tailheavy

How about 3c1p E-tech 1200 on a GWS 300c-C gearing? Would that be OK with a 10x4.7 prop?

drksyd

That would be close, you might not want to hold it full throttle too long. You should be fine with the 3S and 9x7 prop. Nominal voltage for the 3S is 10.8, actual charge voltage up to 12.6 volts, much higher than a 8 cell nicad/nimh which is the highest suggested amount of cells to fly with.
In KenSP's thread of his EStarter with floats, his plane looks pretty strong and powered only by a 2S with timed motor so that's another method to increase power for free.

tailheavy

True. My motor is untimed right now. I am waiting on the batteries to get here.

drksyd

I looked at the motors and not sure how you time it. I know you turn the endbell clockwise(?) but it doesn't look like you can turn it without damaging it. The car motors had screws to hold the endbell, these don't.

Manga

My Feedback: (4)

I am new to this type of battery, but it seems that either overcharging or completely discharging them are the most common problems. Is there a charger that will effectively prevent overcharging? and Is there an onboard device that will prevent discharging the batteries below the safety zone?

tailheavy

I couldn't get the e-techs so I got the kokam 1200 high capacity 3 cells instead. I already re-timed the motor since putting on this pack and wow, talk about a difference in power. There was no need to even go to full throttle with this set up. I can basically shoot out of a hover no problem on my fan fold ultimate bipe. How do you measure the current with an amp meter. I tried hooking the amp meter in series with the battery but the esc cuts out real quickly. It runs fine without going through the meter. Maybe I'm supposed to hook it up in series with the motor instead? Yea that's the ticket.

drksyd

Did the Kokams just hit the market? Last time I looked they still weren't available. What kind of amp draw can they handle?

Manga
There are chargers designed specifically for lithium packs and I would suggest getting one if you do get lithiums. It's failsafe and you won't regret it.

JJ HONG

--------------------------------------------------
new kokam 1500HD cell handle 9Amp constant and 15Amp burst for 10 sec.kokam 12ooHD /6Amp draw constant,9A burst.

I also recommend to use lithium special charger like kokam lipo-402 or TRITON or equivalent lithium chargers which have constant current -constant voltage controllerable argorism to get full charging.only constant current charging will give only 60-70% charging and may cause fire due to the overvoltage charging.

tailheavy

Not sure where you got that info from but the data sheet that came with my new kokam 1200HC said that it can handle 8C average maximum current. That works out to be 9.6 amps continuous. And with the settup I have now I am running about 15 amps static with WOT so that unloads to 12-13 amps in the air. I am only running less than half throttle most of the time anyway. I need about half throttle to hover. It hasn't cut out on me yet. The motor does get a little hotter than normal but the kokams are in a normal range of warm.

I almost forgot, at the very top of the brochure that came with my battery pack it said that the 1200HC was a high discharge type. I'm not sure what the 1200HD reference is.

Greg Covey

Just a little clarification for you guys.

JJ Hong is the CEO of Kokam in Korea and he has a vast knowledge of all his products. His 9amp burst rating and 6amp continuous current rating for the 1200HC (aka 1200HD) cell is correct.

I am typically pushing the burst current of the 1200HC cell to 12amps for 5-10 second bursts using good throttle management.

The HC designation was a slight downrating from the HD rating. You will notice that the 1200HC cell has a continuous current rating of 5C while the newer 1500HD cell has a 6C rating. Other new cells like the 340SHC have an unbelievable rating of 20C!

I guess that I can believe it because I am using them.

Here are some places to buy Kokam cells in the USA.

Hobby Lobby
Bishop Power Products
FMA Direct

tailheavy

I guess that little piece of paper that comes with the battery is a little misleading then cause it say's 8C for high discharge batteries. And right at the top of the sheet it lists the 1200HC under the heading "High Discharge". ??????????????????????

I also guess I am misunderstanding the term "average maximum current". I thought that as long as you're under 8C your good to go. I also thought 8C for a 1200ma pack is = 9.6A. But on the web site for fma direct it definitely states 5C. I am so confused.

But the kokams seem to be working well for me (w/throttle management). Just waiting on my brushless motor to get here then my amp draw should go down.

JJ HONG

1200HD /5c is correct.
new 1500 HD will be 6c continuous.Thanks

Greg Covey

tailheavy,

Don't worry about being confused, it is understandable since the Lithium revolution is so new. The fact that you are using Lithium in electric flight means that you are on the cutting edge.

Sometimes, paperwork is wrong and it takes time to correct. The paperwork stating 8C discharge may have reflected the original target but not the production cells for 1200HC. Each cell type is different, even within the same HD catagory.

Lithium cells are now getting several ratings, one is for continuous current delivery and another is for peak short term delivery. Since you use throttle management, you can take advantage of the peak short term rating when picking a cell type or designing your power system.

The 1200HC cell (aka 1200HD) has a continuous current delivery of 5C or 6amps. The peak short term delivery is rated to 8C or 9.6amps. You will find that for short bursts you can exceed the 8C rating without damaging the cells. I often suggest an 8C-10C range for short term bursts on the 1200HC cell, hence the 6-12amp capability.

The even newer 1500HD cells, just hitting the market, deliver a continuous 6C current or 6*1500 = 9000mA or 9amps. Again, the peak current delivery is 8-10C or 12-15amps. This is an impressive cell.

Super high current packs can be made from smaller cells but the cost usually goes up. Look at the Bishop Power Products site. They make super high current packs from the smaller Kokam 340SHD cells that can deliver up to an amazing 20C! A 3s3p configuration like the Kokam 1020SHC 11.1v pack for $99.95 can deliver 20amps in a 3oz package. Compare that to an equivalent 10-cell 2/3A 1000mAh HECELL NiMH pack at 7.3oz that can only deliver 16amps and you can see why the Lithium revolution is so exciting to the world of e-flight!

cork

My Feedback: (1)

On the other hand, the Etec 1200ma cells have been able to deliver 8C continuously since they were first introduced and even higher C rates when used as burst. The great part about the Etec cells is that they deliver over 90% of their capacity when used at these high rates. The Kokam 1200HD cells at 8C or even 5C will only deliver about 50% of their capacity at those rates. That is why the Etec cells have become so popular with e-flyers. They deliver more of their capacity under heavy loads. Since the Kokams only deliver 50% capacity, you will get longer flight times by using the Etecs. This has been documented several times in various graphs and reports that have been posted elsewhere.

And then there are the recently introduced Thunder Power lipo cells that may exceed even the Etec cell specs, as they are being tested by several well known e-flyers who are reporting excellent results. The Thunder Power cells are just now becoming available from online vendors and were designed for R/c to replace some of the commonly used nimh and nicad packs as they are similar in size but much lighter. Recent reports have stated that they retain a higher voltage under load than the Etec cells.

Since this thread is about Li-Polys in general, I thought it would be best if all the lipo manufacturers were respresented.

hoppyfl

Cork, those ETEc 1200 cells really are good. They do provide high current for long time.

tailheavy

I tried to order the etech 1200c's through my LHS and they couldn't get them. Where can I get some of these etechs?

BTW I just got my hacker b20-26s motor in and was using a 11x4.7 prop with the 3s1p 1200HC kokam and the motor seems to be getting real hot. I don't want to damage the motor is that too much prop for this motor?

hoppyfl

Try http://www.lightflightrc.com/ Nice guy, great after the sale service, and good prices.

robhoneycutt

Tailheavy,

yes, that is too much for that motor!!

You will have to replace the field in it or demag it one..

I tried a 3S2P w/ same motor and it is on it way back from the repair shop now!

You need a "L" can and a 18 wind for the 11" prop, or you can amp down to the 2S and maybe use that motor.. Be sure to check the amps, though..

Rob

JJ HONG

Etec 1200 has good performance but not for 8c continuous due to the heat generated.
new kokam34OSHD/700HD/ 1500HD has equivalent or better performance in the field.KOKAM first model is also meaningful to open the lipoly market innitially.second models are very well developed based on the request of users.

hoppyfl

This thread started with a discussion of LiPo safety. A car fire was recently reported. It was thought that a damaged LiPo started the blaze.
http://www.rcgroups.com/forums/showt...hreadid=139208

cork

My Feedback: (1)

----Etec 1200 has good performance but not for 8c continuous due to the heat generated.----

Mr. Hong do you remember a life cycle test that was run by a Mr. Shimizo of Japan on the Etec and Kokam cells? He ran the Etec 700ma cells at 5.2 amps or 7.5C for 100 cycles over three weeks. The results showed the Etecs performed nearly as well after 100 cycles as they did for the 1st cycle. He then tested the Etec 1200ma cells at 8.4 amps or 7C and obtained similar results. I'm sorry to say that the Kokam 1020ma cells he tested didn't perform very well.

You even asked Mr. Shimizo if he would test your 700ma and 1500ma cells and even offered to them to him for free. Do you remember? In any case the Etec cells performed very well at those high discharge rates and didn't fail because of the heat being generated as you stated.

If you would like, I could post the link to those tests if it will help refresh your memory.

tailheavy

Ok I just bought the hacker b20-26s and I am not about to go modifying it. I just need a battery that will give the best performance without burning up the motor. How about the 2s2p Etecs? or what if I use my current 3s1p kokam with a 10x4.7 prop instead? I tried to retard the timing as much as possible in the programing of my cc pheonix 25 controller but the motor is still getting pretty darn hot after a run.

robhoneycutt

a 2S pack will be fine for it, and still watch the heat for sure..
and set the timing back for the hacker motors on the controller..

Scott Clarke

I'm sure JJ doesn't need reminding.

I'm sure you have been around long enough to know the 1020 are first gen (rc) cells and as such do not perform as well as the second gen 1200 cells. The 1020's are rated to 4A max, the 1200's to 8A max, 6A continuous. Currently, Kokam have the best performing high discharge cell bar none, in the form of the 340. So, what is your point?

Scott

houfek

I agree with Scott.....
We are very fortunate to have the participation of several manufacturers in these chat groups.......usually, the information they furnish is good, valuable and cutting edge...........if you want to believe what they say, fine....if you don't, that's fine too.......over time, it will be pretty apparent who's words you can trust and whose you can't. What do we gain by confronting a manufacturer or its rep with tests that somehow show his/her product to be less than someone else's ??
IMHO, we gain nothing, and in addition we risk losing thier participation and cooperation in answering our questions............and if we lose them, we have managed to decrease the value of this list to us all. Make your own evaluations of input from the manufacturers.........but let's not antagonize them into leaving.

Jim