VK Powermate II Report
Shortcomings in original design
- Inadequate rectifier diodes
- DC fuse difficult to replace (inside case)
- Marginal transformer
- Lack of protection against over-temperature
Modifications
- Constructed in smart instrument case
- Front and rear binding posts for 12V output
- 35A bridge rectifier mounted on rear panel
- Filter capacitance 2 x 4700 uF
- DC Fuse located on front panel
- Heatsink (Rth=12°C/W) fitted to Q1
- IC1 socketed
Performance Test
246AC, ambient 23
Held regulation up to 8A, not tested further.
After a half hour test at 6A,
12.6>14.8 ohms. 44C rise in copper temp.
Temperature of key components (lid on during load, lid off for measurement)
| Component |
Temperature |
| Transformer iron |
35 |
| Rectifier |
76 |
| IC1 |
38 |
| Q1 |
46 |
| Q2 |
93 |
| Outer edges of heatsink |
63 |
| |
|
Idle, Pin=9W pf=0.4
At 6A output, Pin 161, pf=0.85, Iin=0.77A, Pout=80, n=50%
Above, rectifier current at 6A load, 1A/V.
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Owen Duffy 1995, 2021. All rights reserved. Disclaimer.