Understanding ev specs

Hi Cavahlo,

Good questions.

First for performance it's the same as the gas bike world - peak power output tells you a fair amount of the story. Some manufacturers will tell you the peak amps that the controller will supply and tell you the voltage of the bike. For example, an XM-3000 controller puts out peak amps of 55A and has 60V so it's theoretical maximum is 55*60 = 3.3kW (which is 4.4hp). This is the theoretical maximum and doesn't take into account the efficiency of the motor and the controller. For power at the rear wheel I'd multiply that theoretical by 0.8. Even if you don't account for efficiency losses you can compare bikes power outputs this way. e.g. the Vectrix lists a peak power of 21kW vs. the XM's 3.3kW. Hence the Vectrix is quicker (both top speed and acceleration) than the XM-3K (this isn't a surprise the XM-3K is equivalent to a 50cc and I've heard the Vectrix compared to a 250cc).

Next, looking at the capacity of the batteries it's best to convert to kilowatt hours (kWh). Some manufacturers quote the kWh capacity (the Vectrix has 3.7kWh). Some manufacturers quote the Amp Hours of the battery (Ah) - multiply this by the system voltage to get kWh, the XM-3000 has 27Ah batteries and 60V so it has 60 x 27 = 1.62 kWh.

That's the theoretical maximum power stored in the batteries. However, you're really interested in comparing the range of the bikes. So now you have to consider two additional things (1) the power usage of the bike & (2) the chemistry of the battery. For (1) some manufacturers have started quoting Amps drawn at a particular speed, others don't do this so generally you just need to go by the ranges they quote - but be sure to look at the fine print to see what average speed is used for that range. For (2) manufacturers will usually list the chemistry - lead acid (SLA - in the XM-3000), Nickle Metal Hydride (NiMH - in the Vectrix) and Lithium Iron Phosphate (LiFePO4 - in the XM-3500Li). Generally speaking Lithium is best, NiMH next and Lead last. "Best" means that the battery is lighter and more compact and, perhaps more importantly, can deliver more of the stored energy before the voltage sags (resulting in a slower bike and then the bike cutting off). For the technicalities behind that look up Peukert's effect.

Finally, volts equate to speed and amps relate to acceleration. So, if I want to make my XM-3000 go faster I would "over volt" it by adding an additional 12V battery and making it a 72V system. If I want to make my XM-3000 accelerate quicker I need to upgrade the controller to increase the maximum amperage that it can output.

Hope this helps.

Hi Cavahlo,

Good questions.

First for performance it's the same as the gas bike world - peak power output tells you a fair amount of the story. Some manufacturers will tell you the peak amps that the controller will supply and tell you the voltage of the bike. For example, an XM-3000 controller puts out peak amps of 55A and has 60V so it's theoretical maximum is 55*60 = 3.3kW (which is 4.4hp). This is the theoretical maximum and doesn't take into account the efficiency of the motor and the controller. For power at the rear wheel I'd multiply that theoretical by 0.8. Even if you don't account for efficiency losses you can compare bikes power outputs this way. e.g. the Vectrix lists a peak power of 21kW vs. the XM's 3.3kW. Hence the Vectrix is quicker (both top speed and acceleration) than the XM-3K (this isn't a surprise the XM-3K is equivalent to a 50cc and I've heard the Vectrix compared to a 250cc).

Next, looking at the capacity of the batteries it's best to convert to kilowatt hours (kWh). Some manufacturers quote the kWh capacity (the Vectrix has 3.7kWh). Some manufacturers quote the Amp Hours of the battery (Ah) - multiply this by the system voltage to get kWh, the XM-3000 has 27Ah batteries and 60V so it has 60 x 27 = 1.62 kWh.

That's the theoretical maximum power stored in the batteries. However, you're really interested in comparing the range of the bikes. So now you have to consider two additional things (1) the power usage of the bike & (2) the chemistry of the battery. For (1) some manufacturers have started quoting Amps drawn at a particular speed, others don't do this so generally you just need to go by the ranges they quote - but be sure to look at the fine print to see what average speed is used for that range. For (2) manufacturers will usually list the chemistry - lead acid (SLA - in the XM-3000), Nickle Metal Hydride (NiMH - in the Vectrix) and Lithium Iron Phosphate (LiFePO4 - in the XM-3500Li). Generally speaking Lithium is best, NiMH next and Lead last. "Best" means that the battery is lighter and more compact and, perhaps more importantly, can deliver more of the stored energy before the voltage sags (resulting in a slower bike and then the bike cutting off). For the technicalities behind that look up Peukert's effect.

Finally, volts equate to speed and amps relate to acceleration. So, if I want to make my XM-3000 go faster I would "over volt" it by adding an additional 12V battery and making it a 72V system. If I want to make my XM-3000 accelerate quicker I need to upgrade the controller to increase the maximum amperage that it can output.

Hope this helps.

"...Amperes, KWh, Watts, Volts, the engine, the battery, the charger..."

Electrical components are often effectively described in terms of water in a pipe.

Volts can be described as the pressure, and Amps can be described as the diameter of the pipe. You can get the same amount of water using low pressure from a fat pipe (low volts/high Amps), or high pressure from a thin pipe (high volts/low amps).

A Watt is a measurement of power (Kw/KiloWatt is 1,000 Watts) and 745 Watts is one horsepower, and is "Volts X Amps". If you need 3 horsepower (2235 Watts), you can get it from.

48 Volts @ 46 Amps, OR
72 Volts @ 31 Amps.

The higher voltage motor can be smaller, and the wires can be smaller, too. If wires are too thin for the amps you are asking them to flow (full throttle), they will get too hot.

The starter of an 18-wheeler is 24 volts because if it was 12 volts, the motor and cables would have to be twice as fat.

The horsepower rating of a motor is deceiving, as electric motors have full torque from a standstill.

Controllers get much more expensive at voltages over 72 (6 Batts X 12V) so, shoot for 72 volts, but put it through the smallest motor that can provide your power goals without overheating. A really big motor is expensive, bulky, and will suck your battery dry much too soon.

Amp/Hours (size of gas tank), a "10 Ah" battery can provide one Amp for 10 hours, or 10 Amps for one hour. In truth, a slow discharge (one Amp/10 hrs) will give you the full battery use, but with a fast discharge, you won't get all the Ah's.

When reading manufacturers claims, they lie. Big fat stinking lies, one right after the other. Not that their products are bad, a really great product that gets 32 MPG will say that it gets 41, but, "your mileage may vary".

This is why forums are so important.

The horsepower rating of a motor is deceiving, as electric motors have full torque from a standstill.

Meaning the acceleration of an EV off the line is much stronger than the acceleration of an ICE vehicle with similar peak power.

But this is only true if the amps are not electronically limited, like in the Vectrix.

Have a look at this video:

The RETAMPI shows in big red letters the percentage of the maximum current leaving the battery (- in front of the number) or going in during regen braking (positive number).
Without electronic limitation the amps would start with the maximum value at the start, then fall gradually until the lowest value is reached at top speed. That would be true for most EV's, I believe.

As you can see this is not happening in the Vectux. The power is reduced drastically below 45km/h or so. Off the line it feels as if it could not pull a wet herring of a plate, then it gets stronger and stronger until it is really good around 75km/h.

Mr. Mik

Car batteries are not "deep cycle". They are drained for about 3 seconds to start the car and are immediately topped off.

They have very thin plates to expose as much plate surface area to the chemicals as possible in order to have as many amps as possible in a small package. deep cycling will erode the plates, so deep cycle batteries have thicker plates so they last longer under severe use.

If they are put on a bench charger once a year and are handled badly, they will still work OK for a useful amount of time, but...

On an E-Scoot/E-Bike you will be charging EVERY day you ride. Bad charging habits by a cheap charger without sensing features will fry your battery pack quickly.

Read this, it will be confusing at first. Read it anyways, think about it for a while, then read it again.

Sometimes if you try to save a dime, you end up losing a dollar...

http://visforvoltage.org/forum/2969-simplified-bank-charger-wiring