Transformer temperature

[2 picoDumbs]

so , for aleph J , without official article , lean on sole known data - 200W of power consumption from wall , for stereo amp

so , taking losses in account , that would be - roughly - 85W to 90W per channel;

assuming 22V5 rails .......... 90VA/(2x22V5) , means 2A

Is that 200W peak or 200W rms



Hehehehe

I'm just trying to give you a headache. Hahahaha

 

[AndrewT]

Watts is an average, not rms.

200W from the wall socket could be the average draw for whatever the equipment is drawing over a period of continuous operation, or it could the the instantaneous peak power draw for a particular time. i.e at one instantaneous moment in time.

In the context used by ZM, I would guess he meant 200W average for a period of continuous operation.

 

[folkdeath95]

you should always ask, what is the ambient temperature?,
my amp's heatsink reads 45*C on an ambient of 30*C, barely warm when i touch it....

on your traffo do the 10 second hold hest, if you can stand the heat for 10 seconds, then not really a concern....

it is not the temperature per se, but how effcient can your chassis get rid of the heat...

listening to music your 300va traffo is probably putting out 30 watts at ear spltting volumes,
testing with sine waves and dummy loads otoh, that traffo will be stressed...

Room temperature is around 20°C. Yesterday evening, transformer temperature was 65°C, after being switched on for 4 hours (it seems that the longer it is on, the hotter it becomes). I managed to leave my hand on it for more than 20s.

Thanks everybody for your answers. It seems that we have two camps:
-the optimitics, like ZM or Nec3, saying that my transformer is big enough for the job (I didn't choose the 300VA by chance, I must have read it somewhere).
-the pessimistics, like AndrewT or Loudthud, saying that it is too small, hence the heat.

Replacing the existing unit by a bigger one is certainly safer, so maybe its time for me to try a 500VA transformer.

 

[TonyTecson]

the laws on physics rule....although i am the hopeless optimist....😀

20secs, that is cool.....😎

and i am also a big fan of oversized power traffos, since i make them myself...😉

 

[2 picoDumbs]

Room temperature is around 20°C. Yesterday evening, transformer temperature was 65°C, after being switched on for 4 hours (it seems that the longer it is on, the hotter it becomes). I managed to leave my hand on it for more than 20s.

Thanks everybody for your answers. It seems that we have two camps:
-the optimitics, like ZM or Nec3, saying that my transformer is big enough for the job (I didn't choose the 300VA by chance, I must have read it somewhere).
-the pessimistics, like AndrewT or Loudthud, saying that it is too small, hence the heat.

Replacing the existing unit by a bigger one is certainly safer, so maybe its time for me to try a 500VA transformer.

Or you could buy a second 300 VA and do dual mono

 

[AndrewT]

tell us more.
What is the AC current rating of your 300VA?
What PSU type have you fitted: Choke input or capacitor input?
What continuous DC current is/are your ClassA amplifier/s drawing?



70°C for the surface temperature is very hot for a toroid transformer.

Have you any idea how much hotter the primary and the core is?

If the DC output from a capacitor input filter is 6.94Adc then the MINIMUM AC rating for the secondary is roughly twice that. i.e. ~14Aac.

This will run the transformer HOT.
For cool running use a secondary AC rating of roughly 4times the continuous DC current draw. This uses the transformer at roughly 50% of it's continuous (capacitor input filter) power.

Watts is an average, not rms.

200W from the wall socket could be the average draw for whatever the equipment is drawing over a period of continuous operation, or it could the the instantaneous peak power draw for a particular time. i.e at one instantaneous moment in time.

In the context used by ZM, I would guess he meant 200W average for a period of continuous operation.

.............................
-the pessimistics, like AndrewT or Loudthud, saying that it is too small, hence the heat.

Replacing the existing unit by a bigger one is certainly safer, so maybe its time for me to try a 500VA transformer.

Nowwhere did I say your transformer is or was too small.
I questioned how HOT the interior is.
I questioned whether 70°C was an acceptable surface temperature.
I suggested a modelling method to arrive at a suitable AC current rating based on a DC current demand.

 

[Zen Mod]

........
-the optimitics, ......

well ,what I said from what I understood is - if it's declared as 300VA and you don't have it loaded more than nominal 150-160W of dissipation on amp side ..... just let him (Donut) choose will it live or die .

I didn't said it's cool enough (as normal )

 

[TonyTecson]

Or you could buy a second 300 VA and do dual mono

very good advise....

 

[juma]

... transformer temperature was 65°C...
... I managed to leave my hand on it for more than 20s...

Your temperature measurement is not correct.
No one can endure 65°C for 20s without a glove.
If that really was 65°C you'd be having serious burns, with blisters on your palm...
Check your temp. measurement equipment/procedures.

 

[oreo382]

Transformer losses have 2 components, core loss and copper loss. Typical core loss is 1 watt/kg core weight. Typical copper loss for a 300va toroid is around 22 watts. At 1/2 load normal temp rise is about 20 Celsius over ambient. This all from Superior Toroidal Transformers data. I know my Aleph J internal case temp is about 45 C. So 70 C is not out of the question especially if the mfr. in question is pushing his designs a bit.

 

[oreo382]

I don't know the consumption of the amp.😱 It's an Aleph J, on Fistwatt's website, announced consumption is 200W.[/QUOe

I see from the pic that there is metal at both ends of the support bracket. Is that metal contacting the chassis at both ends. If so make sure the bolt running through is insulated at one end otherwise you have a shorted turn or if it is making some type of resistive connection a partial short.

 

[juma]

.. 70 C is not out of the question...

Sure it's not. Holding a hand on it for 20s is.

 

[folkdeath95]

I'm not at home at this time, so I can't make new temperature measures.
I used a cheap IR thermometer, so I don't know how reliable it is. I will try with a cooking thermometer to see what it says.

Concerning the transformer mounting, the sketch attached show how it's done. I thought it was correct, but now I have a doubt.

The fact that I can keep my hand on the transformer is reassuring, but what scares me is the temperature of the washer: keeping my finger 2s on it really hurts.

 

[Zen Mod]

mounting bracket (confirm that is L shaped ?? ) and washer are not touching on washer circumference ?

 

[Hi_Q]

You need to use your digital Multimeter to measure the resistance of your amplifier WHILE IT IS COLD.
Before you use your amplifier for the evening, unplug the amplifier from the mains and apply the Multimeter across the pins of the mains plug, making sure of course that the mains switch on the amplifier is set to ON.
We will take my amplifier as an example and it measured 5.8 Ohms.
We now use the formula –
Maximum allowed resistance rise = (measured resistance x 0.1965) + measured resistance.
Which in my case is (5.8 x 0.1965) + 5.8 that works out as 1.1397 + 5.8 = 6.9397 Ohms.

The 6.9397 Ohms is the maximum resistance you want to see when you repeat the measurement exercise when the amplifier is hot.
Now connect your amplifier back into the supply socket and run the amplifier for the evening so it is nice and hot.
Switch off the amplifier and measure the resistance as before, my amplifier measured 6.7 Ohms, close but ok! Phew!
The increase in the resistance reading is due to the resistance of the copper wire in the transformer rising with temperature and now you have the two readings we can do some more easy calculation.
For example; we can find the % change in the transformer resistance which we don’t want to be more that 20%.
Once again taking my amplifier as an example, the formula here is –
Percentage rise = ((Hot resistance divided by Cold resistance) times 100) minus 100 or
((6.7/5.8) x 100) – 100 or
(1.155 x 100) – 100 or
115.5 – 100 = 15.5%

Finally we can use this % figure to deduce the temperature rise (which I have taken to be no more than 50°C above ambient) with the formula –
Temperature Rise = Percentage rise divided by 0.393 or 15.5/0.393 = 39.44°C.
So if you suspect over heating of your mains transformer then the above may be helpful.
Please note that the formulas are not precision but given to me by a friend who suggested that they just gave a reasonable guide as to what is going on inside the transformer.

 

[TonyTecson]

I'm not at home at this time, so I can't make new temperature measures.
I used a cheap IR thermometer, so I don't know how reliable it is. I will try with a cooking thermometer to see what it says.

Concerning the transformer mounting, the sketch attached show how it's done. I thought it was correct, but now I have a doubt.

The fact that I can keep my hand on the transformer is reassuring, but what scares me is the temperature of the washer: keeping my finger 2s on it really hurts.

now this is odd.....

 

[2 picoDumbs]

now this is odd.....

Sounds like electromagnetic inductive heating.

 

[oreo382]

Sounds like electromagnetic inductive heating.

Sounds like the bolt is a load (shorted turn).

 

[2 picoDumbs]

Sounds like the bolt is a load (shorted turn).

Could very well be the case, but you can't tell by the photo

 

[2 picoDumbs]

Concerning the transformer mounting, the sketch attached show how it's done. I thought it was correct, but now I have a doubt.

If that is exactly how the bracket looks, then there is nothing wrong with that.
If the top mounting plate is in contact with the bracket or chassis then that is bad.
Take some more pictures of the bracket and transformer from the side or take the front plate off the amp for a better front view of the transformer.