Power supplies

Power supplies commonly used to power the M1500, M1550, M1650, M550 and similar units are either a Meanwell model AD155A or a Meanwell DR-120-12.

The above mentioned power supplies are set with an output of 13.8 VDC, a nominal voltage required to charge the batteries used for backup in case of a line power outage.

To test power supplies, set your voltmeter to read AC and check the incoming power (Black and White wires to power supply terminals). Verify there is around 130 volts AC coming into the unit. Next, set the voltmeter to read DC volts and measure the voltage on the output terminals (Red and Blue wires). The DC voltage should be close to 13.8 volts DC.

If you do not measure any voltage on the AC input terminals, check RTU fuses and connections back to the supply at the breaker box.

If you do measure the proper AC voltage, but do not measure DC voltage on the output terminals, then the power supply is faulty and must be replaced. Likewise, if you measure a DC voltage lower than 13, the power supply may be weak and should be replaced.

Load testing

Under ‘listening’ conditions, the RTU and radio will pull a very small amount of power from the power supply. However, when the radio keys up to transmit, it will pull something closer to 4 amps from the power supply. A good way to load test a power supply is to connect a voltmeter to the DC output terminals of the power supply and make the radio transmit by connecting a microphone and pushing the transmit button. The voltage measured on the output of the power supply should not drop below 13.5 volts or so.

If you do not have a microphone for testing, Micro-Comm has a radio test switch available to serve the same purpose.

Power supplies for the model S3000, S4000 and S4500 PLC’s

The power supply for the S3000, S4000 and S4500 comes in two parts. First, a step down transformer, usually mounted on the inside of the RTU enclosure door takes 120 VAC incoming line voltage and steps it down to 24 volts AC. The 24 vac is fed into terminals on the upper right side of the controller and then internally to the unit is converted to 12 and 24 volts DC.

Testing is essentially the same as above- check 120 vac coming into the transformer, 24 vac out of the transformer, then switch to DC and check the 12 and 24 volt terminals on the controller.

12 volts DC supplied to the radio comes from the controller board as well. A load test of the power supply would be the same as mentioned above- connect voltmeter to 12 volts DC terminals, key up the radio and look for a drop not to exceed ½ a volt or so.

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