C number

[Rip King MC]

What does the number followed by the letter "c" on a battery mean, and how does it effect the performance?

 

[Grimbles]

Discharge rate. Higher = better. 1c = discharge entire battery in 1 hour. You are often given 2 c ratings - the lower is the sustained discharge rate, the higher is the peak rate.

So a higher c rating can discharge the entire battery quicker. Normally this is more punch!

 

[Jay R]

Example. If you have a 4,000mah battery that is 1C you can discharge it at 4 amps over one hour. If it is 2C you can discharge it at 8 amps over half an hour. 3C will be (4x3)16 amps over 20 mins, etc...

These are 'theoretical' numbers, they don't quite work like that in real life but it's a guide.

The higher the C, the higher the current you can draw out of it without damaging the battery.

 

[olds97_lss]

Example. If you have a 4,000mah battery that is 1C you can discharge it at 4 amps over one hour. If it is 2C you can discharge it at 8 amps over half an hour. 3C will be (4x3)16 amps over 20 mins, etc...

These are 'theoretical' numbers, they don't quite work like that in real life but it's a guide.

The higher the C, the higher the current you can draw out of it without damaging the battery.

I've never heard it explained that way in relation to time. I guess it makes sense, just seems confusing now. lol!

So a 50C 1000mah lipo will discharge at max current (50A) in 1.2 minutes, or a 50C 5000mah (250A) 1.2 minutes.

 

[DoNoHarm]

Just done confuse discharge C rating with the charging C rating

 

[olds97_lss]

Just done confuse discharge C rating with the charging C rating

Fire = bad!

 

[DoNoHarm]

Fire = bad!

Nothing wrong with a surprise bonfire ?‍

 

[Jay R]

I've never heard it explained that way in relation to time. I guess it makes sense, just seems confusing now. lol!

So a 50C 1000mah lipo will discharge at max current (50A) in 1.2 minutes, or a 50C 5000mah (250A) 1.2 minutes.

That's right in theory. In practice it doesn't work out that way as the max C rating is usually meant only for bursts. If you did it for the full charge, the battery would end up stuffed. Also manufacturers tend to exaggerate their C rating so it's just useful as a general guide. If you are drawing huge amounts of power, you need higher C.

 

[olds97_lss]

That's right in theory. In practice it doesn't work out that way as the max C rating is usually meant only for bursts. If you did it for the full charge, the battery would end up stuffed. Also manufacturers tend to exaggerate their C rating so it's just useful as a general guide. If you are drawing huge amounts of power, you need higher C.

Yep. I get that. Just never read it explained how you did and never really thought about it.

 

[Rip King MC]

So a higher c rating means more power but less run time, and a lower C rating means more run time, but less power?

 

[DoNoHarm]

So a higher c rating means more power but less run time, and a lower C rating means more run time, but less power?

No run time stays exactly the same. It just means more power.

 

[jkflow]

Let me see if I can confuse everyone a bit more. It's all in the details.

The mAh rating spelled out is 'milli Amp per hour' or 1/1000 A per h. Marketing prefers a lot of 0's and technical nonsense.
A 5000mAh (5Ah) rating will give you 5A for 1h and you exhausted the capacity. This is the theoretical limit.

The C rating for discharge is the max allowed 'Amps' you are allowed to pull. C is to be used as a multiplier for the 'AMP rating' again per hour
A 10C rating allows you to pull a max of 10x 5A = 50A, to get to the same capacity it's now for only 60min/10 = 6 minutes.

There is a separate C rating for discharge and charge. Exceeding either will damage the battery.

Higher C rating means that you can pull more power in a lesser amount of time. In reality though, the motors will pull what they want and either you battery collapses under the stress (low C rating) or you have a lot of fun (higher C rating).
The minimum rating for stock ARRMA is 35C BUT that translates into marketing terms to ~ 65C or higher, really depends on the Vendor.

Hope that helped.

 

[arrma_tigger]

No run time stays exactly the same. It just means more power.

I don't think this is right - at least it doesn't read right. If you have 2 ponds both filled with water - pond 1 uses a 25" pipe and pond 2 uses a 100" pipe, the water will obviously move alot quicker in the 100" pipe (if you're requesting it) but there is no more water available after you deplete it, therefore you will drain pond 2 quicker.

 

[jkflow]

Correct . Capacity remains constant, if you pull it out faster it will empty out a lot quicker. By all means, that is unrelated to the C rating.
The C rating will only 'allow' you to do it.

 

[arrma_tigger]

Correct . Capacity remains constant, if you pull it out faster it will empty out a lot quicker. By all means, that is unrelated to the C rating.
The C rating will only 'allow' you to do it.

Agreed - if you're not calling for extra power, then it will drain the same .. but who is not calling for more power.

 

[LibertyMKiii]

It is also worth noting that if you are asking for 200 amps out of a LiPo that is low rated like 20C, the cells will be overly stressed. You can bet that LiPo won't last long. This is part of the reason why many ESC brands recommend batteries with 60C or higher.

 

[DoNoHarm]

I don't think this is right - at least it doesn't read right. If you have 2 ponds both filled with water - pond 1 uses a 25" pipe and pond 2 uses a 100" pipe, the water will obviously move alot quicker in the 100" pipe (if you're requesting it) but there is no more water available after you deplete it, therefore you will drain pond 2 quicker.

Interesting. See I’m not really that smart with electrics so I didn’t know this. I always thought that it worked differently, that no matter what battery you have, it’ll deliver whatever current the motor asks for, it’ll just get way hotter and possibly even kill itself if it’s not up to the task.

 

[LibertyMKiii]

Interesting. See I’m not really that smart with electrics so I didn’t know this. I always thought that it worked differently, that no matter what battery you have, it’ll deliver whatever current the motor asks for, it’ll just get way hotter and possibly even kill itself if it’s not up to the task.

Exactly!
Even the best motors are only around 90% efficient turning the power into rotation. The rest turns into heat.
Then you have other factors in the system like the wire, solder joints, and connectors. Some times we see bad connectors/solder joints build heat due to their resistance to the flow and cause a failure.

 

[jkflow]

@DoNoHarm you are not incorrect but the next variable that comes along is the infamous internal resistance (IR).
A lower C rating typically has a higher IR. Also true, that a damaged battery shows itself by a higher IR (when compared with equivalent).
Pure Ohm's law at play.
That little values determines the true C rating.

In addition all the other things that @LibertyMKiii is listing.

 

[DoNoHarm]

@DoNoHarm you are not incorrect but the next variable that comes along is the infamous internal resistance (IR).
A lower C rating typically has a higher IR. Also true, that a damaged battery shows itself by a higher IR (when compared with equivalent).
Pure Ohm's law at play.
That little values determines the true C rating.

Always thought higher IR means it can’t deliver the current it needs to. So while it still does, it just gets hotter. I see this is not the case.

Learn something new every day.