Isolation Transformer Question - Electronic Circuits Projects Diagrams Free

paragon37 · 3rd November 2009, 10:32 PM

Hello All,

I am looking for an isolation transformer for use while working on smps's.

Could one of those yellow site transformers be used?

They transform 240v down to 110v.
Ideally I would like to have 240V - 240V isolation?

Any ideas?

Regards,
SRG

RCinFLA · 3rd November 2009, 11:07 PM

You can buy any combination 120v to 240v, 240v to 120v, 240v to 240v, and 120v to 120v.

You can buy one with two 120v primary windings and two 120v secondary windings and connect it up as any of the above combinations. I have two 2kW transformers of this configuration.

Need to get wattage size that exceeds your switching power supply.

paragon37 · 4th November 2009, 12:21 AM

Thanks for the info...

I should have mentioned I am located in the UK which 240v domestic.

I was looking at the one of these but I need 220V.
I guess as you mentioned I could connect the two 110v secondary's to produce 220V.

I just remember someone mentioning that they are not completely isolated due to having a centre tap to earth or something?

Kind Regards,
Steve

mbarazeen · 4th November 2009, 07:56 AM

if you need a isolation transformer, dont go for the 220/110 convertor, its a autotransformer, you can check there will be a reading between primary and secondary.

as you heard its centre tapped to be connected as 110/220

you can follow the idea of RCinFLA

or rewind a transformer 240/ 24 V, dont open the primary and make the winding of secondary as the same SWG of the primary and number of turns is 10 times of the secondary you unwind. if you use 240/12v T/F then you can calculate the number of turns. and it will be 20times.

or you can use two 220/12V or 24V transformers connected 24V side together, so input and out puts would be 220/220 and will give a good isolation.

indulis · 4th November 2009, 12:17 PM

Quote:

I am looking for an isolation transformer for use while working on smps's.

What kind of SMPS... off-line, or DC-DC? The front end of an off-line converter is the isolation transformer... rectify the line voltage to hi voltage DC and then "chop" it. For a DC-DC converter use a DC supply to feed it.

JimB · 4th November 2009, 01:20 PM

230v/230v isolation transformers are available, look here:

Carroll & Meynell | Transformers | Transformers | Safety Site Transformers | Portable 230V ac & 110V ac Output_Safety Site |CM7501/230

A bit expensive though.

I have a couple going spare for a much lower price, but not knowing where you are in the UK the carriage could be a bit high.

JimB

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3rd November 2009, 10:32 PM	#1
paragon37	Isolation Transformer Question Hello All, I am looking for an isolation transformer for use while working on smps's. Could one of those yellow site transformers be used? They transform 240v down to 110v. Ideally I would like to have 240V - 240V isolation? Any ideas? Regards, SRG

3rd November 2009, 11:07 PM	#2
RCinFLA	You can buy any combination 120v to 240v, 240v to 120v, 240v to 240v, and 120v to 120v. You can buy one with two 120v primary windings and two 120v secondary windings and connect it up as any of the above combinations. I have two 2kW transformers of this configuration. Need to get wattage size that exceeds your switching power supply.

4th November 2009, 12:21 AM	#3
paragon37	Thanks for the info... I should have mentioned I am located in the UK which 240v domestic. I was looking at the one of these but I need 220V. I guess as you mentioned I could connect the two 110v secondary's to produce 220V. I just remember someone mentioning that they are not completely isolated due to having a centre tap to earth or something? Kind Regards, Steve

4th November 2009, 07:56 AM	#4
mbarazeen	if you need a isolation transformer, dont go for the 220/110 convertor, its a autotransformer, you can check there will be a reading between primary and secondary. as you heard its centre tapped to be connected as 110/220 you can follow the idea of RCinFLA or rewind a transformer 240/ 24 V, dont open the primary and make the winding of secondary as the same SWG of the primary and number of turns is 10 times of the secondary you unwind. if you use 240/12v T/F then you can calculate the number of turns. and it will be 20times. or you can use two 220/12V or 24V transformers connected 24V side together, so input and out puts would be 220/220 and will give a good isolation. Last edited by mbarazeen; 4th November 2009 at 10:25 AM. Reason: another way

4th November 2009, 01:20 PM	#6
JimB	230v/230v isolation transformers are available, look here: Carroll & Meynell \| Transformers \| Transformers \| Safety Site Transformers \| Portable 230V ac & 110V ac Output_Safety Site \|CM7501/230 A bit expensive though. I have a couple going spare for a much lower price, but not knowing where you are in the UK the carriage could be a bit high. JimB __________________ Experience is directly proportional to the value of the equipment ruined.