5000mAh almost 6000mAh and C rating - RC-Monster Forums

Mentat · **5000mAh almost 6000mAh and C rating -** 07.07.2009, 07:38 PM

I know i have asked something like this earlier at some point, but i am still curious, I have the following batteries and when they get re-charged they get almost 6000mAh capacity put back in. How is this so? also whats the deal with the 20c 25c etc... batteries and how is that factored in. what would be the biggest difference with a 5000mAh 20c and a 5000mAh 25c? I dont think i can tell a difference when running them.

4s1p 5000mAh 20c zippy flightmax

4s1p 5000mAh 25c turnigy

4s1p 4900mAh 25c Rhino (zippy)

5s1p 5000mAh 20c Rhino (zippy) sold to SuicideNeil tho.

suicideneil · 07.07.2009, 07:56 PM

Someone explained it recently in another thread/forum- its basically to do with the charge process not being 100% efficient, so the charger may often push more current to the lipo than actually goes in as such. Also, the lipo's mah rating may not be 100% accurate due to god knows how many factors to do with construction and chemical composition over time etc etc.

Discharge rates is only important when using (discharging rapidly) a lipo- the higher the C rating, the quicker it can be discharged & therefore the more punch it has, although capacity is also an important factor combined with C rating, in order to calculate the total amount of current it can push.

4s 5000mah x 20c = 100amps continuous, 1440 watts.
4s 5000mah x 25c = 125amps, 1850watts.
4s 4900mah x 25c = 122.5amps, 1813 watts.
5s 5000mah x 20c = 100amps, 1800watts.

They are all fairly even in terms of power potential and current output, though the 1st one may be a bit warmer by the end of the run. If you gear for the same speed with the 20 & 25c 4s lipos, I doubt you would notice much of a difference really- maybe if you turned down the punch the 25c lipo would turn out to be a little more 'feisty' under acceleration, but I wouldnt worry about anything really.

Posted my lipo yet?

Mentat · 09:07 PM

so it appears that a 4900mAh 25c is a better buy then a 5000mAh 20c? Neil could u PM me your address. I dont have it. Also how can u find out the TRUE mAh and the TRUE C discharge Rating?

spartan805 · 07.07.2009, 11:54 PM

4s 4900mah x 25c = 122.5amps, 1813 watts........ I just got this from HC. Cant wait to try it at the track with my 2650.MMM combo!

Mentat · 07.08.2009, 12:17 AM

Quote:

Originally Posted by spartan805

4s 4900mah x 25c = 122.5amps, 1813 watts........ I just got this from HC. Cant wait to try it at the track with my 2650.MMM combo!

yeah i love the Rhino (zippy) packs u wont be sad

Patrick · 07.08.2009, 06:34 AM

Quote:

Originally Posted by Mentat

I know i have asked something like this earlier at some point, but i am still curious, I have the following batteries and when they get re-charged they get almost 6000mAh capacity put back in. How is this so?

If your doing a balance charge the balancing process will use a bit of the mah put back into the back. The longer the cells are balancing the bigger the difference will be between what has actually gone back into the pack and what the charger has put out.

Patrick · 07.08.2009, 06:36 AM

Quote:

Originally Posted by Mentat

I know i have asked something like this earlier at some point, but i am still curious, I have the following batteries and when they get re-charged they get almost 6000mAh capacity put back in. How is this so?

If your doing a balance charge the balancing process will use a bit of the mah put back into the back. The longer the cells are balancing the bigger the difference will be between what has actually gone back into the pack and what the charger has put out. Might not be the full 1000mah's difference, but could be some of it.

BL_RV0 · 07.08.2009, 11:52 AM

Quote:

Originally Posted by Patrick

If your doing a balance charge the balancing process will use a bit of the mah put back into the back. The longer the cells are balancing the bigger the difference will be between what has actually gone back into the pack and what the charger has put out. Might not be the full 1000mah's difference, but could be some of it.

Great explanation Patrick, I was wondering about that.

Mentat · 05:54 PM

how can u measure the true mAh of a lipo pack and also measure the true C discharge rating? What is the down side to running lets say a 3s1p 5000mah 20c or 25c battery in a CC Monster Mamba 2200kv combo? What is this ripple current or voltage i keep seeing tossed around?

BrianG · 06:11 PM

I don't agree fully with the theory that the charger is not 100% efficient causing more mAh to be put back in. I agree that the charger is not 100% efficient, but the mAh into the battery is mAh put into the battery, period. I would suspect an LVC value that was set too low (and so charges up more) or actual capacity is higher than rated (I have a MA 2s2p pack rated for 8Ah that is made up of 4.2Ah cells, which would be 8.4Ah). Any losses during battery charging would be evident in cell heat. And since lipos stay cold when charging, that's not it. Oh, there may be a tiny bit of heat losses, but nowhere near the amount you'd see with NiMHs.

Determining capacity (mAh) depends on what you accept as the terminating voltage. I like to see a depleted pack at ~3.6v/cell after about 10 minutes of being disconnected from anything. I then just charge it back up and see how much was put back in. Alternatively, you could use an Eagletree device to measure mAh removed during a run, but cells heat up when run hard, which is lost energy, so I wouldn't see that as an accurate measure of actual pack capacity.

And measuring true C rating is even more difficult. Just as above, you have to set what you accept as a suitable voltage drop. Example with a 5Ah battery:

If I accept 3.5v/cell as the minimum loaded voltage, I will increase the current load until it hits that level. I might get 100A as an example. I would rate this cell as 20C.

But, if I accept 3.0v/cell as the minimum loaded voltage, I will probably be able to increase the current to 130A before it hits that voltage. This would equate to 26C.

Which is right? They are both the same battery, but different ratings.

See? This is where battery manufacturers play games with us. Let's say we have Brand A and Brand B batteries. They might both be rated 5Ah @ 20C, but Brand A is $50 more. Let's say that during testing, Brand A maintains 3.5v/cell at that load, and Brand B maintains 3.0v/cell at that same load. Since Brand A is pricier, people will buy Brand B because it seems cheaper for an equal quality cell, when it clearly isn't.

The only way to get a true measure would be to consistently test each battery using the same procedures, which is lacking in the industry. Standardized testing has been talked about a number of times, but goes nowhere because it is simply too expensive to get the equipment to do proper testing.

Sorry about the long post, but I hope I made sense.

zeropointbug · 07.08.2009, 08:41 PM

Well said BrianG, my thoughts exactly! My G3 Hyperions I am sure I would be getting around 3.5v/cell @ 35C discharge based purely on the voltage drop at a lower current discharge, then calculating from there. The thing is I don't even know, because I have never, and can't draw that much current with my smaller 1512/3D. The most I have seen, when trying my hardest to do so, is ~120 amps... the voltage at those rates is roughly 3.6+v/cell, at around the 70% SOC point.