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Discussions Question and Answer Forums Razor Electric Scooter, Bike, and Go Kart Modification Forum

Volts vs. Wattage, Speed vs. Torque

I have a Razor Ground Force that is currently 24v, 250w. I am going to upgrade it for more torque and higher top speed. I am trying to understand how changing the voltage (upgrade to 36v or 48v) compares with upgrading the motor wattage (500w, 750w, or 1000w). I understand the basic of voltage times amperage equals watts. But how does this affect a scooter or go kart?


What if you replace a 250w 24v (running at 24v) system with a 250w 48v (running at 48v) system? Will a higher voltage motor with the same wattage have more torque? Longer battery life?


What if you replace a 250w 24v (running at 24v) system with a 500w 24v (running at 24v) system? Will a higher wattage motor with the same voltage have more torque? Longer battery life?


So I am trying to decide if I should upgrade the big three (battery, controller, motor) to 36 or 48v. I don't plan on over-volting but rather use gearing to do it right. I am also trying to decide if I should upgrade the motor to a higher wattage? But I don't know how these factors interact. 

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So let's say a 48v 12ah battery is capable of giving 12a of current to the motor at max load yes? And less if going downhill, ie less load yes? I have an 1800W motor, 48v 12ah battery, this gives me 48 x 12 = 576 watts of max power to the motor? Thats a lot less than 1800 watts the motor is capable of running. This means i could overvolt to lets say 60v without worrying the motor could overheat? And is 12ah too little for 1800 watt motor? It produces less torque? My max speed is 25mph now with the current setup and i have a 1:5 gear ratio.11:55. Whats the best solution for more speed? Decrease gearing ratio to ~ 1:4? Or not because i dont have big enough amps to produce the torque? Could you please help me with?

The 12ah is the amount of capacity of the battery as measured at the 20hr rate. How long can you go before the battery goes dead. It is not the max amp output of the battery. The max output of the battery is regulated by the controller. If you have an 1800w motor and a 48v 12 ah battery you are looking at pulling 37.5 amps at full throttle which gives you very little run time. That is a lot of amps for a very small battery! A 12ah battery is way too small for a 1800w motor and won’t give very much fun time.

 

What is the voltage rating of the motor? Based on the voltage rating of the motor you will match your battery pack voltage and controller voltage to it. Gear the setup to get the speed or acceleration you desire.

 

If you can’t get the speed you want then switch to a larger wattage motor or re-gear for higher top end at the sacrifice of acceleration.

 

If you are running too many amps for your wiring, switches, controller, etc then run a higher voltage motor and upgrade the battery and controller. Run the largest ah battery setup you can fit to maximize run times.

 

You can overvolt the motor but the motor will run hot and you will shorten the life of it. It may last one time. It may last a year. Who knows. All depends on build quality of motor.

 

The wattage of the motor (geared properly) will determine how fast you can accelerate or top speed. Voltage of the motor, controller, and battery should match for best life of components. If you overvolt the motor it will spin faster than it is rated for producing more speed but at the sacrifice of motor life.

 

The higher the voltage the less amps. A battery drains faster the higher the amps are drawn from it.    

 

1. Choose wattage of motor to get power/speed you want.

2. Choose highest battery voltage you can run based on battery setup (higher voltage= lower amp draw).

3. Match controller to the voltage and watts.

4. Fit largest battery setup you can to maximize run times. (Or switch to lipo for longer run times as well)

4. Gear to get the speed or acceleration you desire.   

what do you mean by the 20hr rate, and thanks for the explanation

The 20hr rate is a measurement of the capacity of the battery as measured over 20 hours. The higher the number the more capacity the battery has and the longer it will last. For example a small 20Ah battery will put out 1 amp per hour for 20 hours. A large 100Ah battery will put out 5 amps per hour for 20 hours. 

So will a 36v 1000 watt motor go faster than a 36v 350 watt motor. With the same gearing as the previous 350 watt motor?

Not faster necessarily unless the RPM of the 36v 1000w motor is higher than the 350w version. It will be able to draw more power to conquer hills, carry heavier riders, etc. This means that it will deplete your battery a bit faster as well though! If you're looking at a straight speed boost try over volting your motor by 12v (48v battery on a 36v motor). This will tell your motor to run at a higher RPM than its rated for but usually will not damage the motor if you stick to 12v over. 


I run a 24v 350w motor with 36v battery system and can hit high 20s / low 30s MPH. It can't climb me up a hill worth a darn though. You can gear for speed or torque, not both. I as well am considering the jump to 36v 1000w motor but unfortunately, since I'm still using heavy SLA batteries, 4 on there isn't ideal. 


What's your setup Drake?

OLD SETUP: Motor: 36v, 350 watt, 2500RPM Controller: 36v, 500 watt Battery: 36v 12ah "diy lithium ion" NEW SETUP: Motor: 36v, 1000 watt, 2800RPM Controller: 36v, 1000 watt Battery: 36v 24ah "diy lithium ion" Gas to electric conversion.
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I have a question about batteries. SLA batteries are said to have 200 recharges or so. How do you define a recharge? Suppose I only go to the shop and back and still have 90% battery capacity left, and I charge it to 100%. Would that be considered one full cycle/recharge? So if I only discharged the battery to 90% and charged it to 100% 200 times, would the batteries be dead? Or is a 100% recharge considered one cycle? And how do lithium batteries differ to this as opposed to SLA batteries. Thank you
Could someone explain to me how to get the most life out of lithium LiFePO4 batteries? I read that you should never fully discharge it, and only discharge it to when it reaches about 20% and only charge it up to 80%?
The 200 to 300 recharge cycle battery life expectancy is based on deep discharges. If the batteries are lightly discharged then the number of times they could be recharged will be longer. A 100% deep discharge of a 12 Volt lead acid battery is taking it from 13.8 to 10.5 Volts. This is around a 3 Volt discharge. If the battery was only discharged 10% to 13.5 Volts then its life expectancy and number of times that it could be discharged and recharged would be greatly increased.

Lithium batteries are a lot like lead acid batteries in regards to how deeply they are discharged and how many time they can be recharged, except of course that they have a 1000 deep discharge cycle life expectancy instead of 200-300 like lead acid batteries do.


I have not researched about the effects of undercharging LiFePO4 batteries to increase their lifespan so I can not comment on that. I imagine that the less amount they are discharged the longer their life would be as that seems to be a common trait of most types of rechargeable batteries.

Is a 1.8A AC/DC charger suitable for a 20ah battery lithium lifepo4?
Also its making a slight humming sound
A 1.8 Amp charger will recharge a deeply discharged 20Ah battery pack in around 13 hours. Some battery chargers make a low volume humming sound when they are being used.

So in my new electric skateboard setup I have:


24v 350W motor

24v 350W (~15A draw) controller

24v 7s4p (29.4v really) lithium battery


This setup is pretty close to perfect for me but I'm definitely restricted when going up long, gradual hills. I had considered getting a 24v 500W controller but then would need a second battery to combat the amp draw being higher. If I got the 500W controller would my motor see any difference? 


I'm trying to relate it to your earlier post about load on the motor and requested amps. When I'm on a gradual uphill and can feel my board not achieving it's normal top speed is the motor requesting a higher amperage (>15A) and that's what's limiting me? Or is it that the motor itself can only request so many amps?

You should regear it so your skateboard provides more torque to go up hills at the sacrifice of top speed or switch to a larger motor/controller combination that can provide more torque output. 

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