Lipo quessies
 

Considering them greatly. Going to keep sub-c cells because they are great for the odd run. Anyway, I have a few questions on Lipo.

1) Are these suckers really unstable? I hear so much about them exploding, setting on fire, etc. Can somebody clear my mind on the safety of these?

2) The foil cells, are these like the outside of a sub-c cell, so if they touch they spark?

3) What charger do you reccomend? I like the look of this: http://www.flightpower.co.uk/proddet...d=Schulze_330d

Can someone confirm it does upto 30cells nimh and 1-11s Lipo? I might sell my Triton for one, as it seems to be clearly better?

4) Sort of links in with question 3. If I charge a 4000mah Lipo, how long do they take to charge? Whats all the 1C about?

Thanks alot guys,
Nick.

1, they can become unstable, when discharged below 3V per cell. Overcharging also can cause problems, if you use a proper balancer you can't go wrong with the charging process. I personally still charge my lipoly cells outside or in a concrete like (small) bunker.. Just in case..
you need to use a cutoff device with the discharging. (that 3V/cell thing)
2, no, the outside is of an isolating polymer.
3, that is one of the chargers you can use.
4, depends on the type of cell, normally a lipoly can be carged with 1C (1X their own capacity, so in this case 4000 mAh.)

The normal charge character of a lipo cell is they charge with 1C (4000 mAh (4A) ) till the 4.2 volts per cell is reached, after that, the current is turned back, and the voltage stays at about 4.2V. so with normal cells (nimh's) charging them with 1C, it takes 1 hour to charge, and with lipoly it takes about 1.25-1.5 hour.

I feel to charge for over 1.2+ hours is a long time in comparison to Nimhs, where I charge them in nearly under 45minutes.

What other advantages are there to lipos? Are they efficent, as in have a long life span in comparison to Nimhs.

Thanks Serum.

Lipos are more efficient than NiMhs. They have more surface area for heat disappation, except when put into packs. Lipos generally give more usable life cycles with pretty consistant power throughout their lives. They are lighter, and hold a higher voltage.

There are Lipos out there than can do about 80-90% charge in only 20mins (TP Lipos). Kokams (sold by FMA) can be charged to 90% in half an hour. I have some LiFePO4 batteries that could be fully charged in about 35mins. if I had a different charger.

Where do you get the LifePo4 & Kakam Lipos from?

I've been using FMA Scorpion lipos for about a year now and yes they are expensive,but they seem to eliminate the safety issues.They have a built-in devise that prevents overcharging when charging and a built-in cutoff devise that protects them from discharging to low,all in one package.This setup also balances the cells while charging.Just my 2 cents worth.

Kokam:
http://www2.towerhobbies.com/cgi-bin...ct&FVPROFIL=++ (a European distributor would be better for you)

LiFePO4:
http://www.overlander.co.uk/results.asp?categoryid=89
http://www.power-motion.com/shop/
These are not in a standard cell format - they are 18mm in diameter and 65mm long.

what would it take to equal 6s lipo in those cells? if im not mistaken it comes out to more or less voltage. also, whats the mah of those packs? i seek like 2.4Ah so multiply that times 1000 (milli-1000 correct?) and thats the answer? i really like the looks of those packs. sorry for all the questions.

7s LiFePO4 would be pretty close to 6s Lipo. Each cell is 3.2v 1200mah. You can parallel cells, like I did (3600mah). I bought the cells loose (the product name is "New Product"), and they have nickel strips for easy soldering.

So how would I charge LiFePO4 at to do them in around 35minutes? Do you think they are good cells?

What determins how fast you can charge them, with Nimhs they are all the same, with Lipos it seems that the batteries determine it?

...and I see 6s packs, which is around 19.2v, do I only need 1 pack? So I only have on pack on my truck instead of 2 nimh packs of 8 cells or how ever many? Do I go for 2x 3s Lipo, or just 1x 6s Lipo. :S

You would charge them at 2C (2 times capacity). The first 30mins is a CC charge, which is to about 90%. The rest of the charge time is the CV phase, which with these batteries is short.

The charge time with Lipos/LiFePO4 depends on how much was taken out, and how quickly the CV charge phase goes. The LiFePO4 CV phase goes quickly.

With Lipo in a dual-battery monster truck, usually it is a good idea to get two 3s packs and put them in series like you would with NiMh cells.

ON these life po 4 cells. How many could you run on a 9920. It comes out to 7.5. I was wondering if it would take 8s or not.

What charger would you reccomend to do 6s LiFePO4 at 2C? How many amps is 2C or is it a charge setting?

Thanks peeps,
Nick.

I think 7 is the limit. 8 may be too high, but it would be worth a try (IMO) if you have the cash to fry a 9920 (which I don't).

You can use any Lipo charger to charge these batteries. Their rated maximum voltage is 3.65v (their CV voltage), but they are capable of 4.20v. Personally, I use a Li-Ion charge setting, which is to 4.10v, which is easier on the cells.
2C just means that it is twice the capacity of the pack, so a 3600mAh pack charged at 2C is 7.20amps (7200mA).

so about how big is a 4s pack that is 4s4p? i think i would run a 3s4p and a 4s4p although i think it would be to big. i think i would be better of with a couple of 3s2p 8000mah lipo packs correct?

A 4s4p LiFePO4 (Lithium Iron Phosphate, for those that don't know) would measure about 36mm tall x 70mm wide x 144mm long, and this would be for a side-by-side configuration (like what I use). If you did a shotgun style, it would be 36mm tall x 72mm wide x 140mm long.

It's all your choice as to what to get. Each type have their advantages and disadvantages (relative to each other), and both are better than NiMh.

I'm still unsure of the charging.

Why can't I buy just any Lipo and charge it at 2C? Also, if I bought 2 different packs, say a Kokam and LiFePO4 both 6s 3500mah, will they take the same time to charge at 2C?

Lipos usually can't handle 2C without dramatically reducing the number of cycles that they will run for. As newer and better technology comes out, Lipo cells are starting to be able to be charged at greater than 1C (but still only a few are capable).
A Kokam and LiFePO4 will finish the CC (constant current) phase of the charge at the same time, but the LiFePO4 will finish the CV (constant voltage) phase way ahead of the Kokam, just because its normal CV voltage is 3.65v and it is being pushed with extra charge all the way to 4.20v.

Thanks,

Since I'm in the UK, I've been looking at these:
http://www.flightpower.co.uk/proddet...p?prod=4200016

My Triton (by Great Planes) can do 4s lipo @ 2.5a max. So I can charge a pack at time. I thought I want to try Lipos before buying a new charger to do them faster or more cells at once, seems logical.

If I did 2.5a for 3300mah, is that like 1.5C? What else would I need to charge, any sensors or anything? Does the Triton detect when it is charged and stop, safety etc?

Accually nick it is not 1c for the 3300 mah at 2.5 amp. It would be 3.3 amp for a 3300 is 1c.

Whats the price of that in US dollars? And do they ship in the US, I might look into those also.

Would it be better to get a 3s and 2s or just one 5s pack if I wanted to run 5s total? Or in other words, if I wanted to run 5s now and 6s later with a different motor, could I get the 3s and 2s now and just get another 3s later to make 6s? Or would that 1 3s pack being older and run more cause conflicts? However looking on that website, I dont see them in a 2s configuration. What would I do there?

2500ma /3300mah = 0.76C.
A balancer would be nice to have, and is a good investment since it will keep the cells at the same resting voltage, which will increase the overall life of the pack.

Instead of getting Flightpower from the UK, you can get Hyperion or Polyquest XP or Duralite or Impulse in the U.S. Any packs that are almost the same size/weight at the same capacities from these vendors will use the same cells as the Flightpower packs.

If you want to run 6s later, why not just get it now? It isn't a good idea to mix and match new/old packs in series during discharge because the older pack will hit LVC sooner than the newer pack.

Well I'm running a 7xl right now. I think 6s would be a bit too much. I was thinking abou getting like a 9 or 10XL later on thats why I wanted the possiblilities of 6s. You got links for those manufacturers?

http://www.hobbypeople.net/mfr/IMPLSE01.asp
http://duralitebatteries.com/batteries-egold.html
http://aircraft-world.com/shopdispla...o+%2D+HYPERION (the ones in the blue wrapping)
http://www.brchobbies.co.uk/?page=sh...ory=4&start=24

There are lots of other sites, these are just a few of the ones I know of.

I'm looking for a charger now, the Astroflight looks good, anyother? Wanting to be able to have high amps (Astroflight does 7.5), for future flexibility but only around 8s cell limit.

Looked at the Schulze but they don't provide any information except how many cells they do.

Man, my LHS handles the Polyquest XP packs for the air crowd. I was looking at them yesterday in the glass cabinet, couldnt see them well but thats them. They have the 3s 3700mAh pack atn$137 and I didnt see the 2s price. They also have the Triton charger. What kind of balancer would I need to get?

Personally, I'd be wary of the AF109 for high cell counts. I've read multiple stories of it "switching" the cell count, and the user not being able to stop it unless they unplug the battery.

For chargers, there's the Super Brain 989 that can do 8s Lipo (not sure how many amps):
http://www2.towerhobbies.com/cgi-bin...?&I=LXLTW4&P=7
Or, there is the Multiplex LN5014 that can do 5s Lipo at 5amps:
http://www.rc-monster.com/proddetail...531lipocharger

IMO the Triton isn't a good Lipo charger. Only 4s up to 2.5amps. You can get a $50 charger with those capabilities.