Mixing Different LiPo Batteries Good or Bad?

[Planky]

Hi,
I use four packs of 6s 5000mAh 20C by Turnigy, running in a 12s2p configuration to give 44.4V and 10AH.

Now that I have a Cycle Analyst (thanks Justin) and no longer need my Watt Meter, which has a maximum of 60V, I can run 18s and would like two extra packs of 6s 5000mAh to give me 66.6V and 10AH, but they are always out of stock at HobbyKing.

So I am asking for advice on mixing either different C rates from the same manufacturer (i.e. Turnigy 25,30 or 35C) or different manufacturer but same C rate (20C).

Has anyone had any experience doing this?
Which is the safest to do?

Thanks

 

[neptronix]

You can mix different C rates in parallel but not series.

So if you have 4 6s packs, and want to run 18S2P.. set 1 pack aside as a spare, order yourself 3 6s packs of your chosing, and go for it.

Zippy sells a 20C battery, it may work as a good substitute.

 

[knoxie]

as a general rule you shouldnt mix different C rate cells in series (cells whose C rate is wildly different) but 5C makes no odds and with Plankys relatively low power use and it wont be a problem at all, I have done this for years with no problems at all I use a booster pack on my 48V 10AH pack made up of 20C cells with the main cells being 25C, works like a charm you just have to watch them at the end off capacity, well you should do that anyway, so yes go for it, try and stick with quality cells or at least the same brand.

 

[dogman dan]

Go for it. mixing in highe c rate batteries couldn't possibly harm your lower c rate ones, if they already do fine. It's not like you are increasing the c rate of your discharge eh? In the same brand, it's likely that you will have very close to the same real capacity cells in them. Turnigy for example, may have cells that are actually 5.1 ah in them.

Mixing brands, there may be a very small capacity difference. Zippy is more likely to have actual 5 ah cells and so may have a tiny bit less capacity in them.

But if you are riding your packs to a dod so deep this matters, we can't help you. The inevitable is coming.

So stop in time, and go for it.

For other readers contemplating something a bit more radical. Just figure out which section of the series pack has the least capacity, and monitor the voltage on that section. Simple. So you could have a section that is 10 ah, and another section in the series pack that is 8 ah, and simply keep an eye on the 8 ah part.

Of course, it's ideal, and much simpler to make packs out of matched stuff. But you can mix c rates and brands, provided you just keep an eye on whatever portion of the pack is weakest or smallest.

 

[veloman]

Go for it. mixing in highe c rate batteries couldn't possibly harm your lower c rate ones, if they already do fine. It's not like you are increasing the c rate of your discharge eh? .

This makes sense, but you guys above say not to?

Is there anything wrong with adding a lipo brick in series with lifepo4? As long as amp hours are the same (or at the very least, you cease and disconnect the booster pack once it hits 80% DOD), this shouldn't be a problem, right? I will be most likely running even lower amps if I do this, so I don't understand why it would harm my main lifepo4 pack? Of course I would monitor that my booster pack doesn't go too low.

My intent is to add power (wattage) to my main lifepo4 without raising the amp limit on the controller. I've already seen that adding voltage gives more torque and power, even though it raises the efficiency band speed. So if I am only using 4ah of my 36v lifepo4, I should be able to just series connect a 3s 5ah lipo pack. Varying voltages won't charge each other when in series only when in parallel.


End result:

More power with same amp limit
or
Same power, and I can turn down the amp limit to be nicer to my lifepo4 battery.

What do you think?

 

[SamTexas]

Is there anything wrong with adding a lipo brick in series with lifepo4?

It's fine to serialize different chemistry. They don't even have to have the same capacity or discharge rate. The one with the lowest capacity and/or discharge rate will dictate the pack's characteristic.

 

[dogman dan]

If there is, I've done it anyway. The main thing in an oddball series setup is to stop when the smallest capacity part of it is discharged. Paralell is where voltages need to be very similar at the time you hook em up.

 

[Planky]

Thanks for the advice.

I will look at getting three more Turnigys at 25 or 30C and a couple of extra cell monitors to keep an eye on all the packs.

 

[ohzee]

So I have 12 25C 6s 5000mah Zippys. One is having issues so I was going to replace it.

Could I swap in nano tech 25-50c 6s 5000mah packs as id rather upgrade some ?Was thinking id
order a couple at first and go from there.. If not I will just order another 25c pack.

Read this thread , but was not 100% clear seemed to get conflicting advice.thanks

 

[SamTexas]

So I have 12 25C 6s 5000mah Zippys. One is having issues so I was going to replace it.

Could I swap in nano tech 25-50c 6s 5000mah packs as id rather upgrade some ?

Yes you can. But you won't be able to take advantage of the higher discharge rate offered by the nanotech.

Read this thread , but was not 100% clear seemed to get conflicting advice.thanks

I did not read the whole thread, what were the conflicting advices?

 

[ohzee]

So I have 12 25C 6s 5000mah Zippys. One is having issues so I was going to replace it.

Could I swap in nano tech 25-50c 6s 5000mah packs as id rather upgrade some ?

Yes you can. But you won't be able to take advantage of the higher discharge rate offered by the nanotech.

Read this thread , but was not 100% clear seemed to get conflicting advice.thanks

I did not read the whole thread, what were the conflicting advices?

Well 1st or 2nd post neptronix says you can mix c rates in parallel but not series.

My 18s battery is in series so that's why I asked the question. Neptronix is well known on this thread
and I highly value his advice.

Thread is not that long so let me know if I misread something please. thanks

 

[SamTexas]

Well 1st or 2nd post neptronix says you can mix c rates in parallel but not series.

I understand what you are talking about now. I did not see his post because he's on my ignore list.
You are right, what he said is in complete contradiction with what I said. But I'm not going to waste my time arguing with him. Other people will no doubt step in and clear up the confusion for you.

 

[neptronix]

Sam doesn't like arguing because he hates losing :lol:

You can technically do multiple C rates in series, sure. But in my experience, packs won't drain at even rates since they have different levels of internal resistance. They also will wear differently over a long period of time as you are working one battery harder than the other.

One pack will attempt to give more juice than the other. That's what i saw on an iCharger when i tested this theory out.

Here is a 5S zippy 20C ( overrated, and in reality 10-15C ) discharging in series with a 5S Turnigy 20C pack.

They were both charged to the same voltage at the beginning of the test.
Notice that one starts falling off the cliff much sooner?

Now this could be because 1 pack has say.. 5100mAh at this discharge rate and the other has 5000mAh at the other..

But if i put these packs in parallel, i would not be having this issue. Each battery would put out what it can. One may work a bit harder, but their voltage will never differ. They will hit the cliff at the same time. no problems.. seamless operation.

 

[neptronix]

By the way, nanotech is a bit of a waste of $. With 10AH of 20C stuff, you can safely output 50A constant all day with no concern about voltage sag, pack heating, etc. 15AH is even better.

Now if you truly only want 5 amp hours ( 10 mile range or less on most bikes ), then OK, go for the nanotech. But really... more amp hours is the better buy for your cash. The more you have, the lower the effective C rate is on the battery.

As for the longer life claims, well that has yet to be proven. Even liveforphysics hasn't backed up that claim yet. Hobbyking also doesn't state how many extra cycles ya get with it.. so take that with a big grain of salt.

 

[dogman dan]

Neptronix is not exactly wrong, just more picky than I am for sure. Also he's more informed than I am.

Nevertheless, I am right also when I say mixing high c rate with low c rate in series won't usually harm the high c rate packs. But you could ovedischarge whatever part of a series pack of any kind is the weakest. That is to say, lowest capacity for whatever reason.

The key thing is to monitor at least the section of a pack that is known to be weak. Preferably the whole pack, at cell level.

I say that, but do I do it? Of course not. Rode out yesterday with one pair of my 20s 10 ah pack known to have a poor cell in it. No monitor on the paired pack, just the CA. The bad cell worse than I thought, it was nice and toasty hot when I got home, but fortunately nothing set off the leaking flamable gasses. Took the paralelled good pack with it too. Bye bye $120.

 

[veloman]

Why do my 5ah 20c Turnigy's get warm at 21amp limit then? I find it pretty weird that lipo gets warm and sags 3-4v (13s pack) at just 4c.

 

[SamTexas]

All numbers provided by HobbyKing should be taken with a large grain of salt. Have you ever seen a discharge graph provided by HobbyKing at the advertised C rate? Me neither.

9% sag at 4C is not bad at all, if you can get past the overly optimistic 20C rating.

 

[neptronix]

Dogman: yes i am very very picky. You know why? i live in an apartment so i take 0 risks with lipos. I'm also a tightwad, so i don't like breaking things. I do have a 15S pack of differing C rate lipo. It requires running separate chargers to prevent the capacities from varying. I also have to cut about 1AH off my total pack's size to be safe. I do not recommend this to anyone, unless they are a black belt lipo handler.

Why do my 5ah 20c Turnigy's get warm at 21amp limit then? I find it pretty weird that lipo gets warm and sags 3-4v (13s pack) at just 4c.

veloman, that is abnormal, but not off by too much. Is your lipo a bit older?
I'd run either 10ah or invest in some nanotech packs if you are insistent on running 5ah.

 

[dogman dan]

I can't say I've ever really brought lipo back to the barn cold. Even on just a 20 amp controller. Always at least warm, and for sure warmer when using a 5 ah pack. Nearly what I'd call hot, when used at 40 amps on a 5 ah pack of 30c lipo. Still not as hot as nicad packs get every discharge though.

Warm, hot, pretty subjective descriptions really. Even my ping warms to about body temp when riding a 1c discharge.

Without more info, I'd call that normal, a 20c lipo discharging at 4c getting to body temp. DOD matters too, the hot part is the last 10% of juice. Really hot, the last 1% as I demonstrated yesterday. I need to develop some more picky too. Like get some good lvc's.

 

[veloman]

I suppose keeping them in an insulated lunch bag (though not zipped shut) doesn't help with heat dissapation either. Yeah, they definitely didn't get as hot as my trimmer's nicad did in 100 degree heat, full discharge :lol:

I will likely be ordering another 13s 5ah to fully complete my battery selections. My current lipo came from HK in the spring.

 

[pumasong]

Hi folks,

I've had a read of this thread with interest. I have a related question.

I run a TSDZ2 mid-drive off LiPo cells, running the custom firmware designed by casinho. It runs great on 12S (3x 4S 5000mah currently) but previously I have also run it at 14S (2x 5S 4000mah + 1x 4S 4000mah Turnigy Nanotech) which was amazing. I noticed though that the 4S seemed to discharge faster than the 5S packs, meaning I had to be careful not to over-discharge that pack.

Based on the thread above, it seems that the config above should be OK? If so is it just possible that the 4S pack was bad in some way?

I'm looking to get one or two more full sets of cells so I would be very interested to know if 13S or 14S is a sensible choice.

Thanks!

George

 

[eMark]

Warm, hot, pretty subjective descriptions really. Even my ping warms to about body temp when riding a 1c discharge.

If energetic Lipos are too warm to hand hold it could be the fault of an operator that's too energetic