Wiring up an Isolation Transformer

[seibu]

Hi,

I finally managed to get a 200v/230v/250v iso transformer to use here in the UK.

Am I right in assuming that I connect my mains input on the primary side, with "neutral" wired to 0v and "live" wired to 230v? And the monitor on the secondary side with it's "live" wire to 230v and "neutral" to 0v?

Assuming this is okay, what do I do with the Earth connection on both sides? Connect them to the casing of the Iso? Connect them together? I am stuck!

Furthermore, am I correct to use the 230v connections on both sides? I know UK mains is (was?) officialy 240v, but I don't have connectors labelled 240v. My monitor certainly says it wants 230v. So is it better to use the 230v or 250v connectors on the iso transformer?

Sorry if any of these are stupid questions - I just don't want to blow myself or my monitor up!

[AndyWarne]

NO don't connect this way! You need 230 and 0v on the primary, but on the secondary you need 110V and 0v.

Ground (chassis) on the monitor is also connected to 0v on the secondary, and to power cord ground.

Andy

[MonitorGuru]

First, I am in the US and havn't read up everything on 240 volt power supplies in the UK.

But here is what I can tell you, and you should google for verification.

1) In the U.S. we're supposed to have 120 volt AC.  My home measures anywhere between 117.5 and 120.5 volts out of the outlet.  However my transformers have markings indicating 115 or 110 volts.   Therefore the same applies to you.. 240 is the standard and it can vary as low as 220 and as high as 241 or so.   Devices are meant to work in the +/- 10% range typically without adverse affects.


2) If your monitor runs at 230 volts then you need to connect it up exactly the way you did.. 0V +230V on the SECONDARY winding.  If however your monitor runs at 115 volts, then you need a 2:1 step down isolation transformer to covert your 230 to 115.  Being that you're in the UK, I tend to think your monitor requires 230 volts, and the previous poster was incorrect. but you need to double-check the requirements on your monitor before plugging it in incorrectly.


3) Connect earth ground to the FRAME of the isolation transformer (the metal tabs that you screw down into wood to hold it in the cabinet). Also run the wire to the metal frame of the monitor.

[seibu]

Thanks for all the advice. I'm sure I have it figured out now.

The monitor actually says it can handle 120v - 130v *or* 230v - 240v so that pretty much covers everything. Since I only have 200v / 230v / 250v connectors on the primary and secondary sides of the iso (no 110v) I'll use the 230v connectors.

The earthing information was what I really needed - and the "connect it to the frame" advice was what I suspected. So thanks loads for reassuring me!

[MonitorGuru]

Thanks for all the advice. I'm sure I have it figured out now.

The monitor actually says it can handle 120v - 130v *or* 230v - 240v so that pretty much covers everything. Since I only have 200v / 230v / 250v connectors on the primary and secondary sides of the iso (no 110v) I'll use the 230v connectors.

The earthing information was what I really needed - and the "connect it to the frame" advice was what I suspected. So thanks loads for reassuring me!

If your monitor says it will work at both voltage ranges, you likely (90% possibility) have to slide a switch or move a jumper on the board to get it to work at either voltage.  Running 230 in when it expects 115 is very very bad.  

In the U.S. computer power supplies have a "220/110" switch on them and they're set to 110 by default.  Make sure you check the documentation of the monitor to ensure you have it configured to work off of 230 directly, don't assume it's smart enough to step down itself if it sees that voltage, unless it explicitly says so in the documentation.  Otherwise you will burn out various components in it.

[seibu]

Thanks for all the advice. I'm sure I have it figured out now.

The monitor actually says it can handle 120v - 130v *or* 230v - 240v so that pretty much covers everything. Since I only have 200v / 230v / 250v connectors on the primary and secondary sides of the iso (no 110v) I'll use the 230v connectors.

The earthing information was what I really needed - and the "connect it to the frame" advice was what I suspected. So thanks loads for reassuring me!

If your monitor says it will work at both voltage ranges, you likely (90% possibility) have to slide a switch or move a jumper on the board to get it to work at either voltage.  Running 230 in when it expects 115 is very very bad.  

In the U.S. computer power supplies have a "220/110" switch on them and they're set to 110 by default.  Make sure you check the documentation of the monitor to ensure you have it configured to work off of 230 directly, don't assume it's smart enough to step down itself if it sees that voltage, unless it explicitly says so in the documentation.  Otherwise you will burn out various components in it.

Cheers for the warning. I checked this, and the schematics indicate that the motherboard can be configured for either 230v or 115v by changing about 15 components. Having looked closely at the PCB, it seems mine is configured for 230v. Phew!

[Longy]

Hi,

I am living in Ireland (230V mains supply). I have a wei-ya C2620HR chassis which says that it will accept 90-260V input. However, I do not see any jumpers or switches on the chassis board to allow me to configur it one way or the other. The only jumper is can see is an N or W. I do not have a manual for the chassis, so I cannot tell if it will automatically switch depending upon what voltage is fed to it. Any suggestions?

Also, I need to purchase an isolation transformer, I'm not sure whether to go for a 230/115 or a 230:230.  I would like the flexibility of being able to step-down if I ever needed to just in case I had a monitor which only took 100-115V input at some stage in the future.  If I choose a 230/115 isolation transformer, is there some way of connecting the two 115V secondary outputs to give me a 230V output if required?

Thanks,
Alan.

[Longy]

3) Connect earth ground to the FRAME of the isolation transformer (the metal tabs that you screw down into wood to hold it in the cabinet). Also run the wire to the metal frame of the monitor.

I'm not convinced that you should wire an earth from the frame of the monitor back to the transformer.  I have read a few articles on this, and this is the first one that suggests doing it this way.  This poses a risk - if the frame of the monitor ever accidentally becomes live, then it will transfer current back to the rest of your components sharing the common earth. Whereas, is the frame is not connected to the transformer via an earth, then you have isolated the monitor with the isolation transformer (which is the whole point of using an isolation transformer). Am I incorrect is saying this?