Step down trafo to 220v.

Help Support GroupDIY:

Matt Syson

Well-known member
Joined
Dec 17, 2005
Messages
156
Location
France
Oh, the suggested method to boost LOW mains is to use a motor/generator unit (yes a motor incorporated with a dynamo).
 

moamps

Well-known member
Joined
Sep 24, 2005
Messages
1,861
Location
Croatia, HR
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'!
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.
 

Brian Roth

Well-known member
Joined
Aug 20, 2005
Messages
1,888
Location
Salina Kansas
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.
Reply #12 in this thread seems to be the best answer...a "buck" transformer.

Bri
 

Khron

Well-known member
Joined
Apr 8, 2010
Messages
1,964
Location
Finland
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.

And how exactly would a plain old resistor alter whatever phase angle there is, between the voltage and current going through the transformer?
 

Newmarket

Well-known member
Joined
Oct 10, 2016
Messages
761
Location
Brighton Sussex UK
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.

I'm fairly certain that its -6% / +10% (not "minus 10 and plus 6")
I thought I's better do a quick websearch...
Main Voltage - an overview | ScienceDirect Topics.
 

moamps

Well-known member
Joined
Sep 24, 2005
Messages
1,861
Location
Croatia, HR
And how exactly would a plain old resistor alter whatever phase angle there is, between the voltage and current going through the transformer?

I have a feeling that your question is cynical and does not deserve an answer, but here I am today in good spirits.

Ruud used Kirchoff's law for DC when calculating the value of a resistor. Such a simple calculation can also be used for AC networks only if all impedances are connected in series of the same nature (only resistors as in the attenuator, or only capacitors for capacitive dividers in microphone pads, etc.). If different types are mixed, complex algebra should be used to obtain an accurate result by Kirchoff's law. If the load is additionally nonlinear (full wave rectifier on the secondary side), the calculation becomes even more complicated.

For more information ask Google for
"Kichhoff's law AC circuits"
 

fallout

Well-known member
Joined
Jun 3, 2004
Messages
402
Location
Caldwell, NJ
As mentioned earlier in the thread (with diagram), I'd go with the bucking transformer setup. Very easy to wire and effective. I built one to drop the line voltage for some old tube stereo amplifiers. Works great!

 

honkytonk

Well-known member
Joined
Oct 17, 2004
Messages
56
Location
Norway
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.
 

Attachments

  • 220V.jpg
    220V.jpg
    93.1 KB · Views: 7

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
21,110
Location
Hickory, MS
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.
More likely it is your mains voltage that is changing as load on the system changes with daily demand, not the auto-former ratio.
======
This is an old story but I haven't told it lately. Back last century one night after returning home from work, I noticed that all my incandescent lamps were brighter than normal. Since our long term memory of brightness is not that accurate, I decided to drag out my VOM and meter my outlets. My nominal 115VAC mains was running around 140V+.... I called my utility and gave them a heads up. The tech who answered my call said I must be wrong, but it was a slow night so he'd come check it out.

Sure enough his meter confirmed my over voltage and he disappeared up the street to the substation about a mile away. The substation uses a huge auto former to boost mains voltage that sags under heavy load. This auto former was stuck boosting and as the load dropped off that night the voltage kept climbing. The tech probably whacked the stuck auto former with a hammer.

I probably saved them some burned out appliances that night.

JR
 

honkytonk

Well-known member
Joined
Oct 17, 2004
Messages
56
Location
Norway
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​

 

JohnRoberts

Well-known member
Staff member
Moderator
Joined
Nov 30, 2006
Messages
21,110
Location
Hickory, MS
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​

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.

JR
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
3,167
With the modern mains metering here which also has GSM connection to report back your consumption, the utillity must be able to work out to a high degree of accuracy , expected demand .
The utillity company sold us all on the idea of new metering , which means now they can juice better performance out of the system , which means they can sell more power to industry ,
Here were looking at around 30% higher electricity bills this year , home heating oil has doubled in price from a year ago , gas customers have also seen price rises .

My electrical install tester shows 235-237v at 5pm , a time when you'd expect lots of fluctuations , it also measures the resistance of the wiring back to the fuse board , so poor sockets or outlets are easily spotted. 237 is still on the high side for gear destined for 220 . I suppose in the case of an individual preamp or tube mic psu , it shouldnt be any bother to adjust the series resistors to get the HT where it belongs , likewise with the heater supply , but then again do you want to be modifying your precious V series when there are other options . You might get more magnetically induced hum/noise by feeding the transfomer primary +10% voltage , lower is definately better in this respect . Running things off a variable auto former is convienient , but due to the inherent unbalanced connection could it be noisier than an isolating transformer in certain situations ?
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 ?
 
Last edited:

abbey road d enfer

Well-known member
Moderator
Joined
Jan 22, 2008
Messages
13,233
Location
Marcelland
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 ?
Ther would definitely be a benefit, not so much for you than for the electricity company.
One thing that plagues distribution of electricity is inductive loads and current waveform distortion, because they both increase line losses, so they have to produce more electricity than what they invoice.
In addition your meter may be more accurate (it was the case with the older disc meters).
However in order to make it significant, you would need to add serious capacitance, so much that your circuit breaker may trip.
 

Tubetec

Well-known member
Joined
Nov 18, 2015
Messages
3,167
Thanks Abbey ,
Just a quick check on my meter , reveals 240 volts this morning .
 

Matt Syson

Well-known member
Joined
Dec 17, 2005
Messages
156
Location
France
Mains wiring, within any premises is already current balanced to the major degree as 'earth leakage' breakers would trip if the 'imbalance was as much as 30 Milliamps for the whole section of wiring.
As the Neutral side is often taken to ground at the incoming fuse/breaker cabinet there is some imbalance in live and neutral current due to the fact that the Neutral is at 'ground' potential (within certain tolerance) but the live is 220-240 Volts so the capacitance between live cabling and conduits/walls etc.
I have a feeling the maths of using the step up/down autotransformer are a little awry as you have to remember the voltage you are putting into the primary. But then there is internal winding resistance etc to consider so without a lot of extra calculations using some numbers you don't yet know, and the mains supply varies anyway the only solution is to try it.
 

Latest posts

Top