Thread: DIY PSU build query...
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29-02-2020 #21
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.
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The Following User Says Thank You to Doddy For This Useful Post:
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29-02-2020 #22
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.Last edited by Desertboy; 29-02-2020 at 11:04 AM.
http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm
If you didn't buy it from China the company you bought it from did ;)
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29-02-2020 #23
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.
Doddy is correct...Clive
The more you know, The better you know, How little you know
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29-02-2020 #24
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29-02-2020 #25http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm
If you didn't buy it from China the company you bought it from did ;)
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29-02-2020 #26
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.!
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29-02-2020 #27
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29-02-2020 #28
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.An optimist says the glass is half full, a pessimist says the glass is half empty, an engineer says you're using the wrong sized glass.
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The Following User Says Thank You to Kitwn For This Useful Post:
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02-03-2020 #29
Posting error.
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02-03-2020 #30
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