12V vs 48V on an electric vehicle.

[veewee77]

Suppose for example you have a one horsepower motor. One horsepower is 745 watts.

Study Ohm's Law formulas for how to figure this stuff. . .

E=Volts=V

P=Power=W

I=Amps=A=current   <--this is key for this explanation. . .

R=Resistance=Ohms

Now, if you have a 12V system, and you are drawing 745 watts (745W) then you will be pulling about:

745. W (745 watts) over 12V (12 volts) = 62A (62 Amps). Wire size required is AWG8 or AWG6 (pretty thick) to carry the current.
     
745. W (745 watts) over 48V (48 volts) = 15.52A (15.52 Amps). Wire size required is AWG14 or AWG12, relatively light.
     
     

Now which would you like to buy, thick, heavy copper wire or thinner, lighter copper wire.

Ohms law formulas are like this:

Study these and you will be on your way!

To find Power (Watts), multiply Volts by Amps P=E*I

To find Current (Amps), divide Power by Voltage I=P/E

To find Volts , divide Power by Current e=P/I

Resistance works into these as well but gets a bit deeper. Volts and Current are easy to figure, but watts is a bit harder unless you just do the formula to convert power to volts or amps then do the math for volts or amps to resistance.

E=I*R

R=E/I

I=E/R

Doug

[spinningmagnets]

I am not any kind of electrical expert, but I have been reading for a while about electrical-assist bicycles.

If your interest is in e-motorcycles, e-bikes, and e-scooters, there are many helpful enthusiasts at:

http://visforvoltage.org/

Starter kits (for bicycles) often have a modest 250-watt/400-watt motor, and use 24 volts (two 12V lead/acids) to keep the price, size, and weight of the battery pack small.

It appears that anyone who likes it, and sticks with it, quickly graduates to a 500W+ motor and 36/48 volts.

With 48V being the desireable upgrade, keeping the battery size/weight down often means expensively upgrading to NiCD's or Li-ions.

Since batteries wear out and have to be replaced, and motors are well-known to be very durable, I thought that if I payed extra for a very big motor in the beginning, it would be a good upgrade (Etek-750W/1HP). I then read that a big motor draws many amps, which shortens range, so you should seek the smallest motor that "just" meets the loads you will put on it, without getting hot. Its difficult to calculate, because it depends on how steep your hills are, how long the hill is, and how many hills you have to hit on your route.

I live around frequent medium hills and am now considering a Scott-600W using 48volts. Bike riders who live in fairly flat regions have often reported being pleased with 500W/36V.

Higher volts means getting the same power from a smaller motor, which draws fewer amps. This will translate into less motor/controller/battery heat, and more range.