Re: Clean water = low immunity = more disease

Thus spake Oz <Oz@xxxxxxxxxxxxxxxxxxxx>
>Charles Francis <charles@xxxxxxxxxxxxxxxx> writes
>>Thus spake Oz <Oz@xxxxxxxxxxxxxxxxxxxx>
>>>Charles Francis <charles@xxxxxxxxxxxxxxxx> writes
>>>
>>>>>someone
>>>>>might be to get a 240 to 110 volt transformer, fairly
>>>>>common to allow US equipment to run in Europe.
>>>>
>>>>Might work, but a transformer is just a big coil of heating wire.
>>>
>>>Not really, it has significant inductance.
>>
>>Funnily enough, I am actually aware of this. But since it is has no
>>direct relevance to the coil overheating and the transformer blowing,
>>the inductance is insignificant to the question in hand, so I have
>>ignored it.
>
>Try connecting a transformer without the iron core to the mains and then
>you will see how important the inductance is.

I think I would have difficulty. I have noticed that the coil is
generally tightly bound to the iron core, so that I would have trouble
extracting it. If I did get the wire off it really would be just a load
of heating wire.
>
>>However the current is determined by the loading.
>
>Yes.
>
>>In
>>this case the output voltage is regulated and we may take the output
>>current to be constant.
>
>A computer psu will deliver constant POWER pretty well regardless of the
>input voltage. Its switched-mode remember.

This is accepted under its rated loading. The question is what happens
when you overload the input. Which bit blows first, the coils or the
semiconductors controlling the output?
>
>>Then the input current should also be constant.
>>In which case the heating effect will actually go up linearly with the
>>voltage.
>
>Er, no. Actually a higher input voltage means a lower current and thus a
>lower dissipation in the windings because the output power is constant
>due to the psu design.
>
>This is why the psu takes about twice the current at 110V as it does at
>230V, it has to to deliver the same power.
>
>>>>and when it starts
>>>>to get warm it will heat even faster.
>>>
>>>Not so as you would really notice.
>>
>>I think so.
>
>You would be wrong.
>
>>The resistance of wire goes up with temperature.
>
>Very very small and the wire resistance is not a major loss when the
>transformer is used within its proper ratings.

The point was that the transformer is probably not being used within its
proper ratings. Either constant overvoltage or substantial spikes are
suspected.

> Of course if the core
>saturates its a different matter.

Then talk about that.

>>At constant current the heating effect will be
>>proportional to the resistance. Observe that inductance is insignificant
>>to heating.
>
>Not if the core saturates (which is usual when a transformer is grossly
>overloaded).
>
>Moral: do not overload transformers duh!

Quite. But we are talking of what happens when the mains voltage does
that for you.

>>>>You could just end up blowing
>>>>transformers, which is what we were doing.
>>>
>>>Twit, you were overloading it then.
>>>
>>Twit, yourself. I had no control whatsoever. In an oil fired cooker the
>>transformer generates a voltage to create a spark across the electrodes
>>and thereby to ignite the burner. It was only overloaded because the
>>input voltage was too high.
>
>usually this type of transformer fails because the secondary insulation
>breaks down.

Yes. I think that was happening due to overheating, due to an
overvoltage mains supply.

>To be honest I have found the commercial ones remarkably
>reliable (drier ones still working from 1952 and 1974). What they don't
>much like is high temperatures such as might be found in a poorly sited
>boiler in a small hot room with little ventilation and a heating system
>poorly designed so that the flame is turned on and off repeatedly. The
>latter is bad for internal sulphuric acid damage as well. This is why it
>is preferable to switch the mains supply to the boiler on and off rather
>than the radiators/circulation pump.

Duh. This was in a cooker in a largish kitchen. It's designed to get
hot, or it wouldn't be very good for cooking. The transformer was only
used to ignite the burners, and then only briefly. There was therefore
no current through it except when the cooker was too cool.

>>Or better still, if you just want to beat the shit out of me, have a go
>>at the paper.
>
>I'm still seriously hung over after a family get together.
>I have made a start but I need my exercise first and to do a few other
>jobs. You do after all get what you pay for.

Best money I ever spent.



Regards

--
Charles Francis
Please reply by name
.

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