Troubleshooting Guide > Vehicle Runs Slowly

Vehicle Runs Slowly

Overview

The most common cause of a vehicle that runs slowly is an old, worn out, or faulty battery pack. When a lead-acid battery pack is under load and between a 10% and 0% state of charge the vehicle will still run, however it will run at a significantly decreased power level. The battery pack's power output level will also decrease between a 100% and 10% state of charge, however not as noticeably as when it is at a 10% or lower state of charge. Once the battery pack reaches or goes under a 0% state of charge then most speed controller's have an under Voltage protection circuit will turn the motor off to prevent over-discharging and damage to the battery pack. To determine what the battery pack's under load Voltage level and state of charge is we have a Battery Pack Load Testing Guide to determine what its under load Voltage is, and a Battery State of Charge Chart to determine what that Voltage's state of charge level is for the battery pack.

A less common cause of a vehicle that runs slowly is a faulty motor. Diagnosing a faulty motor which runs but does not output a normal amount of power is not as easy as diagnosing a battery pack because there are no tests that can be performed to see if the problem is the motor. Fortunately we have found that around 99% of the time that battery pack is the cause of the problem and not the motor so that is on your side and testing the battery pack first is the best course of action to take.

The throttle does not commonly cause a motor to run slowly. While it is possible for the magnet inside of a throttle to come dislodged and move to a position where the throttle cannot operate in anything but the slow position this is very rare and usually the throttle will not work at all if its magnet becomes dislodged. The only time that a throttle magnet usually becomes dislodged inside of a throttle is if the throttle has been in an accident and is physically damaged.

The speed controller practically never causes a motor to run slowly as it is the nature of speed controllers to either work 100% perfectly, or to not work at all. Controllers have multiple output transistors and if one of these transistors fails it will overload the other output transistors and cause a chain reaction which causes the rest of the output transistors to also fail. For this reason the speed controller can be disregarded as the cause of a motor that runs slowly.

Try Deep Charging The Battery Pack for 48 to 72 Hours

Sometimes lead-acid battery packs need a deep charge to equalize the cells and help the battery pack regain capacity. Try charging the battery pack for 48 to 72 hours and then see if that helps. It is a good practice to perform a deep charge a couple of times a year or whenever a significant loss of capacity is noticed.

Inspect By Sight, Touch, And Smell

Remove the footplate or wiring cover and look for any burned or melted wires, wire connectors, or electrical components. Also look for loose, disconnected, or damaged wires or wire connectors. Pull and push on all of the individual wires and wire connectors to make sure they are not loose or disconnected. Get your nose close to the speed controller and motor and smell them. Any components that look burned or melted, or that smell like burned plastic are almost always defective and should be replaced. Motors that smell burned should be replaced to prevent damage to the speed controller.

Test The Battery Charger Port

(No Tools Needed) If the battery charger is plugged into the wall, unplug it. Plug the battery charger into the battery charger port on the vehicle and look for an illuminated indicator light on the battery charger. If an indicator light on the battery charger illuminates then the wiring and wiring connectors going to the charger port are good and the charger port itself is good. Not all battery chargers have an indicator light that will illuminate when the charger is only plugged into the vehicle, so if the light does not illuminate then a secondary Voltage test with a multimeter should be performed as described below.

(Tool Needed: Multimeter) If you have a multimeter the battery charger port's Voltage can be tested. The Voltage level present at the charging port should be the same as at the battery pack. If the charger port has male terminals then great care needs to be taken to avoid short circuiting the terminals to each other or to the charger port's housing if it is metal.

Test The Battery Charger

(Tool Needed: Multimeter) After testing the charger port and confirming that it has Voltage then the battery charger can be tested. If the charger port has no Voltage then that issue will need to be fixed before testing the battery charger. To test the battery charger to confirm that it is recharging the battery or battery pack, first test the Voltage of the battery or battery pack to confirm that it is below a 100% state of charge and that it needs to be recharged. We have a Battery State of Charge Chart to help with determining if the battery or battery pack needs to be recharged. Once it has been determined that the battery or battery pack needs to be recharged, plug the battery charger into the vehicle's charger port, and then plug the battery charger into the wall. Next test the Voltage of the battery pack with a digital multimeter to see if its Voltage is slowly climbing. The multimeter should be set to a DC Voltage range that allows reading the tenths or hundreds of a Volt of the battery or battery pack. If the battery or battery pack's Voltage slowly climbs to a higher number then that indicates that the battery charger is recharging the battery or battery pack. Continue to charge the battery or battery pack until the light on the charger indicates that it is fully charged, then test the battery or battery pack Voltage to see if it is at a 100% state of charge as specified in our Battery State of Charge Chart. If the charger is not charging the battery or battery pack up to a 100% state of charge then the charger is faulty.

Test The Battery Pack On A Scooter That Runs

Visit our Battery Pack Load Testing Guide.

Test The Battery Pack On A Scooter That Does Not Run

(Tool Needed: Load Tester) If the scooter is not running, a load test can be performed on its batteries by removing the battery pack from the scooter and taking the individual batteries out. The individual batteries can then be tested with a automotive battery load tester. Most entry level automotive battery load testers place a 100 Amp load on the battery which is too high so an adjustable carbon pile battery load tester is required and should be adjusted to place a 30 Amp load on the batteries.

Test The Voltage Of The Battery Pack

(Tool Needed: Multimeter) If you have a multimeter the battery packs Voltage can be tested to determine its condition. A good battery packs Voltage will be above its rated Voltage level even if it has been fully discharged and allows to sit a few minutes, or if it has been in storage. If a battery packs Voltage does not bounce back to above its rated Voltage level within a few minutes after being discharged that points towards a defective or worn-out battery pack. When a battery pack has been fully charged and its Voltage is below its rated Voltage level that also points towards a defective or worn-out battery pack. Good scooter battery packs will bounce back to above their rated Voltage level within a few minutes after the scooter has been driven.

Test The Throttle

(Tool Needed: Multimeter) Visit our Throttle Testing Guide page.

Inspect The Motor

Look for any burned or melted wires or wire connectors attached to the motor. Burned or melted wires or wire connectors indicate overheating of the motor which may cause the plastic insulation to melt off the motors copper wire windings.

Smell the motor for any burned plastic smells. If the motor smells burned that indicates that its coils have been overheated. Motors with overheated coils should always be replaced to prevent damage to the speed controller.

If the insulation melts off the copper windings they will short circuit and cause the motor to not run or to run slowly. Short circuited motor windings can also burn-out the speed controller by giving it too much resistance which makes it work too hard and overheat.