DIY PSU build query...

[Desertboy]

No don't stop asking questions. Start a Build thread and ask all your questions in there. Don't worry about asking what may feel like dumb questions or offering up weird and wonderful suggestions. This way everything related to your machine is in one place and others coming to the party late can look back and see what's been said before.



Not sure who that's aimed at but 1000Va is on the large side and not really needed for anything but larger motors on typical 4 axis machine. Also for anyone with 70Vdc drives then 50Vac Secondaries are too large because they will be right at the 70Vdc mark so not enough safety margin. Always leave roughly 10% safety margin from the drives Max volts. Only use 50Vac secondaries with 80Vdc drives.

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.

It's also the reason I got 1Kva transformers there's was a limited choice of what was left, was in the voltage range and was cheap.

[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

[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.

[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.

[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.