and may damage themselves, and its altogether very unstaisfactory.

Have a look at the datasheets in

Irates are in my opinion the best high burst current cells out there right now. You can just about get 25A out of 3s2p 1100 Irates. But I'd go top 1300 or bigger to be safe.

Well, if you discharge with 20C, you can't get more than 3 minutes, no matter what battery you use. That's how the C ratings are defined. Get the double capacity, and you can get 6 minutes. Your current will only be 10C then. The point is that you don't actually need such high C ratings with LiPo because the energy density is much higher. A LiPo has about 4 times the capacity of a NiCad at same weight, so if your discharge rate with that NiCad was 20C, and you replace it with a LiPo of the same weight, it only needs to support 5C. Your flight time will then be 4 times as long as with the NiCad.

Actually, the 20C are continuous load (if you can speak about that when discharging in 3 minutes). Those cells are said to support up to 35C for short periods (30 seconds).

The Kokam 1500 seem to be good. They can do 10A continuously and 15A for short periods.

Then you overloaded them. The batteries can support higher loads for about 30 seconds, but not longer.

If you notice such a drop-down, you have to reduce the load immediately to prevent damage (if they haven't been damaged aready at that point).

Kokam High Discharge Li-Poly 1500 mAh 3-cell (11.1 V) Pack Would you think the battery pack above be of sufficient Amps for the performance I want if I connect them 2P?

You bet! Would the ESC detect the heat from the cells and shut down?

I will look at the sites you provided, thanks. I'll pick up some pointers from them.

Why wouldn't the Kokams be equal to the Irates if hooked up the same way? I have 2 of those Kokam packs reserved at the LHS. Maybe I should wait until after the Toledo Weak Signals' show in Arpril and see if there may be better batteries out?

One answer leads to others, but as I said, I'm learning, Wan

Oh, Oh. Lately, if I send anything to GP for repair, they claim that it cannot be repaired economically. Typically, they offer to replace it at about 2/3 the normal price. If you are a member of their Super Saver's club, then they double the warranty. So maybe the Super Saver club is really worth the money.

Jim - AMA 501383 (remove .nospam to reply)

Doug McLaren wrote:

| Oh, Oh. Lately, if I send anything to GP for repair, they claim that | it cannot be repaired economically. Typically, they offer to replace | it at about 2/3 the normal price.

They better not ...

| If you are a member of their Super Saver's club, then they double | the warranty. So maybe the Super Saver club is really worth the | money.

I am (it pays for itself in shipping pretty quickly) -- but it says it only covers `Tower Hobbies brand items'. From

Extended Warranties: The warranty periods on all Tower Hobbies brand products are automatically doubled!

I know that Tower Hobbies and Great Planes are the same company -- does this mean that Great Planes stuff has the same doubled warranty? If so, then I'm just fine -- 14 months is less than 24 months.