Lipo vs. Life(A123)

[ThomasIreton]

Hello,

I have just completed building a Brushless Jammin CRT.

I am very new to both the lipo and A123 batteries.

Can someone please tell me the differences between them?

Thanks,
Thomas

[Sammus]

This is a fairly good read

http://media.hyperion.hk/dn/a123/123-brief.pdf

Basically, LiFe are tougher and generally have higher discharge capability, but they take up more room and are slightly heavier. LiFe can also receive a full charge in under 15min, whereas (in my experience) lipo is usually 1-1.5hrs. (charging at 1C).

My A123 hit the CV phase of their charge about 20s before they finish, but for my lipos It was normally like an extra half hour to get that tiny bit of extra capacity (if you don't know much about how lithium batteries are charged it is worth finding it, note that you can't use a nimh peak charger, you need a charger designed to do lithiums. Also, lipo and life use slightly different charge algorithm, nearly all new chargers do both though).

Life's cells have a larger voltage drop than lipo, I think this is largly due to people comparing them to bigger lipos though. E.g, I used to run 6s 4000mah 20C lipo's in my revo, then swapped to 7s1p A123. You can notice slightly less punch, but remember the A123's are nearly half the capacity of the 4000's. Running 2p A123 would probably be just as good, but take up nearly twice as much room lol.

On a truggy I think space isn't really a premium, so A123 is certainly a viable option. If your racing I'd tend toward lipo because of the weight reduction (which would be in the order of 100s of grams, depending how much battery you plan to run)

And lastly, A123 stay tend to balance themselves with cycles, so balancing isn't as crucial with A123 as it is with lipo (though still recommended).

[ThomasIreton]

Hmm...
That all helps a lot!
Thanks very much!

But what kinds of run times do you get on life batteries?

Lipos come in many different Mah, Life only come in 2300mah. Why is that?

[Sammus]

Theyre a new cell chemistry. You can also get life in 1200 (or 1100, I can't remember). I think we will see more sizes in the future.

I have tried a few combinations. Geared for roughly the same speed as nitros (in a buggy) I get about 7-8min on 4s1p, and about 15min on 3s2p. I only got like 6min on 5s1p, but I was way overgeared plus using a too high kv motor, so most of the energy would've gone in heat from the motor lol. 3s2p seems good for racing on anything but a big open track. I will probably stick to 4s2p though, and should get close to 20min runs.

In a truggy I think 4s2p would be the bare minimum, and would be tempted to run at least 7s1p (max for a 6s esc, like mmm) or maybe 5 or 6s2p, depending on the tracks you race on. If its just for bashing I'd go life for sure, but for racing I'd be tempted to use lipo anyway.

[lincpimp]

Personally, lipo seems to package better than a123. I have not really tested a123 cells, but have had great success with lipo. A 5000mah 5-6s lipo with the appropriate motor will produce great power and runtimes. A123 cells are 2300mah, so 2p is required for decent runtimes. But 2p setups get heavy.

I like lipo, and see no benifit from a123 for my use. Plus you have more choice with lipo for a charger, as not every lipo charger will do a123.

[ThomasIreton]

Thanks...

I would only be using for bashing right now.

Could you clear one thing up for me? What would be the difference between the 6s2P and the 6s1P. What does the 'P' mean?

[lincpimp]

Originally Posted by ThomasIreton

Thanks...

I would only be using for bashing right now.

Could you clear one thing up for me? What would be the difference between the 6s2P and the 6s1P. What does the 'P' mean?

P refers to cell arrangement. A 2s2p pack has 2 pair of 2 cells. Both pair are wired in series, to add the voltage, then the pair are wired in parallel to double the capaicity. So a 2s2p a123 pack would be 6.6v and 4600mah, 4 cells total. A 6s2p pack would be very large and heavy, twice the weight of a 6s1p pack, as it has 12 cells total. Hope that makes sense...

[JThiessen]

THis might help you on the pack set up (it can also be found in the sticky thread "Speed Calculator") http://www.scriptasylum.com/rc_speed/_lipo.html

[ThomasIreton]

Thanks for all the Help!
I think i am going to go with the A123 cells.

Is there any suggestions on what who to buy them from?

And Should I go 6s2p or 7s2p

Keep in mind that i am using a Mamba Monster and a Fiegao 8XL

[othello]

A123 cells are a good choice for bashers.
. With the right charger(s) you will only need 2 battery packs to run all day long, as you can recharge them with 10A -> around 15 min for a charge with a 1p battery pack with 2200mAh.
. LVC is not a must as they drop in voltage abruptly when they are empty. You'll stop immediately to drive as power decreases rapidly.
. Powerwise 8 cells are more then enough for a truggy. I do calculate with peaks of 250W per cell (eagletree data with peaks of 2.5KW+ with 10s1p A123).

7s2p will rev the XL8 (2084kv) up to 44000rpm (3V per A123 cell under lighter load). With a 13t pinion your overall gearing is 1:15,775. With typical truggy tires (145mm) your speed will already be at 45mph+. Your Feigao would run way too hot and smaller pinions are not ideal.

6s2p A123 will rev the XL8 (2084kv) up to 38000rpm. Still a bit on the high side. With a 13t pinion your speed will be around 40mph. Already too fast for a small pinion for my liking.

5s2p A123 would be my choice (with a 2p setup) and will rev the XL8 up to around 31500rpm (this is slightly below what you can expect from a typical nitro engine under load in a truggy). With a 13t pinion your CRT will be at 35mph with plenty of pinion options to cover 35-50mph. A 14-15t pinion would be the perfect choice to reach 38mph (about what you can expect from a nitro truggy), a good speed for a track and the load for your motor should be alright to keep temps in check even on a hotter day.

If you would stay with a 5s2p setup (10 cells, around 750-800gr) you will only need 1 dewalt (ebay->DC9360) pack which contains exactly 10 cells.

I did run 10s1p A123 in a truggy and now do run 9s1p with a 1100kv Neu 1515/2Y. Runtime is between 8-9 minutes with a gearing for 38mph (62km/h) on a bigger track. A good friend of mine did run his Mugen MBX5T truggy with 6s2p A123, Neu 1515/1Y (2200kv) and a gearing for 42mph (68km/h). During hotter summerdays (86°F+) his motor got quite hot (up to 176°F). He was already using a small 13t pinion and didn't wanted to use a smaller pinion. He therefore switched to a HV setup with 11s1p A123, Neu 1515/2Y. Motor temperatures dropped somewhat between 150-160°F. Runtime also about 8 minutes as he is geared for higher speed and does run a heavier truck (thus consuming more energy).

Eventhough he is geared for higher speeds we do run head to head. Eventhough he runs 2 cells more (= more energy on board) then i do, his runtime is slightly shorter then mine as he uses more energy to push his 1lb heavier truggy to similar or higher speeds.

[ThomasIreton]

OK,
If I buy the Dewalt pack, is there a lot of modifications that i have to do to it?

[Sammus]

I've heard and read in several places that DeWalt packs don't use A123 cells anymore because they didnt need the enormous discharge rate or the price tag that comes with it (but I haven't been willing to test these claims). I would recommend you buy the cells from an rc store that sells them (aircraft-world, hobbycity, tanicpacks are 3 I know of).

When I got my cells from h-c they had solder tabs welded to them which made pack construction a breeze. From a-w they didnt, and I bought battery bars. Assembly was more tricky but still wasn't too bad. I did have to buy a much more powerful (80W) iron and be careful not to overheat the cells. Something to keep in mind.

And yes I agree with pimp, size weight and fitmentwise, lipo wins. I just love the 15min charges and a123 :)

[ThomasIreton]

Well, I would rather go with lipos but they are just too darn expensive.
Does any one know where i can get good lipos for a good price?