C number

[jkflow]

That's why we have this forum, I learn every day as well!
I've just been doing this electrical stuff as a profession for quite a while

 

[arrma_tigger]

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.

All I was replying to was the battery - and I didn't specifically say you were wrong; I said it might read wrong. a 25C battery and a 100C battery may or may not have the same run time. Sure - all the other stuff plays into it - but the question was about the C number. If the driver is driving the same way with both packs, sure, they will last the same amount of time. If the driver decides to access the 100" pipe, that pond is going to drain alot faster - and that same run time no longer exists.

 

[Jay R]

but who is not calling for more power.

You might for a couple of reasons.

First: lower C batteries are usually cheaper than higher ones.
Second: size for size, a lower C battery of the same type will have more energy (ie a higher mah rating.)

Batteries have 2 things inside them, electrolyte and plates. The electrolyte holds the energy and the plates help take the power out of the electrolyte and convert it to electricity. To get more power out in a single go, you need more plates but that means there is less room for the electrolyte. If you have 2 batteries the same size and of the same chemistry but one is higher C, it will have less stored energy capacity (Mah).

This is why a full size car battery designed for high current when starting may only be 40Amp/hour where as a leisure battery the same size may be 70Amp/hour.

If you see same size batteries with same mah rating but one is higher C, it's because it has better quality or better chemistry inside and therefore more expensive.


So... if you have a rock crawler (not drawing large amounts of power in one go) and want to fit the 'biggest' battery possible, you will probably be better off with a lower C rated one as it will have more stored energy and longer runtime.

 

[LibertyMKiii]

I have also heard the low C-rated batteries, for example a 2 to 5 C 3s LiPo intended for use as a battery for your radio transmitter can handle staying charged for long periods of time without the damage/explosive concerns of traditional LiPo's.

Any truth to that? Given the chemistry is likely 95% the same I have a hard time believing it...

 

[jkflow]

I have also heard the low C-rated batteries, for example a 2 to 5 C 3s LiPo intended for use as a battery for your radio transmitter can handle staying charged for long periods of time without the damage/explosive concerns of traditional LiPo's.

Any truth to that? Given the chemistry is likely 95% the same I have a hard time believing it...

Yes, true. Good examples are the 18650 type batteries in flashlights and battery packs for screwdrivers, trimmers etc.

This issue with staying charged and danger is only in the high performance packs.

Car batteries, all but Tesla have moved to only charge to ~ 4-4.1V to maintain battery life.
Cellphones and laptop batteries have also migrated to packs with less risk but have have lifetime issues, if they stay fully charged.

Don't get this wrong, they all have the same issues but based on their design it's less of an impact. They are designed for a 5 year life and can stay charged all the time, comes at the cost of discharge performance.

 

[LibertyMKiii]

Yes, true. Good examples are the 18650 type batteries in flashlights and battery packs for screwdrivers, trimmers etc.

This issue with staying charged and danger is only in the high performance packs.

Car batteries, all but Tesla have moved to only charge to ~ 4-4.1V to maintain battery life.
Cellphones and laptop batteries have also migrated to packs with less risk but have have lifetime issues, if they stay fully charged.

Don't get this wrong, they all have the same issues but based on their design it's less of an impact. They are designed for a 5 year life and can stay charged all the time, comes at the cost of discharge performance.

For some of our RC setups the idea of charging 2+ LiPos for the ESC/Motor. One for the radio, and another to run the cooling fans is quite a pain!

 

[arrma_tigger]

You might for a couple of reasons.

First: lower C batteries are usually cheaper than higher ones.
Second: size for size, a lower C battery of the same type will have more energy (ie a higher mah rating.)

Batteries have 2 things inside them, electrolyte and plates. The electrolyte holds the energy and the plates help take the power out of the electrolyte and convert it to electricity. To get more power out in a single go, you need more plates but that means there is less room for the electrolyte. If you have 2 batteries the same size and of the same chemistry but one is higher C, it will have less stored energy capacity (Mah).

This is why a full size car battery designed for high current when starting may only be 40Amp/hour where as a leisure battery the same size may be 70Amp/hour.

If you see same size batteries with same mah rating but one is higher C, it's because it has better quality or better chemistry inside and therefore more expensive.


So... if you have a rock crawler (not drawing large amounts of power in one go) and want to fit the 'biggest' battery possible, you will probably be better off with a lower C rated one as it will have more stored energy and longer runtime.

True - I'm simply saying if you have a 100C battery and not a 25C battery, would you not take advantage of that bigger pipe?