Guide to Electric Scooter RepairOverview:.
Aside from observable loose battery connections, most scooter problems are related to something called the controller. This guide will give you some ideas to help you diagnose and repair your scooter. Please be careful. Use this guide entirely at your own risk.
Batteries and Motors
Electric scooters are typically driven by brushed DC (direct current as from a battery, not house AC) motors, powered by SLA (sealed lead acid) batteries. Most motors are rated for use at 12 volts, 24 volts, or 36 volts. They are also rated in watts to measure their "horsepower", with 750 watts being equal to one horse. A higher wattage rating means that the motor can draw more amps from the battery without frying its internals. Since multiplying volts times amps equals wattage, increasing either voltage or amperage to a motor also increases its wattage. Connecting more voltage into a motor than it is rated for can shorten or end its life. Allowing a motor to draw too much amperage will do the same.
Testing a brushed DC motor. (Typically marked MY1018, MY1020, etc. available on EBAY)
Mount the scooter in a safe sturdy position so that if/when the motor turns, nothing will be in contact with it or its chain, wheel or other moving parts. Then unplug or otherwise remove all connections to the motor, leaving just the two leads that enter the body of the motor, usually red and black. Connect a 12 volt battery carefully as follows. Red connects to the battery's positive terminal, black to the negative terminal. There will be a spark as the final connection is made, and the motor will instantly spin, so I connect the positive lead to the battery terminal firmly and then just brush the negative lead from the motor against the other battery terminal. I do this, because a dead short in the motor would burn up the wire leads if tightly connected, and damage or heat the battery. If the motor is good, it will spin, so again, make sure it is mounted in such a way that it will not harm anything. If the motor is rated for 36 volts, and you connect a 12 volt battery, it will go slower than its maximum speed. If it is rated for 12 volts, it will go at its maximum speed. If you connect the wires backwards, many scooter brushed motors will go in reverse.
Controlling a motor's speed.
The best way to control a motor's speed is to vary the voltage to it. But, the easiest way,is to just turn the motor on and off. Some scooters used this method. The throttle was either full power or full off. The problem is that full power is instantly applied and control is limited. To get variable speed from a motor, you have to vary the voltage sent to it from the battery. Transformers are too heavy. Rheostats are too wasteful. So, we need to have a lightweight device that efficiently controls the voltage delivered by the battery to the DC motor. This device is called the controller. It is used in conjunction with a handlebar mounted "throttle" which sends a tiny variable voltage (1 to 5 volts) to the controller, that then sends the larger voltage (1 to 36 for example), with far more current, to the motor being controlled. A controller is rated by how many volts, its maximum output will be, and also by the maximum number of amps it can pass, without burning out. If you have a 24 volt motor, you need a 24 volt controller. If your 24 volt motor is rated for 150 watts, you can get by with a lower ampere-rated controller, than if your motor is rated for 750 watts. Typically, controllers for sale are rated at either 30 or 40 amps. Using a higher amp-rated controller is a good idea, because it is typically the controller than burns out first during overload conditions. You will pay a little more, but it is worth it. But be sure to get a controller that has the correct voltage to match your motor, and is for brushed motors (unless yours is the rarer brushless type as used on some hub motors).
Repair or Replace The Controller
The controller used in my scooter is a small aluminum box, 1.5"X2.5"X3.5". Others can be a little bigger. Controllers work by switching the battery on/off very, very quickly, leaving it on longer if the throttle is set high, and shorter if the throttle is set low. The actual switching is usually done by two, half-inch sized, solid state devices called mosfets that can handle a rated amount of amperage. A motor will draw more amperage as its load increases. The load on a motor is highest at startup. If you are completely stopped and the motor has a hard time getting started (you are in a rut for example), the
motor will draw a tremendous amount of current (amperage). This is when most controllers burn out. To save your motor and your controller, do a little kick start, or push off, and it will also increase your battery life. A typical mosfet device as used in my three wheeled scooter is the P75NF75. It is available from JAMECO.COM for 72 cents each plus $8.00 shipping. In my case the device was visibly blown out and smelled awful. You need to open the controller, unsolder the old device and install and solder in the new one. Since there are two of them in my controller, it is best to replace them both. Because other parts may also have burned out, you may wish to simply buy a whole new controller. A controller specifically made for your scooter will cost $50 to $80, and it will plug into the existing wiring harness without cutting or soldering. But won't it just burn out again? If you think that way, you can buy a "generic" controller on EBAY for $20 to $40 that will be stronger than your original model, but may require some cutting and splicing of plugs/connections. I like this route, but it does require careful attention to details.
More About Controller's Functions
Controllers also serve to protect your battery, by shutting down when the battery voltage falls too low. Draining every last bit of energy from a battery seriously shortens its life, so this is a very good feature. Some generic controllers have other various features/connections added to them, that you can choose to use or skip. A most important one is a control wire that connects to your brake system, so that power to the motor will cut off when the brake is applied, regardless of the position of the throttle. In my three wheel scooter there is a little box separate, but similar looking to the controller, that is used to shut off power to the two rear motors, when the brake is applied or the steering wheel is too far left or right (jacknife positions). By using a separate shut-off box, the manufacturer was able to use the simplest controller in my trike. But other manufacturers combine the shut-off function inside the controller.
This guide is primarily about the mass produced, imported, scooters that are sold everywhere. There are of course scooters and bikes that contain more expensive parts such as custom-made motors, brushless hub motors, lithium batteries, etc. Keep that in mind as you examine your electric scooter, since these devices can pose problems not considered in this guide.