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why do you make EVs with such high voltage? Why not 48V?

33739 Views 24 Replies 12 Participants Last post by  floydr
Why are DIY's electric vehicles made to work on such high voltages, like 96V, 144V and over 200V? Wouldn't it be better to run everything on something around 48V, so its safe to touch?

I know the wires would need to be 3-4 times thicker to get the same resistance (voltage drop) and current handling, but so what? Wire is expensive, but not so extremely expensive not to afford to spend 3-4 times as much on wire (which are not so long in a car anyway) in the name of significant safety.

We are not ever running more then 20kW though the wires, no?
So at 50V that would be 400A. About 200 mm^2 would do, no? Or about ten AWG4 wires in parallel for US guys. That would be about 150 EUR or 200 USD per meter, right? So how many meters of 20kW capable wire do you need in total in an EV?

OK, if you use a few meters, it's quite an amount of money, but still cheaper then getting a new life after touching 200V. And you can design the car to place batteries close to the motor to save on wire. At least I could imagine placing them withing 1 meter.

So are there any other reasons to use anything significantly over 48V, then saving money on copper wire?

If I can afford the wire, should I build a EV out of my 2035 kg van on 48V for safety (only 16 LiFePO4 cells in series, instead of 48 or 64 - what I spend on wires I can save on having a simpler 16S BMS, instead of trying to balance 64 cells...)?
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48 volts car will be awesome! Like you said, only 16 cells, easy bms wiring, safety, etc.

But do you realise than 48v and 400A is only 16 Kw at motor shaft? It's a poor power. And your peak power with normally availiable controller (1000A) will be only 40 Kw.
And at such high amp, you need a lot of copper to have good efficiency. All wires, motor, battery, controller need to be stronger to pass high amp continously

Many of us need to go at high voltage because we need good performance electric car. My car for example, can give 156v (130v sag) x 1000A to have around 105 Kw at motor shaft.
Also, at high voltage, I will probably need less than 100A to cruise at relatively high speed (80 km/h, 50 mph).

48 volts electric car will be good idea only for a city car with poor performance(always under 60 km/h, 37 mph). Over that speed, you will need too much power and more power at 48v = too much amps.
I'm not 100% sure, but personnaly, I think a 72v systems is enought safe.

The main advantage of a 72v systems is you can drop the amps draw by 1/3 for the same power.
200A instead 300A for a motor or a controller is a important difference.
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