Background

Enoki has scrapped a broken fax machine made more than 30 years ago. The power supply had 12V. It is good, because Enoki has voltage variable 10A and 0.25A ones only.

Summary

Enoki estimated that the power supply has capacity of 12V0.6A with a linear regulator. Without regulator, it will be able to feed more than 1A.

経緯

Fax を分解すると，12V 電源があった。現有の 10A は余りにも重く，0.25A 品は電流容量が少なすぎる。

要約

1A 以上を要する制御機器にも実験に使えそうである。

No regulator

The power supply had no regulator as shown in Photo1. The output wave was a typical full‐wave rectifier. It weighs 453g.

Photo1 The power supply outside

So Enoki measured peak-to-peak output voltage DSO SDS1102 CH1.

Method

DSO CH2 monitored base voltage of the loader power transistor 2SD553.

Enoki replaced 2SD553 base current limiter resistor 1k for 300Ω, because output current saturated less than 0.8A.

DMM PC510 measured output current instead of the 1A panel ammeter as shown Photo2, because the panel meter was scale over.

Photo2 Panel ammeter scale over

The result

Fig.1 shows the result. DMM PC510 measured the current.

Fig1. Output voltage dropout

Conclusion

Looking to Fig.1, The power supply is able to have capacity of 12V0.6A probably. Because a linear regulator has 1.3V dropout when connecting the regulator to the power supply output.

The power supply has no screw holes to fix the enclosure. Enoki has to devise insulation for practical use.

Photo2 The power supply inside

The 125V 2.5A fuse is connected to the secondary of the transformer. Enoki had learned how to use it connecting to commerce power line. Does UL approve this method?

The power supply may apply in Enoki's experiment.