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Old Jan 29, 2013, 06:22 PM
Jim in the Desert
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Relationship between C rating and amps you can charge at?

Been gone a while, and am told you can charge lipos much faster now. Is this because of the higher C ratings?

Can you determine what amps you can charge at based on C ratings (normal and burst)?

Thanks
Jim
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Old Jan 29, 2013, 07:02 PM
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LIPO's can be charged at 1C. Example a 3,000ma LIPO can be charged at 3 amps.

Vince
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Old Jan 29, 2013, 07:09 PM
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5C charge rates are common these days.
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Old Jan 29, 2013, 07:27 PM
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Here you go.
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Old Jan 29, 2013, 08:12 PM
Jim in the Desert
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Thanks all. My lipos printed C on the pack does not match its mah.
Using Rayne's link, C = mah capacity/1000.

So is this a correct determination of how I can charge the following lipos?

I have a:

7 year oid, 13C written on pack, 5300 mah, 4S. C = 5.3a. Cx5 = 26.5 amps charging.

5 year old 20C written on pack., 2400 mah, 3S. C = 2.4a. Cx5 = 12 amps charging.

I see on chinahobbyline a
new 50C written on pack, 5400mAh 2S. C = 5.4a. Cx5 = 27 amps charging.

Is this correct?
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Old Jan 29, 2013, 08:30 PM
Jim in the Desert
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Ok, I spoke too soon. Rayne's like explains the C rating on the pack is the discharge rate.

Still, I have problems with the idea that it's OK to charge my 7 year old 4S pack at 5C. Seems like back in those days 2C was the max charge rate. I'm afraid of having a bonfire called my house.

So back to my question: how do you know for a particular lipo what the maximum charge rate is? a 7 year old 13C discharge rate vs a new 50C discharge rate would I think have different coefficient of C for determining safe charge rates...????

Jim
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Old Jan 29, 2013, 09:05 PM
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Originally Posted by cloud_9 View Post
Ok, I spoke too soon. Rayne's like explains the C rating on the pack is the discharge rate.

Still, I have problems with the idea that it's OK to charge my 7 year old 4S pack at 5C. Seems like back in those days 2C was the max charge rate. I'm afraid of having a bonfire called my house.

So back to my question: how do you know for a particular lipo what the maximum charge rate is? a 7 year old 13C discharge rate vs a new 50C discharge rate would I think have different coefficient of C for determining safe charge rates...????

Jim
Usually the battery will have the maximum charge rate specified on the label somewhere if it's higher than 1C. If you can't find it then I'd assume it's unsafe to charge those batteries at anything higher than 1C.
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Old Jan 30, 2013, 04:51 PM
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A good rule of thumb USED to be 1C , and a good rule of thumb I used for a few seasons was the actual discharge "C" rating divided by 10. For charging most all users and chargers have the cv to protect against an outrageous charge current. We don't have that during the discharge.

Your two packs were probably listed as 1C max rate and would be 5.3 and 2.4 amps respectively. Your new pack is probably a 5C rated charge rate so you have that one correct as 27 amps.

Please be advised that your old 13C pack and your old 20C pack may now be less than half of those numbers now.
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Old Jan 30, 2013, 05:05 PM
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1C charge rates were very common and standard up until a few years ago, then some manufacturers approved 2C rates, then 5C, etc.. The Thunder Power packs I use now are rated up to 12C charge rate. You shouldn't charge older batteries higher than they were originally spec'ed for, if the label doesn't clearly indicate higher than 1C charge rates then stick to 1C...

Jack
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Old Jan 30, 2013, 08:39 PM
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all good information however, whats a matter for you, can't you check your batteries while they are charging? Of course you can.

First rule of thumb is that lipo's should not get warmer during charge and in fact, if you charge just after a flight (and the lipo is already warm) then it should cool down during the charge.

Second, check to see if your lipo is puffing during the charge and if so, stop the charge!

Basically, it comes down to common sense vs printed media and what someone else said. With lipo's, it pays to err on the side of caution! I love lipo's and I assume that all is NOT well, until I can prove otherwise!

Michael (if your not fryin, your not tryin!)
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Old Jan 30, 2013, 11:33 PM
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A question that has never been adequately explained, in so far as I know, is, if a pack can be specified as having a 25 C continuous discharge rate, then why cannot it have also a 25C charge rate?
I see no reason why it can't be charged as fast as it can safely be discharged, but I willingly profess ignorance and would like to be educated on the matter.

Does the reason for the difference in charging rate as opposed to discharging rate lie in the way a battery charges as opposed to discharges?
Is it a matter of affecting longevity of capacity or is it actually a safety issue? If either one or both an explanation of what is happening to the battery would be most welcome.

Also, and related, why has it always been assumed that a 1C discharge rate has been the norm?
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Old Jan 31, 2013, 02:49 AM
Jim in the Desert
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Thank you all for the great help. I think I understand how to proceed now. With my old lipos, I'll just keep charging them at 1C, which my Thunder Power TP-101C defaults to. I have some newer packs that I can charge faster.

Thanks
Jim
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Old Feb 03, 2013, 03:54 AM
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[QUOTE=midnite;23986871]A question that has never been adequately explained, in so far as I know, is, if a pack can be specified as having a 25 C continuous discharge rate, then why cannot it have also a 25C charge rate?
I see no reason why it can't be charged as fast as it can safely be discharged, but I willingly profess ignorance and would like to be educated

Not trying to be smart but many battery manufactures are generous with the ratings they give their product .Never is there any specific as to is that a burst current and for what period i.e. 1 second or 1 hour
If you do a search there are posts covering extensive tests undertaken to determine the correct rating
Try running at the stated C rating where good chance the battery will curl up and die
Another factor is you would need a massive DC power supply to have sufficient output to charge at very high C ratings
Cheers Jim
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Old Feb 03, 2013, 04:27 AM
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Quote:
Originally Posted by midnite View Post
A question that has never been adequately explained, in so far as I know, is, if a pack can be specified as having a 25 C continuous discharge rate, then why cannot it have also a 25C charge rate?
I see no reason why it can't be charged as fast as it can safely be discharged, but I willingly profess ignorance and would like to be educated on the matter.
One reason is the balancing power that a charger has. Many chargers have balancing currents limited to 200ma or so. There are some newer ones that have balancing currents as high as 1 amp. The point is if you are charging at very high currents the balancers cannot keep up and so it is very possible for an individual cell to be charged over 4.2 volts.

It has always been my opinion that the quality of the charger is the limiting factor on charge rates. As long as the charger balancing circuit can keep any cell from going over 4.2 volts the charging amps are safe. About six years ago I inadvertently charged a pack at 5C. The pack did not even get warm and all cells were at 4.2V at the end of the charge. I was using an FMA 10S charger.

Glen
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Old Feb 03, 2013, 05:19 AM
Jim in the Desert
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[QUOTE=Jimob23;24018230]
Quote:
Originally Posted by midnite View Post
A question that has never been adequately explained, in so far as I know, is, if a pack can be specified as having a 25 C continuous discharge rate, then why cannot it have also a 25C charge rate?
I see no reason why it can't be charged as fast as it can safely be discharged, but I willingly profess ignorance and would like to be educated

Not trying to be smart but many battery manufactures are generous with the ratings they give their product .Never is there any specific as to is that a burst current and for what period i.e. 1 second or 1 hour
If you do a search there are posts covering extensive tests undertaken to determine the correct rating
Try running at the stated C rating where good chance the battery will curl up and die
Another factor is you would need a massive DC power supply to have sufficient output to charge at very high C ratings
Cheers Jim
Thanks...

How massive?
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