24v vs 36v vs 48v motors and the various powering options

[zogthegreat]

Hi everyone,

I was wondering if anyone had the time and patience to explain to to a noob the advantages/disadvantages of using 24v vs 36v vs 48v motors and the various powering options you can configure.

For example I see some people choosing a 24v motor for a vehicle and another person choosing a 36v for the same type of frame. But most people do not state their reasons for why they are choosing that motor/wattage combination. Another thing I see is people running 24v systems at 36v or higher. Once again, what are the advantages/disadvantages of such systems.

I am asking because I am in the planning stages for a build project this winter, (yes, I know it June, but where I live, that's when you start planning!), and I am trying to choose the best motor voltage/wattage configuration for my project.

Thanks

zog

 

[drsolly]

I built a bike with a 24v motor because I already had a 24v battery. If you're starting from scratch, then:

Watts is how much oomph the motor has. But you can't tell much from manufacturer's stated motor watts.

The advantage of 48v over 24v, is that for the same power, it draws less current, which means slightly less is wasted in heating your bike's wiring.

That 24v motor I mentioned ... I usually run it at 30v, and when I want it to be really peppy, I run it at 37v, that means more watts from the same motor.

The first thing you want to think about, is whether you want the bike to be "street legal", and what that means, depends on where you live. Probably a Canadian can tell you the rules where you are. That will tell you the maximum watts that your motor can be.

 

[mateusleo]

Higher voltage leads to higher speed and higher amperage leads to more torque. As an example my 48v 1000w bike leads me to 55kph on 26 inch wheels

 

[teslanv]

A Motor will have a rating of say 36V & 700W. But that same motor will typically take whatever voltage and current you feed it. If you want the motor to spin faster, supply it with 48V. You just have to be careful with how many amps your controller feeds it, since too much current (amps) will overheat the motor. Also overvolting the motor will cause it to draw more amps as well, especially from a stop, as it tries to get up to it's "unloaded speed"

Total power (Watts) given to the motor is just Volts x Amps. The typical cheap ebay or Yescomusa Direct Drive Hub motor can handle about 30-40 Amps of current, so depending on how many volts you want to run it on, it can provide upwards of 3000W of power. I am currently building a bike with 74V & 40A (~3000W) with one of these "9C Clone" motors. The Controller i am using is a Lyen 18x4110FET, NOT the standard controller.

Note that if you are using the controller that came with your kit, it will likely NOT be able to handle higher voltage or current than the kit specifies. You can modify the controller (Solder in better FETS & Capacitors), or buy a better controller that can be over-volted.

 

[biohazardman]

For the most part running 24V system is for low wattage set ups so it gets decent range, can use cheap batteries as it does not ask to much of them in its low speed and performance envelope. Another plus of the low voltage systems is they are less expensive. 48V is more of a mid powered machine with increased, acceleration, top speed and hill climbing abilities. It probly has a higher wattage rating on the controller so will need better or more batteries to feed it without damaging them. Also as the number of batteries goes up with the voltage increase so does the range if you can keep your speed down that is. In my upgrades from 36 to 48 to 60 and 72V I noticed a speed increase for sure but usually the higher voltage goes with a new controller that has a higher amperage rating as well so a big boost in performance in every upgrade. My upgrades in voltage from 48V on were with the same 600W BMC V2S that now runs 66 or 72V depending on the day. With higher voltages and wattage limits I constantly think of how much I am asking from my motor and try to be reasonable so I don't toast it as I have seen others do. Everyone needs more voltage some just don't know it yet.

 

[gogo]

48V is the 'safe' limit before electricity becomes dangerous enough to stop a human heart. About 20-22A seems to be a sweet spot for controllers, so if you need only 24v*20A = 480W, then you might just use 24V. 36V*22A = 792W, which corresponds to the common limit in the USA. 48V tends to be used by those not concerned with regulation.

Many ebike motor/controller/battery systems are vestiges of the 'lead acid' era, which is being phased out in China and elsewhere, hence the multiples of 12V. 12V itself doesn't play nice with electronic controller circuitry, so is only found in rare low-power 'switch-based' systems.

The components that are commonly available generally narrow your choices, but any range of 12-48V could work fine for ebikes. You won't find many vendors selling anything higher than 48V 'ready to ride' due to the liability inherent with the higher voltage.

 

[dmwahl]

Higher voltage motors are theoretically more efficient since at a given power level the current required is lower. Higher voltage battery packs are more expensive though. The whole "voltage gives you speed" and "amps give you torque" is misleading. Sure you can increase voltage to increase the top speed, but you can't just "increase the amps" to get more torque. A high voltage motor at low current can easily produce more torque than a low voltage one with a higher current.