Isolation vs auto wound step down transformer.

[Dr.Lakshay]

Hello members.
Looking for a comparison of auto wound step down transformer vs isolation step-down transformer pros and cons.
Does it make sense to get an isolation transformer by spending some extra bucks?
Please enlighten me. Couldn't find much knowledge by googling.

 

[newlash09]

Hi lakshay....

Iam not an expert in this field. But I have been reliably advised by a number of experienced forum members that isolation transformers give really good results. There is lots of noise in our home power lines, even tube lights give off noise which pollutes the power. And if you have any component in the house with a switch mode power supply ( most cellphone chargers and small adaptors of theta size are all switch mode supplies ) then these supplies dump high frequency interference in the power lines. So a isolation transformer will be required to clean that up.

So all in all, the ideal combination that I have been suggested is a CVT transformer for the entire audio setup. And individual isolation transformers for dac ( or cd player if you use one ) and amp.

 

[kmathan88]

@newlash09 @Dr.Lakshay
Can you provide some product links for each category, so that we can get better idea of what is needed and what to expect from them.

For now, my AV devices are connected to Vguard stabilizer with belkin surge protector. And there is a home inverter sitting in the main power / DG line to home. Online inverter seems to be better, but cost wise I am settled with normal inverter for now. Network equipment's are connected through APC UPS instead of stabilizer. PC is connected through APC Backup Pro UPS.

-Thanks.

 

[newlash09]

Hi kamathan...

Oops sorry. I don't have any ready links as of now to share. But I had posted my query for a 6 kV constant voltage transformer and two 2.1 Kva isolation transformers. Several indian manufacturers contacted me, and qouted prices were in the region of 40 to 60k for the CVT. And around 10k for each isolation transformer.

Recently I had a power surge at home. It blew the fuse of my V-gaurd stabiliser, then the fuse of a cheap power strip connected to the stabiliser, and finally blew my amp. Iam a little wiser after the above catastrophe. And iam seriously looking for the above products. Unfortunately iam travelling now, and using internet via satellite's. So I have restricted access to my email inbox. Otherwise would have forwarded the offers I got. Anyways I think it is a good option to post a query on Indiamart.com

 

[kmathan88]

Recently I had a power surge at home. It blew the fuse of my V-gaurd stabiliser, then the fuse of a cheap power strip connected to the stabiliser, and finally blew my amp.

That's bad. So, V-Guard / MCB / fuse won't help in all cases.

I will start my research, but price seems to be on higher side.
I will need to understand if online ups can safely replace CVT and Isolation transformers in terms of safety.

Thanks for your message. Keep us updated on your progress on this. Helps a lot.

 

[Dr.Lakshay]

I was specifically looking at
http://maxineshah.in/index.php?route=product/product&path=292&product_id=146
Vs
http://maxineshah.in/index.php?route=product/product&path=293&product_id=160
Would cvt be better than isolation transformer?

 

[newlash09]

Hi lakshay...

Unfortunately iam unable to access the above links at the moment. Will try again in the evening and let your good selves know.

CVT and isolation transformer are very different to each other.

CVT - the input voltage in a domestic environment at the power sockets is not constant. It varies between 170 to 250V at most times. A CVT will accept this input and output a constant voltage of 220 or 230V as desired. ( The manufacturer will ask you what output voltage you want when placing the order. ) A stabiliser does something similar, but can't match a CVT's response time in actual use. And a CVT also has spike protection in that, if the input voltage becomes so high that it can no longer output a steady 220 or 230V , it will break the circuit and prevent the spike from entering your equipment.

Isolation transformer - all switch mode power supplies and most home appliances dump noise back into the main lines. The only way to filter this is a isolation transformer. For example my class D amp has a switch mode supply. And it dumps high frequency noise into the power sockets. This noise is picked up by my dac and transport. So when I plug the amp into a isolation transformer, it grounds that returning noise and prevents it from getting into my home wiring. And vice versa...the noise in my home wiring won't get into my amp as well.

So to me a combination of the above two was suggested by lots of forum members during my queries. So iam not considering normal spike gaurds or UPS or stabilizer systems anymore.

 

[Selvin]

Most of the time what we are thinking as isolation is not a real isolation.

If the house electricity connection is 'Single Phase' type then it is potential between Line and Neutral. The Neutral point is always grounded at sending end i.e at distribution transformer side. In a normal domestic 230/230V transformers the secondary side one point will be usually grounded. So that the system is not isolated really. To overcome this we may opt Medical environment isolation transformers where the secondary Neutral point will not be grounded internally and be in floating. But domestic environment IE rule not allowed it due to safety reason.

If the house electricity connection is 'Three Phase' type then a 415/230V isolation transformer may be opted where primary shall be between Line -Line (two phases) and secondary winding one point shall be grounded. Which enables real isolation.

There are multiple other isolation methods also available but those are more complex types.

Consider below two points while considering isolation transformers.

1. Consider minimum three times higher size transformer than the one which inside your amplifier/equipment for better headroom.
Eg. If the amplifier power consumption is 300W consider minimum 1000VA transformer and 1500VA is a better option.
2. Be aware about the inrush current of the transformers. Usually transformers takes about 6- 20 times (depend the design) larger current than it's rated current for the first few cycles (about 60-100ms time) of every charging. Proper fuse / MCB's need to be considered to withstand such large inrush current. MMS is an alternative option which are designed to withstand such inrush currents. The normal current of a 1000VA transformer at 230V supply is about 4.35A and then calculate the inrush current accordingly.

 

[Hari Iyer]

IME, balanced isolation transformer offered better noise figures than only isolation transformer. There are some risks involved by going only balanced incase the transformers fail. Check out pros and cons of going only isolation or balanced and weigh them before you plunge or you risk safety parameters in your setup.

My 2 pause.

 

[Dr.Lakshay]

Thanks @newlash09 that was very helpful and clears a lot of doubts.
Thanks @Selvin for the information.

IME, balanced isolation transformer offered better noise figures than only isolation transformer. There are some risks involved by going only balanced incase the transformers fail. Check out pros and cons of going only isolation or balanced and weigh them before you plunge or you risk safety parameters in your setup.

My 2 pause.

That is what I couldn't figure out properly.
I don't have very high fluctuations in my area. But I do suspect noise in my house electricity because sometimes even when I switch a light/fan my TV switches off and on. So I thought I should buy isolation step down transformer by Maxine for my avr.
Could you please help me figure out the pros and cons of an isolation step down transformer with respect to a normal step down transformer?
Can isolation transformer be risky for my avr anyhow?

 

[Dr.Lakshay]

I contacted the seller - maxine.
They told me that the isolation step down transformer doesn't have any such benefit of filtering the noise and the only benefit is that it has separate primary and secondary coils so that if there is a surge only the primary coil will get burnt and the secondary coil will be saved and it would help save my avr from the surge.
Is that the only benefit of isolation transformer?

 

[Hari Iyer]

Thanks @newlash09 that was very helpful and clears a lot of doubts.
Thanks @Selvin for the information.

That is what I couldn't figure out properly.
I don't have very high fluctuations in my area. But I do suspect noise in my house electricity because sometimes even when I switch a light/fan my TV switches off and on. So I thought I should buy isolation step down transformer by Maxine for my avr.
Could you please help me figure out the pros and cons of an isolation step down transformer with respect to a normal step down transformer?
Can isolation transformer be risky for my avr anyhow?

I am not an expert in this area, but can tell that if switching your light on/ off causes TV to mute image and sound then it's noise in the mains due to EMI coupling from light/ fan. Your TV should already have an SMPS supply which would have noise suppression and harmonics filters. I am suspecting your set top box as they too can pick up EMI/ RF noise as it has a microwave Freq feed. A simple cheap check is try adding a ferrite clamp type connector to your set top box DC line or maybe your coax RF cable. If that does not work try isolating your set top box. You can try by connecting a 9V dry cell ( as required) to test. Once you are tested decide if you want to isolate the set top box.

 

[Dr.Lakshay]

I am not an expert in this area, but can tell that if switching your light on/ off causes TV to mute image and sound then it's noise in the mains due to EMI coupling from light/ fan. Your TV should already have an SMPS supply which would have noise suppression and harmonics filters. I am suspecting your set top box as they too can pick up EMI/ RF noise as it has a microwave Freq feed. A simple cheap check is try adding a ferrite clamp type connector to your set top box DC line or maybe your coax RF cable. If that does not work try isolating your set top box. You can try by connecting a 9V dry cell ( as required) to test. Once you are tested decide if you want to isolate the set top box.

The thing is that the TV that goes off is the one that is connected to cctv and is used only for that purpose. So may be its not the set top box.
Now that you mention it I did buy some of those ferrite clamp ring for my rca. Didn't realize I could try using it this way also. Will try it on the set top box and the DVR too. Thanks.

 

[newlash09]

Most of the time what we are thinking as isolation is not a real isolation.

If the house electricity connection is 'Single Phase' type then it is potential between Line and Neutral. The Neutral point is always grounded at sending end i.e at distribution transformer side. In a normal domestic 230/230V transformers the secondary side one point will be usually grounded. So that the system is not isolated really. To overcome this we may opt Medical environment isolation transformers where the secondary Neutral point will not be grounded internally and be in floating. But domestic environment IE rule not allowed it due to safety reason.

If the house electricity connection is 'Three Phase' type then a 415/230V isolation transformer may be opted where primary shall be between Line -Line (two phases) and secondary winding one point shall be grounded. Which enables real isolation.

There are multiple other isolation methods also available but those are more complex types.

Consider below two points while considering isolation transformers.

1. Consider minimum three times higher size transformer than the one which inside your amplifier/equipment for better headroom.
Eg. If the amplifier power consumption is 300W consider minimum 1000VA transformer and 1500VA is a better option.
2. Be aware about the inrush current of the transformers. Usually transformers takes about 6- 20 times (depend the design) larger current than it's rated current for the first few cycles (about 60-100ms time) of every charging. Proper fuse / MCB's need to be considered to withstand such large inrush current. MMS is an alternative option which are designed to withstand such inrush currents. The normal current of a 1000VA transformer at 230V supply is about 4.35A and then calculate the inrush current accordingly.

Thanks a lot selvin...your post was very informative indeed

 

[newlash09]

Most of the time what we are thinking as isolation is not a real isolation.

If the house electricity connection is 'Single Phase' type then it is potential between Line and Neutral. The Neutral point is always grounded at sending end i.e at distribution transformer side. In a normal domestic 230/230V transformers the secondary side one point will be usually grounded. So that the system is not isolated really. To overcome this we may opt Medical environment isolation transformers where the secondary Neutral point will not be grounded internally and be in floating. But domestic environment IE rule not allowed it due to safety reason.

If the house electricity connection is 'Three Phase' type then a 415/230V isolation transformer may be opted where primary shall be between Line -Line (two phases) and secondary winding one point shall be grounded. Which enables real isolation.

There are multiple other isolation methods also available but those are more complex types.

Consider below two points while considering isolation transformers.

1. Consider minimum three times higher size transformer than the one which inside your amplifier/equipment for better headroom.
Eg. If the amplifier power consumption is 300W consider minimum 1000VA transformer and 1500VA is a better option.
2. Be aware about the inrush current of the transformers. Usually transformers takes about 6- 20 times (depend the design) larger current than it's rated current for the first few cycles (about 60-100ms time) of every charging. Proper fuse / MCB's need to be considered to withstand such large inrush current. MMS is an alternative option which are designed to withstand such inrush currents. The normal current of a 1000VA transformer at 230V supply is about 4.35A and then calculate the inrush current accordingly.

Hi again selvin...

Iam still a bit confused at deciding my isolation transformer. My house supply is single phase. So should I consider a normal isolation transformer or balance or medical grade. Didnt even knew these types even existed. So any advise or suggestion will be very helpful.

And if you can elaborate a bit on the single phase wiring. I will try my best to explain to the electrician what has to be done. Thanks again

 

[Selvin]

I am not sure about your exact requirement. What purpose you are looking for this transformer? Is it of Step-Down the voltage or Reducing the voltage fluctuation or Safe guard your equipment's from line surges or Isolation from Line and reducing EMI/RF effects?

For your system (already your house is single phase) the solution as below.

Step-Down/Up Voltage - Auto wound transformer (Economical) or Normal Two winding transformer with Grounded Secondary.
Isolation from Line and reducing EMI/RF effects : Medical grade Isolation transformer.
Safe guard your equipment's from line surges : Surge Arresters or Medical grade Isolation transformer
Reducing the voltage fluctuation : Normal Two winding transformer with Grounded Secondary

Products can be found in below links.

http://www.miracle.net.in/transformers/medical-isolation/

https://obo-bettermann.com/article/display/en-wo/surge-arrestor-1-pole-npe-7.html

 

[veekm]

Hello members.
Looking for a comparison of auto wound step down transformer vs isolation step-down transformer pros and cons.
Does it make sense to get an isolation transformer by spending some extra bucks?
Please enlighten me. Couldn't find much knowledge by googling.

Isolation transformers isolate a device under test from the mains which means that when using an Oscilloscope and repairing a device, even if you do something silly, current won't flow through your oscilloscope probe into the Mains circuit. It usually uses a 1:1 winding ratio - neither step up|down.

There's not a lot of difference between normal run of the mill transformers and isolation transformers .. from a functioning perspective.. depending on who's conning you, they may use a better dielectric and shielding..

Most 2 winding single phase transformers are isolating by their very nature..

It's called 'Isolating' because they are electrically separate but magnetically coupled using a laminated core.. so.. for you to get shocked when you probe a circuit.. there is no electric field/closed loop through your probe.. current flow requires a closed loop of electric field/a closed path - in the transformer secondary - the closed path is set/fixed to between the two terminals of the secondary so current can't leave that circuit and work its way towards mains..

---
With an autotransformer/(not sure what auto wound transformer is) you get a single SHARED winding NOT 2 Windings and a shared magnetic core.. so.. it'll do step /up/down but your device isn't electrically isolated from mains unlike above.. so they are cheaper [fewer cheaper materials] but just as effective and easier to use.. (variable voltage)

---
People say that in an Isolation Transformer you don't get capacitive coupling/electric field coupling because capacitors work on the basis of electric fields whereas inductive coupling is magnetic but.. just check your Earth-Neutral voltage <2V before you waste money on an Isolation transformer.. it's mostly meant for repair/service engineers.. IMHO [also telecom]

[the idea being that the iso-xfmr shielding will prevent electric distortion - Faraday cage effect]