24V battery vs 48V battery for 1200W motor

[Just]

Hi All,

I have 1200W motor and now need to choose what system to build - 24V or 48V (I'm not considering the 36V one).

As for 24V system, the motor will receive 50A continuous current; for 48V it will receive 25A continuous current - in both cases 1200W (24V*50A=48V*25A=1200W).

So, what's of the above systemes preferable for the city touring? What is better - higher voltage and lower current or vice versa? I know that voltage is usually for a speed and current for torque... As for the speed, 24V would okay for me. Is there something I'm not taking into account?

I think that 24V is preferable due to a lighter weight of the battery (twice lighter). It seems it would also consume less total current than 48V system... Am I wrong?

Thank you in advance for your comments and tips!

[truly_bent]

Your motor will draw current to 1200W. As you say, at 48V it will draw 25A, and 50A at 24V. You don't say whether this is a hub motor or a mid-drive. There's going to be a big difference in speed, depending on gearing perhaps, but you're already aware of that.

One downside to the lower voltage is that everything carrying current has to be beefier. This includes wires and connectors. Your controller has to be capable of handling the higher currents as well. The BAC-0283 external controller, for example, is only capable of handling 30A at 24V.

As for weight, I'll think you'll find that your battery will equal about the same weight for the same range. A 24V 10AH battery is likely to give about the same range as a 48V 5AH and weigh something similar.

Ain't no free lunches in this business.
Jeff

[Just]

"at 48V it will draw 25A, and 50A at 24V" - as for Amps, it's programmable in Controller... I meant that both of the systems may provide the same power to the bicycle (in ideal).

"includes wires and connectors" - I'm using 75A Anderson connectors and 10AWG wires ...

You don't say whether this is a hub motor or a mid-drive" - mid-drive motor

going to be a big difference in speed" - twice: for 48V is 500RPM, for 24V is 250RPM, but the final RPM might be compensated/adjusted by chain-wheel.

As for the 24"-wheel bicycle with gearing ration of 1.6, in ideal the max speed for 24V system (250RPM) would be nearly 45km/h:
(250*60)*(3.14*(24*2.54/100)/1000)*1.6=~45(km/h)

Your controller has to be capable of handling the higher currents as well" - it has, I'm going to purchase Kelly's Controller, which support up to 50A of continuous current and up to 120A in peeks.

Hmm... What's value of DC current starts to be dangerous?

A 24V 10AH battery is likely to give about the same range as a 48V 5AH and weigh something similar" - I'm not so sure... Will 24V 10Ah battery provide the same range as 96V 2.5Ah?

Since the Controller is programmable, it's always possible to play with a maximum allowed current... I think it's comparable with a driving style on the car - driving without kick-downs should save a lot of gas! 

Please correct me if I'm wrong

[truly_bent]

24V x 10AH = 240Wh (Watt hours)
96V x 2.5AH = 240Wh

You're getting the same amount of power out of both systems. Watt/hours is a common measure over distance - as in Wh/Km. Obviously, the 96V will cover those kilometers a bunch quicker.

Apparently, the Tesla Roadster uses 135 Wh/Km (21.7 kW·h/100 mi, 13.5 kW·h/100 km or 490 kJ/km). Neat, eh?

Jeff
My apologies to any Americans who don't know what a kilometer is. You can Google it.

[Just]

the 96V will cover those kilometers a bunch quicker" - only in ideal on the flat surface without stops, so on... 

Will 1.0L car spend the same amount of gas on the same distance as the 4.0L car?

[Just]

Acceleration is another point of the gas/currency spending. As less accelerations as less gas & currency spending. 24V system has less acceleration in comparing to the 48V. These are my thoughts ... 

[Just]

truly_bent, in your calculations of Wh/km you did not take into consideration the motor itself. Some motors are rated to 650W, but others to 1200W. Although the 1200W motor is more powerful twice in comparing to 650W motor, it also consumes twice Watts/hour for the same distance - just in analogy to the 2x4 and 4x4 cars... So, splitting the 48V10Ah battery to two 24V10Ah ones and using them with 650W motor will increase the overall range at least twice in comparing with 48V 10Ah 1200W system.
Setting the Controller to less current limit @1200W system (converting it to 650W one) would also increase the range.   
These are just my thoughts.... Hopefully I explained myself...

[Just]

An electric motor will consume as much current as you would allow it to consume until it gets burned