# Machsupport Forum

## Mach Discussion => General Mach Discussion => Topic started by: cncfreakcncfrea on August 07, 2014, 12:40:38 AM

Title: Transformer DIY qquestions
Post by: cncfreakcncfrea on August 07, 2014, 12:40:38 AM
Hello all,
I'm about to build a AC/Dc transformer 110VAC to 24VDC.
I have a toroidal coil and 1 bridge rectifier KBPC3506 (35A), my questions are:
1. the coil stated 50HZ, Pri: 0-220V/Red-Red, Sec: 12-0-12v/blue-white-blue, the mains are 60Hz here in Tw would it be ok to use this Toroidal coil?
2. How do I tell the power (wattage) for this coil?
3. what capacitance should I use?

thanks,

Title: Re: Transformer DIY qquestions
Post by: Tweakie.CNC on August 07, 2014, 02:54:29 AM
No problems using the toroid at 60Hz.

The capacitor value is calculated from :-

C  = (80,000 * I ) / V

C=uF, I=amps, V=volts

Watts = Volts * Amps

Tweakie.
Title: Re: Transformer DIY qquestions
Post by: cncfreakcncfrea on August 07, 2014, 12:08:01 PM
Thanks Tweaky CnC,
(http://i1220.photobucket.com/albums/dd459/happytriger2000/Forum/Machsupport/Toroidal%20AC-Dc%20transformer/IMG_6920.jpg) (http://s1220.photobucket.com/user/happytriger2000/media/Forum/Machsupport/Toroidal%20AC-Dc%20transformer/IMG_6920.jpg.html)

What's the value for current "I"?
C = (80,000 x I)/24
Should have kept the label/tag, will find out what wattage of the coil.
Title: Re: Transformer DIY qquestions
Post by: Tweakie.CNC on August 07, 2014, 12:45:15 PM
I suggest you connect your rectifier bridge first then measure the a/c voltage output (it is liable to be higher than 24V). Tot up the total current you will be drawing from this PSU (Steppers, relays etc. etc.) then you have the figures for your capacitor calculation. Also best to make certain that you are not going to try to draw more current from this transformer than it's manufacturers specification.  ;) (should have kept the label)

Tweakie.
Title: Re: Transformer DIY qquestions
Post by: cncfreakcncfrea on August 08, 2014, 03:24:21 AM
I have complete set transformer, 220 VAC, 45.2V, the capacitor is 10000uf 100V and 1 spare 110VAC 12-0-12 50W coil , new. I swap the coil around. Applied 110VAC, then measure the 12 12 leads with voltmeter I get 10v, shoudn't it be 24 or more?. the 12 and 0 leads give 12v, this is ok. the 12-12 leads were not connected to rectifier yet.
Title: Re: Transformer DIY qquestions
Post by: Tweakie.CNC on August 08, 2014, 03:46:49 AM
Best talk to the manufacturer of your transformer to find out how it has been wound.
I would expect to see 24 Volts across the blue / blue but it sounds like you have two 12 Volt windings in parallel (sharing a common start) rather than two 12 Volt windings in series.

Tweakie.

Title: Re: Transformer DIY qquestions
Post by: cncfreakcncfrea on August 08, 2014, 10:58:00 PM
I measured the 12 12 leads today again and it is normal now, 24V without rectifier.
After connecting 12 12 leads to the rectifier, then to 10000uf 100v cap, I get 34.2V DC, ok...I do not mind 34.2v, as the Stepper driver can take up to 60VDC, but why is it 34.2vdc?

Title: Re: Transformer DIY qquestions
Post by: cncfreakcncfrea on August 09, 2014, 02:13:24 AM
This transformer power the A axis of my knee mill cnc conversion:
http://vimeo.com/102987002

Title: Re: Transformer DIY qquestions
Post by: Tweakie.CNC on August 09, 2014, 02:16:05 AM
The 34.2 Volts is correct. When rectified and smoothed the dc voltage will be 1.4 times the ac voltage.

Tweakie.
Title: Re: Transformer DIY qquestions
Post by: Tweakie.CNC on August 09, 2014, 02:25:44 AM
Excellent video - pleased to see you have it all working OK  :)

Tweakie.
Title: Re: Transformer DIY qquestions
Post by: cncfreakcncfrea on August 09, 2014, 04:30:42 AM
I need to optimize the knee mill backlash settings, will do this on Monday.