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Jul 29, 2020, 12:26 PM
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Different c lipos in parallel


Hi Guys, I have two 11.1v 2200maH which i want to join in parallel to make a 4400maH pack. The problem is one of them is 25c pack and another is 30c pack. Both are cheap chinese packs so I cannot guarantee if they have genuinely written or not. I am not going to alter internals just join the lead wires .Will it be safe and will it work ? This is what I want to know. Please help.
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Jul 29, 2020, 12:46 PM
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Panther6834's Avatar
Personally, I would neither suggest, nor recommend, doing so. Whenever running in parallel, or in series, you should ALWAYS use 'like' with 'like'.

Using your packs as an example, those 25C & 30C ratings are probably "continuous", so let's assume that "peak" is possible 40C & 50C (actual "peak" doesn't matter...this is just to explain possibilities). Now, let's say your vehicle's "continuous" operating draw is 20-25C. For that, you wouldn't have any problem. However, under acceleration, let's say your ESC/motor has a "peak" draw of 45C...NOW you have a potential problem. An ESC can supply higher wattages to the motor...but, the higher the wattage, the shorter the period of time that the ESC can supply that wattage.

The same holds true for battery discharge...the higher the rate of discharge, the shorter the period of time that the pack can handle said discharge. As I understand it, there are a few factors that determine a pack's C-rating. Among them is the wire gauge, and the size of the internal tabs. The larger the wires & tabs, the higher the C-rating...which also means the higher the temperature the wires & tabs can handle. Conversely, the smaller the wires & tabs, the lower the C-rating...which also means the lower the temperature the wires & tabs can handle. Exceed a certain 'temperature', and........well, you can figure the rest.

If both packs had higher C-ratings, there might be any problem...but, with those C-ratings as low as they are, I'm fairly certain that I wouldn't be willing to take the chance. Try it, if you want...and, if anything happens, you'll only have yourself to blame. Again, the best 'rule of thumb' is always "like with like".


~ More peace, love, laughter, & kindness would make the world a MUCH better place
Jul 29, 2020, 12:53 PM
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The C-ratings typically are totally fictitious, your 25C may be better than your 30C, even with the same mfr label. Many people including me have verified that by measuring IR using an accurate meter such as the Wayne Giles ESR.

Most non-graphene packs run a true continuous C of about 16-18.

At any rate, 25C is close to 30C and it is a moot point anyway because the battery with the lower IR will take a bit more current at first, and as the charge continues, both batteries will be about the same (voltage has to be the same thru both packs, basic law of electronics)
Jul 29, 2020, 01:14 PM
Frankenstein recycled packs
rampman's Avatar
Archit Bubber, yes you can but take a short flight first, measure the mAh you put into each separately and if very close you are good for a full flight down to around 3.7 volts per cell after landing.

Rick
Jul 29, 2020, 01:34 PM
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Quote:
Originally Posted by zerts2
The C-ratings typically are totally fictitious, your 25C may be better than your 30C, even with the same mfr label. Many people including me have verified that by measuring IR using an accurate meter such as the Wayne Giles ESR.

Most non-graphene packs run a true continuous C of about 16-18.

At any rate, 25C is close to 30C and it is a moot point anyway because the battery with the lower IR will take a bit more current at first, and as the charge continues, both batteries will be about the same (voltage has to be the same thru both packs, basic law of electronics)
So what do you suggest should I go on and use them in parallel?
Jul 29, 2020, 02:25 PM
Having more fun every day.
MrEFlyer's Avatar
Measure the IR of each cell and if they are close then go ahead and parallel them.
Jul 29, 2020, 02:28 PM
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Quote:
Originally Posted by Archit Bubber
So what do you suggest should I go on and use them in parallel?
Just make sure they are fairly close in voltage (about 0.2V) then charge them. If not close, charge the weaker pack a bit first.
Jul 29, 2020, 02:48 PM
Proud to eat Kraut ;-)
Julez's Avatar
You can put all kinds of LiPos in parallel, as long as the cell number matches. Old, new, crappy, good, big, small, it does not matter.
You just need to follow this one rule:
Operate the combined pack in a way that the least capable component is operated within it's specs.

So, if you combine a 10C pack with a 50C pack, you get a bigger 10C pack.
That's basically it.
Jul 29, 2020, 03:12 PM
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Thread OP
Quote:
Originally Posted by Julez
You can put all kinds of LiPos in parallel, as long as the cell number matches. Old, new, crappy, good, big, small, it does not matter.
You just need to follow this one rule:
Operate the combined pack in a way that the least capable component is operated within it's specs.

So, if you combine a 10C pack with a 50C pack, you get a bigger 10C pack.
That's basically it.
That means a 4400maH pack of 25c if I got it right.
Thank you all .
I'll try all of these advices tommorrow and post update.
Thanks again
Jul 29, 2020, 05:17 PM
Registered User
Quote:
Originally Posted by Julez
You can put all kinds of LiPos in parallel, as long as the cell number matches. Old, new, crappy, good, big, small, it does not matter.
You just need to follow this one rule:
Operate the combined pack in a way that the least capable component is operated within it's specs.

So, if you combine a 10C pack with a 50C pack, you get a bigger 10C pack.
That's basically it.
+1

Julian for the win!

Mark
Jul 29, 2020, 11:56 PM
Registered User
Bookstar75's Avatar
Hey guys,
My situation is the same but with Li-ion packs and the C ratings are similar...maybe about 5 c's difference. I have a 4s 7000 and a 4s 3500 Li-ion that i want to turn into a 4s 10500 pack. Im assuming this will work without damaging the packs?
Thanks!
Jul 30, 2020, 12:09 AM
If it flies, I can crash it.
rocketsled666's Avatar
Consider:

Pack A is 20C and 2000mAh. So it's rated for a max of a 20*2 = 40A load.
Pack B is 10C and 4000mAh. So it's rated for a max of a 10*4 = 40A load.

If you connect them in parallel and draw 40A, it's not going to be a problem.

It's not the C rate alone that you care about, it's C multiplied by Capacity that matters.
Jul 30, 2020, 02:58 AM
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Bookstar75's Avatar
Ok thank you. Sounds like it should work!
Jul 30, 2020, 12:02 PM
Koo
Koo
Registered User
You won't be damaging the packs, but the risk you run to is that the "weaker" pack can discharge either faster or slower than the "stronger" pack if you don't monitor your pack voltages. Using a battery monitor with a beeper set to a certain voltage threshold on the pack that discharges faster will ensure peace of mind.
Jul 30, 2020, 12:07 PM
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Quote:
Originally Posted by Koo
You won't be damaging the packs, but the risk you run to is that the "weaker" pack can discharge either faster or slower than the "stronger" pack if you don't monitor your pack voltages. Using a battery monitor with a beeper set to a certain voltage threshold on the pack that discharges faster will ensure peace of mind.
I'm confused. Are you suggesting that batteries connected in parallel can be at different voltages?


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