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Post by Deleted on Feb 17, 2007 8:12:09 GMT -8
Just wondering,if it is possiable to modify a Leviton Push On / Off Dimmer with RFI Filter. This is a Single Pole, rotary dimmer switch, Rated: 600W-120VAC. I am trying to control the 120 AC into a Transformer, So that the 30V transformer output can be variable controlled. This Idea works for 0-30 V without a load but It Will fail at loads over 10V drawing 25 amp. Help me make this work. oupower.com/index.php?dir=_Other_Peoples_Projects/Beshires1/Powering%20up
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Post by Deleted on Feb 17, 2007 9:57:28 GMT -8
My 25amp 50V bridge just burned-out, I think the dimmer survived. Was running about 10V when transformer hum got loud and sputtered (bridge burned out) . Would a smoothing capacitor and voltage regulator have helped ?
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Post by Gary Lecomte on Feb 18, 2007 6:31:56 GMT -8
I'm Not Sure about That Dimmer, BUT MOST Dimmers are only made to operate NON-Inductive Loads. LIKE LIGHT BULBS.
Also, Without Filter capacitors, your Not really getting Much DC Current. Mostly a lot of 120 Hz Ripple.
Lastly, Did you put your Bridge Rectifier on a BIG "HEATSINK"? You SHOULD HAVE! All Bridge Rectifiers Require Suitable Heatsinks.
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Post by Deleted on Feb 18, 2007 11:39:04 GMT -8
Hi Chemlec. I'm using a 6681, but if I have any more trouble out of it I'll go to the 6616-X Its a Fan Control rated to 5 amps. assets.twacomm.com/assets/pdf/21504.pdf Yes I had the Rectifier heat sinked , But I had it bolted to the 1/4 inch aluminum plate, that also serves as a mains ground. The rectifier shorted internally and blew the 15 amp, 120V fuse.I do not have a filter capacitor installed . I have one 200V 680uf 3281(M) TSU CE +85 degrees C . Would it work? also don't I hook the + post of the capicitor to the + wire DC coming off the bridge? And the - to the neg DC wire off the Bridge? I know if I hook it up wrong the capacitor will explode. Problem is determining which is the + and the - on the bridge. The bridge I used showed the AC + and - connections but showed no polarity orientation on the DC post. (The bridge is a single square unit with spade connectors.) I assumed that the coils secondary winding wire coming off the outside of the coil was the +. The other end that starts the winding next to the Transformer core would be -. In other words I'm useing a single wire wrapped around the transformers secondary core one end of the wires end is- , wrapped 32 turns around core the other end of the same wire is +. this is a single wire secondary (No Center Tapp) Problem is, again, I feel stupid using it this way, It go against every thing I know about basic electricity functions. But at electricity I,m not a genius, thats why I came here to talk to one, and maybe advise me thru this project.
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Post by Gary Lecomte on Feb 19, 2007 7:04:42 GMT -8
I Have NO REFERENCES to those Dimmer Controls, So I Won't comment on that.
First you need to Measure the Full AC Output of your Transformer when its connected to the 110 Volt Line.
Than Consider that the AC Output, When Rectified is 1.414 Times this RMS AC OUTPUT. EXAMPLE: So if your transformer puts out 20 Volts, the Rectified output will be about 28 Volts DC. So you would use a Capacitor with a Rating Greater than 28 Volts. (Possibly 35 to 50 Volts.)
Also You need to Make Sure that your Bridge Voltage Rating is at Least, DOUBLE This Voltage Rating. If not you will Burn it out even with Low Current.
As to Capacitance: Generally speaking, you should have 1000uF for every Amp you expect to get out. So if your output is 10 Amps, you would use a 10,000 uF Cap.
As to the Bridge: It has two Terminals Marked AC. That goes to the Transformer. It has Two other terminals, One with a Minus Mark and the Other With a Plus Mark. They Go to the Capacitor. + to + and - to -. That is your output.
Lastly, A Metal Plate, Inside that Box has Relative Little Cooling Effect to the Outside Air. And it Should be a Proper Heatsink With FINS to Dissipate the Heat better.
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Post by Deleted on Feb 19, 2007 23:41:37 GMT -8
Thanks Gary, I should use a filter cap 25-30,000uf at least 35 to 50 V or more. according to my multimeter I am getting 32V ac off my secondary. this will be 45.248 VDC when rectified. This means that I will need a 100V 50amp bridge rectifier. Cool . I didn't realize the DC voltage increased when rectified. Got any idea where I can get the large filter cap? Also can't I use two smaller 15,000 uf caps in series? As long as they are Identical, like two 50V 15,000uf ?
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Post by Gary Lecomte on Feb 20, 2007 7:01:47 GMT -8
50 Volt Capacitors Should be OK. And YES, Paralleling Caps is OK. But you Might also Consider REMOVING some Turns from the Secondary Winding. Possibly Even by Half as many.
That 42 volts is really too much.
Not sure What Gauge of Wire your using on the Seconday? But from what I see in your Picture, I think it should be Bigger than what you have.
What you Might Do is Remove All the Turns, But COUNT THEM as you do it. Than, As an Example: if 32 Volts = 50 Turns, that equils .64 Volts per Turn. 32/50 = .64 Volts Per Turn.
So Say you only want 15 Volts AC, Divide it by .64, Equils 23.5 Turns. This will give you 15 X 1.414 = 21 Volts when Rectified.
Now you could use 25 Volt Caps.
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Post by Deleted on Feb 22, 2007 1:58:45 GMT -8
Hi Gary. This power supply project is drawing more attention than I expected in the ourpower forums. Under " Build your own Shop Equipment " topic. I have a large heatsink for the Bridge rect when I can locate one large enough. I Placed bid on 50V 30,000 DC filter cap. Will be a few days til I Know about that. I am also planning on installing a volt and amperage pannel meters. But that to will be later. I,m concentrating on the Cap and bridge for now. Thanks again for pushin me in the right direction.
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Post by Gary Lecomte on Feb 22, 2007 6:25:55 GMT -8
Be Advised that buying a Capacitor from Ebay May NOT be a good Idea.
Capacitors Degrade with Age. And than they Don't work Properly. You would be Better off to buy a New one from Digikey.
If all you want is an Old Cap, I can probably send you one for Free or charge, EXCEPT you will need to Pay for the Shipping Cost.
You Never said What Amperage you Expect to get Out of this transformer, But if you gave me More Details, I could give you some better advice.
What DC Output Voltage do you want. At What Amperage?
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Post by Deleted on Feb 22, 2007 21:36:15 GMT -8
My idea was to build a 30V 25 amp ,variable voltage Lab type power supply. Maybe have a switch from strait DC to a Variable frequency pulse generator (PWM) . I'm probably going to build a larger sized box to be able to house the transformer, large filter cap (The Ones I Bid on are a pair of 50V 30,000uf, each having a diameter of about 3 inches and are about 6 inches tall. Maybe I,ll get out bid, 3 days left.) I also want to include in the box the small microwave blower, for coolin things down.
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Post by Gary Lecomte on Feb 23, 2007 6:48:58 GMT -8
30 Volts at 25 Amps is NOT Possible with the Transformer you have.
With Filtering and Transformer Efficiencies, That would require a Transformer capable of 1000 Watts. Looking at the Picture you posted, My GUESS is that transformer will only handle about 600 Watts max.
It would also require that your Seconday Winding be an "8 AWG" size wire. Your Secondary Wire looked MUCH SMALLER than that, also not the correct type of wire for a good efficiency. You need to get a Good Enamel coated wire.
Also consider this: When you rectify the output and filter it, the voltage increases by about 1.414 times the RMS Voltage. But the Output Current is only about .707 Times the Origional AC Current. And because of Filtering, to get out 30 Amps, your transformer will need to deliver about 40 Amps. Probably about 10 Amps will be Lost in the Filter Capacitor.
As to a capacitor, I have one here, rated at 22,000 uF and 40 Volts (50 Volt Surge) that you can have for FREE. But you will need to pay the Shipping Cost to get it to you. It should Filter your supply OK.
I also have another cap, rated at 90,000 uF, but its only rated at 20 Volts. It is Too low of voltage if you want 30 volts out.
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Post by Deleted on Feb 23, 2007 19:14:39 GMT -8
Thanks for the offer on the caps. I am currently the high bid on E-bay for the two 50V 30,000uF caps. I am commented to purchase these if I remain the high bidder for 2days and 11hrs.If I get out bid in this time limit I shall not bid on them again and then I'll need to take you up on your offer.I have pulled the old stranded #12 wire and replaced the secondary winding with a high-temp insulated #10 single strand wire. the copper wire without insulation is about 1/8 inch in diameter.I wound the secondary tightly and cannot get anymore wire thru the secondary window. I now have a RMS AC output of 20.2 without a load. That means I can get a rectified DC output of 28.56 So I think I'll go with that. Please go to my projects page. and check out the pictures of my latest rewind. oupower.com/index.php?dir=_Other_Peoples_Projects/Beshires1/Powering%20up&PageNum=5 Also can I now use a bridge rated 25amps at 50 volts? I had to use a wooden wedge (In the top and bottom of the window) to keep the windings tight. I used a hammer to lightly tap the windings into place on the exposed face of the transformer. I don't think I could wind a secondary with this gauge of wire with enameled magnet wire without skinnin it all to hell. Others I know can do it but I think I have found a limit on my capabilities.LOL but maybe after I heal up some.............
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Post by Gary Lecomte on Feb 24, 2007 7:09:13 GMT -8
Yes, the No Load Output should be about 28 Volts. But it will Pull down somewhat as your Load Current Increases.
Normally they use Enamel Coated wire on transformers because the Closer together the wires are, The Better the Efficiency.
That Plastic insulation is quite thick and Definately Not the Best to use.
Your Picture Looks fine.
Not Sure Where you live, But a "Variac" is a MUCH Better way to Contol this, Rather than a Dimmer. Unfortunately also More Expensive.
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Post by Deleted on Feb 24, 2007 14:01:10 GMT -8
Yea I know, about the variac , I mean. I am currently lookin at some 120 AC 15 to 25 amp AC motor speed controllers. They are basically a soupped up dimmer switch for inductive loads. Their are some good ones out there. Maybe I can get you to design and build me one for this project? Here is one in particular that shows promise. www.heatersplus.com/18tbp.htm This is for restrictive loads like I guess heaters and electrolizers. Says it can be used to replace variac transformers.But it is pretty costly, tho I bet you could build one better than that ........LOL
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Post by Gary Lecomte on Feb 24, 2007 14:42:10 GMT -8
A Variac Actually Changes the Voltage Out.
A Dimmer of Any type Does Not.
A Normal Dimmer uses an SCR to control the output. (Single Direction Control)
This Control your talking about uses a Triac. Bi- Directional Control)
BUT Both these devices Do Not actually Control the Voltage Out. Basically they control Phase.
A Variac is MUCH Better.
Yes I could build one, But I'm not really interested in doing that. I Personally only use Variacs. They are MUCH Better. Especially so, For what your doing.
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