Battery design

[Jonndeka]

Hi dear friends,

I would like to know if we want to design the battery module, do we need to consider energy consumption of components or power demand?

For example if we have 3 motors 20 kw, 380Vac, what else parameters do we need to design the battery module/pack?

 

[Eastwood]

Hi dear friends,

I would like to know if we want to design the battery module, do we need to consider energy consumption of components or power demand?

For example if we have 3 motors 20 kw, 380Vac, what else parameters do we need to design the battery module/pack?

What controller are you using?
Why do you need 3 motors?

The controller output will primarily dictate what type of battery design you’ll need. They all work together though. We first need to figure out what type of motor we need based on the power needs. Then we need to find a controller that’s compatible with those power ratings of the motor. Then the battery should not be pushed to its max limit, and should be overbuilt for safety and longevity of the battery.

I’m on my first battery build as well, but there’s more experience guys on here that can help you with more of the details.

 

[Jonndeka]

What controller are you using?
Why do you need 3 motors?

The controller output will primarily dictate what type of battery design you’ll need. They all work together though. We first need to figure out what type of motor we need based on the power needs. Then we need to find a controller that’s compatible with those power ratings of the motor. Then the battery should not be pushed to its max limit, and should be overbuilt for safety and longevity of the battery.

I’m on my first battery build as well, but there’s more experience guys on here that can help you with more of the details.

I think it doesn't depend on the controller. Because we are investigating the HV line and energy/power demands. But controller works based on LV signals.
3 motors is an example. You can assume any type of this. My main issue is how we design battery pack based on power/energy demand. Power of motor is important or energy consumption?

 

[fechter]

You need to consider both. The battery's maximum safe discharge current should be high enough to meet the expected power demand. The energy will determine the range or how long it can run.

 

[spinningmagnets]

Also, a battery that is "adequate" to provide "X" amps might occasionally get hot if you demand a high temporary peak amps (a 3 second acceleration), or if you have a long and steep hill while pulling "more than average" cargo-weight. The extra heat plays a part in how many years the pack will survive. Warm is OK, but hot is bad.

If you NEED a small pack and your job also demands high amps, you must buy high-amp cells, which may have less capacity and will have a higher price. If you can fit a larger pack, then you have more options when it comes to choosing which cell to use.

 

[Eastwood]

You need to consider both. The battery's maximum safe discharge current should be high enough to meet the expected power demand. The energy will determine the range or how long it can run.

Also, a battery that is "adequate" to provide "X" amps might occasionally get hot if you demand a high temporary peak amps (a 3 second acceleration), or if you have a long and steep hill while pulling "more than average" cargo-weight. The extra heat plays a part in how many years the pack will survive. Warm is OK, but hot is bad.

If you NEED a small pack and your job also demands high amps, you must buy high-amp cells, which may have less capacity and will have a higher price. If you can fit a larger pack, then you have more options when it comes to choosing which cell to use.

The OP mention something about not using a controller, or at least that’s what it sounds like. That’s not possible right, you have to have a speed controller to use any electric motor, right?

 

[Jonndeka]

The OP mention something about not using a controller, or at least that’s what it sounds like. That’s not possible right, you have to have a speed controller to use any electric motor, right?

Yes. but it's not the main task of battery. We are talking about high voltage and how much power/energy do we need from battery side to run our electric consumptions.

 

[ImperialSB]

Correct me if I’m wrong but does the VESC tool (and all compatible controllers) not have current-limiting parameters for both the battery and motor phases? So in designing a battery pack to meet a requirement you could leave it to the VESC a little, as the VESC ultimately determines what power the motor needs.

So as an example, a motor with 300A peak could be served safely by a 100A capable pack, provided this was established in the VESC settings - allowing, say, 80-100A max battery current and 80-100A max motor current. Not sure what to factor the motor current down by to get the phase current but hopefully I’m making sense.

I could be wrong, happy to be corrected!

 

[ImperialSB]

Yes. but it's not the main task of battery. We are talking about high voltage and how much power/energy do we need from battery side to run our electric consumptions.

The rule of thumb I have heard is that you should give your batteries a ‘safety factor’ of 1.5-2x the current the motor could ask for. At least with LiPos, lest they burst into flame. So if you have a 100A peak motor, your battery should be able to handle a peak of 150-200A.

And in general the battery design should be one which doesn’t stress the batteries too much. The closer to 1C you can get under normal expected operation, the better (C-rating in case you don’t know is current compared to capacity, 20Ah at 20A is 1C, 20Ah at 40A is 2C, 20Ah at 10A would be 0.5C etc.)

Thermal management is another important consideration, ensure that the batteries, controllers, motor and connections don’t get too hot. Factor in their materials, passive air flow and in some cases (high current applications) forced air flow.