Hello sharpi, Is the chassis of the component(s) you are plugging into the iso tranny connected to the earth conductor? If so, then connecting the secondary of the iso tranny neutral would be unnecessary. If the component(s) do not have the chassis connected to earth, it would be wise to do so, for your own and others safety. One of the purposes of an isolation transformer is to create a balanced power signal to the component you are powering. This tends to help reduce hum problems. The iso tranny also helps filter out high frequency signals on the AC lines, due to the intrinsic low pass behaviour of a transformer. If you connect one of the legs of the secondary of the transformer to earth, you may actually induce noise into the AC power going into your component(s). Hope this helps.
Peace,
Dave
Peace,
Dave
Typically in isolation transformers the GND connects to GND. The secondary of the transformer is left floating.
This is safe, because as the name implies, the isolation transformer isolates the power from the mains, in other words the secondary winding is at a zero voltage potential to ground.
Connecting the GND to the secondary actually defeats most of the purpose of an isolation transformer.
This is safe, because as the name implies, the isolation transformer isolates the power from the mains, in other words the secondary winding is at a zero voltage potential to ground.
Connecting the GND to the secondary actually defeats most of the purpose of an isolation transformer.
I installed the isolation transformer with neither secondary connected to ground.
The transformers in both my preamp and power amp have started to buzz - not dramatically, but louder than when connected directly to the mains.
The isolation transformer is a 1000VA (and remains cool during use) so I don't think the problem is a lack of current...
Any ideas?
The transformers in both my preamp and power amp have started to buzz - not dramatically, but louder than when connected directly to the mains.
The isolation transformer is a 1000VA (and remains cool during use) so I don't think the problem is a lack of current...
Any ideas?
Problem solved!
The transformer was not truly 1:1, so my kit was getting 254VAC when the mains was sitting at 242VAC. The high voltage was causing the buzzing.
I swapped primary and secondary windings to make a step down (rather than step up) transformer. Now my kit is getting 230VAC and transformer hum is lower than when the kit is connected directly to the mains.
Sound wise, the addition of the isolation transformer seems to have added some warmth and fine detail. I was worried that running my amp from the transformer would reduce bass power but this hasn't happened - if anything, bass focus and depth has increased.
I guess my 25wpc chip amp doesn't suck too much current so the 1000VA isolation transformer isn't being worked too hard.
The transformer was not truly 1:1, so my kit was getting 254VAC when the mains was sitting at 242VAC. The high voltage was causing the buzzing.
I swapped primary and secondary windings to make a step down (rather than step up) transformer. Now my kit is getting 230VAC and transformer hum is lower than when the kit is connected directly to the mains.
Sound wise, the addition of the isolation transformer seems to have added some warmth and fine detail. I was worried that running my amp from the transformer would reduce bass power but this hasn't happened - if anything, bass focus and depth has increased.
I guess my 25wpc chip amp doesn't suck too much current so the 1000VA isolation transformer isn't being worked too hard.
no.panomaniac said:
the UK had and still has 240Vac mains power.
It used to be +-6%.
We have been forced to respecify it to conform to the EC requirement of 220/240Vac.
We complied with this by increasing the -ve tolerance to -10%, but without changing our supply voltage.
We are now 216V to 254V, instead of the former 226 to 254Vac. But we are still a nominal 240Vac mains supply.
As far as I know we never deliberately use the 216 to 226Vac range for load shedding. Instead we use frequency to adjust to the load as demand varies.
Thanks Andrew, that's all news to me.
Kinda surprising, the change, as you are an island nation. The EU is not going to force you to give up your big, bulky mains plugs are they?
Back in the old days I saw 245 or even 250 on British mains. Luckily not every day. That had to be pushing some of the gear that was really made for 220V but sold in 240V counties.
Kinda surprising, the change, as you are an island nation. The EU is not going to force you to give up your big, bulky mains plugs are they?
Back in the old days I saw 245 or even 250 on British mains. Luckily not every day. That had to be pushing some of the gear that was really made for 220V but sold in 240V counties.
For balanced power you need an isolation transformer like shown below...........
For UK you will need input 0 - 230V output 115-0-115V.
http://www.equitech.com/articles/widescreen.html
For UK you will need input 0 - 230V output 115-0-115V.
http://www.equitech.com/articles/widescreen.html
An externally hosted image should be here but it was not working when we last tested it.
AndrewT said:no.
the UK had and still has 240Vac mains power.
It used to be +-6%.
We have been forced to respecify it to conform to the EC requirement of 220/240Vac.
We complied with this by increasing the -ve tolerance to -10%, but without changing our supply voltage.
We are now 216V to 254V, instead of the former 226 to 254Vac. But we are still a nominal 240Vac mains supply.
As far as I know we never deliberately use the 216 to 226Vac range for load shedding. Instead we use frequency to adjust to the load as demand varies. [/QUOTE
panomaniac said:Thanks Andrew, that's all news to me.
Kinda surprising, the change, as you are an island nation. The EU is not going to force you to give up your big, bulky mains plugs are they?
Back in the old days I saw 245 or even 250 on British mains. Luckily not every day. That had to be pushing some of the gear that was really made for 220V but sold in 240V counties.
The UK is now -6% to +10% @ 230v nowadays, the joys of European
Harmonisation.
In reality though you will still get from 230 to 250 v regularly at supply terminals.
Power is regulated by having an increased Power Factor, not by varying frequency as was previously suggested. If you varied the frequency then you can kiss goodbye to running AC motors at their specified speed. Big steel-works cannot afford this situation especially when they can use (upwards of) 10,000hp motors in rolling mills.
These ratings are not for manufacturers either, it is more to cover supply fluctuations from the generating set. Christmas Day in the UK has seen some extremely warm armoured cables.
Gareth
OzMikeH said:
Valid point. Code in certain areas requires the ground connection after an isolation transformer to be wired. I'm not sure what the intent is, perhaps to offer protection in the even of a double fault, or perhaps in case an appliance gets energized by an external source that is not isolated.
Chassis earthing is used in non-double insulated enclosures to prevent 'extraneous' conductive parts from becoming live.
Double-wound isolation transformers are used where there is an increased risk of electric shock so removing the supplied equipment from your mains supply and providing an extra degree of protection.
A very good example of a double-wound isolation transformer and what they are primarily designed for is a shaver socket outlet used in bathrooms near a sink. You have extraneous conductive parts (taps and pipework) and also water.
In this instance the double-wound isolation transformer would minimise the electric shock as you are electrically isolated from the mains supply and thus unlikey to recieve the full fault potential of the mains supply which will go into the KiloAmps range.
The maximum fault potential likely can be ascertained from the Supply Voltage and the Loop Impedance.
Gareth
Double-wound isolation transformers are used where there is an increased risk of electric shock so removing the supplied equipment from your mains supply and providing an extra degree of protection.
A very good example of a double-wound isolation transformer and what they are primarily designed for is a shaver socket outlet used in bathrooms near a sink. You have extraneous conductive parts (taps and pipework) and also water.
In this instance the double-wound isolation transformer would minimise the electric shock as you are electrically isolated from the mains supply and thus unlikey to recieve the full fault potential of the mains supply which will go into the KiloAmps range.
The maximum fault potential likely can be ascertained from the Supply Voltage and the Loop Impedance.
Gareth
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