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Discussion Starter · #1 ·
Hello, complete beginner here. From all of the reading and videos that I've watched (bless all of you here for your efforts), I've pieced together a basic understanding.
Don't be afraid to call me an idiot or point out some really stupid misconceptions, I'd really appreciate any help.

Here are the basic components I planned for a hypothetical "build" that isn't practical but more for the sake of understanding.

First, I've chosen:

LG Chem Super Cells (LG Chem Super Cells 1.6 kWh - JH3 63Ah 7S High Power Battery Module - For Tesla Systems, EV West - Electric Vehicle Parts, Components, EVSE Charging Stations, Electric Car Conversion Kits)
AM Racing 250-90 Motor (AM Racing AMR 250-90 Single AC Motor - Liquid Cooled, Permanent Magnet - Remy Cartridge, EV West - Electric Vehicle Parts, Components, EVSE Charging Stations, Electric Car Conversion Kits)
Rinehart Inverter (Cascadia Rinehart PM150DX/DZ 150KW AC Motor Controller, EV West - Electric Vehicle Parts, Components, EVSE Charging Stations, Electric Car Conversion Kits)

These are just some random core parts I picked to help me understand the parting process.

Now, The AM Racing Motor has a Max Voltage Input of 360V and a max current of 600 arms(I have no clue what this means).
The LG Chem Super Cells have 1.6 kWh of storage and 63 amp hours of capacity(no clue either)

Doing the math from a previous post explaining how to size up your battery (Sizing your Battery Pack), I got:
350 Wh/mile x 80 miles= 28 kWh
Therefore, would it be correct to assume that I need 28 kWh from my batteries to reach this range?
So with my battery packs, I would have to chain them in series until I reached 28 kWh? 28/1.6=17.5 battery packs
However, the article does mention that this process was applied to a 120-volt system. How does the 360V motor change this, if at all?

Then, 28 kWh/360V= 77.78 Ah x 1.32= 102.67 Ah
Now, this is where I can't follow anymore. What does the amp-hour requirement mean? How does it apply to my battery and my motor requirements? Would I have to place my batteries into parallel until I achieved this value?

What about with the motor? It has a max draw of 360V and I have no clue about the current. If I wanted to power this motor, I would realistically need at least 360 volts from my batteries. Then I would have to chain my batteries in series to achieve the correct voltage, correct?
If so, 360V/25.55V=14.1 battery packs.

How do these all connect to one another and how do I ensure that my battery choice will match the power draw required by my motor?
Thanks so much!

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Discussion Starter · #10 ·

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Discussion Starter · #11 ·
Yes. :)

You would need that many modules ("packs" usually means something a little different), but how they're connected doesn't change the energy capacity.

It doesn't change the required energy; the motor needed to operate the motor properly determines how the battery needs to be configured, not how much total battery is needed.

What's the factor of 1.32 for - are you converting 360 VRMS of motor current to DC battery current?
Yes, if your battery is to have 28 kWh of energy capacity and 360 V nominal voltage, it would have 78 Ah of charge capacity.

A motor doesn't draw voltage. It gets whatever voltage the controller gives it. The voltage specified for a motor is usually the voltage that it need to deliver the stated power output at the stated speed. At low speed the controller will give it much lower voltage; the controller can put out less voltage (and proportionately more current) than it gets from the battery, as required to operate the motor as desired.

The stated motor current will be a maximum - more than that and it gets too hot. That same amount of current will be required to produce the maximum rated torque - torque is basically proportional to motor current.

If you want to get the full rated performance over the expected speed range, then yes you need that voltage. Yes, you connect modules in series to reach that voltage, since the controller can only reduce voltage from the battery, not increase it.

Power is something that you haven't addressed at all before this. With a large enough battery to get the desired range, it's usually large enough to handle the power demand, although an unusually high-power motor and a battery capacity chosen for short range can combine to result in a battery that can't handle the power requirement.

In this example, the motor is apparently capable of 210 hp peak output, which is 157 kW. Due to motor and controller inefficiency you might need 170 kW. If you had 17 of the linked modules providing 500 amps (which is what the EV West spec claims they can do), that would be 17 times 25.55 volts times 500 amps which is 217 kW... more than enough.

The other way to look at power requirement is to compare it to energy capacity: a 28 kWh pack could deliver 170 kW for 1/6th of an hour before running out... if it could handle that rate of discharge. That's called "6C" (six times the battery capacity per hour), which is substantial but probably manageable (briefly) for typical EV modules.
Thank you so much for all of the help. You really cleared a lot of points for me. I did a bit more reading and my understanding of amp hours clicked with help from your explanation.

However I did want to ask that since the motor will accept whatever voltage it gets, that means that having a lower voltage available from the battery won’t necessarily cause trouble right? It’ll just have less performance. What about with amp hours? If I don’t meet the amp hours that I calculated, that would simply mean that my range is reduced compared to what I wanted, correct?

The 1.32 was to account for the peukert effect and not wanting to drain the battery fully (80%).

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Discussion Starter · #13 · (Edited)
Right - lower battery voltage will only affect performance at higher motor speed, where more voltage is required (for the same current and torque) to overcome back-EMF.

Correct... except that if you make the battery small enough in energy capacity it may also have insufficient power capability for peak power demands.

There's not much peukert effect with lithium-ion, but allowing for a reserve makes perfect sense. In published specs for EVs you'll often see "nominal" and a substantially smaller "usable" battery capacity for this reason.
Once again, thanks, you're an absolute legend.

With your advice, I was inspired and did some math/theorizing to come up with a few examples.
Font Screenshot Number Document Circle

This really helped solidify my basic understanding of Ah, Voltage, and battery requirements. Also taught me that dual motors will drain a budget faster than you can blink.

If I could bother you with a few more questions, say for the first example (top left) with the two 144V Hyper 9's:
A single motor can output/draw a max of 88kW. Going by your math to calculate the total power output, a battery pack with 1p7s would be able to output 119.7 kW, which is enough for a single motor. If I were to double down on the motors, would that require double the power at 176 kW?

Also, I say 1p7s because doing two in parallel is ungodly expensive, so I was thinking that I could sacrifice the range of the vehicle by half in turn for having a fun driving machine. However, if there is an increase in power requirement from two motors, then that means the plan is out of the window haha.

Most importantly, am I even thinking about dual motors correctly? Parallelly connected motors would maintain voltage and double Ah requirements right?

Edit: Just realized that it would in fact not double Ah since that only concerns range. It would double actual Amps meaning that power would in fact be doubled, meaning it would indeed be 176 kW for peak power draw. Upon further reading, also learned that 750 A is the peak for the Tesla Batteries, meaning the rating is about 500, making the battery modules in 1p7s output only 79.8 kW. Does this mean that I would not be getting the full performance out of a singular motor (88kW) with the 1p7s set-up? However, would it be the case that the 750 peak amps from the battery would be reached and allow me to reach peak power when it is required? (I know that I probably won't be there for a majority of the time spent driving). Therefore the only solution to dual motors (for this battery) is 2p7s because that would provide enough power to power both motors at peak (with the belief that the 750 peak amps will kick in).

A lot of rambling happening. Sorry to keep coming at you with random things.
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