"C" rating on LiPo batteries?

[Coelacanth]

I'm eventually going to be buying a few LiPo batteries and I'm familiar with the number of cells, mAh rating, and voltage...but the "C" rating is a new one on me. I've researched that a higher "C" rating may result in more punch as those batteries have less internal resistance...but in a real-world situation, what are your observations comparing LiPo batteries of different "C" ratings?

[Jay Dub]

The "C" rating refers to the amount of amperes (in relation to the capacity) that a particular pack it rated to safely produce. However, this doesn't necessarily mean more punch, but rather the availability of power to a particular system. So this means that in high power draw systems, the motor will be less limited by the power availability of the pack. In low power systems (e.g. a closed endbell 540 mabuchi motor) the "C" rating is less important because you will never be drawing enough amperes to tax a lower rating pack. -Jeff

[jwscab]

The C rating is the way to determine how efficiently the cells will discharge.

Here is an example:

Say you have a system that is capable of peaking at 90 amps during a full throttle punch.

One pack is 3000mAh, rated at 25C. This pack has an effective current capability with minimal temperature rise of 3.00A x 25c = 75A. This pack will work with the above system, but you will potentially overheat the cells due to trying to pull more current than the cells are rated for.

Another pack is 4500mAh, rated at 25C. The pack can sustain 4.5A x 25C = 112.5A. This pack will work efficiently for the system above.

And yet another pack is 3000mAh, rated at 35 C. This pack can sustain 3.0A x 35C = 105A. This pack will also work for the system above.

[THEYTOOKMYTHUMB]

C ratings are like everything else in the power world(stereos, tools etc…) in my opinion. Don’t mean anymore than what the manufacturer wants to advertise. I’ve raced or ran against many many other lipos and unless you’re at the World Championship level or something just save your money and get the stuff listed below. Very strong middle of the road pack and very reliable in my experience.

You’ll see this same pic from a lot of stores. Just find the cheapest after shipping. They run a lot of variations with pricing and shipping, but you should get one for about $25-30 to the door with the right deal. This is just the first link I happened to find w/o a hardcore search. Love these packs.

http://cgi.ebay.com/7-4v-5000mAh-30C-2-cell-2S-Lipo-RC-Battery-AKKU-7-4-WnF-/160394400391?pt=RC_Modellbau&hash=item2558405287

Charger with compatible balancing tap. It’s out of stock here, but you can find it somewhere. I use a different charger because I didn’t know any better. I know lots of people that use this one though.

http://www.hobbypartz.com/thac6smbachw.html

I’ll admit I have not shopped lipos in a good while because mine have held up well so you may do a bit of research. I have seen a lot of the Venom packs running lately and they do well if you’re not comfortable with these.

I know people have probably gotten tired of me promoting these packs, but I naively spent about $350 to get one lipo and one charger several years back and wish I’d had this info then. IMHO



P.S. Don’t worry too much about a lipo cut off. You’ll get a good feel after a while. Just stop at the first sign of fading. A 5000mah pack runs a good while before danger.

[AscotConversion]

Really the only relation to punch is that with less expensive lipos, the higher C rating usually results in lower internal resistance, since they have to use better construction/material to get to the higher C rating. Higher end lipo companies often have a lower IR throughout their product range since they use better construction/material in general.

[Greebo]

Just one extra bit of info... as mentioned above, C rating is all about sustained Amps.
What this is supposed to mean is that a fully charged pack will deliver the C rating specified while maintaining 3.7V per cell.
Thats the critical point.

You want to make sure your LiPo's don't drop below 3V or you risk them catching fire or worse (people argue about the value but 3 is close enough for my point). If you try to draw too much current from a low C rating LiPo, the pack voltage could drop to dangerous levels.

[RC104ever]

Great thread, thanks. Was wondering about websites vs uncensored, what's the difference?