Connecting 3S + 2S Lipo

[bscheife]

Is there any reason to avoid connecting a 3S lipo in series with a 2S to make a five-cell? I know it’s normal to connect two 2S to make a four-cell, or two 3S to make a six-cell, but I have never seen anyone connect two different cell-count batteries. I’m wondering if there’s a reason for that, or if it’s fine but just uncommon

in my case they’re both Spektrum smart batteries, 50C - 5000mah.

 

[Exc3l]

Is there any reason to avoid connecting a 3S lipo in series with a 2S to make a five-cell? I know it’s normal to connect two 2S to make a four-cell, or two 3S to make a six-cell, but I have never seen anyone connect two different cell-count batteries. I’m wondering if there’s a reason for that, or if it’s fine but just uncommon

in my case they’re both Spektrum smart batteries, 50C - 5000mah.

In theory, I don't see anything wrong. Ill let others comment away on this one.

 

[The Donut Man]

NEVER. If either the cell counts are different or the capacities are different, the batteries will discharge at different rates and you’ll risk destroying one of them by going under LVC. That’s why no one does it

Edit: this only applies to parallel setups; the OP was asking about series connections and I misread his post.

 

[Gdub34]

I was told to never mix lipo brands or cell counts by the gurus here. good luck

 

[bscheife]

NEVER. If either the cell counts are different or the capacities are different, the batteries will discharge at different rates and you’ll risk destroying one of them by going under LVC. That’s why no one does it

Do you know more details about why that is?

I ask because, as far as I can tell, the ESC can’t distinguish between a single battery and two batteries connected in series. So, given that, it makes sense that all the cells must have the same discharge rating, roughly the same IR, and the same total charge capacity. But if those things are all the same (e.g. like I assume they are for a 2S Spektrum 50C 5000 mah and a 3S Spektrum 50C 5000 mah), I don’t understand why they would discharge at different rates. And then wouldn’t the two packs effectively form a single 5-cell lipo with five identical cells...?

 

[K-BASH]

I do it all the time.i always run same packs but diff cells.ran these on 7s today. I've never had problems long as same mah,discharge rate.mostly only h-wing an castle esc will run 5,7s.on h-wings you must turn off lvc.quikrun has programming for 5s.ran 7s with mmx8s today.

 

[The Donut Man]

Do you know more details about why that is?

I ask because, as far as I can tell, the ESC can’t distinguish between a single battery and two batteries connected in series. So, given that, it makes sense that all the cells must have the same discharge rating, roughly the same IR, and the same total charge capacity. But if those things are all the same (e.g. like I assume they are for a 2S Spektrum 50C 5000 mah and a 3S Spektrum 50C 5000 mah), I don’t understand why they would discharge at different rates. And then wouldn’t the two packs effectively form a single 5-cell lipo with five identical cells...?

I'm sorry; I didn't pay close enough attention to how you want to connect the batteries. I thought "parallel" in my mind instead of "series." What I wrote only applies to parallel setups; I did a quick search and the consensus is that different cell LiPos of the same brand, capacity, and C-rating are perfectly fine to hook up in series. I stand corrected! I'll edit my original post.

 

[jkflow]

If the cells are same brand, c rating and capacity it should be fine. You will run into issues with Lvc as the ESC detects even cells and will go into Lvc. Just turn it off and bash away.
This is for a series setup only.