Cooling of overloaded transformer

On Sunday, 1 April 2018 18:03:42 UTC+1, John Larkin  wrote:
> On Sun, 1 Apr 2018 09:53:18 -0700 (PDT), tabbypurr wrote:
> >On Sunday, 1 April 2018 17:49:38 UTC+1, John Larkin  wrote:

> >> I do most house wiring live, because getting bit by 120V isn't a big
> >> deal. 240 makes a lot of sense - less current, more power - but I bet
> >> it hurts a lot more.

> >After 1 bite people are usually scared senseless.

> 120-0-120, like we use in the US for bigger domestic loads, would be a
> good compromise. Too late!

We don't have pole pigs, our local distribution is 3 phase at 240v L-N, so accommodating 120-0-120 within that is not really workable. 120-0-120 also adds issues & costs since N is then live as well as L. Incoming fusing was double pole in the 1930s, and caused well established safety hazards, it's long since banned.

Building sites used to be required to use 55-0-55, that has now been dropped in favour of 240v & a RCD/GFCI.


NT

On Sunday, 1 April 2018 18:14:44 UTC+1, Klaus Kragelund  wrote:
> On Sunday, April 1, 2018 at 7:00:36 PM UTC+2, amdx wrote:
> > On 4/1/2018 9:16 AM, Klaus Kragelund wrote:

> >   OK, I'm not suggesting this, but since it is a resistive load, Could 
> > you put a non-polarized 260uv cap in series with the toaster. The 
> > capacitive reactance would be equal to the resistance of the toaster,
> > or 11.3 ohms. (think speaker crossover caps,it may not be cost effective)
> > I would break this up into 13- 20uf capacitors to reduce the current in 
> > each down to about 1 amp.
> >   Also the voltage rating, I think it has to be at least 400V, but I'm 
> > not sure how to calculate that. (hope it's 200V, they are available)
> > I once used this to drop about 40V down before a bridge for a 5V 
> > regulator, where I didn't want anymore heat. I just substituted until I 
> > had a reasonable input voltage. Harder to calculate because of gulps of 
> > current at the peaks.
> >   I would like some comments about calculating this for the resistive 
> > toaster.
> > If you think it is a stupid idea, explain why.
> > Explain the pitfalls.
> >                     Mikek
> 
> Capacitive droppers are good, but in this case the load is all over the place (low resistance when cold, higher when warm, different power levels etc)
> 
> But good point about thinking outside the box :-)
> 
> Cheers
> 
> Klaus

For some toasters that's fine, for many not. You can always drop the electronics & elements separately, but it gets more work.

FWIW the cheapest way to do 260uF NP is 2x lytics back to back with a diode on each so neither sees more negative than -1v.


NT

On Sunday, 1 April 2018 18:57:07 UTC+1, Pimpom  wrote:
> On 4/1/2018 11:04 PM, amdx wrote:

> >    How much lower is the R when cold?
> > It would just heat up a little faster, a  little more current through
> > the caps for a short time, nothing unusual.
> >    Does your toaster actually have different power levels, or just
> > different toasting times. My toaster is early 20th century technology.
> > 
> Mine has a fixed 1200W power, with a timer based on a CD4541. The 
> timer works nicely but the mains voltage varies widely and this 
> results in varying degrees of toast.

Your 4541 needs to not just measure time but voltage too so it compensates. I wouldn't be too surprised if that's a doable mod. If you had nothing more useful to do.


NT

On Apr 1, 2018, Klaus Kragelund wrote
(in article<6c166a81-64a7-4ed6-af8b-f79545106401@googlegroups.com>):

> Hi
>
> When I go to the states, I usually buy white goods, half price than in Europe
>
> So I have a 600W 230V to 115V transformer installed in a cabinet
>
> Now I have bought a 1300W toaster
>
> Instead of buying a new transformer, I am seriously considering just
> overloading it, but then keeping the heat down by forced convection, namely a
> fan
>
> Anyone tried overloading transformers before?

Won&rsquo;t really work, as others have said. My wife burn&rsquo;t her favorite hair 
dryer out by forgetting to turn the swith from 115 to 230 on a trip some 
years ago. Solution was to buy a local (European) hair dryer.

I wouldn&rsquo;t think that toasters are so expensive (even in Europe) as to be 
worth buying a big transformer.

Joe

Den søndag den 1. april 2018 kl. 16.16.27 UTC+2 skrev Klaus Kragelund:
> Hi
> 
> When I go to the states, I usually buy white goods, half price than in Europe
> 
> So I have a 600W 230V to 115V transformer installed in a cabinet 
> 
> Now I have bought a 1300W toaster
> 
> Instead of buying a new transformer, I am seriously considering just overloading it, but then keeping the heat down by forced convection, namely a fan
> 
> Anyone tried overloading transformers before?
> 
> Regards
> 
> Klaus

modify the toaster to run on 230 with a diode in series with the 
heating element ?

Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

> Den s&oslash;ndag den 1. april 2018 kl. 16.16.27 UTC+2 skrev Klaus Kragelund:
>> Hi
 
>> When I go to the states, I usually buy white goods, half price than in 
Eu
>> rope 
 
>> So I have a 600W 230V to 115V transformer installed in a cabinet 
 
>> Now I have bought a 1300W toaster
 
>> Instead of buying a new transformer, I am seriously considering just 
over
> loading it, but then keeping the heat down by forced convection, namely a 
f
> an
 
>> Anyone tried overloading transformers before?
 
>> Regards
 
>> Klaus
 
> modify the toaster to run on 230 with a diode in series with the 
> heating element ?
 
That would cause a huge unbalanced current in the source transformer.

There are optical triacs that activate on zero crossings. Set one to give a 
50% duty cycle. The toaster element won't care, but the RC timing circuit 
might. That doesn't matter. The potentiometer is not very accurate anyway, 
and it drits badly.

I simply set the toaster pot to maximum and use a separate digital timer to 
adjust the browning. I have three settings: 2:15, 2:30 and 2:45 min:sec, 
depending on the type of bread, thickness, and length of the slice. The 
nice thing is if I somehow forget to set the timer, the toaster timer will 
expire before it sets fire to the toast. (BTDT)

I don't know if that would still work with a 50% duty cycle AC, but it's 
worth a try. Maybe the AC rectifier in the toaster would have to be 
modified. The circuit is very simple and easily traced. Do the needful.
(Indian phrase. Useful at times.)

Den søndag den 1. april 2018 kl. 21.34.07 UTC+2 skrev Steve Wilson:
> Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:
> 
> > Den s&oslash;ndag den 1. april 2018 kl. 16.16.27 UTC+2 skrev Klaus Kragelund:
> >> Hi
>  
> >> When I go to the states, I usually buy white goods, half price than in 
> Eu
> >> rope 
>  
> >> So I have a 600W 230V to 115V transformer installed in a cabinet 
>  
> >> Now I have bought a 1300W toaster
>  
> >> Instead of buying a new transformer, I am seriously considering just 
> over
> > loading it, but then keeping the heat down by forced convection, namely a 
> f
> > an
>  
> >> Anyone tried overloading transformers before?
>  
> >> Regards
>  
> >> Klaus
>  
> > modify the toaster to run on 230 with a diode in series with the 
> > heating element ?
>  
> That would cause a huge unbalanced current in the source transformer.
> 

skip the transformer, modify the control to run on 230 and stick a diode in series with the heating element

1.4x overload is tolerable, given monitoring, limited duty cycle, that sort 
of thing.  >2x gets into the questionable range.

Tim

-- 
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Contract Design
Website: https://www.seventransistorlabs.com/

"Klaus Kragelund" <klauskvik@hotmail.com> wrote in message 
news:6c166a81-64a7-4ed6-af8b-f79545106401@googlegroups.com...
> Hi
>
> When I go to the states, I usually buy white goods, half price than in 
> Europe
>
> So I have a 600W 230V to 115V transformer installed in a cabinet
>
> Now I have bought a 1300W toaster
>
> Instead of buying a new transformer, I am seriously considering just 
> overloading it, but then keeping the heat down by forced convection, 
> namely a fan
>
> Anyone tried overloading transformers before?
>
> Regards
>
> Klaus 

Lasse Langwadt Christensen <langwadt@fonz.dk> wrote:

> Den s&oslash;ndag den 1. april 2018 kl. 21.34.07 UTC+2 skrev Steve Wilson:
>> > modify the toaster to run on 230 with a diode in series with the 
>> > heating element ? 
  
>> That would cause a huge unbalanced current in the source transformer.
 
> skip the transformer, modify the control to run on 230 and stick a diode
> in series with the heating element 

Brutal. 
 
 

Klaus Kragelund <klauskvik@hotmail.com> wrote:

> Hi
 
> When I go to the states, I usually buy white goods, half price than in
> Europe 
 
> So I have a 600W 230V to 115V transformer installed in a cabinet 
 
> Now I have bought a 1300W toaster
 
> Instead of buying a new transformer, I am seriously considering just
> overloading it, but then keeping the heat down by forced convection,
> namely a fan 
 
> Anyone tried overloading transformers before?
 
> Regards
 
> Klaus

Check Amazon US. You can get 220V appliances real cheap. Have them ship to 
your hotel. Here's some toasters:

https://tinyurl.com/ya79ml7n