I decided to replace the auto transformer arrangement with a custom wound
230 - 2*130V transformer.
Could someone please verify J chose the voltage correctly, please?
I need 350V at 45mA max. The shunt regulator has constant current of
35mA-45mA which results in up to about 16W of power turned to heat. I
choose 50VA transformer in the following way.
350V+10V for losses or sags /1.41=255V AC
I can order these transformers with a step of 10V up to 230V so 2x130V
seems a correct choice.
73,
Luk - SP4IT
On Sat, 30 Nov 2024, 11:49 , <flynth@gmail.com> wrote:
> Now that you say it that way I start suspecting the auto transformer.
> Assuming nothing is miswired (and I have to rewire anyway to route the
> wires nicely - currently it's only a "working" setup) it is the only place
> that is not fully isolated.
>
> As expected in an auto transformer the neutral just passes through to the
> rectifier then minus of the rectifier is connected to the ground/case.
>
> I had RCD trigger before I fitted the auto transformer, but only once, so
> it may have been a temporary short.
>
> This is not ideal. I have to use it as auto transformer as all normal
> transformers I have, have far too high voltages. (for example a 230 to
> 415,after rectifying it results in 580V. That turns into a pot of heat if
> it has to be shunt stabilised to 350V. It's very hard to find 230-300V
> transformer.
>
> The "auto transformer" is a normal 240-2*36V toroid but connected like
> this:
>
> Low side of 240V is neutral that passes through, high side is connected to
> live 240V, then low side of the first 36V is connected to that, high side
> is connected with low side of the other 36V. Finally the remaining high
> side has approximately 300V AC and goes to the rectifier. I think it is the
> most likely culprit.
>
> 73,
> Luk - SP4IT
>
>
> On Fri, 29 Nov 2024, 20:20 Michael Tope, <W4EF@dellroy.com> wrote:
>
>> Luk,
>>
>> At least for amplifiers I've seen here in North America, the isolation
>> between the chassis metal and the power mains neutral typically come
>> from the HV transformer (and any additional transformers that are used
>> for producing things like filament voltage, control voltages, etc). Do
>> you have any connections between the lines on the primary side of your
>> transformers and the grounding conductor? In other words, I am trying to
>> understand why you need an isolation transformer to prevent RCD/GFCI
>> trip when the transformers in the amplifier should provide that function?
>>
>> 73, Mike W4EF
>>
>> On 11/28/2024 3:52 PM, Lukasz wrote:
>> > Hi Jim,
>> >
>> > It is similar here in the EU as far as I know.
>> >
>> > A typical way devices, are constructed here is that the ground
>> (including
>> > the case if made of metal) is not used as a normal current path in the
>> > device. One sees current flow on that ground only in a fault scenario.
>> >
>> > This means RCD/GFCI protections can work as when it see any discrepancy
>> in
>> > the live/neutral current balance it shuts the circuit down.
>> >
>> > These rules normally mean one always has a return current path within
>> the
>> > device that is separate from ground (neutral, DC minus etc), but this is
>> > difficult when the amplifier is entirely made of metal and one would
>> prefer
>> > to have a current return plane (for example the floor if the case)
>> rather
>> > than route separate connections for DC minus and RF ground.
>> >
>> > This is not how OLD devices were made. I have a couple of old lathes and
>> > mills that do use the steel frame as neutral/ground(one connector called
>> > PEN) . This is how, it seems, all tube amps are built I saw pictures so
>> > far.
>> >
>> > So my question is, if one wants to build a tube amp in a modern way.
>> > Properly grounded, is building a case within a case and electrically
>> > isolating the two the only way? Or has anyone managed to build a tube
>> > amplifier in a single grounded steel case. That works normally within
>> the
>> > usual electrical systems (with gfci/rcd protected circuits). If so,
>> please
>> > describe how are all the current return paths done.
>> >
>> > 73,
>> > Luk, SP4IT
>> >
>> > On Wed, 27 Nov 2024, 23:05 Jim Brown, <jim@audiosystemsgroup.com>
>> wrote:
>> >
>> >> Hi Lukasz,
>> >>
>> >> In North America, the protective earth MUST be carried in the same
>> cable
>> >> with the current-carrying conductors, and MUST be bonded to the
>> chassis
>> >> at the point where that cable enters. I'd be surprised if it's
>> different
>> >> in EU -- it must be done that way to be protective!
>> >>
>> >> There's another requirement in NA -- all grounds (earths) MUST be
>> bonded
>> >> together. Again, protective against both lightning and electrical
>> shock.
>> >> So when power goes through ANY transformer that's not part of
>> equipment,
>> >> protective earth MUST be carried from one side of the transformer to
>> the
>> >> other.
>> >>
>> >> I don't remember about EU, but I do remember that in the UK, no earth
>> >> connection to the power system is permitted -- that happens only within
>> >> the power distribution system.
>> >>
>> >> When thinking about this and antennas, remember that the earth is a big
>> >> resistor, and parts of antennas like radial systems are NOT intended to
>> >> couple to the earth, but rather to shield the EM field from the earth,
>> >> and to provide a low resistance path for the antenna's return current.
>> >> The only antennas that benefit from an earth connection are SOME
>> >> receiving antennas, like Beverages and loops.
>> >>
>> >> 73, Jim K9YC
>> >>
>> >> On 11/26/2024 8:10 AM, Lukasz wrote:
>> >>> Hi,
>> >>>
>> >>> Is there some way to build a tube amp in a metal case, using the case
>> as
>> >> RF
>> >>> ground, and not have current flow out of the amp through the grounding
>> >>> conductor? (other than isolating that ground from the case entirely,
>> >> which
>> >>> presents it's own problems - for example capacitive coupling to the
>> >> case).
>> >>> I'm currently experimenting with an amp and I have to power it via an
>> >>> isolation transformer (the high voltage is 3 phase on its own circuit
>> >> with
>> >>> no GFCI temporarily) or my RCD will trigger.
>> >>>
>> >>> The high voltage power supply is an old military device that used its
>> >>> chassis as ultimate DC ground (hv ground connects to it through a
>> >>> overcurrent protection coil).
>> >>>
>> >>> Then I also used the chassis as ground for DC HV, screen and grid
>> >> supplies.
>> >>> This I could swap, but it's the RF ground (especially the Pi tank) I'm
>> >>> concerned about.
>> >>>
>> >>> Is essentially isolating amp RF ground from the grounding conductor
>> >>> (PEN/EGC or whatever it's called where you are) the only way?
>> >>>
>> >>> 73,
>> >>> Łukasz, SP4IT
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