I have the parts of a PSU kit, but don't have the schematic... which should I build?

[lamir35]

At first, a little ironic:
<snip>

I would place the better ones near the amp, the "worse" of them near the tranny.

I don't understand what do you mean by "near". They are very close to each other, 2cm of wire.

For a tranny of this size a soft-start is normally not needed.

I already ordered a soft start.

I would not only place the better caps near the amps, but (referring again to post 19) i suggest to place XXX µH inductors (instead of resistors) between the rail-poles of the different e-lytic types. Inductors can have very low DC-resistance, though their better filtering action.

Do you have any schematic or a source for that? I never saw such a circuit.

Thank you for your suggestions so far, but I fairly confused and will try to research this some more online.

 

[AndrewT]

...............

I already ordered a soft start..............

your 300VA operating on a 230Vac supply will need a T1.25A or T1.6A fuse for normal running.
But this size of fuse will blow on start up after a few cold starts. Fatigue of the fine wire !
Without a soft start you will probably need a T3.1A fuse to get reliable cold starting over many months/years. You might find that even the T3.1A ruptures after a few weeks of use and you may need to go upto T4A for long term reliability.

I recommend you use the soft start and try using about 80ohms of soft start resistance. You might get away with as little as 60ohms for the T1.25A fuse. Worth experimenting.

 

[mchambin]

Tu stop the fuse blowing, for good, wrap it with aluminum foil or replace with a twisted paper clip.

 

[KatieandDad]

I don't understand what do you mean by "near". They are very close to each other, 2cm of wire.

Physically they might be very close to each other. We are referring to what the amplifier sees at the output of the PSU.

Use the cheaper caps as the raw smoothing caps at the output of the rectifier. The better caps are then separated by a small resistance CRC, the better caps provide a low impedance output to drive the amplifier.

Even without the R, the better caps provide a low impedance source for the amplifier.

 

[mchambin]

One more advice: I would not only place the better caps near the amps, but (referring again to post 19) i suggest to place XXX µH inductors (instead of resistors) between the rail-poles of the different e-lytic types. Inductors can have very low DC-resistance, though their better filtering action.

Please, think of this idea. Good dimensioned inductors would allow a much more dynamic.

If you decide to follow my advice (i would be glad, if you do ... especially related to "my" inductor advice (smile)

Wake me up when you find these inductors for a solid state powerful amplifier.

 

[lamir35]

I still haven't found a PSU circuit with an inductor as #20 suggested.

The better caps are then separated by a small resistance CRC, the better caps provide a low impedance output to drive the amplifier.

Thank you, I think I have it, it's Rectifire+ to Cap1 and to 0.1R, 0.1R to Cap 2 and to + output.
Only question remaining is, will it be better than using identical caps without a resistor?

I'm hope I'm not asking here too novice questions, but it's my first high W build...

 

[asuslover]

How about some pictures?

 

[lamir35]

How about some pictures?

 

[AndrewT]

You need to connect the rectifier -ve to the the bottom of C1. That would complete the charging circuit.
I suggest you remove the "ground" symbol from the bottom of C2 and insert a zero Volts (0V) instead.
The PSU is your power supply: 0V & 40V

 

[asuslover]

wow !
Post some pictures of the kit, usually a kit comes with a pcb (board) and components.
take a picture of those and attach them...

 

[KatieandDad]

The difference will only be slight.

 

[DF96]

Put the caps with the highest ripple current rating nearest to the rectifier.

 

[mchambin]

I understand, ripple rating, wich is actually ripple current through the cap, has to do with capacitor heating, the same as ESR.
I think the voltage ripple has mostly to do with the cap bank capacity value and supply current draw.

 

[DF96]

Yes, ripple current rating is related to ESR, but it is not the same thing. ESR tells you how much heat is generated. Ripple current rating also tells you how well this heat gets out.

 

[mchambin]

I see. Ripple current sort of includes the thermal resistance, I presume this is assuming free air convection.
I wonder why, as far I know, we do not put heatsinks on the power supplies big caps.
While we are at this, what should be known about the temperature rating of these caps, just a max temp rating ?

 

[DF96]

Temperature relates to lifetime, for electrolytic caps. Go above the rated temperature and they don't suddenly fail, but they do live shorter lives. Keep well below the rated temperature and they will live a long time, the cooler the better.

 

[lamir35]

I put together this little PSU and I get 62V measurement on each of the capacitors - what could be the explanation for this?

 

[mchambin]

40 x 1.41 is 56 volt.
The cap charges at peak voltage minus one diode drop.
Vrms x √2 - Vd
Usually, one takes Vs=0.7 but here, it is smaller because of no load but the cap current leak.
Australia mains is 240V, France is 230V but they keep naming it 220V as it used to be.
Mains voltage is +/- 5%.
40V transformers don't care about these details.

 

[mchambin]

10k is very little load, it makes about no voltage drop and very little ripple, so your DC measurement is ok regardless of actual type of DC measurement.
10 k does some load current easy to calculate.
With known cap value and load current value, one can calculate the ripple peak to peak voltage.
Beware of mF that is milli Farad, uF that is micro Farad.

 

[lamir35]

40 x 1.41 is 56 volt.
The cap charges at peak voltage minus one diode drop.
Vrms x √2 - Vd
Usually, one takes Vs=0.7 but here, it is smaller because of no load but the cap current leak.
Australia mains is 240V, France is 230V but they keep naming it 220V as it used to be.
Mains voltage is +/- 5%.
40V transformers don't care about these details.

Thank you so much for your reply.
So let me get this straight, the ac in the secondary should be 43V (since the mains is 236V ac and the trans is rated 220-40), but the dc output of the rectifier measures 62dc. Why does rms comes into play suddenly? This is confusing and frustrating especially because the rating of the amp is in DC and 62Vdc is so close to the required V up to around 58-60V max....

Another issue is what kind of measurement my meter makes in a non pure dc voltage... probably not true rms on the caps.
I also added two 10k resistor for loads and it didn't change the voltages.