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

33739 Views 24 Replies 12 Participants Last post by floydr, Feb 21, 2022

miernik

Discussion Starter · Apr 7, 2011

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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steven4601

· #10 · Apr 7, 2011

Think I have posted this before on a different thread regarding efficiency. Most of it boils down on I^2R losses. (That is Current squared times the resistance)

Resistance is everywhere. Batteries, wires, motor windings.
I^2R losses mean if you double the voltage of your system for the same power, you reduce the losses factor 4. (read: only considering ohmic losses)

Something about safety:
High voltages are not dangerous, it is touching them which may have consequences. (no fun intended) If you are uncertain about your system and the (required) voltage's within it, my advice would be to step away and call a friend who can help on site.
(Educated) electronic (design) engineers often pause for a second to re check their decisions before continuing installation/removal/testing high voltage equipment.

Something about ' high ' voltages:
Voltages between 42-60DCVolts (rather large variations exist per country and industry class) are named SELV. Safe/Seperated Extra Low Voltage. Safe to touch, does not cause direct danger.

Between SELV and Low Voltage is the voltage range named ELV. Extra low voltage. This goes up to 120VDC .

Low Voltage lies between 120 to 1.5kVdc
High Voltage is 1500VDC and up....

I doubt any EV car uses High voltage systems

//Steven

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