110v Transformer

[Joet]

Need some help understanding the 110v site transformers...

Want to know whether i should get a 3.3kva or a 5kva transformer. Can get the 5kva second hand for the same price of a 3.3. Would anyone advise against a second hand one?

I will be mainly running a 1800w mixing drill and some lights but potentially other drills and saws.

What sort of thing can a 3.3kva handle compared to a 5kva (is it overkill). Not worried about the weight.

thanks

 

[EFLImpudence]

Watts/power factor = VA

So if no power factor is involved (1) you have -

3,300W or 5,000W capability.

 

[maltaron]

Most transformers are rated for intermittent use i.e. Drills etc witch are not running continuously. So a 3.3Kva transformer will supply 3.3Kva for drills etc but only around 2.5Kva for continuous loads like lights.

 

[Joet]

so having maybe 800w of lights on all the time then running the 1800w mixer for 5-10mins will be fine on a 3.3kva. Is it just worth getting the 5kva incase?

 

[bernardgreen]

Would anyone advise against a second hand one?

I would advise against. It may have been overloaded or otherwise damaged making it dangerous to use tools supplied from it.

 

[Robin0577]

To add to matarons point about intermittent vs continuous rated transformers, in general the moulded plastic cased models will be rated for intermittent use, the ones with ventilated steel cases will be continuously rated. There are some exceptions though so always check the specification.

Although a 5kVA does give you more scope as to what you can use on the output, I wouldn't bother unless you really need to because....

1) It'll be ****** heavy.
2) You can't safely draw 5kVA from a standard 13A socket outlet anyway, so you'd need a larger supply in order to be able to load the transformer fully.
3) Even with no load connected to the output you may well find the inrush current of the 5kVA will be high enough to trip a B32A breaker on a domestic ring final circuit. Even a 3.3kVA will sometimes trip a B20A on a radial if you happen to switch on as the mains waveform is rising to it's peak.[/i]

 

[333rocky333]

3) Even with no load connected to the output you may well find the inrush current of the 5kVA will be high enough to trip a B32A breaker on a domestic ring final circuit. Even a 3.3kVA will sometimes trip a B20A on a radial if you happen to switch on as the mains waveform is rising to it's peak.

Thats a good point, many times been called out due to the builders tripping out circuits

 

[RF Lighting]

I've a 3.3kVA tranny which trips the B16 breaker in my garage very regularly.

 

[ericmark]

As already stated there are two types of transformer the yellow brick are in the main designed to be plugged in and go up to around 3.5kW and are not efficient they will get quite hot in use and often only have fuse or cut out on the input and as a result under fault conditions can have huge currents on the output of 50 plus amps and have been responsible for a number of fires.

The larger transformers tend to be better made and will sit there powered up without getting really hot and are protected from overload both input and output and are far safer. However they are not designed to be plugged in but to be hard wired into a supply. One would normally use D rated MCB's to hard wire to cope with inrush and often they are three phase.

For a temporary use of 110 volt hand tools on a 230 volt supply the yellow brick is fine where plugged in as and when required. But for any long term work then the tin box type are really what we should use.

If we are to look at the regulations it would be hard to see how the Yellow brick complies with CONSTRUCTION AND DEMOLITION SITE INSTALLATIONS (SECTION 704) regulations in BS7671:2008 not read the amendment so could have changed. Many homes have a TN-C-S supply with is not permitted for construction sites. So for a true construction site the large orange boxes with multi outputs all protected by MCB's on the 110 volt side are really required.

The Yellow brick is to allow tools used on a construction site to be used elsewhere. They are not really designed to be used on the construction site itself.

So the question has to be where are you going to be using the transformer? And how long will the transformer be powered for? And what types are the 3.5kW are they yellow brick type or a proper construction site type designed to be powered 24/7.

 

[OwainDIYer]

The Yellow brick is to allow tools stolen from a construction site to be used elsewhere.

There, I changed that for you.

 

[RF Lighting]

Why? I do some site work and some none site work. All my tools are 110V, and bought by my business.

 

[Joet]

Thanks for the help. I bought a brand new 3kva and its works fine but has got quite a bit of a hummm to it, is this normal?

 

[ericmark]

Yes quite a lot do hum. The main point to look at is how warm does it get. The hotter it gets when powered up and not in use the more energy it is wasting.

So if one no load it runs cool then leaving it switched on is not really a problem if however it gets hot then make sure you switch it off as soon as you have finished.