Hello

How safe and effective is it to wire two 4s batteries together into an 8s?

Thank you

you need to use two brand new ones from the same batch, if its crafted well, its as save as use them as single 4s cells.

Do keep in mind that 8S is where you cross the 30V threshold. This is where the voltage begins to become capable of penetrating dry human skin. Stay safe buddy!

Thank you. How do I know they're from the same batch? If I buy two new ones at the same time, could one be from a different batch

You really want (very) similar internal resistance. That’s more likely from the same batch, but the batch itself doesn’t technically matter. If you order two at the same time and they’re both new and from a decent brand, I would think the IR would come out very close

I have a 600 sized helicopter that uses two 6S in series!

This is kind of the norm in surface RC with the big 1:5 scale trucks but with much bigger mah 4s batteries on an 8s low kv motor.

(12-Mar-2023, 10:05 PM)Suros Wrote: Do keep in mind that 8S is where you cross the 30V threshold. This is where the voltage begins to become capable of penetrating dry human skin. Stay safe buddy!

Anything over 24V is sketchy IMO and when helping a friend build a 48V LTO Array for his house I did get zapped at one point and it did hurt.

Even on 24V systems, I still wear gloves.  On two 4S Lipos, I would definitely wear rubber gloves.

how do you like to wire them, by a simple adapter plu or by open them and fix it to onw pack?

I did a write-up on how you can wire battery in series and use anti-spark plug. At 8S, you can get quite a jolt when you plug in.

https://intofpv.com/t-criss-cross-x-clas...6#pid76356

Thank you

Wait we are all going 8S already?
When did this happen. Oh man I fell asleep and I am behind the times again.

(16-Mar-2023, 02:00 PM)romangpro Wrote: Wait we are all going 8S already?
When did this happen. Oh man I fell asleep and I am behind the times again.

The most I've seen is that Rotor Riot did a freestyle quad and FalconRad has been flying long range on it. The RR guys appeared to barely have a handle on theirs, but did manage some cool stuff. FalconRad does mountain surfing on Li-Ion packs, so it makes sense to want to retain the ability to punch out if a surprise rock appears.

we are mostly limited by marked options to change the common way we fly, maybe there isnt need enough to go higher with the cellcount.
6s didnt gave us better laptimes, it gave us just another voltage consisdency. do we realy need higher cellcount and how long will it take to get as much and as good options for parts?

its still somehow experimental to go for hv, also something good :-)
a buddy is trying a 12s 5inch quad, 2206 1000kv on 550mah 12s :-)

(08-Apr-2023, 09:11 PM)DragonTheta Wrote: Thank you, so if I didn't mind changing the plug on the lipos, I could solder the anti spark female xt90s onto the lipo cables, then make a harness with male anti spark xt90s to connect both batteries to? Would that harness look like the one in the picture minus the top two plugs, with anti spark on both sides where the battery plugs in?
In the picture, the plug on the left has two black cables. I thought one side of the xt90s was for positive and one side for negative. Which side of that plug is positive, left or right?

Thank you

You are correct. If you replace your lipo connector, then you can remove the two top plugs.

The middle black wire could be any color. I just decided to use black. That wire is what connects the two lipos in series. When you connect in series, the positive of one of the lipo connects to the negative of the second.