Forums

Cooling of overloaded transformer

Started by Klaus Kragelund April 1, 2018
Joerg <news@analogconsultants.com> wrote:

> On 2018-04-04 08:05, Steve Wilson wrote: >> Joerg <news@analogconsultants.com> wrote:
>>> As little as they often weigh these days I assume many microwave ovens >>> now have switching power supplies.
>> Yes, you can buy switching microwave ovens in Walmart. They are usually >> much more expensive.
> Simple microwave ovens have switchers as well, since a long time:
> http://www.vk3hz.net/amps/Microwave_Oven_Inverter_HV_Power_Supply.pdf
The control circuit looks complicated.
>> I womder if it would be possible to repurpose a switching power supply >> into a spot welder? Why not?
> It's being done.
> http://www.jatit.org/volumes/Vol51No1/11Vol51No1.pdf
I meant to convert a standard microwave oven switcher into a spot welder, like waht is done with a conventional microwave oven transformer. It looks like the control circuit might require considerable modification to handle the variable load. For example, there would be no requirement to monitor the load since there is no magnitron filament to keep warm. Rewinding the transformer to supply low voltage and high current might be a problem. Probably easier to just find a junk microwave oven and go the conventional route.
On Wednesday, April 4, 2018 at 8:05:43 AM UTC-7, Steve Wilson wrote:
> Joerg <news@analogconsultants.com> wrote: > > > As little as they often weigh these days I assume many microwave ovens > > now have switching power supplies. > > Yes, you can buy switching microwave ovens ...
Yeah, mine is a Panasonic 'Inverter' model... it's not notably lightweight, though.
> I womder if it would be possible to repurpose a switching power supply into a > spot welder? Why not?
Some pliers-type spot welders are, nowadays, switching-power input, but that's not the case for the cheapest Harbor Freight models... the problem is, you don't want or need DC for a spot welder, but that's what the inverter style has to offer. So, iron being cheap, the welders use heavy 60 Hz iron transformers. I hear a lot about Cuk converters, but does that still have a DC power storage capacitor? Such storage is wasted for welding.
whit3rd <whit3rd@gmail.com> wrote:

> On Wednesday, April 4, 2018 at 8:05:43 AM UTC-7, Steve Wilson wrote: >> Joerg <news@analogconsultants.com> wrote:
>> > As little as they often weigh these days I assume many microwave >> > ovens now have switching power supplies.
>> Yes, you can buy switching microwave ovens ...
> Yeah, mine is a Panasonic 'Inverter' model... it's not notably > lightweight, though.
>> I womder if it would be possible to repurpose a switching power supply >> into a spot welder? Why not?
> Some pliers-type spot welders are, nowadays, switching-power input, but > that's not the case for the cheapest Harbor Freight models... the > problem is, you don't want or need DC for a spot welder, but that's what > the inverter style has to offer.
I think the inverters are AC. In any event, the question is can you convert a junk inverter microwave oven into a spot welder like you can with a MOT?
>So, iron being cheap, the welders use heavy 60 Hz iron transformers.
Probably handles short circuit loads better than an inverter. Also, as Tim points out, less problems with skin effect.
On Sunday, April 1, 2018 at 7:16:27 AM UTC-7, 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
Was this an April Fool's Joke? If not, why not just toast your bread in a pan on the stove, over a flame? Michael
"whit3rd" <whit3rd@gmail.com> wrote in message 
news:ae499615-599d-4c8c-902a-6a01d3a43852@googlegroups.com...
> I hear a lot about Cuk converters, but does that still have a DC power > storage > capacitor? Such storage is wasted for welding.
Yes, the capacitor is between the inductors as coupling. It's optional, but the inductor is smaller with. Incidentally, the ground return of a Cuk carries the sum of input and output currents. Duh, but since the voltages are opposite, the current is the sum of the magnitudes, i.e., a 5V to -5V, 1A converter delivers 2A through its ground node. All three nodes (in, out and GND) carry continuous current (just inductor ripple). You might then suppose, well, let's ground the output and allow the GND return to lift. Well, after some rearrangement, you can reduce this to a single winding inductor, and you've just invented a buck converter (and full switching ripple is back, because of the sum of input and "output" currents). :-) I wouldn't think there would be anything wrong with DC for spot welding. Just build a bigass multiphase buck, dump all the outputs together, don't even bother with output capacitors. (You need a current mode controller to do this.) A CPU VCORE controller might do the job. You still need a shitton of 12V to get there, of course; if the controller doesn't mind what the supply voltage is, you might do 160VDC (rectified 120V, or higher for that matter), with a fairly low switching frequency and awfully low duty cycle. Bonus points for tacking on PFC, so you can draw several kW in the seconds before the breaker pops. Actually, just run it constant duty (with a fixed peak current limit to maintain protection) -- pulsating power is no worse than usual. Alternately, use supercaps (and maybe a 24V bus instead) to deliver much more power than available (over the same time frame) from the outlet, and also enable "portable" applications. Hmm, you'd only need about a dozen Boostcaps, that's not all that horrible. It could actually be luggably portable (if not handheld). Might also be good to use a current multiplier for the output: https://www.seventransistorlabs.com/Images/Current_Multiplier.png Just the series-parallel transformation of a Cockroft-Walton ladder. (Incidentally, the inductors have to be separate, you can't really share any on a common core.) Doesn't seem to be any reference to it on the internet; perhaps I'll call it the Williams ladder. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Contract Design Website: https://www.seventransistorlabs.com/
Den torsdag den 5. april 2018 kl. 01.58.52 UTC+2 skrev mrda...@gmail.com:
> On Sunday, April 1, 2018 at 7:16:27 AM UTC-7, 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 > > > Was this an April Fool's Joke? > > If not, why not just toast your bread in a pan on the stove, over a flame?
he's got a wife ;)
On Wed, 04 Apr 2018 13:51:21 -0400, Neon John <no@never.com> wrote:


>I'm curious as to the benefit of DC. When I went through welding >school many decades ago, all we had were AC machines. Anybody know >what the benefit of an AC spot welder is?
<https://www.cromweld.com/ac-vs-dc-welding/>
On 4/4/2018 7:24 PM, Lasse Langwadt Christensen wrote:
> Den torsdag den 5. april 2018 kl. 01.58.52 UTC+2 skrev mrda...@gmail.com: >> On Sunday, April 1, 2018 at 7:16:27 AM UTC-7, 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 >> >> >> Was this an April Fool's Joke? >> >> If not, why not just toast your bread in a pan on the stove, over a flame? > > he's got a wife ;) >
Toast her first.
On Thursday, 5 April 2018 01:33:05 UTC+1, k...@notreal.com  wrote:
> On Wed, 04 Apr 2018 13:51:21 -0400, Neon John <no@never.com> wrote: > > > >I'm curious as to the benefit of DC. When I went through welding > >school many decades ago, all we had were AC machines. Anybody know > >what the benefit of an AC spot welder is? > > <https://www.cromweld.com/ac-vs-dc-welding/>
That's all about arc welding. IMLE ac gives a lot more spatter. Spot welding is another matter altogether. NT
Den torsdag den 5. april 2018 kl. 03.45.36 UTC+2 skrev tabb...@gmail.com:
> On Thursday, 5 April 2018 01:33:05 UTC+1, k...@notreal.com wrote: > > On Wed, 04 Apr 2018 13:51:21 -0400, Neon John <no@never.com> wrote: > > > > > > >I'm curious as to the benefit of DC. When I went through welding > > >school many decades ago, all we had were AC machines. Anybody know > > >what the benefit of an AC spot welder is? > > > > <https://www.cromweld.com/ac-vs-dc-welding/> > > That's all about arc welding. IMLE ac gives a lot more spatter. Spot welding is another matter altogether. >
no splatter with TIG, but yes spot welding another matter altogether