Need Help ! DIY Router Table Power Supply

[Schweinhund227]

Hello !

The Step Down Transformer feeding my DIY CnC router table "POWER SUPPLY" has an OUTPUT of 30VAC which is too high ! The Stepper Controller Circuit Maximum Input power is 42VDC.

Since I am going thru a Bridge Rectifier... that 30Vac is transformed into 42.3VDC { 30Vac X 1.14) Not counting Voltage Spikes...

I am looking for a quick and Dirty way to Burn off that extra Voltage prior giving it to my PCB board ... I was thinking about a Large Ceramic Resistor .... Any Ideas ....??? High Res Pot ??

I don't want to COOK my Board !
Thanks for Reading this !!!

Norm

OUT !

[Drools]

You can use diodes in series, each diode will drop the output .7 of a volt.

[steve323]

Resistors won't work unless you have a nearly constant current. Diodes might work, but you would need to account for the line voltage running high plus the transformer produces more than 30V unless it is running at the max current. You would need many high current diodes in series.

The best solution is to buy a 24VAC transformer. www.mpja.com has some 10A 24VAC transformers for US$19 plus shipping. They also have 24VDC switching power supplies in the 6-8A range for about the same price.

Steve

[Drools]

We use doides in series all the time on our slotcar power supplies to tweat the voltage. They are placed on the DC output not the AC side.

[jalessi]

Depending on what type of transformer you have it may be very easy to remove a few turns off the secondary to drop the output voltage.

Jeff...

[Schweinhund227]

MPJA won't ship to Canada ! ?

Digikey seemed to be out of the 25vac ones when I ordered !

I didn't mean to Lower the Voltage Directly at the Transformer output ! sorry if I lead you to that conclusion in my Question !

What I meant was to do is Choke the Voltage just after the Bridge Rectifier !!! I want to lower my DC Vin to 25VDC so I need a Resistor or Diode that will Burn off 5 Volts * quick and dirty and still enable 10Amps to feed my Steppers....


Thanks for helping....
don't let me Release the Magic Smoke !!! LOL

[Drools]

1N4001 diodes are what we use but you can always a higher rated rectifier diode.
http://slotcarillustrated.com/portal...ghlight=diodes
10A01TR-ND maybe...

[Schweinhund227]

Thank you Drools ~

Basically that's what I was after.... I understand that I must take in consideration.... the Voltage at Idle ! and while under Load ! Since the Diodes don't Cut down at the same Rate !!!

Thanks for pointing out a Possible 10A Diode from that Online Vendor !

I guess I have a few more Purchases to do !!!

Thanks to all !

I'll report in ... once I got something put together... that is satisfactory !

[pminmo]

If you can get a small 12V or 24V transformer you can autotransform the primary to lower the primary voltage to the transformer by wiring the smaller transformer out of phase. The exact opposite of this: http://pminmo.com/PMinMOwiki/index.p...le=40vdcsupply

[Al_The_Man]

I didn't mean to Lower the Voltage Directly at the Transformer output ! sorry if I lead you to that conclusion in my Question !

Removing the turns as Jalesi suggests achieves the same thing, but in the most efficient manner.
This is the route I always take, when it is practical. It is much easier if toroidal type transformer.
Al.

[Schweinhund227]

Ok Al !! after reading some more about this....

it could also be the cheapest !

I have a big Hammond HM562-ND or a 165S30 type transformer... and if I follow your Lead !!! To go down roughly 5 volts ? is there a Quick'n'Dirty Formula to get it just about right ?

It's packed pretty tight in there and ... I would be concerned about scratching the remaining Windings Coating... Last thing I need is a Melting transfo ! LOL

Thanks in Advance !

[Al_The_Man]

The best way to find out the turns/volt before hand is to wind on a 10 turn winding of very small gauge wire, if you measure the AC across this winding you can extrapolate the turns/volt, then you know fairly accurately how many to take off.
Probabally around 2 turns/volt.
The only occasion where it may not be practical to take turns off is you are not using a full bridge, but 2 rectifier full-wave with centre tap winding.
Also if you have a secondary with two windings in parallel, both winding have to be reduced together.
Otherwise for a single winding, it should not be a problem.
Al.