230v European to 120v US converter

[awatson]

I need to power some 120v equipment from a heavy duty European uninterruptable power supply (UPS) that has 230v output on 2 wires (230v and Neutral). The transformer/converter should have a power capacity of 3KVA. It seems that every transformer I found requires two hot leads and a neutral on the primary, which I assume won't work with this UPS. What are my other options? Thanks.

 

[JimB]

I am guessing that you are in the USA and "every transformer" is a 240 to 120volt transformer.

I suspect that these transformers have a 240 volt primary which is centre tapped.
In which case, just connect the ends (240v) of the primary to the UPS outputs (230v and neutral) leaving the centre tap (120v) floating and connect your 120v load to the secondary of the transformer.

JimB

 

[awatson]

Yes, I'm in the US. Most of the US transformers also say they're for 240. Is there a problem feeding them with 230? And what about the earth grounds of the stuff on the 120v side of the transformer? Will that be connected to the earth ground of the UPS? The neutral of the UPS is at the same potential as the UPS's ground, so one leg of the primary of the transformer will be neutral and earth ground. Is that okay?

 

[crutschow]

Yes, I'm in the US. Most of the US transformers also say they're for 240. Is there a problem feeding them with 230? And what about the earth grounds of the stuff on the 120v side of the transformer? Will that be connected to the earth ground of the UPS? The neutral of the UPS is at the same potential as the UPS's ground, so one leg of the primary of the transformer will be neutral and earth ground. Is that okay?

230V is fine for a 240V transformer. You can always go lower in voltage but not higher.

Having the earth ground of the UPS connecting one wire of the transformer primary to earth ground is fine. One side of the 120V output (the "neutral") should also be connected to earth ground.

 

[ChrisP58]

Like crutschow said, running the transformer on 230 is OK, just be aware that the output will be 115 instead of 120.

Something else you need to consider is frequency. Europe uses 50Hz. The US uses 60Hz. Shouldn't be a problem, but you should check the transformer data sheet.

Also, what is the output waveform of the UPS? No problem if it is a true sine wave. But modified sine wave outputs don't always play well with transformers or inductive loads.

 

[awatson]

Very helpful information, thanks guys!

 

[KeepItSimpleStupid]

In the US, we really have a "split-phase" type system. It'd basically a center tapped 240 V xformer and the center tap is ground. Europe doesn't have this arrangement. They just have a 240 transformer where one end is connected to ground just as the US has groun and neutral tied together at one point when it enters the premises. Ground only carries fault currents and is used as a reference.

 

[ronsimpson]

the US has ground and neutral tied together at one point when it enters the premises. Ground only carries fault currents and is used as a reference.

At the main breaker box ground and neutral are tied together. This is the only place where N and G are tied together. When wiring your project together do not connect N and G together.

Yes, I'm in the US. Most of the US transformers also say they're for 240. Is there a problem feeding them with 230? And what about the earth grounds of the stuff on the 120v side of the transformer? Will that be connected to the earth ground of the UPS? The neutral of the UPS is at the same potential as the UPS's ground, so one leg of the primary of the transformer will be neutral and earth ground. Is that okay?

All grounds should be connected together. The 110V neutral might have about the same voltage as ground but it is not the same thing.

 

[Nigel Goodwin]

To clarify the 230V situation - it's purely a theoretical supply voltage, standardised across Europe.

The UK is still 240V, and the rest of Europe 220V, but both are within permitted limits of the 230V standard.

Essentially it means any equipment sold in Europe should be perfectly happy from a little more than 240V, and a little less than 220V (allowing for the spread of voltages) - in the past this wasn't true, and 220V equipment commonly had a short life on the UK's 240V mains (usually the mains transformers failed).

 

[awatson]

Like crutschow said, running the transformer on 230 is OK, just be aware that the output will be 115 instead of 120.

Something else you need to consider is frequency. Europe uses 50Hz. The US uses 60Hz. Shouldn't be a problem, but you should check the transformer data sheet.

Also, what is the output waveform of the UPS? No problem if it is a true sine wave. But modified sine wave outputs don't always play well with transformers or inductive loads.

Frequency won't be a problem, we have confirmed with the manufacturer of the load device that it will operate fine with 60Hz. However, the spec sheet for the UPS says the output waveform is a "computer grade sine wave". (page 19 of https://www.electro-tech-online.com...ries202400-8000VA2043535-00520-20UC3_3391.pdf). Will that be a problem for the 230 to 115 transformer?

 

[crutschow]

Frequency won't be a problem, we have confirmed with the manufacturer of the load device that it will operate fine with 60Hz. However, the spec sheet for the UPS says the output waveform is a "computer grade sine wave". (page 19 of https://www.electro-tech-online.com...ries202400-8000VA2043535-00520-20UC3_3391.pdf). Will that be a problem for the 230 to 115 transformer?

It states the harmonic distortion is 3% which is relatively low. I would think there would be no problem going through a transformer with that.

 

[()blivion]

The spec sheet for the UPS says the output waveform is a "computer grade sine wave"

As you recognized and hinted at, the statement "computer grade sine wave" is kind of ambiguous. I would take it to mean one of the following...

(1): It is clean enough to use with modern PC's. Like a lot of power supply's, computer power supply's have an internal frequency that they operate at. If the power going into them has a sufficient amount of certain frequency's already on it, this *CAN* cause all sorts of nasty problems. Though this is usually filtered out quite well.

(2): The output is a computer created approximation of a sign wave. More likely as this is what most inverters do (UPS working circuit). For a US device, they take the ~168 volts and connect it to the out line with a varying ON/OFF time (duty cycle). This creates an average voltage for a small moment in time that represents a single point on a sign wave. This is repeated at several kilo hertz (can be up to a few mega hertz) for the rest of the wave. The output power is passed through a filter (low pass filter) that only lets the sign wave through, because it is a lower frequency. The result is mostly clean 60hz AC with an RMS (average) voltage of ~120. This general technique for creating AC wave forms from a DC supply is called Pulse Width Modulation.


In either case, adding an appropriately rated step down transformer to the circuit will almost certainly not cause any damage. In fact, the transformers intrinsic inductance will add even more filtering to the circuit, further removing high frequency components and making the output power "more clean". Provided that the circuit creating the wave is mathematically correct of course.