M-Magic “S” Controller Load Test
I recently had a controller come back for repair. One of the owner’s concerns was the transistor operating temperature. The controller’s problem involved the UVL pot which can cause the power transistor to generate more heat than normal. As part of the repair process I developed a load test for the M-Magic S controller to determine if the repaired controller was operating normally.
Load Test for CMPM, Drop-In Neo and Unlimited Cars
The load test consists of both filaments of an 1157A automotive light bulb wired in parallel. The bulb represents a load of 2.5 Amps at 12 VDC and 3.2 Amps at 18 VDC. The test will place the TLC switch in the center (2) position. The UVL dial will be set to maximum voltage. These settings remove the full power bypass and the transistor is operating 100% of the time. Operating the transistor in this manner reduces the voltage to the bulb by 1.4 VDC and the current to 3.0 Amps. Tests performed by M-Magic owners using a high-speed recorder have shown that an unlimited car draws a maximum of 1.0 Amps while running at speed. The cars starting current is much higher. The starting current spike lasts only a few mill-seconds and can be ignored.
From personal experience and discussions with others I would never expect the TLC switch to be in Position 2 when running such a car. I also cannot conceive of the UVL dial set at anything but maximum voltage. Therefore, the test is significantly more severe than any real world CMPM, Drop-In Neo or Unlimited car experience. For T-Jets, G-Jets and Superstock cars the transistor is operating at or slightly above room temperature and no test is required for these cars.
The load test operates the controller in two different modes. The transistor is at, or close to, ambient room temperature at the start of each test. Test number one (Test #1) operates the controller at full throttle for three minutes. Test number two (Test #2) operates the controller in a Pulse mode between 0% throttle and 100% throttle for a period of three minutes. The time spent at 100% throttle shall be less than 1 second. The time spent at 0% throttle shall also be less than 1 second. The acceleration and deceleration times shall be approximately 1 second. The duration of each test is three minutes. The controller will be allowed to cool down to near room temperature between tests. The temperature of transistor will be measured at the start and finish of each test using a non-contact infrared thermometer.
Load Test Setup
The following photo shows the test setup. The controllers black lead is connected to the Digital Multi-meter (DMM) which is set to measure amps. The controller is configured in accordance with the second paragraph. The DMM is reading the load of the spinning armature and the light bulb. With the trigger fully depressed, the TLC switch in Position 2 and the UVL dial set to provide maximum voltage the measured load is 3.02 Amps. The load consists of a free-wheeling superstock car and a 1157A light bulb which can be seen suspended underneath the bench. The two filaments of the 11157A bulb are wired in parallel.
LOAD TEST SETUP
Controller #1 Test Results
Test #1 (Full throttle for three minutes). Transistor Starting Temperature 81°F. Transistor Ending Temperature 97°F.
Test #2 (Pulse 0-100-0% throttle for three minutes). Transistor Starting Temperature 85°F. Transistor Ending Temperature 110°F
Controller #2 Test Results
Test #1 (Full throttle for three minutes). Transistor Starting Temperature 82°F. Transistor Ending Temperature 95° F.
Test #2 (Pulse 0-100-0% throttle for three minutes). Transistor Starting Temperature 86°F. Transistor Ending Temperature 111°F.
Three additional current generation M-Magic “S” controllers were also tested. These three additional controllers preformed in a manner similar to the ones reported above.
A Realistic Load Test for CMPM, Drop-In Neo and Unlimited Cars
To determine transistor temperature under a more realistic scenario the TLC switch was placed in the 0 (Full Up) position and Test #2 was performed. Placing the TLC switch in Position 0, or Position 1 bypasses the transistor at full throttle. As a result, the transistor generates no heat as long as the trigger is fully depressed. The TLC switch is typically in Position 0 for all cars with the exception of Gravity cars and occasionally G-Jet cars running the original 350“/450” slip on tires. For these cars one might place the switch in Position 1. The Pro-Jet variant of the G-Jet is sufficiently low as to not need the switch in anything but Position 0.
The modified version of Test #2 operated the controller in a 0-100-0% pulse mode for a five-minute period as opposed to the three-minute test performed above.
The transistor operating temperature at the end of the extended load test was 104°F. This temperature is consistent with tests performed with unlimited class cars. In these real world tests a maximum transistor temperature of 106°F was reported. During the test is was observed that the small diameter flexible test lead wires going to the load were moving back and forth in concert with trigger position. A demonstration of magnetic forces at work!
Gravity Car Load Test
Can-motor Gravity class cars appear to be a more extreme case as the TLC switch is typically in Position 2 and the UVL dial is rotated to reduce peak voltage to the armature when the trigger is fully depressed. When the TLC switch is in Position 2 the transistor is not bypassed and is continuously generating heat. Reducing peak voltage by adjusting the UVL dial increases the voltage drop across the transistor and the amount of heat generated by the transistor.
To simulate this, the load was reconfigured and controller re-adjusted. For this test the TLC switch was placed in Position 2, sensitivity was set to provide minimum starting voltage and the UVL dial was set to maximize voltage drop across the transistor and minimize voltage at the load. With these controller settings the modified load is 1.8 Amps at maximum throttle. With these settings maximum throttle provides approximately 12V to the load and, as a result, approximately 6V is being dropped across the transistor.
A modified version of Test #1 operated the controller at full throttle for both a three and five-minute period. The transistor surface temperature at the end of the three-minute test was 124°F. The temperature at the end of the five-minute test was 145°F
A modified version of Test #2 operated the controller in a 0-100-0% pulse mode for a five-minute period. The transistor surface temperature at the end of this five-minute Gravity car load test was 140°F.
Despite the higher temperatures the controller was easy to hold and I was never concerned about a heat related controller failure. It was interesting to note that the tip of the TLC switch was approximately 10°F higher than the measured transistor temperature. Touching the tip of the TLC switch was uncomfortable but the switch is easy to avoid.
The worst-case measured temperature of 145°F is significantly less than the transistors maximum operating temperature and the controller was in no danger at any time. All of these tests are conservative. To develop a more realistic Gravity car test, I would need to test a current generation Gravity car to determine controller settings, controller duty cycles and associated armature currents.
Other manufacturers don't dislcose their test results. Wonder what else they are hiding?
