Why not Li-Po's?

I just don't feel comfortable using them. IMO, the potential for catastrophic failure is too great in a MT - overcharge, overdischarge, or puncture them and then poof! Chances are nothing will ever happen, but there is that chance, and one that I'm not willing to take. Of course something bad can happen with any type of cell, but the potential is less. Besides all that, their lifecycle is not all that great from what I've read, and they're too expensive to get poor results.

I think these different companies are on the right track coming up with alternative Lithium chemistries (emoli, A123Sytems, etc) - I just have to find the right one that will work well for me and satisfy my paranoia. :)

That said, does anyone know how those Li-Mn cells work?

Well, there is a penalty for having a more robust metal case around the compounds of the cell. The only way you're going to get half the weight of NiMh with a setup that will perform well enough is to go Lipo. Like squee asked, why not Lipo? I've got 5 Lipo packs sitting right next to me right now, with another on the way. Although I have gone through a few (older) packs, I have yet to have any smoke, let alone fire.

EDIT: Just saw your post. There is always the possibility for a Lipo failure, but there is the same possibility with NiMh, except that it is lessened with NiMh (and they have vents on them). Life cycles on Lipos depend on so many things that you can't judge them - abuse/mischarge/misdischarge/maintenance/brand/etc.
Ask coolhand about LiMn, he runs them.

It looks like I answered Squee while you were typing your response. It all comes down to paranoia I guess. :dft001:

Whenever I build something, I tend to over-engineer and make it tougher and more reliable than it probably needs to be, and Lipos simply don't fit into this scheme...

Lol, it seems we are playing "post-tag". :)

Some of the variables you mention are things I really don't want to worry about. That's one of the reasons why I like electric: plug it in and go. I don't want to have to worry if a cell becomes unbalanced, or if I am pulling too much current. All I have to worry about with NiMH cells is that I don't over-discharge them, and that's pretty easy to do. Like I said, when I build something, I over-do it so I don't have to worry about those things when I play. OK, so it's paranoia and laziness. :)

BTW: It looks like this topic is straying a bit off the power-tool-cell theme. Sorry for the unintended hijack! The conversation sort of evolved. :dft001:

Hopefully, coolhand will see this thread and chime in. In the meantime, I'll still be looking for the holy grail of lightweight, powerful, and small cells...

You act like that never happens. :005: :005:

As of right now I love the limn. I don't know what the performance if any is different from the lipo.

Those look they would fit my requirements for weight, size, runtime, and max current. How about the safety issues?

I got my V28 pack yesterday. So far I've taken all the cells out and cleaned them up, which took about 20 minutes. I checked the voltage on each of them as shipped, and they were all at either 3.89 or 3.90 volts. I'm about to go on a trip for a few days, but I'll make a 4S1P configuration soon and let y'all know how well they work. I'll try them in my Stampede with the 12s first, since that won't pull as many amps as the 9L in my MT2. If I don't get better performance than my 12 NiMH cells, then I'll find another emoli cell somewhere to make it 2P. Luckily, I didn't have to buy a new charger for these cells, since I have access to several Schulze 330d chargers at work. :) I'm not going to bother with adding balancer leads. I'll just charge the cells individually if they ever go out of balance.

I still can't decide between these packs and the True RC 3s2p 8000 Lipo's for $100.........so much money right now though, and I don't have it.

The True RC lipo's are the way to go for sure.

I think for most practical purposes squee is correct.

Pros:
-more run time
-lighter
-cheaper

Cons:
-not as robust/tolerant as Emoli
-can't be charged at 3C

Dabid;
I have 10 of the 3200 mah on order from true rc (roughly 130$). I have some of the Li ion batteries and I would rather have lipos.

(2) 5s packs. for 6400 mah. Put that with a 9xl or 10xl and you could race a whole day and never charge :) and not worry too much about over heating.

I do have a 9xl in my Savage, that'd be the main vehicle the new batts would be going in. More to the point though, you guys got me convinced......just gotta wait for the cash!

I got my two 2S1P packs wired up and charged today. I bought some sub-C SXS shrink wrap for them, but it's too small. I'll have to get some 3" wrap to fit. In the meantime, I wrapped them with electrical tape. I charged them at 1C, and the charger put 1200mah into each 2S pack. The cells now have a resting voltage of 4.05V each. I hope to test them out in my 12S-powered Stampede this afternoon. Depending on the results, I may need to convert the packs to 2S2P to handle the current. So far I haven't had any luck finding someone with an extra cell, so I may need to buy another V28 pack. If I do, then I'll put the other 6 cells up for sale. Here's a pic of the packs.

http://i25.photobucket.com/albums/c9...3/DSC02595.jpg

I tried out the emolis yesterday with mixed results. The power delivery was very strong, and I didn't have any issues with the cells being unable to deliver peak currents. The cells barely even got warm. However, I did a gps test and got a speed of 52 mph. My 12 IB3800 cells had been able to deliver a speed of 54 mph, so I was a bit disappointed.

But, today I charged up the packs again and realized that the charger was set for a max. mah of only 1200! That's why the cells were at only 4.05V after I charged them yesterday. I set up the charger properly this time, and now the cells are at a full 4.2V each. Hopefully, I will be able to get a higher top speed now. I'll find out this weekend.

Even if the speed still doesn't match up/exceed that of 12 NiMh cells, think of it this way: speed requires power. Your Emoli pack can deliver a maximum of about 720W (peak), and your IB3800 cells should be able to do 1200W peak. I'm somewhat amazed that the difference was that small, 500W is a lot!

The emoli cells also weigh about a pound less, which should make a big difference. Btw, I didn't know that NiMH cells were capable of providing that high of an amp spike (14.4V X 83A = 1200W)?

to my understanding. The nimh cells if good ones can go a 100 amp spike but the voltage falls back. They supposed to produce about 100 watts of power per cell.

Right, I was going by what coolhand says. But, I remember those numbers back from when GP3300s were king, and IB3800s are even better, so they might be able to deliver more.

I don't know if these IB's are better metalman. i am hearing different stories.

Test results will show .. (i will do some testing with the eagletree) i've got a set of BK's IB3800's, the best they had.

I don't know if to go for the IBs or Limn, the only thing that puts me off with Limn is the cost and charge times, I'm sure when I get stuck in it will be worth it. Not sure though, it is all very new stuff still.

I know some of the airplane guys (sailplanes I think) use NiMh for short bursts in which they pull something like 200+ amps. I can't recall if they did this with GP3300s, but they do it with IB3800s for sure.

I'm all up in the air about this stuff.

One minute I want to wait for the A123Systems M1 cells from the DeWalt 36v line, but then I find they are only 2.2Ah, are kinda big (26mmD x 65mmL @ 70g), and aren't exactly like typical Li cells; they only charge to 3.6v (not 4.2v like others), which will make charging a little challenging. By the time I set up a 4s2p or 5s2p pack, I'll be at the same weight and size as equivalent NiMHs (or close to it).

Next, I think I'll try those Emoli cells from the v28 packs, but then I don't want to go with a 2p arrangement for weight and space (each cell is 26.5mmD x 70mmL @ 99g) since they don't have the burst capability.

That leaves LiMn, NiMH, or Lipos. LiMn are a bit pricey for what I need, but seem like the best choice so far despite some peoples mixed feelings. NiMH are just too heavy and bulky for what I want to use. Lipos, well, I won't go into that again.

:032: :032:

Did you guys see the new numbers on the flightpower cells? they are awesome.

These look cool, the charts are brilliant:
http://www.flightpower.co.uk/core/da...a_5s1p3700.htm

Would it be best to go for a 3s and 2s, or just a 5s? I guess to balance the weight I should go for two packs.

I love the charge rates with these packs too! Tested at 2.5c.

Those are not even the charts of the new types they have got.

their new cells should do a 50C peak discharge. maxxamps.. Go pack your bags..

50C? I don't know much but who will need 50C Lipos. :D

Can't see them on the site, must not of updated them yet.

http://www.flightpower.co.uk/acatalo...0-3700mAh.html

they are called new formulation.

Woah! So they are doing 50C packs at same price as 20C? Will that mean the packs are more efficent? Can't wait to see the charts.

I've just seen some of these do around 110amp bursts, will the BK9920 be fine with this?

yeah 110A bursts are okay for the 9920.

I only found the evo 20 packs. didn't see no 50c packs.

Serum said they are called the "New Formulation" or something. ;)

These new lipos look great, I wish I could trade mine in for these

just look a bit closer country.. They are there for sure.

Did anyone happen to notice the temperature graph of the cells? 75 deg. C is a lot! (160 deg. F) Lipos usually shouldn't go over 140 deg. F or 60 deg. C.

In case anyone didn't notice, they posted the same graphs for the regular 20C packs as the "New Formulation" 20C-50C packs. So how do we know that the cells are any different?

While it certainly is conveniant, it also decreases the number of cycles that a pack will hold up for. Most Lipos these days are capable of 2C charges, as long as there is a balancer (the differences in the cells' internal resistances is amplified two times with a 2C charge).

If you are that concerned about weight, then round Lithium-based cells are not for you. They weigh more than prismatic cells mainly because of the (usually) steel casing. You just can't get much lighter weight than a plastic pouch!
If you go Emoli and use 1p, you're going to need a high voltage for the pack to hold up well.

Lipos last alot longer than Nimhs though right? If used correctly.

Do lipos "fade out" like some nimhs, for example towards the end of a run there is less power?

From my experence nick. The packs run about the same from beginning to end. I don't see much difference if any. If it was not for a lvc i can see where you would mess up some cells.

On the Flightpower Lipos, what is the little connector (looks like a reciever plug) for?

Balancer