It’s not quite as simple as it looks. The catch is that the primary current does not have a sinusoidal waveform and is not in phase with the primary voltage, so it is necessary to make a calculation with complex variables and nonlinear elements.Why not simply add a series resistor to obtain a voltage drop of 10 Volts?
How much current will flow? 100 mA?
In that case a 100 Ohm/1 Watt resistor would be sufficient. Take a 5 or 10 Watt one and it will work 'for ever'!
Reply #12 in this thread seems to be the best answer...a "buck" transformer.It’s not quite as simple as it looks. The catch is that the primary current does not have a sinusoidal waveform and is not in phase with the primary voltage, so it is necessary to make a calculation with complex variables and nonlinear elements.
It’s not quite as simple as it looks. The catch is that the primary current does not have a sinusoidal waveform and is not in phase with the primary voltage, so it is necessary to make a calculation with complex variables and nonlinear elements.
The 'autotransformer' as proposed by Moamps is what I would have suggested had he not got in there first. The beauty being that it only needs a relatively small transformer (low VA rating) as it is only supplying the difference and not the full power requirement.
In the wrangling over 'European mains supply harmonisation' I believe a bit of wrangling took place and the former 'plus and minus 10 percent was altered to minus 10 and plus 6 percent (for the UK I think) so that practically everywhere could squeeze into the nominal 230 Volt bracket. Of course some countries and locations manage to hit the target 230 Volts better than others.
with the advance of switchmode 'universal' supplies they claim (and I presume do) function correctly to spec from either 90 or 100 Volts up to 264 ? Volts at 47 Hz to 63 Hz so squeezing in the widest of frequency tolerances.
I have just checked my 'reference book' and under 'battery eliminator' it gives the schematic for a unit that uses 'about 200 Volts DC mains' I can only presume that in the UK DC mains was negative grounded as the unit comprises a 'dropper resistor', 30 millihenry choke and some 4uF capacitors. No rectifier. It would be connected to a lighting circuit using a DC (bayonet cap) power plug.
Since BC lamp sockets can have the bulb fitted either 'way around' I presume making your radio work required you to try both ways until your required programme 'bursts forth.
And how exactly would a plain old resistor alter whatever phase angle there is, between the voltage and current going through the transformer?
More likely it is your mains voltage that is changing as load on the system changes with daily demand, not the auto-former ratio.I have been using this module (photo) for some time, but it is not stable and I cannot trust it as it changes values. Maybe from 220v in the morning to 230v into the v76/v72 rack in the evening without nobody touching the "wheel". Apart from that, many thanks for all inputs / comments, though I need something not too complicated. But of course I can ask a tech for help.
It will be proportionate... if the input voltage increases 240/230 or 10.7% the output of a step down transformer/auto-former will increase similar 10.7%. Only if the ratio is set 1:1 would the output voltage change equal the input voltage change.Thanks again everybody for inputs. Very useful to read different views on the 220v/230V topic. As I understand now, if the voltage coming into a step down unit goes up f.ex from 230v to 240v, this will also increase the voltage 10v going out from the step down unit?
However, I bought this one, building it into my rack.
TTH50/230/11.5V BREVE TUFVASSONS
Ther would definitely be a benefit, not so much for you than for the electricity company.Would there be any benefit in using a couple of caps on the secondary of an isolating transformer to form a LPF , to give an extra level of protection to the following equipment from mains borne hash mush and fuzz ?