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Feb 25, 2020, 01:31 AM
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limodune's Avatar
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Joining batteries diffrent c rating


Can you join a 4s 4000 mah 25c battery with a 4s 4000 mah 40c battery to make an 8s battery with out problems

Mike
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Feb 25, 2020, 05:04 AM
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Yes, provided they're both in similar condition and you treat them as a 25C pack.

Edit: It's not ideal with different C ratings but, provided you limit your use to the rating of the lowest C pack, you'll be okay.
Last edited by abenn; Feb 25, 2020 at 05:10 AM.
Feb 25, 2020, 06:31 AM
Registered User
better if they get balance charged separately
Feb 25, 2020, 08:41 PM
Registered User

I would not discharge different mahr batteries together


I have never seen a discharge curve & the internal resistance curve of the 2 batteries into a shared load. Does the big battery protect the small one during discharge ?
Feb 25, 2020, 09:28 PM
Registered User
OP is putting them in series so no - each battery is on it's own seeing the same discharge current.
Feb 25, 2020, 11:17 PM
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Wintr's Avatar
The battery with the lower, real C rating will have a lower Voltage under load, so that has to be taken into account when deciding when to land, too. If the OP stays within the 80% discharge limit, this should not be a problem. Unless the load is high enough LVC is triggered by the drop in Voltage in the weaker battery.
Feb 26, 2020, 01:39 AM
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limodune's Avatar
Thread OP
Thanks guys for the info
I normally come down with about 30% left in my batteries, that's what I set the timer to, so it should be OK to use them

Mike
Feb 26, 2020, 08:28 AM
Space Coast USA
hoppy's Avatar
To check this out, I would suggest measuring the individual cell voltages after landing to make sure no cells are being discharged too low. All should be above 3.7V unloaded.
Feb 26, 2020, 09:20 AM
Registered User
NEVER PUT THEM IN SERIES !!!!! The bigger battery over discharges the small one.

Recharging ? The big battery wants to keep pulling current LONG after the little guy is fully charged.

The little guy is really a fire waiting to happen.

In series it is a very bad idea. In LIPO chemical batteries. Unbalances are always problem.

The C rating ...............SHOULD ........... also be a indicator of battery WEIGHT / capacity also. Which brings us back to the problem of unequal weight & true capacity.

BUUTT

The 2 you have might be a case of dumb luck & both are really the same.........GUTS INSIDE............. Life is about learning .............and..............being lucky.

I think you are lucky with the 2 batteries.
Feb 26, 2020, 10:49 AM
Fire Marshall Bill
Why all the talk of "bigger, larger" battery? OP clearly states both are 4k batteries. That one has a higher C rating does not make it bigger or give it more capacity. At very high rates of discharge, the "larger" (not) battery (higher C) will actually discharge faster, as it is more capable of delivering the goods.
The lower rated battery may sag 1st, and hit lvc first, and even maybe warm up more, but after recovery time, will be at higher voltage. At normal charge and balance rates, it will make no difference, and if used in a conservative manner (as mentioned, by keeping within the lower rated battery's recommended charge and discharge profile) it will be fine.
Feb 26, 2020, 10:58 AM
Registered User
Quote:
Originally Posted by Elmo Te
At very high rates of discharge, the "larger" (not) battery (higher C) will actually discharge faster, as it is more capable of delivering the goods.
Remember, the OP plans to connect the two batteries in series with one another. (e.g. - current will be same in each battery)

"Can you join a 4s 4000 mah 25c battery with a 4s 4000 mah 40c battery to make an 8s battery with out problems?"
Feb 26, 2020, 11:19 AM
Registered User
Although it can be done, I would not recommend connecting batteries in series unless they are basically identical in age, size, manufacturer. The risk is that one will discharge to low cell voltage faster then the other if they differ in age / capacity. If you do this, you need to be conservative on how far you discharge the series pack.
Feb 26, 2020, 11:38 AM
Space Coast USA
hoppy's Avatar
Quote:
Originally Posted by Volt_Ampere
Although it can be done, I would not recommend connecting batteries in series unless they are basically identical in age, size, manufacturer. The risk is that one will discharge to low cell voltage faster then the other if they differ in age / capacity. If you do this, you need to be conservative on how far you discharge the series pack.
In reference to this comment, OP should check post #8.
Feb 26, 2020, 12:19 PM
Registered User
Quote:
Originally Posted by cyclops2
I have never seen a discharge curve & the internal resistance curve of the 2 batteries into a shared load. Does the big battery protect the small one during discharge ?
No, there is no flow between series-connected groups or cells, each acts as if it is independently loaded.

So long as you treat the pack under load as if every cell/group has the capacity of the weakest one it's OK. Not a good practice though.

Charging best done separately as already stated.
Feb 26, 2020, 12:46 PM
Registered User

In a series circuit.


The same current amount flows in all cells. If the C ratings are different ? Then the different I R will cause different heating levels in the 2 batteries. With different life spans.

But since C ratings are mostly lies to boost sales. I recall 100 to 250 C ratings by some ? companies ? on their web ads.


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