lipo? what?

[73fordhighboy]

im very new to crawling & rc in general. a bunch of buddies went out and started buying these crawlers. i purchased a cliffclimber, did all the mods i thought would be simple. now im confused. i bought some banebot motors: 395's trying to ease clod stall. esc would shut down for a while... suspect-heat. so i went out and bought the tekin fx-r (not the pro one). my question is about these lipos. what does it all mean?

input power (cells) 4-7 NiCd/NiMh (2s LiPo) as on the tekin booklet.

lipo: example is a losi battery- 7.4v 3600mah 2s lipo 20c

7.4v: i get
3600mah: yup longer fun time!
2s: huh?:?
lipo: ...
20c: what?:?
hard case: get it
$74.99: will i get to crawl with my buddies again?

i have a 3 dtx 7.2v 1600mah nimh high discharge batteries.
do i even need to buy lipos

any help would be greatly appreciated.
Kurt

[khj94704]

Originally Posted by 73fordhighboy

im very new to crawling & rc in general. a bunch of buddies went out and started buying these crawlers. i purchased a cliffclimber, did all the mods i thought would be simple. now im confused. i bought some banebot motors: 395's trying to ease clod stall. esc would shut down for a while... suspect-heat. so i went out and bought the tekin fx-r (not the pro one). my question is about these lipos. what does it all mean?

input power (cells) 4-7 NiCd/NiMh (2s LiPo) as on the tekin booklet.

lipo: example is a losi battery- 7.4v 3600mah 2s lipo 20c

7.4v: i get
3600mah: yup longer fun time!
2s: huh?:?
lipo: ...
20c: what?:?
hard case: get it
$74.99: will i get to crawl with my buddies again?

i have a 3 dtx 7.2v 1600mah nimh high discharge batteries.
do i even need to buy lipos

any help would be greatly appreciated.
Kurt

2s = two 3.7 volt cells in series
20c = 20 coulomb discharge rate which is 72 amps for this pack

[ultimate_monkey]

just a bit of info for you the FXR (non pro) is compatable with 3s lipo as long as you use a 35t or higher moter.

and lipos are definatly the way to go, they are smaller and lighter then the nimh / nicd cells to get the same power out of them

[clockworks]

The C rating of a battery denotes it's maximum discharge rate, so a bigger number is better. The minimum for recent LiPos is 10C, maximum is 30 or 35C.

A 3600mAH 10C pack can deliver 36amps, a 3600mAH 20C pack can deliver 72amps.
C ratings should be taken with a massive pinch of salt, as there isn't a proper standard for measuring the discharge rate of batteries. As the current draw increases, the voltage drops.
I try and stick to around half the stated discharge rate. If a pack says 20C, count on getting 10C at a decent voltage.

BTW, I don't think that this "C" has anything to do with coulombs. A coulomb is a unit of charge - 1 amp for one second - which is different to battery C, which is a multiple of capacity, not a fixed value. An unfortunate case of an SI unit having the same abbreviation as Capacity.


There's no need to pay $75 for a pack - someone posted a link to a Hong Kong supplier that had Turnigy 5000mAH hard cased 2s LiPos for about $20. Hobbyking, IIRC.

[Reflection]

IMHO,don't fool with lipo's with less that a 25c continuous discharge rate.

Sure,lesser packs will work well with slower motors,like 55t's and such. Your money ahead if you buy a better pack from the start. If you decide to run a hotter motor later,you know your packs will handle it.

Nothing worse than having to deal with a swelled lipo. That is dangerous AND a waste of money.

[khj94704]

Originally Posted by clockworks

The C rating of a battery denotes it's maximum discharge rate, so a bigger number is better. The minimum for recent LiPos is 10C, maximum is 30 or 35C.

A 3600mAH 10C pack can deliver 36amps, a 3600mAH 20C pack can deliver 72amps.
C ratings should be taken with a massive pinch of salt, as there isn't a proper standard for measuring the discharge rate of batteries. As the current draw increases, the voltage drops.
I try and stick to around half the stated discharge rate. If a pack says 20C, count on getting 10C at a decent voltage.

BTW, I don't think that this "C" has anything to do with coulombs. A coulomb is a unit of charge - 1 amp for one second - which is different to battery C, which is a multiple of capacity, not a fixed value. An unfortunate case of an SI unit having the same abbreviation as Capacity.


There's no need to pay $75 for a pack - someone posted a link to a Hong Kong supplier that had Turnigy 5000mAH hard cased 2s LiPos for about $20. Hobbyking, IIRC.

you're right that lipo battery "c ratings" are not the SI coulomb - amp x seconds, not just amps. what you mention about voltage dropping as the current draw increases is a major reason to get a lipo pack over staying with nimh as the drop is much larger for nimh than lipo. i think there's a pretty good chance that the inability of the op's pack to provide the necessary voltage is what was causing his stalls. i'm not a huge fan of the HK lipos but would agree that you don't necessarily need to spend $75 for a decent one.

[73fordhighboy]

^^thanks fellas, i think i get it. so sell my other batteries to my buddies those banebots dont have spec for turn numbers