Winfield said:
Michael A. Terrell wrote on Jan 4 2007 in the
s.e.d. thread, "job thing, maybe"
Vicor's rev 1.7 datasheet says, "Vicor's broad series of zero-
current-switching component-level DC-DC converters, with
over 12 million units shipped..."
Vicor generally has a good reputation. So I have to ask, I notice
your modules were 300V-input (i.e. offline), 5V and 12V output,
with their lowest power rating, 50 watts. The other modules in
the VI-200 series are rated at 75, 100, 150 and 200 watts. Is it
possible the problem wasn't actually the modules, but something
else, like improper DC-input conditioning, or lack of proper
heat-sink cooling? Or perhaps your power circuit allowed the
12V supply to pull the 5V module output above +5 under certain
circumstances, such as at power-up or power-down. Just asking.
They were part of Vicor built power supplies. The ac line was doubled
to get the 300 volts inside the supply. The case was cast aluminum,
with fins. Vicor said our product's case had plenty of air flow, yet
they couldn't tell us why they were failing. I may still have a
complete, scrap supply for the model numbers, but all I could find the
other day was a bad module. Either one of the two module's output would
die, or the regulation would go to crap and have a lot of noise on the
output. The only load that came close to 50 watts was the +5 volts, and
I think it was only 7 amps or 35 watts. We tried for six months to find
a solution before we removed them from the qualified vendor list. They
may have been cause by the defective electrolytic problem, but the
modules are cast in epoxy so we couldn't take a look, in house. We had
too many angry customers to wait any longer. We paid for a bunch of new
supplies that were out of warranty to keep them happy, but the problem
kept growing.
The replacement power supplies had a built in fan, and were through
hole PCB construction. We tested over 20 different OEMs before we
decided on the new supplier. This was some time late in 2000, or early
2001. The replacement supply also ended up being a good choice for a
newer DSP based receiver design. I might have a datasheet on the
replacement power supply in my files. Changing the power supply vendor
meant a change in the bare aluminum chassis, a new wiring harness, and
designing a field conversion kit for high security locations that did
some self service in house. I don't know what conclusion Vicor finally
came to as the cause of the failures, because the company didn't want to
switch back to the old design and take a chance.
It was like the problems we had with a well known SMD trimpot
manufacturer. The failure rate was over 2% because their o-rings on the
shafts were defective. They insisted that we were damaging the pots,
even though we hadn't made any changes to our process in over five
years.
After we switched to Bourns, they finally admitted the O-rings were
undersized, and didn't have enough lubricant applied during
manufacturing. As soon as we switched to Bourns the failure rate
dropped to almost zero in a six month period. Two pots were damaged by
a QC inspector on a finished board, but they were still classed as
defective parts.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.
Michael A. Terrell
Central Florida
