Eric, I ran some load tests on a number of Motorola, GE, Astron, and Samlex power supplies, including the TPN1110. When connected to a suitably "stiff" 120 VAC power source, the TPN1110 is specified to deliver a quasi-regulated output for the PA of 13.8 VDC at 25 amperes. I use the term quasi-regulated because the TPN1110 uses a ferro-resonant power transformer at the AC input side, but the high-current output is not regulated.
Here is an excerpt of my load test on a new-in-box TPN1110B: 15.74 VDC at no load 15.06 VDC at 5.0 amps load 14.71 VDC at 10.0 amps load 14.37 VDC at 15.0 amps load 14.04 VDC at 20.0 amps load 13.74 VDC at 25.0 amps load 13.39 VDC at 30.0 amps load 13.01 VDC at 35.0 amps load The test was performed with no loads on the other, regulated outputs of the power supply. My test bench has a dedicated 20-ampere circuit that varies very little under a heavy load. In fact, the AC input voltage to the TPN1110 supply was 121.7 VAC at no load and 120.2 VAC at 35.0 amps DC load. That's an extremely stiff power source. Most residential receptacle voltages are much less stiff, for a number of reasons, and may contribute to less than satisfactory operation. Try using a true-RMS digital multimeter to measure the AC input voltage of your power supply when it is under load. If it falls below 110 volts, the ferro-resonant transformer may be unable to compensate for the undervoltage condition. The national standard for nominal receptacle voltage is 120 +/- 6 VAC. You must use a true-RMS meter to read the input voltage, because its input current is not a pure sine wave, and a conventional meter will not read accurately. The +9.6 VDC output of the TPN1110B power supply uses the same full-wave rectifier as the high-current output. It the 9.6 VDC output has a high ripple content, one of the diodes in the full-wave rectifier may be open. You can also use a scope to view the rectifier output to verify that conduction occurs on each half cycle. If all of this checks out, the compensating capacitor at the transformer may be bad. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of kk2ed Sent: Friday, September 07, 2007 11:16 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Micor power supply voltage sag Good Afternoon, While going thru my Micor stuff, I found that one of my station power supplies (TRN1011?) suffers from voltage sag under load. I know that by design the power supply voltage should drop under load. Most will idle around 15v, then drop to about 13v under load of a 100w PA. But this unit is sagging to almost 11v under heavy loads, thus resulting in the PA output being lower than normal. Anyone have this issue before and know what the cause might be? One of the two pass/regulator transistors bad? Transformer on the way out? Or bad cap? Suggestions appreciated before I tear into it. Eric KE2D
