[ARC5] Army/Navy transmitters from a NON COLLECTOR viewpoint, the ham version...

[Dennis Monticelli]

The full wave voltage doubler commonly used in transmitter power supplies
since the 70's is a good design.  It utilizes the core well, does not
impose DC on the mains or transformer, and inherently allows use of
capacitor stacking.  I believe this is one to which Ken is referring.  It's
only real disadvantage is that the flying secondary is not ground referred.

It is true that oversized lytics increase I squared R losses, which is not
a kind thing to do to a tired old transformer used to small lytics and/or
chokes input filters. When the full wave doubler was applied to
factory-built transmitters the vendor used transformers with a lower
winding resistance than the plate transformers of old, thus minimizing the
issue.

Hopefully, this low res image came through.

Dennis AE6C

[image: image.png]

On Mon, Feb 10, 2020 at 10:01 PM Brian Clarke <brianclarke01 at optusnet.com.au>
wrote:

> Hello Kenneth,
>
>
>
> Not just transformer-less power supplies. Most Voltage doublers are
> effectively half wave; some Cockcroft-Walton designs are full-wave – but
> they are quite complex. With consumer-level Voltage doublers, DC does get
> back through the mains transformer because with half-wave rectification,
> only one half of the mains cycles are loaded. So, the transformer core is
> compromised, too.
>
>
>
> The mains distribution board fuse or circuit breaker is unlikely to trip.
> Its main purpose is to prevent fire in the wiring hidden inside the walls
> that services the power outlets.  You probably have 60 A fuses / circuit
> breakers for each mains circuit with NEMA-code wiring, and a 200 A fuse on
> the phase wire incoming from your local pole pig.
>
>
>
> However, equipment fuses are there for a different purpose – to protect
> the equipment – and hence, should be selected for their time vs current
> performance for each piece of equipment, with perhaps a 20% continuous
> overload. As you have bumped your smoothing filter capacitor from 150 to
> 640 uF, you have more than quadrupled the start-up surge load. And if you
> have used modern, low-ESR capacitors, all the rage these days, the start-up
> surge may be even higher. One hidden effect of such surge loading is that
> the turns inside the transformer starts to jump about and may hit the
> laminations, especially if an accountant has designed the transformer,
> giving intermittent shorted turns.
>
>
>
> Actually, the average load does increase with Voltage doubling. The
> rectification efficiency is lower than with full-wave rectification.
>
>
>
> When I have made changes to increase the filtering, rather than rely on
> the resistance of the transformer primary, I use a very simple soft-start
> circuit; I use a mains Voltage rated SPST relay, its solenoid across the
> transformer primary, with a resistor (select on test – usually about 10
> Ohm) across the NO contacts in series with the incoming mains. If you don’t
> have mains rated relays, use a lower Voltage one across one of the lower
> Voltage secondaries, eg, a heater winding.
>
>
>
> Cheers es 73 de Brian, VK2GCE
>
>
>
> *On* Tuesday, 11 February 2020 4:15 PM, Kenneth said:
>
>
>
> On 11 Feb 2020 at 15:35, Brian Clarke wrote:
>
>
>
> <snip>
>
>
>
> > Voltage doublers have several problems:
>
>
>
> ...and advantages...
>
>
>
> > 1. if half-wave, DC is fed back into
>
> > the mains; yes, I know it's done in computer SMPSUs, but sending DC into
> the
>
> > mains is against the law in Australia and New Zealand, and if enough
>
> > hornswogglers do it, the distribution transformer (pole pig in USA) gets
>
> > unhappy
>
>
>
> I suspect you are talking about transformer-less voltage-doubler supplies,
> Brian. I don't know too many technically competent hams who would dare use
> such a supply. DC can't get back to the mains through a transformer.
>
>
>
> > 2. at start-up, increasing the capacitance of the filter increases the
> load on
>
> > the diodes, the power transformer and the mains fuse.
>
>
>
> The peak load, yes. I don't think the average load is changed much. At
> least Duncan Amps Power Supply Designer tells me so. But in the case of my
> SB-200s and other rigs I have used this technique with, the diodes I use
> are over-rated for this service and the fuses/circuit breakers have never
> been changed for higher-rated ones. IMHO, that would be kinda dumb.
>
>
>
> > 3. increasing the size of the mains fuse increases the risk of taking
> out the
>
> > power transformer, and no longer protects the power supply from excess
> load.
>
>
>
> Yes, but I most certainly have never done that, and won't. As I said, all
> my fuses and circuit breakers are exactly as they were originally.
> Furthermore, I have never had any problem with any of them.
>
>
>
> Properly designed and implemented voltage-doubler supplies are quite
> useful and work well. They also have several advantages, amongst others,
> the HV transformer doesn't have to be rated for the full DC output voltage.
>
>
>
> Also, FYI, according to Rich Measures (SK) the power transformers in the
> Heathkit SB-200 and SB-220 (and possibly others) are specifically designed
> to ramp up their output voltage "slowly" so that a "soft-start" isn't
> needed with them. I have found this to be true.
>
>
>
> Even with my much larger filter caps, the lights don't dim, even
> momentarily, when I turn the SB-200 amps on, and watching the HV (2250VDC)
> come up on the meter it rises fairly slowly. It doesn't "jump up" to the
> full voltage.
>
>
>
> I have never tripped a breaker or blown a fuse on start-up with any of the
> voltage-doubler supplies I use.
>
>
>
> Ken W7EKB
>
>
> ______________________________________________________________
> ARC5 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/arc5
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:ARC5 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: https://www.qsl.net/donate.html
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20200210/668a89c9/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 9408 bytes
Desc: not available
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20200210/668a89c9/attachment-0001.png>