FrankenPower! Building a 12V Power Supply

[Boulder]

Hey Bob,

I think Brett had the problem I was afraid of, too much current for 20 or 22 gauge wire. When you double or triple the wires to the connection obviously you multiply the capacity of the circuit. This is why I decided to use all of the available 12V wires and triple them up from the start.

Of course, the capacitor idea would also work.

[Uncle Brett]

Thanks Bob for the tip
Kenny, I still have that problem if I power up the PS and then hook up a charger. I just make sure I have at least one charger hooked up before I turn on the PS, after that I can hook up more chargers if needed.

[Boulder]

Is it possible you skipped the addition of the sand resistor? Does your PS power up with nothing connected?

If the PS powers up and after you attach the first charger you get a low voltage reading, I can't help with that one, hadn't run into that.

[toprudder]

	Quote: Originally Posted by Boulder
	I think Brett had the problem I was afraid of, too much current for 20 or 22 gauge wire. When you double or triple the wires to the connection obviously you multiply the capacity of the circuit. This is why I decided to use all of the available 12V wires and triple them up from the start.

Sounds like different problems. The problem with the small wires is that the charger was indicating low input voltage, due to the voltage drop across the small wires under load. The problem Brett is having is that the power supply shuts down the instant he plugs in the first charger.

The fact that it works fine if one charger is plugged in before the PS is turned on, and continues to work if an additional charger is connected, leads me to believe the capacitor idea will work. Most electronics gadgets have a capacitor of some sort on the input to help filter the DC supply. This is probably where the inrush current is going when you plug in a single charger (to charge the cap) but when one charger is already plugged in, some of that inrush current will come from the cap that is already charged to 12v.

Some of these power supplies, if not most, will have some sort of protection circuit (crowbar) that will shut the supply down if the output voltage is wrong. This could be tripping when the first supply is plugged in.

If you do try adding a cap, make sure you get the polarity correct. Electrolytic caps have a nasty habit of popping if you reverse polarity. I prefer tantalum caps myself, they tend to flame.

Bob R.

[ShortBus]

I was thinking about making one of these for my new charger. Anything I need to know so I don't light up like a Christmas tree?

[Boulder]

	Quote: Originally Posted by toprudder
	Sounds like different problems. The problem with the small wires is that the charger was indicating low input voltage, due to the voltage drop across the small wires under load. The problem Brett is having is that the power supply shuts down the instant he plugs in the first charger. The fact that it works fine if one charger is plugged in before the PS is turned on, and continues to work if an additional charger is connected, leads me to believe the capacitor idea will work. Most electronics gadgets have a capacitor of some sort on the input to help filter the DC supply. This is probably where the inrush current is going when you plug in a single charger (to charge the cap) but when one charger is already plugged in, some of that inrush current will come from the cap that is already charged to 12v. Some of these power supplies, if not most, will have some sort of protection circuit (crowbar) that will shut the supply down if the output voltage is wrong. This could be tripping when the first supply is plugged in. If you do try adding a cap, make sure you get the polarity correct. Electrolytic caps have a nasty habit of popping if you reverse polarity. I prefer tantalum caps myself, they tend to flame. Bob R.

Bob,

I must have misunderstood when Brett said one of his chargers was giving him a "low voltage warning". I took it to mean that the charger wasn't getting enough voltage from the PS.

[sweetpea]

Been thinking of getting one of these to go with my new Fromeco Cube

[ShortBus]

Just ordered all the stuff to make the same one you did the build on. Should be ready to go this weekend!

[Mike Bargman]

Good to Hear, Short! Now, go do your homework!

[ShortBus]

At the end you say to get rid of all the unwanted wires. By this do you mean just shorten them and leave them there?

Also...I had to get 2 sets of terminals. Should I stick to using 3 on the PS or should I add the 4th one?

Thanks

[Mike Bargman]

I just cut them down. I didn't de-solder them. I should have, but time was an issue that night.

[Uncle Brett]

Hey Shorty, I put 4 binding post's on mine but I only use 3. I think I'll change the 4th one to 5V. On the other 3, I used all of the 12v (yellow) wires split up so I have 3 wires to each post. The other remaining wires I cut down to about 2", then zip tied them together and threw a piece of electrical tape over the ends. Then I just tucked the whole thing inside the case when I put it back together.