t present, combination switches have been commonly used on forklifts, but there is a problem of unstable performance. After several dismantling, analysis and analysis, the main reasons are as follows: the moment the handle knob switch is turned, the contact area between the contacts is very small, and the current changes greatly, and the contact heats up after a long time; after long-term use, the contact The points produce wear, oxidation and corrosion, increasing the resistance between the contacts, thereby causing the contacts to heat up more.
Contact heating will cause the contacts on the handle body to loosen or stick, making the combination switch generate heat, unstable performance, and even functional failure. The shape and contact position of the combination switch used are shown in Figure 1, and the additional gear wiring of the combination switch and handle is shown in Figure 2.
In order to stabilize the performance of the combination switch and prolong the service life, the contact current should be reduced to reduce the heat of the contact. The most convenient way to reduce the current through the contact is to increase the bypass switch to shunt the current. It is determined by research that the specific method is to add a bypass auxiliary electromagnetic relay to the combination switch, the model of the relay is HD4195A, and the contact capacity is 40 A.
Combination switch before and after the improvement of the circuit shown in Figure 3. The working principle of the combination switch after the modification is as follows: line number 10 is the input end of the switching power supply, line number 11 is the output line of the indicator light switch, and line number 9 is the output line of the headlight switch (the headlight power is 110 W, and the energizing current is about For 10 A). When the headlight switch is turned on, the contacts of the combined switches 10 and 9 are contacted, so that the relay electromagnetic coil is energized, and then the relay main contacts are connected to the 10 and 9 wires. After the improvement, the current-carrying capacity of the switch contact circuit is obviously strengthened. Even if the load current of the power supply fluctuates, the combination switch contact will not be damaged, thereby avoiding the phenomenon of burning the combination switch due to contact heating. After experimental verification, the improved combination switch achieved the expected effect, and the unstable performance of the relay did not occur again.
