Author: BenjaminNelson via YouTube
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How to perform a simple test of an old forklift motor with a 12V battery.
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My friend, Wil, is working on an electric lawn tractor project. He wants to use this motor to power it, so he stopped by so that we could test it.
This very common style of DC motor is "Series-Wound". It can be run directly from a battery or batteries with no other controls required. A motor like this typically has FOUR power connections. Two of them are for the armature – the rotating center coils of the motor. The other two are for the stator – the stationary field windings around the outside of the motor.
Both the armature and stator act as electro-magnets, and the interaction between the two creates the forces to spin the motor.
The important thing to remember on a Series-Wound DC motor is that the armature and the stator are connected in SERIES. Power goes through the stator, is connected to the armature with a bus bar or short cable, continues through the armature, and then completes the circuit back to the battery.
A motor like this can draw very high current, so we will use thick cables when it’s installed in a project. Even just for testing, the current draw of making a connection at the battery can cause an arc.
So, we will use a Contactor to complete the connection. Similar to a relay, a contactor uses a small, low voltage, electric current to power an electromagnetic field to activate a heavy-duty switch. The power that the contactor controls can be much higher voltage and current. By giving 12V power to the contactor (typically with a key switch, main power switch, etc.) we complete the circuit and activate the forklift motor.
When we spun up power to this motor, it was relatively quiet. There was no unexpected bearing noise, and there was no visible light from arcing at the brushes. In short, it appeared to be a perfectly good motor in fine condition.
The ID plate on this motor was unreadable, but these motors almost always ran at 36 or 48V. They can easily be run at higher voltages. On a motor like this speed is proportional to voltage. At 48V, this motor will spin four times as fast as it does at 12V.
A large DC forklift motor was used to power my original DIY Electric Car, a Geo Metro, converted to electric in 2008. You can watch that project at:
It should also be noted that this style motor can NOT spin the opposite direction simply by reversing the polarity of the power by swapping the cables at the battery. Since BOTH magnetic fields are created by the came current flowing through both, reversing the polarity at the battery reverses BOTH magnetic fields. Reverse of reverse is still forward, and the motor will still spin the same direction. To reverse the motor direction, one would need to reverse the armature compared to the stator. That can be done by moving where the jumper wire connects. In this example, on the motor, the left-most and second-from-the left cables could be swapped to reverse the motor direction.
Some of the best, most straight-forward, information I have found on using forklift motors for electric cars was written by motor guru Jim Husted at the following thread on DIY Electric Car. If you have any questions about forklift motors for EVs, please read through the first couple pages of that:
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