1) Can I find a ready made transformer with only one coil but having several tappings? The primary voltage is 230V AC and the preferred tappings at 120V and 60V.
2) How can I restore a rusty transformer core? There is only a thin layer of rust. What paint should I use and what method should I use to remove the rust before applying the paint?
2) How can I restore a rusty transformer core? There is only a thin layer of rust. What paint should I use and what method should I use to remove the rust before applying the paint?
No 1- --"only one coil " ?---you mean an auto transformer --yes ?
If yes in that case--yes you can I have plenty of those both UK & American but they are not mains isolated like a proper transformer .
No 2 --lamination's are iron and do rust so a recognized rust remover should first be used --do NOT damage the lamination's in the process and make sure the lamination's are tightly pressed together after you remove the rust.
While there is paint for ironwork I would not use it better to use the methods used by suppliers to the military for use in tropical areas of the world .
If yes in that case--yes you can I have plenty of those both UK & American but they are not mains isolated like a proper transformer .
No 2 --lamination's are iron and do rust so a recognized rust remover should first be used --do NOT damage the lamination's in the process and make sure the lamination's are tightly pressed together after you remove the rust.
While there is paint for ironwork I would not use it better to use the methods used by suppliers to the military for use in tropical areas of the world .
Farnell (UK ) sell 120V step -down .
One with 120V & 60 V would need to be a custom build and yes there are companies in the UK who will do that for you (for a price ).
Auto Transformers | Farnell UK
Auto Transformers | Custom Auto Transformer Manufacturer | ETC
One with 120V & 60 V would need to be a custom build and yes there are companies in the UK who will do that for you (for a price ).
Auto Transformers | Farnell UK
Auto Transformers | Custom Auto Transformer Manufacturer | ETC
An auto transformer is inherently dangerous as there is no electrical isolation from the incoming supply.
How much rust is on your transformer ? If it only slight you might be able to wipe it down with some WD40.
How much rust is on your transformer ? If it only slight you might be able to wipe it down with some WD40.
The autotransformer will be used to supply the large amplifier I built. Instead of 120V AC (I live in the EU), I plan to use a lower voltage like 60V AC to increase the amplifier's energy efficiency at volumes suitable for domestic use. I have already tested the amplifier using a 24V AC supply into its mains socket with very good results.KatieandDad said:
The goal of all this is to keep the electricity consumption by the amplifier as low as permissible.
The amplifier is a 3-stage amplifier whose circuit is 'immune' to using very low voltage rails. Thanks to forum members like mjona and Mooly, I avoided the use of Zener diodes, which would have very negatively affected the amplifier's ability to work with very low voltage rails. The amplifier is designed to work with 82V DC rails, but I am successfully operating it using 8.5V DC as rails! This is an energy saving of almost a factor of 10.
An auto transformer will not provide any isolation from the mains supply meaning that your input and output connectors may provide a shock risk.
I understand these risks and I am aware of them. I have already used this configuration using a large autotransformer which can only halve the mains voltage.KatieandDad said:
The autotransformet that I currently have, is mounted separately on a shallow wooden stool. The centre tap is connected to the live terminal of a UK style wall socket fixed on the stool. The other two terminals of the autotransformer's primary are connected as follows: one end to the mains live terminal and the other to the output wall socket's neutral terminal. The transforment core is connected to earth and this connection is also connected to the earth terminal of the wall socket on the stool. To get an electrical shock, I must deliberately expose a live conductor and touch it.
With this arrangement, the amplifier power input gets the same mains earth connection, the same neutral connection and a lower voltage live terminal through the transformer.
The current temporary setup is using a Weller soldering iron transformer which has an AC output of 24V. The earth connection is indirectly through a Raspberry Pi minicomputer and the earth terminal to an LCD computer monitor.
It is very easy because it has an audio input. It is an exposed wire. And everything connected to your amp's input became dangerous.
If not (if it is Wi-Fi or SD-card player with the only one wire - mains wire) - then I can agree.
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It is clear my posts are not fully understood.
The amplifier will still use its built-in mains toroidal transformer which is designed to provide all isolation and safety. I am not going to replace it, as it will be operating on a much lower voltage than design voltage of 230V AC. I can feed 230V AC into the amplifier's mains plug safely, although, I do not want to use such a high voltage as it is very wasteful.
The only exposed connection from the 3 mains terminals is the earth connection. Both the live and neutral terminals are isolated.
What I am doing is imitating an electrical sub-station to get a 'mains' voltage of only a few tens of volts.
The amplifier will still use its built-in mains toroidal transformer which is designed to provide all isolation and safety. I am not going to replace it, as it will be operating on a much lower voltage than design voltage of 230V AC. I can feed 230V AC into the amplifier's mains plug safely, although, I do not want to use such a high voltage as it is very wasteful.
The only exposed connection from the 3 mains terminals is the earth connection. Both the live and neutral terminals are isolated.
What I am doing is imitating an electrical sub-station to get a 'mains' voltage of only a few tens of volts.
Ok, thank you, now it is clear.
You may find some suitable transformer but used in series with it's suited secondaries as an auto-transformer. It may be easier to find (may not).
You may find some suitable transformer but used in series with it's suited secondaries as an auto-transformer. It may be easier to find (may not).
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Your "lowering your utility bill" or "being greener" concept is flawed on various points.
1) you may lower the *idle* consumption which on any SS amplifier is minimal.
2) there is not magic energy multiplication or whatever, IF you send 60W RMS to speakers your amp will "eat" 90 to 100W from mains, simply because of amp efficiency, no matter how you kludge the mains voltage.
I´m talking Class AB unless specifically mentioned otherwise.
And those 90/100W are way higher than amp idle consumption.
3) the step down transformer , which must be large by definition to handle any amp demands if asked to, will have a magnetizing current which although reactive will have a real component which will cause resistive loss in the copper wire PLUS a hysteresis loss, typically 2.2W/kg, please go weigh your transformer and do the Math.
You will be surprised (the wrong way that is).
In total, I bet you will DECREASE overall efficiency, or if you are lucky, keep it (= earn nothing) but with added bulk, expense, and needless complication.
1) you may lower the *idle* consumption which on any SS amplifier is minimal.
2) there is not magic energy multiplication or whatever, IF you send 60W RMS to speakers your amp will "eat" 90 to 100W from mains, simply because of amp efficiency, no matter how you kludge the mains voltage.
I´m talking Class AB unless specifically mentioned otherwise.
And those 90/100W are way higher than amp idle consumption.
3) the step down transformer , which must be large by definition to handle any amp demands if asked to, will have a magnetizing current which although reactive will have a real component which will cause resistive loss in the copper wire PLUS a hysteresis loss, typically 2.2W/kg, please go weigh your transformer and do the Math.
You will be surprised (the wrong way that is).
In total, I bet you will DECREASE overall efficiency, or if you are lucky, keep it (= earn nothing) but with added bulk, expense, and needless complication.
It will improve efficiency to lower the rail voltages.
Imagine an ideal class AB supplying 10W to a speaker. If the peak output voltage is the rail voltage it will be about 70% efficient. Now, imagine increasing the rail voltage to 1,000,000V. It may still supply 10W to the speaker but it will be almost 0% efficient.
Imagine an ideal class AB supplying 10W to a speaker. If the peak output voltage is the rail voltage it will be about 70% efficient. Now, imagine increasing the rail voltage to 1,000,000V. It may still supply 10W to the speaker but it will be almost 0% efficient.
Aside from an autoformer, you can use a bucking transformer to drop the mains voltage. You just want to be sure your amplifier will have appropriate bias at the lower voltage.
I have an 845 amplifier that I can switch from lower power to full power with a bucking transformer.
I have an 845 amplifier that I can switch from lower power to full power with a bucking transformer.
While I duly respect your opinion as one of the most knowledgeable members of these fora, who often write useful and helpful replies, I will take the opportunity to further expose my setup. At this very moment, that amplifier is supplied a pseudo-mains AC voltage of only 24V. The amplifier is producing beautiful detailed sound which is enough to fill my dwelling with the right comfortable acoustic intensity.
You are right, I am lowering the idle consumption. However, due to having very low voltage rails, the output transistors' Vcb has to be much much lower compared to with the full rails of 82V DC. The heating effect on the output transistors to deliver the same output current is the product of Vcb and Ic. Both of these are low due to a reduced maximum power rating which is a direct result of using a lower rails voltage.
In my dwelling, 60W RMS using professional compression speakers is too much. The acoustic intensity would be too high and extreemly uncomfortable. My investigations have consistently shown, a 1W RMS provides a respectable volume for a home setting. With my setup, a 3V peak voltage sent to the speakers is far more than enough. At 8 Ohms this is a peak power of 3^2/8 = 1.125W.
I am using class AB.
High quality transformers using low peak magnetic flux intensity restrict the magnetic hysteresis to almost a line greatly reducing magnetisation/demagnetisation losses in the core.
A low peak magnetic flux intensity transformer can be made using an ordinary good quality tranformer by connecting the secondaries in series-aiding with the primary to form an autotransformer but with an increased primary inductance. The increase in the latter, reduces the magnetisation current requirements of the transformer.
I am certain your intention is to guide me not to make unnecessary expenses. So, thanks for your advice.
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In your comment on --a 1W RMS provides etc you are in full agreement with JLH who said nearly exactly those words on EW.
Who needs blasting volumes of output unless the speakers are highly inefficient but selling something requires taking a position of greater profit .
I have my own house but still don't need loud volumes of music as to my ears it completely defeats the whole raison etre of why we listen to music.
Who needs blasting volumes of output unless the speakers are highly inefficient but selling something requires taking a position of greater profit .
I have my own house but still don't need loud volumes of music as to my ears it completely defeats the whole raison etre of why we listen to music.
You could use a common 60–0-60 volt toroid with a 120 volt primary and put all 3 windings in series, with the appropriate phase (determined with a dim bulb limiter). That would make an auto transformer with 240, 120, and 60 volt taps. You might want to add an extra layer of Mylar tape (or two) around the outside to increase the insulation rating, since the outer secondary will be attached to mains.