TTE/XFR8 DCC Power Supply Test Report | Tech News at Tony's Train Exchange.

I tested the XFR8 that you sent me (New XFR8) and also tested one that I bought from you 12/30/99 (Old XFR8) that I have been using to run my layout. Short answer: they seem to be the same. I also tested the XFR12 that I use as part of my bench test setup since I had everything set to go anyhow. I use it to power whatever booster I am using during a test, although most of the time I have it connected to an NCE PHPRO for general testing.

The results are shown in the graph below. I have also included the source Excel spreadsheet so you can look at the data directly. The line voltage was wandering around a bit while I did the test, which is why the XFR12 seems to drop down a bit. The open circuit voltages are probably worst case at a line voltage of 122 volts.

The XFR8 has an open circuit voltage of about 18.6. This is within the maximum value of 19.2 volts stated in my NCE Powerhouse Pro manual (page 20, second paragraph). As near as I can tell, there is no problem with the XFR8 and the PHPRO. My readings were done at a line voltage of 122 volts, so they are probably on the high side.

One note of caution: although the diode approach does drop the voltage, the diode package gets EXTREMELY HOT. I measured 94.3 °C at 5.00 amps on the 8 amp bridge. I did not even try the 4 amp version. This is near the boiling point of water and will definitely cause bodily injury (I know this for sure because I grabbed the diodes while testing them and burned my finger). I am not convinced that the diode approach is a good one, particularly since the XFR8 appears to be within the ratings of the NCE PHPRO. If people are going to use the bridge approach, we should recommend that the bridge be mounted to an appropriate sized heat sink.

All of the babble on the chat site about transient margin, etc. is a load of used vitamins. Power line transients can be several hundred volts. Whether you have a 50% or a 10% margin makes little difference when the transient is several hundred volts and several times the normal line voltage. Transient suppression power strips are typically rated for 400 volts maximum transient let through unless you spend a lot of money on them. This is over 3 times the normal line voltage, so whether the transformer is outputting 15 volts or 18.5 makes little difference, the transient will cause you to exceed the NCE input rating whether you have diodes in place or not. The real question I have for Jim at NCE is whether he has some input protection for power line spikes. If not, a better answer may be to use an XFR8 or any DCC Power Supply with a transorb on its output to limit the transients allowed through to the booster. I will confer with the manufactures and specify a suitable transorb.

Without Diodes		With Diodes
Current	Voltage	Current	Voltage
0.00	18.63	0.00	17.61
0.25	18.51	0.25	17.15
0.50	18.45	0.50	17.01
0.79	18.37	0.75	16.89
1.00	18.35	1.01	16.80
1.50	18.24	1.52	16.61
2.05	18.09	2.00	16.41
2.50	18.00	2.50	16.24
3.02	17.86	3.03	16.09
3.53	17.73	3.50	15.93
4.01	17.60	4.01	15.73
4.50	17.45	4.51	15.56
5.00	17.32	5.00	15.32
5.51	17.17	5.53	15.05
6.00	17.04	5.99	14.92
6.51	16.97	6.49	14.72
10.59	15.78	9.17	13.66

Sheet 2: OldXFR8_12_30_99_

Without Diodes		With Diodes		Diode
Current	Voltage	Current	Voltage	Temp
0.00	18.57	0.00	17.67
0.25	18.43	0.25	17.17
0.49	18.35	0.50	16.94
0.78	18.26	0.75	16.84
1.00	18.20	1.01	16.75
1.50	18.04	1.51	16.53
2.04	17.87	2.00	16.32
2.54	17.69	2.49	16.10
3.05	17.54	3.00	15.88
3.52	17.37	3.52	15.63
4.00	17.17	4.03	15.41
4.52	17.04	4.50	15.07
5.02	16.87	5.00	14.89	94.3 C
5.50	16.72	5.50	14.79
6.00	16.58	6.02	14.50
6.51	16.34	6.51	14.27
10.21	15.21	9.19	13.69	125.9 C

Sheet 3: XFR12

Without Diodes
Current	Voltage
0.00	19.46
0.25	19.29
0.55	19.18
0.75	19.10
1.00	19.02
1.50	18.87
2.02	18.70
2.50	18.53
3.00	18.15
3.50	17.99
3.98	17.65
4.51	17.52
5.02	17.30
5.51	17.05
6.00	16.85
6.49	16.63
7.46	16.11
10.45	15.15
12.03	14.68
13.50	14.18