A Linear Power Supply For LX200 type Telescopes

LX200 type telescopes are supplied by the manufacturer with a switched mode power supply that delivers 18 volts at up to around 2 amps. We have encountered problems with this type of power supply, both in reliability and stability. We have found that replacement of the switched mode power supply with a regulated linear power supply resulted in noticeable improvement of the image quality (due to improved tracking) taken using an LX200 telescope.

The advantages of a swtiched mode power supply are low cost and light weight. However, a linear power supply has the advantages of greater reliability and improved voltage regulation. These, of course, are offset by the higher cost and greater weight, due to the need for a large transformer and filter capacitors.

The linear power supply design presented below will provide adequate current for any of the LX200 series telescopes up to the largest 16" model.

Notes:

1. Components are over-rated for long life and reliability.
2. Bridge rectifier BR1 and voltage regulator VRG1 must be mounted on a substantial heat sink.
3. Output current meter M1 (0 to 3A) is optional but can give an indication of telescope drive operation (eg fault condition of no current or excessive current).
4. The red LED (light emitting diode) is also optional, but provides an indication that the power supply is operational.
5. D1 and D2 are protection diodes and are probably not required in this application.
6. The trimpot VR1 (500 ohms) is adjusted to give exactly 18 volts at the output.
7. Transformer T1 should be chosen to suit the available mains supply (eg 110V or 240V). The secondary output voltage should lie between 16V and 20V.
8. All capacitor values are in microfarads.
9. All resistor values are in ohms, and are 0.5W unless stated otherwise.
10. Note the correct polarity of the diodes and the electrolytic capacitors.

This is a view of the linear power supply built for Norcape Observatory. In this model an additional voltmeter was fitted to monitor the output voltage.



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