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?