Forums

Cooling of overloaded transformer

Started by Klaus Kragelund April 1, 2018
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
On 2018-04-01 07:16, 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? >
Afraid it won't work. Before the core has a chance to heat up one of the windings will likely start to smoke. Or if the transformer has one it may irreversibly blow an internal thermofuse. It might even work with just one round of toasts but you know how it is. Guests come over and then "Oh, let's prepare 10 slices of toast". There could also be some "discussion" with the adjuster of your home insurance about replacing the kitchen furniture after it has gone wrong :-) What I have done in Europe, but that was not legit per code: I needed 115V in my lab so I used a big 2kW transformer with center tap, not two separate windings. Those are smaller and in Germany they are called "auto-transformers" for some reason. However, I had to make sure that the 115V gear was connected between neutral and tap, never between hot (phase) and tap because that can blow Y-caps in there. -- Regards, Joerg http://www.analogconsultants.com/
Thanks Joerg

I suspected the same, better not to take any risk at all

Normal transformers are heat limited, and if the 600W was rated at 60 degrees ambient and I will be running it low temp

But secondary winding losses is on the square of current, so would probably not be wise
On Sunday, 1 April 2018 15:16:27 UTC+1, 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
Of course, have overrun them hugely. Don't. You don't need a transformer, you need a dropper. NT
On Sun, 1 Apr 2018 07:16:21 -0700 (PDT), 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
Copper loss goes as current squared, so you can't overload it much. (1300/600)^2 is probably too much, even with extra cooling. How much does a good 240V toaster cost where you are? I like this one https://www.amazon.com/gp/product/B00A6Z6U30/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 but a 240V toaster can go to 1800 watts, which would sure save time. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Sunday, 1 April 2018 17:37:08 UTC+1, John Larkin  wrote:
> On Sun, 1 Apr 2018 07:16:21 -0700 (PDT), 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 > > Copper loss goes as current squared, so you can't overload it much.
you can heatsink it a lot too. But don't. Life expectancy goes down a lot, the interior still gets hot.
> (1300/600)^2 is probably too much, even with extra cooling.
Memory is a bit fuzzy but I think I once pushed a mains transformer to about 3x output current long ago. It's terrible for regulation & MTTF, I wouldn't consider doing it today.
> How much does a good 240V toaster cost where you are? > > I like this one > > https://www.amazon.com/gp/product/B00A6Z6U30/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 > > but a 240V toaster can go to 1800 watts, which would sure save time.
I once had a 3.5kW one. I think you can still get 3.1kW. NT
On Sun, 1 Apr 2018 09:42:13 -0700 (PDT), tabbypurr@gmail.com wrote:

>On Sunday, 1 April 2018 17:37:08 UTC+1, John Larkin wrote: >> On Sun, 1 Apr 2018 07:16:21 -0700 (PDT), 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 >> >> Copper loss goes as current squared, so you can't overload it much. > >you can heatsink it a lot too. But don't. Life expectancy goes down a lot, the interior still gets hot. > >> (1300/600)^2 is probably too much, even with extra cooling. > >Memory is a bit fuzzy but I think I once pushed a mains transformer to about 3x output current long ago. It's terrible for regulation & MTTF, I wouldn't consider doing it today. > >> How much does a good 240V toaster cost where you are? >> >> I like this one >> >> https://www.amazon.com/gp/product/B00A6Z6U30/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 >> >> but a 240V toaster can go to 1800 watts, which would sure save time. > >I once had a 3.5kW one. I think you can still get 3.1kW. > > >NT
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. -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
On Sunday, 1 April 2018 17:49:38 UTC+1, John Larkin  wrote:
> On Sun, 1 Apr 2018 09:42:13 -0700 (PDT), tabbypurr wrote: > >On Sunday, 1 April 2018 17:37:08 UTC+1, John Larkin wrote: > >> On Sun, 1 Apr 2018 07:16:21 -0700 (PDT), 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 > >> > >> Copper loss goes as current squared, so you can't overload it much. > > > >you can heatsink it a lot too. But don't. Life expectancy goes down a lot, the interior still gets hot. > > > >> (1300/600)^2 is probably too much, even with extra cooling. > > > >Memory is a bit fuzzy but I think I once pushed a mains transformer to about 3x output current long ago. It's terrible for regulation & MTTF, I wouldn't consider doing it today. > > > >> How much does a good 240V toaster cost where you are? > >> > >> I like this one > >> > >> https://www.amazon.com/gp/product/B00A6Z6U30/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 > >> > >> but a 240V toaster can go to 1800 watts, which would sure save time. > > > >I once had a 3.5kW one. I think you can still get 3.1kW. > > > > > >NT > > 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. NT
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
On Sun, 1 Apr 2018 09:53:18 -0700 (PDT), tabbypurr@gmail.com wrote:

>On Sunday, 1 April 2018 17:49:38 UTC+1, John Larkin wrote: >> On Sun, 1 Apr 2018 09:42:13 -0700 (PDT), tabbypurr wrote: >> >On Sunday, 1 April 2018 17:37:08 UTC+1, John Larkin wrote: >> >> On Sun, 1 Apr 2018 07:16:21 -0700 (PDT), 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 >> >> >> >> Copper loss goes as current squared, so you can't overload it much. >> > >> >you can heatsink it a lot too. But don't. Life expectancy goes down a lot, the interior still gets hot. >> > >> >> (1300/600)^2 is probably too much, even with extra cooling. >> > >> >Memory is a bit fuzzy but I think I once pushed a mains transformer to about 3x output current long ago. It's terrible for regulation & MTTF, I wouldn't consider doing it today. >> > >> >> How much does a good 240V toaster cost where you are? >> >> >> >> I like this one >> >> >> >> https://www.amazon.com/gp/product/B00A6Z6U30/ref=oh_aui_search_detailpage?ie=UTF8&psc=1 >> >> >> >> but a 240V toaster can go to 1800 watts, which would sure save time. >> > >> >I once had a 3.5kW one. I think you can still get 3.1kW. >> > >> > >> >NT >> >> 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. > > >NT
120-0-120, like we use in the US for bigger domestic loads, would be a good compromise. Too late! -- John Larkin Highland Technology, Inc trk jlarkin att highlandtechnology dott com http://www.highlandtechnology.com