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Transformer to regulated power supply

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jetblack750il

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Good day,

I have 2 unit of transformer rated:

1) Input 230VAC and output 60V 40Amp (60V 0V 60V)
2) Input 230VAC and output 12V 45Amp (12V 12V)

I want to make both of them into a regulated power supply, the first is to power servo motor drive for my CNC project and the second is for supplying power to battery charger.

Please let me know the value of rectifier, capacitor, bleed resistor, and regulator to use for above transformer.

Where can I find formula for it and wiring diagram to connect it up? Thanks

Regards,
Lionel

Good day,

I have 2 unit of transformer rated:

1) Input 230VAC and output 60V 40Amp (60V 0V 60V)
2) Input 230VAC and output 12V 45Amp (12V 12V)

I want to make both of them into a regulated power supply, the first is to power servo motor drive for my CNC project and the second is for supplying power to battery charger.

Please let me know the value of rectifier, capacitor, bleed resistor, and regulator to use for above transformer.

Where can I find formula for it and wiring diagram to connect it up? Thanks

Regards,
Lionel

The first thing you have to do is write the output specs for the regulated outputs. Min/max voltages, min/max currents, maximum ripple voltage allowed, efficiency required, etc.

Thanks Mike for the thread, I read it and try to understand.

Bountyhunter,

Unit no.1 is 60V/59V max/min 40A/39A max/min currents.
The servo drive is rated 75V max and the servo is rated 60V max at 4A max. There are total of 7 drive and servo motor.

Unit no.2 is 16V/15V max/min 45A/44A max/min currents.
The charger rating is 11V to 27V , I'm charging at 8.4Vmax @ 6A , I'll use it to power up to 6 charger.

I need min ripple voltage and max efficiency possible for both, I don't know the min/max value that can be obtain, when I order the transformer the guy just ask me how much power and how many watt/voltage is needed and he recommends topping up the power, hence the output of transformer . Please advice. Thanks

Regards
Lionel

A 60V transformer will output 60√2-0.7 = 83V after the rectifier (assuming bi-phase rectifier).

If you want 60V, get a 45V transformer.

I'd recommend using a switching regulator to save yourself the pain.

A 60V transformer will output 60√2-0.7 = 83V after the rectifier (assuming bi-phase rectifier).

If you want 60V, get a 45V transformer.

I'd recommend using a switching regulator to save yourself the pain.

Thanks for the info and the formula, I don't know about that. Now, no one is hiring engineer to do sales anymore, only salesman; when I tell them I want max 60V this is what I get.

The servo drive manufacture recommends transformer type PS; the switching type will have noise? According to the instruction manual.

Is there any other way to solve this problem? Thanks

A 60V transformer will output 60√2-0.7 = 83V after the rectifier (assuming bi-phase rectifier).
It's actually a lot more complicated as you load the winding and draw current. Transformers are usually rated for an RMS voltage at a specific RMS current. At very light load, the rectified/filtered DC voltage out will be considerably higher than the voltage rating times the square root of 2. At heavy load, it probably will be less because the loading distorts the waveform (flattens off the tops) so it's no longer sinusoidal and thus the square root 2 doesn't apply exactly. I remember this stuff was a royal pain because the simple formulas don't really work as the load current goes up.

Last edited:
It's a 2.4KVA transformerwhich should have fairly good regulation, probably <10%, so I wouldn't expect the off load voltage to be too high.

Anyone with a solution ? Thanks.

Anyone with a solution ? Thanks.
As I had said to my old boss on more than one occasion:

I'm not sure I even understand the question.....

At heavy load, it probably will be less because the loading distorts the waveform (flattens off the tops) so it's no longer sinusoidal and thus the square root 2 doesn't apply exactly. I remember this stuff was a royal pain because the simple formulas don't really work as the load current goes up.

This simple truth should be taught to college students in their first year and they are asked to do a load test experiment with an "transformer+rectifier" to see the result for themselves.

I'm amazed so many still boldly said the DC voltage increases after rectification, with no concern about possible effect of output loading, and the simple rule of conservation of energy. It is impossible to get 60V 40A from a 40V 40A transformer secondary, its that simple.

Yes, if one has a 10KVA transformer, a 1F smoothing capacitor and a 0.1A output loading, it will work.

I know the LM138/LM338 form National Semiconductor to serve your purpose... ...check the datasheet. I suggest you build a half wave rectifier with a 40A schottky dual doide as rectifier, two 4700uF capacitor separated by a 25uH inductor as filter and then the regulator. Schematics suggested in the datasheet can build you a 10A power supply, more than decent for your service.

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