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Message |
    
James Webster
Registered
Username: Wti
Post Number: 20
Registered: 02-2007
| | Posted on Saturday, March 03, 2007 - 05:28 am: | 
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Total cost to build the 300VA power supply was:
AN-3225 transformer $33.50
two 5600uf 100v caps $10.00 ($5 each)
USPS priority shipping $11.35
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subtotal $54.85
All of the above came from http://www.toroid-transformer.com/
They shipped the next day
I already had a rectifier KBPC2502($1.75) and four-way fuse block 43-214($3.49) from http://www.hosfeltelectronics.com/ where shipping on a whole box of junk was $7.00 . |
James Webster
Registered
Username: Wti
Post Number: 26
Registered: 02-2007
| | Posted on Wednesday, March 07, 2007 - 11:53 am: |
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Here is the hookup guide to the AN-3225 based power supply for USA:
120V power comes in through the IEC Jack.
Neutral conductor connects to both black transformer wires
Hot conductor connects to one leg of circuit breaker.
Circuit breaker connects to both red transformer wires
AN-3225 transformer has two 25V AC output windings (refer to picture for letter codes)
(A) green conductor goes to ~ symbol on rectifier
(B) blue is connected to (C) green. This is the ONLY way you can get 50V AC, no other pair will work!
(D) blue connector goes to remaining ~ symbol on rectifier.
Rectifier has a chopped corner to mark the + output. If you really look hard the - is marked on opposite side. You now have 50V DC.
Two 5600uf 100V (uf is pronounced MICRO FARAD) capacitors are soldered together in PARALLEL (that means positive to positive, negative to negative). The + conductor from the rectifier runs across the positive terminals of the capacitors, the - conductor from the rectifier runs across the negative terminals of the capacitors.
At the end of these two conductors you measure 71V DC.
Notes:
1. If you mix up the B+C windings on the transformer, it will overheat and could start a fire, BE CAREFUL and get it right the 1st time.
2. The capacitors hold their charge even after the power is off. They can zap you even years later. A bleeder resistor could be added to drain them after power is cut.
3. The rectifier should be mounted to a metal plate to dissipate heat (it will last longer that way).
4. Be sure to use a fuse or circuit breaker.
USUAL DISCLAIMER: THIS STUFF IS DANGEROUS. I SUGGEST YOU DO NOT FOLLOW THESE DIRECTIONS AND JUST BUY A POWER SUPPLY. I CAN NOT BE RESPONSIBLE IF YOU DO NOT FOLLOW MY ABOVE ADVICE.  |
Gerald_D
Registered
Username: Gerald_d
Post Number: 1120
Registered: 11-2005
| | Posted on Wednesday, March 07, 2007 - 12:27 pm: |
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For some strange reason, the capacitor guys go to a lot of trouble to mark their negative (-) pole while most othey guys mark the positive (+) pole. Don't assume that the marked poles are all the positive ones. A reversed capacitor can explode. At minimum, turn your back to this power supply before switching it on. Or, be a wimp like me, and put it on the driveway with a 50' extension lead from the workbench and close the door on the lead before switching it on "remotely". (a blown cap makes a papery oily mess). Of course, keep pets and kids away.
A temporary bleed resistor across the output is highly recommended if the Gecko's are not there. 22K 1/4Watt or 11K 1/2Watt, etc., etc. Even with a resistor, check the residual voltage before touching the outputs to anything.
Mike then picked up on the bleed resistor and other issues - that discussion has been moved here. |
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Power Supplies