Hello,

How safe and effective would it be to wire two 4s batteries into an 8s battery?

Thank you

 

It's not safe, and it probably won't be very "effective", ( whatever effective means ??? ).

Since You are describing your Batteries as "4s" and "8s"
we can only assume that they are Lithium-Batteries.

Lithium-Batteries can be very hazardous,
and must be used strictly "by-the-rules".

You evidently have not done any investigating into what the "rules" for Lithium-Batteries are.

https://batteryuniversity.com/
.
.
.

 

It seems to be fairly normal to do this in drone applications

 

It's not safe, and it probably won't be very "effective", ( whatever effective means ??? ).

Since You are describing your Batteries as "4s" and "8s"
we can only assume that they are Lithium-Batteries.

Lithium-Batteries can be very hazardous,
and must be used strictly "by-the-rules".

You evidently have not done any investigating into what the "rules" for Lithium-Batteries are.

https://batteryuniversity.com/
.
.
.

Can you expound? batteryuniversity.com is an excellent resource but it's vast, and if there's something specific you want OP to see, it may be better to link directly to it. AFAIK, lithium batteries are commonly wired as described. I don't know what is the problem(s) you are referring to.

 

My Bad .........
I miss-read the Thread-Starter's question.
There is no problem with wiring 2 identical Batteries in series, Lithium or not.
Sorry for any confusion.

As long as the Batteries are separated during Charging, there's no problem.
.
.
.

 

Doubling batteries in series doubles the voltage which also doubles the current producing 4 times the power and 4 times the heat.
Which blows up first, the batteries, the motors or both?

Some guys use 3s batteries in RC model airplanes that are designed for 2s. The manufacturer says then there is no guanantee since the power is 2.25 times.

 

Hello,

How safe and effective would it be to wire two 4s batteries into an 8s battery?

Thank you

Depends on how effectively you can manage them. Balancing, adherence to charge and discharge rates, and temp monitoring should allow you to have an effective stack. Pushing a weak cell can create problems. Safety is your choice. We string cells to 100 + volts, and handle them accordingly.

 

Doubling batteries in series doubles the voltage which also doubles the current producing 4 times the power and 4 times the heat.

The above is true but below makes an assumption (that the application calls for 4S) which I see no justification for making. Maybe TS application calls for 8s but he only has (2) 4S packs.

Which blows up first, the batteries, the motors or both?