[ARC5] Cool New DC-DC Converter

[Bob kb8tq]

Hi

Since this has sort of morphed from “can I run the filaments” over to “how 
can I improve the life of my filaments ….”:

These little switchers are not super duper mil spec devices with lots and lots
of derating built in. They are very much a low cost commercial / low bidder 
item. Even run “in spec” (good luck finding the actual specs …) they have a 
limited life. Run them hot and that life gets shorter. Overload them on a regular
basis, that life gets shorter. 

Their “end of life” can be quite spectacular or it can be totally benign. Over the 
years, most of the benign failures I’ve seen have been when powering cheap 
easily replaced stuff. The spectacular failures seem (for some odd reason) to
only happen when they also take out something down stream that is very hard
to replace ….

Bob

> On Mar 16, 2018, at 12:39 PM, Peter Gottlieb <kb2vtl at gmail.com> wrote:
> 
> It’s a bit different with switchers, a lot depends on the design.  The input section has a power limitation and each output section has limitations. In a very simple design the output section limitations may be the components, such as diodes, acting like fuses. A lack of load on one section could well allow a lot more output on another section before the input section reaches its limit. However, in this case, filaments may take long enough when cold to cause a diode failure. You may need to replace the low voltage section diode with a beefier version to handle the warm-up overload. 
> 
> A more sophisticated power supply would have overload protection on each output and may limit current or even shut down the supply trying to light filaments. 
> 
> 
> Peter
> 
> On Mar 16, 2018, at 12:19 PM, Dennis Monticelli <dennis.monticelli at gmail.com <mailto:dennis.monticelli at gmail.com>> wrote:
> 
>> Brian,
>> 
>> I think there is a misunderstanding.  I think Scott was only trying to point out that the primary winding and mag core are shared by all secondary loads.  You can only get so many VA out of a transformer before hitting the limitations of primary winding resistance and/or core saturation.
>> 
>> Dennis AE6C
>> 
>> On Fri, Mar 16, 2018 at 2:42 AM, Brian <brianclarke01 at optusnet.com.au <mailto:brianclarke01 at optusnet.com.au>> wrote:
>> Hello Scott,
>> 
>> Where did you get this idea that power supplies share their output loads?
>> Doesn't apply to any SMPSU I know, nor to any rotary supplies either.
>> 
>> 73 de Brian, VK2GCE.
>> 
>> On Friday, March 16, 2018 1:35 AM, Scott claimed: 
>> Folks,
>> 
>> Cold heaters take about twice as much as when warm. But, there's no B+ drain then, so the supply can direct all its primary power capability to the heater circuit. Most of these are power limited at about 1.3 times the rating so:12V 3A is 36W + 60 mA x 520V = 25W makes a total power limit of 61W. If all that is directed to a 12V heater circuit, you could get 5A, or 10A for 6V. I'm not sure the 10A would actually work bu the 12V 5A ought to.
>> 
>> Someone needs to buy one and see what it actually does.
>> 
>> Happy glowing,
>> 
>> Scott  Robinson
>> 
>> 
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