ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades US power tools/ UK

Erm... considering today's prices I'd say if you don't need very specialised tools or already own very expensive US tools it'd probably be cheapest just to buy new tools. Or go with the 55-0-55 transformers.

All my US tools - which I imported with me recently - are working just fine using a 3kVA site transformer. The only CEE 110V plugs connect with the transformer after which the whole system is NEMA 5-15. For historical reasons the 240V system utilises South African BS546 outlets and extensions where required. The workshop is quite cosmopolitan

Guys,

I'm confused :-)

I'm only a thick carpenter. :-)

Maybe I wasn't clear but I'm in the U.K. born here and lived here all my life.

I just happen to have an American wormdrive saw that I'm running off a 1.5kVa site transformer. The saw works fine but when I was speaking to an electrician at work about it he seemed to think it would maybe run a little better on a normal 120V Live 0V neutral.

We did talk about moving the centre tap towards the neutral in a site transformer.

So, the question is would it run any better. The sparky at work suggested that at the moment I'm only getting about 2/3rds efficiency.

Thanks

David Lloyd

Dave,
As long as you're happy with the performance with the saw ripping timber, and the motor isn't overheating, I'd carry on as before. I can't see a great difference possible between 50 vs 60 cycles in terms of cutting efficiency- I regularly put different blades between 250mm & 320mm diameter in my table saw, [which is a bigger change in peripheral cutting speed], with no problems or noticable differences. As to voltage, that affects the overall maximum power and thus speed of cut = feed rate. But a big improvement in electrical efficiency? I'll leave that to the 'electrical brains' on the forum, but I think that's unlikely, whether it's a brush or induction motor.

Alan

After all voltage is just a potential difference, and as long as the potential difference between the two wires is 120V everything should be ok. The different frequency might affect the magnetic characteristics as well as electrics a little, since inductance depends on the frequency, but that shouldn't be much, I assume that only becomes a problem with extreme low-end stuff with zero tolerances.
UK transformers don't supply a neutral, just two lives. Apart from the fact that there is a 180 degree phase angle (and not 120 deg) it's the same as with some older European systems that only brought 2 lives of a 127/220V system into the houses. Motors worked (and in some cases still work) quite happily on both systems.

I think Dave has happily been using his saw and will do so in future.

An asynchronous single-phase (capacitor) motor will run 20% faster on 60 Hz than on 50Hz. Its torque will be more or less equal. A lower voltage won't primarily affect torque, only current and possible overheating.

Voltage does not care at all whether it is leg-grounded, center-grounded or not grounded at all. (More a safety issue). American tools have to live with any voltages from 100V to 120 V as far as I know.

And single phase current will never care about phase angles, will it?

So what's the real problem, I ain't got it?


[This message has been edited by Wolfgang (edited 11-18-2005).]

The fact that the supply is a balanced 55-0-55 vs. 110V with one grounded conductor (neutral) is neither here nor there as far as the motor is concerned. It's still getting 110V with either system.

3-phase transformers can be found on building sites which give 63V from any phase to ground but still 110V between any two of the phases. As Wolfgang says, the 180 vs. 120 degree phase difference with respect to ground is of no consequence, since the motor is connected across two points only thus "sees" just a simple sinewave of 110V.

I can't see any way that changing from a center-tapped supply to one which is 110V with one conductor grounded is going to make any difference to the efficiency of the motor.

The frequency is more likely to have an effect, but I've never found this a problem on smaller motors under relatively light duty. I have an old 120V 60Hz Skilsaw which runs on 50Hz just fine, for example.

I suppose that a heavily loaded 110V site xfmr could result in the voltage dropping a little on the low side compared to the marginally higher nominal voltage of the typical U.S. supply, but it's probably not very likely unless the xfmr is really being run on the limit.

Thanks,

There's no real problem as such and as I said earlier the saw works fine.

It's just that the electrician on site suggested that it may run better with a proper US supply. I have nothing to compare the performance to so, I have no idea if he's right or wrong.

Thanks again

Dave

With the majority of power tools the difference in frequency would not present any problem as the motors on most tools are universal motors. Those types of motors will run off of 50Hz, 60Hz and even DC (although with DC many speed controls will not work, ON or OFF only) Large induction motors, as found on air compressors, may not like the frequency difference as much, but even in the case of induction motors, the lower voltage 110 vs. 120 will help offset the less than ideal reactance at 50Hz vs the 60 Hz they were designed for.

Personally Dave(Llyod),
I think the site electrician is just trying to confuse you.
If the saw has worked OK for the time that you've used it on site, stay with your current set-up.
As they say, if it ain't broke, don't fix it.