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Why does it spark when I plug battery pack into controller?

Every time I plug in the power from the batteries to the controller there is always a spark, is this normal?
I just bought a CT-660B9 motor controller and every time I plug in the power from the batteries to the speed controller I always get a spark. A lot of the time the sparks are large and frightening and damage the terminals. I would greatly appreciate it if someone could provide some help on this issue.

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It is normal for there to be a spark when connecting the battery pack to the speed controller. The spark is caused by the capacitors in the speed controller charging when they are connected to the power source. The CT-660B9 controller, like most other speed controllers, has a lock (power) switch connector which should be used for turning the controller on and off instead of turning it on and off by disconnecting the battery pack from the controller. Using the lock (power) switch to turn the controller on and off will help reduce the sparking problem that you are experiencing.

However, if you have two battery packs on the vehicle and need to switch from one battery pack to another then I recommend using a power switch to accomplish the switching instead of hot swapping the connectors. Switches are designed for being used under heavy power loads and they snap the power load as opposed to a connector which slowly make or break the power load which causes sparks that can damage the connector.

Most connectors can handle an occasional connection between a battery pack and controller, such as when replacing a worn out battery pack. However they can not handle multiple connections between battery packs and controllers from continually hot swapping between two different battery packs. In that case wire a switch in the circuit and turn the switch off when hot swapping the battery pack.

If you absolutely want the sparking to not happen then it can be eliminated with the following method. When connecting the battery pack to the controller first disconnect one of the battery harness leads from one of the batteries. Then connect the battery pack to the controller. Next hold a 10 Ohm resistor between the detached battery harness terminal and the battery lead that it goes to for a few seconds. The 10 Ohm resistor will slowly charge the capacitors in the speed controller so that when you remove the resistor and attach the connector to the battery the sparking will be eliminated or greatly reduced.

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