DIY PSU build query...

[Doddy]

I use 45v secondary's when wired in serial and rectified gives me 72v without load and 68v with load.

I also have a 50v one I don't use which gives 78v without load and 73v with load, I bought 2 because when Maplins went bankrupt they sold them 1/2 price and that's when I built the PSU.

Also I blew up the first transformer I bought which I paid full whack from RS for, wired the rectifier the wrong way round I seem to remember. So buying 2 was my insurance policy lol.

Sorry, pedantic mode (it might be important for someone blindly following this to avoid damaging drivers etc.):

Wired two 45V windings in series and you get 72V DC off load?, there's something amiss there. Perhaps in parallel? - I'd expect a 45Vrms winding to present around 64Vpk-pk, probably 62V after rectification and smoothing. Add 10% for the 220VAC rated primary and the nominal 240VAC UK supply and you're getting within a gnats of the 72V.

Two 45V windings in series you should expect 90VACrms, leading to around 128Vpk-pk, around 126V after rectification and smoothing. And then you can play games with the 220VAC primary versus nominal UK supply.

For reference, I also bought a toroidal tx from Maplin on closure...



That pokes out 72V off-load, rectified and smoothed, measured with cheap Chinese current/voltage DMM panel meters. Two secondaries driving two separate circuits - but this should give the same voltage as two secondaries in parallel (not series). The maths for mine = 50VAC * SQRT(2) - 2 * Vf(rect) = 69V - within about 5% of measured - I'm happy with that.

[Desertboy]

Sorry, pedantic mode (it might be important for someone blindly following this to avoid damaging drivers etc.):

Wired two 45V windings in series and you get 72V DC off load?, there's something amiss there. Perhaps in parallel? - I'd expect a 45Vrms winding to present around 64Vpk-pk, probably 62V after rectification and smoothing. Add 10% for the 220VAC rated primary and the nominal 240VAC UK supply and you're getting within a gnats of the 72V.

Two 45V windings in series you should expect 90VACrms, leading to around 128Vpk-pk, around 126V after rectification and smoothing. And then you can play games with the 220VAC primary versus nominal UK supply.

For reference, I also bought a toroidal tx from Maplin on closure...



That pokes out 72V off-load, rectified and smoothed, measured with cheap Chinese current/voltage DMM panel meters. Two secondaries driving two separate circuits - but this should give the same voltage as two secondaries in parallel (not series). The maths for mine = 50VAC * SQRT(2) - 2 * Vf(rect) = 69V - within about 5% of measured - I'm happy with that.

The bridge rectifier drops the voltage, it converts AC to DC you connect both outputs in series run it through the rectifier and 72v out the other side in DC.

You need capacitors to clean up the DC.

In center tapped full wave rectifier, only one diode conducts during each half cycle. So the voltage drop in the circuit is 0.7 volts. But in the bridge rectifier, two diodes which are connected in series conduct during each half cycle. So the voltage drop occurs due to two diodes which is equal to 1.4 volts (0.7 + 0.7 = 1.4 volts). However, the power loss due to this voltage drop is very small.

https://www.physics-and-radio-electr...rectifier.html

[Clive S]

I use 45v secondary's when wired in serial and rectified gives me 72v without load and 68v with load.

Are you sure you about the serial or do you mean parallel ?

The bridge rectifier drops the voltage, it converts AC to DC you connect both outputs in series run it through the rectifier and 72v out the other side in DC.

You need capacitors to clean up the DC.

I think you need to re visit this as I don't think you understand it. It is also misleading for others.

Doddy is correct.

[JAZZCNC]

The bridge rectifier drops the voltage, it converts AC to DC you connect both outputs in series run it through the rectifier and 72v out the other side in DC.

You need capacitors to clean up the DC.



https://www.physics-and-radio-electr...rectifier.html

You need to SHUT UP until you know what your talking about because your going to cause people serious damage with your WRONG information.

[Desertboy]

I should just link the Clive S build it's how I built mine, 2 years ago bad memory.

Whatever I did I did it right I just copied Clive S's build, 3 capacitors to smooth the DC.

This is what it tests out at without load

[JAZZCNC]

I should just link the Clive S build it's how I built mine, 2 years ago bad memory.

Whatever I did I did it right I just copied Clive S's build, 3 capacitors to smooth the DC.

Yes, you should have because Clive S knows what he's doing unlike you.!

Giving information out like you are doing without actually knowing what you did or why is dangerous. The only reason it works for you is that Clive S does know what he's doing and knows the difference between Series and Parallel so sized the transformer secondaries correctly.

If you had wired those 2 x 45 in series then your drives would now be toast and anyone reading your WRONG information would also fry their drives because of you.! . . So please don't post anything about anything electrical unless your 100% sure you know what your doing or why you have done what you copied from someone else because your not helping, your actually dangerous.!

[Doddy]

I should just link the Clive S build it's how I built mine, 2 years ago bad memory.

Whatever I did I did it right I just copied Clive S's build, 3 capacitors to smooth the DC.

This is what it tests out at without load

Refer to post 330 of your own build log - you wired your secondaries in parallel.

[Kitwn]

You need to SHUT UP until you know what your talking about because your going to cause people serious damage with your WRONG information.

A little knowledge is a dangerous thing. Sometimes you really do need to make the effort to understand the subject correctly. Read the information in the first page or two of the link I gave in post #10.

It's also worth noting that anything other than a 'True RMS' meter can give false readings of voltages that are neither continuous or sinusoidal, as seen at the output of a rectifier without smoothing capacitors.

[joe.ninety]

Posting error.

[Doddy]

Posting error.

Maybe, but a good price, if they’ll honour it!