Cooling of overloaded transformer

On Sunday, 1 April 2018 20:15:56 UTC+1, Lasse Langwadt Christensen  wrote:
> 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 ?

Double voltage quadruples power, diode only halves it
And the electronics wouldn't work, usually powered by a capacitor dropper.


NT

On Sunday, 1 April 2018 20:34:07 UTC+1, Steve Wilson  wrote:
> 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.)

Chopping the waveform = immediate death to RC dropper supplies


NT

On Sunday, 1 April 2018 23:08:04 UTC+1, Klaus Kragelund  wrote:
> On Sunday, April 1, 2018 at 10:38:11 PM UTC+2, Steve Wilson wrote:
> > 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
> 
> Hah, Kitchen Aid folks aren't stupid
> 
> The 220V versions are the same prices as in Denmark
> 
> https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=220v+toaster+kitchen+aid&rh=i%3Aaps%2Ck%3A220v+toaster+kitchen+aid
> 
> 110V is less than half price
> 
> Cheers
> 
> Klaus

well, you only get half as many volts.


NT

On 2018-04-01, jrwalliker@gmail.com <jrwalliker@gmail.com> wrote:
> There may be a much simpler solution.  Toasters have multiple
> heating elements, so why not check whether they are all in series
> or in a series/parallel arrangement.  If they are in
> series/parallel, then converting to series connection might
> allow correct operation at 230V.
> Manufacturers might make the elements operate at 115V each and
> adjust the internal wiring to suit different markets.
>
> It may not work out, but it would be worth a look inside.
>
> The solenoid in the "pop-up" mechanism might be a bit harder
> to deal with. 

the mechanism's powered from a tap on one of the elements, get the
element voltage right and it's solved

> John


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On 2018-04-01, 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 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 ?

That would be a mod for 160V operation, not 230 and could leave the
electromagnet under-powered.  V^2/R and all that.

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On 2018-04-01, Steve Wilson <no@spam.com> wrote:
> 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. 

but if it works, and doesn't self-combust your toast's done in half the time.

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whit3rd <whit3rd@gmail.com> wrote:

> On Sunday, April 1, 2018 at 12:15:56 PM UTC-7, Lasse Langwadt
> Christensen wrote: 
 
>> modify the toaster to run on 230 with a diode in series with the 
>> heating element ? 
 
> A 1kW toaster on 120V has circa 14  ohms resustabce when hot.
> On 230V, with 50% duty cycle, that will dissipate circa 1900 watts.
 
> The solution lies elsewhere...
 
Very good point. E^2/R = 230^2 / 14 = 3,778.5 Watts. At 50% duty cycle, 
3,778.5 / 2 = 1,889.2 Watts. 

A 40A 220V optoisolated zero cross SSR is $3.83 on ebay : 172531429031

Here's the datasheet:

http://www.kvc.com.my/StorageAttachment/Kvcsb/datasheet/510/fotek-ssr-40aa-
h.pdf

Set it for 25% duty cycle and fix the toaster DC supply to handle 230V. This 
will make a nice 12.5Hz pulsation in the source transformer, but it should be 
far enough away to not bother anyone.

On Monday, April 2, 2018 at 12:29:30 AM UTC+2, Steve Wilson wrote:
> Klaus Kragelund <klauskvik@hotmail.com> wrote:
> 
> > Kitchen Aid products are half price. Over the last 2 years I have saved
> > more than 1000 USD, compare that to the cost of a transformer of 70 USD? 
>  
> > Cheers
>  
> > Klaus
>  
> So then buy a transformer. What's your problem?
> 
> After saving that much, there shouldn't be that many Kitchen Aid products 
> left. A toaster is a pretty small investment. Why spend $70 for a transformer 
> to power a $19 toaster?

Well, not a big problem, just wanted to see if I could use an existing one

The Kithen Aid toaster is a 55 USD part, and I am not powering one device, but 5 different devices, all though not at the same time

Cheers

Klaus

On Sunday, April 1, 2018 at 7:14:44 PM UTC+2, 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:
> > > 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
> > > 
> > 
> >   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)
> 
I was wrong about the resistance

Apparently, a the toaster design underwent some design effort to find a material that could hand the many cycles of heating and cooling:

https://en.wikipedia.org/wiki/Nichrome

Only 6% increase in resistance from cold to hot

Cheers

Klaus

On Monday, April 2, 2018 at 1:07:54 AM UTC+2, Joseph Gwinn wrote:
> On Apr 1, 2018, Klaus Kragelund wrote
> (in article<1dd94705-9628-42c6-a6b5-bb7b3f36be1b@googlegroups.com>):
> 
> > On Sunday, April 1, 2018 at 9:07:26 PM UTC+2, Joseph Gwinn wrote:
> > > 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 burnt 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.
> >
> > Kitchen Aid products are half price. Over the last 2 years I have saved more
> > than 1000 USD, compare that to the cost of a transformer of 70 USD?
> 
> A 1500 watt 240:120 transformer for 70 USD? I&rsquo;ve seen lots of 
> &ldquo;Converters&rdquo; for small dollars, but they are unlikely to be real 
> transformers (that is, made of iron and copper). One way to tell is to look 
> at the shipping weight.
> 
> I&rsquo;d believe $140, though:
> 
> .<http://www.rockler.com/step-up-step-down-voltage-transformer-110-120-to-220-
> 240v?sid=V9146>
> Rockler is a well-respected seller of woodworking equipment and supplies in 
> the US, and I&rsquo;ve bough many things from them.
> 

56 USD:

https://www.ebay.com/itm/Step-Down-Up-Transformer-230V-110V-AC-UK-to-US-Voltage-Converter-500W-1KW-2KW/282901899954?hash=item41de446ab2:m:mopAAzqmEbGVAKpB9lpsPjw

Cheers

Klaus