Electrical Question

[Lead Head]

Right now I'm working on a "control" panel of sorts to hold my output switch, circuit breaker and in the future, fuses. Having some slight difficulties since my dad took most of the tools when he moved out

[Reloadron]

Originally Posted by Lead Head

Right now I'm working on a "control" panel of sorts to hold my output switch, circuit breaker and in the future, fuses. Having some slight difficulties since my dad took most of the tools when he moved out

Well that sort of sucks! Tell your dad you need to use some of the tools for your continuing education project. Let me know if there are any pices / parts I can help you with.

Ron

[oldman_gamer]

Originally Posted by Lead Head

Right now I'm working on a "control" panel of sorts to hold my output switch, circuit breaker and in the future, fuses. Having some slight difficulties since my dad took most of the tools when he moved out

I have household electrical parts..a small switchbox and other goodies.If there is anything you need or can use,let me know.Maybe you could post a picture of your idea,this would help me out on understanding more of what your building. I have some electrical tools that I have more than one of also.I have a multi-meter I tried to use but too complicated for me your welcome to it if you need it.
I will be out of town from the 30th - 4th down Atlantic City.I will check the posts often till then.

[screwballl]

as long as you aren't trying THIS then it should be fine

[Lead Head]

Well I got my control panel finished. Just has the output selector switch, and the circuit breaker. Will try to pick up a fuse ASAP. Future plans include redoing the thing, and making a full enclosure for the transformer, and maybe even add another transformer and use some voltage regulators for variable output DC

[Reloadron]

Originally Posted by Lead Head

Well I got my control panel finished. Just has the output selector switch, and the circuit breaker. Will try to pick up a fuse ASAP. Future plans include redoing the thing, and making a full enclosure for the transformer, and maybe even add another transformer and use some voltage regulators for variable output DC

Keep us up on how things go.

Ron

[Lead Head]

Well, cleaned things uptoday, mounted the rectifier on its own sink - then blew it again. I wanted to make sure the circuit breaker and everything was hooked up right, but I forgot that the rectifier blows almost instantly :-/

I think im going to pick up 3 this time, if I can find another heatsink, I will probably put two in parallel

[Reloadron]

Originally Posted by Lead Head

Well, cleaned things uptoday, mounted the rectifier on its own sink - then blew it again. I wanted to make sure the circuit breaker and everything was hooked up right, but I forgot that the rectifier blows almost instantly :-/

I think im going to pick up 3 this time, if I can find another heatsink, I will probably put two in parallel

You don't want to do that. Placing a pair of full wave bridges in parallel is not a good way to go.

Think about this a little. You are currently using a full wave bridge rectifier. If we draw things out as you propose it would look a little like this:



Each bridge basically contains 4 like silicon rectifiers. Each rectifier in the bridge has a forward voltage drop. Now even though they are by definition identical in reality they are not. This is no big deal in the bridge configuration as they are close enough in forward conduction characteristics.

Now if you place another bridge in parallel with the first bridge, looking at the drawing, you see each of the four rectifiers has a rectifier in parallel with it. Because no two are perfectly matched one will conduct a little sooner and a little harder than its counterpart. That one will also get a little warmer a little faster. The heat also now becomes a factor. As they heat up from doing a little more of the work, their forward current conduction changes. The problem begins to compound as a result of an inbalance.

This can be done but generally involves the addition of "ballast resistance" to the circuit. Very high current sub one ohm resistors. They serve to shunt the current and drop the excess voltage difference.

That is it in a nutshell.

The solution would be the use of a higher current rated bridge. If you have a 25 Amp bridge and want 50 Amps you would use a 50 Amp bridge.

You need to consider something else too. When you place a dead short accross your output for all purposes, despite fuses and line current and circuit breakers and all that wonderful stuff, the current is instaneous and for all purposes infinite. Like in bam right now but quicker.

That is what is toasting your bridges. Each diode has a single PN junction and it takes very little to punch the substrate of a silicon junction. Bam as in micro seconds. The junction is now a dead short.

This is a pretty good explenation of what is going on within your full wave bridge:

Rectifier circuits : DIODES AND RECTIFIERS

Bottom line is if you want to parallel bridges you can, but I think rather than toasting a single you will burn them up two at a time.

Ron

[Lead Head]

I figured something like that would stop me. I've learned about the differences in voltages causing stuff like that.

I've had diode bridges that have handled more current then they were rated for, for at least brief periods of time, but these bridges seem more finicky then others I've used before. Also could be that those diodes were pushing maybe like 4-5 amps, when they were rated for 2-3, instead of 120 amps when they are rated for 25 :-P

Sometimes I forget exactly how much current this thing can push *accidentally* welded two pennies together earlier, and vaporized some sewing needles. But I was demonstrating its capability to a friend

[Reloadron]

Originally Posted by Lead Head

I figured something like that would stop me. I've learned about the differences in voltages causing stuff like that.

I've had diode bridges that have handled more current then they were rated for, for at least brief periods of time, but these bridges seem more finicky then others I've used before. Also could be that those diodes were pushing maybe like 4-5 amps, when they were rated for 2-3, instead of 120 amps when they are rated for 25 :-P

Sometimes I forget exactly how much current this thing can push *accidentally* welded two pennies together earlier, and vaporized some sewing needles. But I was demonstrating its capability to a friend

Welding pennies can be interesting. Depending on what you want to do with this thing, you may want to look at a higher rated bridge. I mean other than making some hydrogen, like if you want an all around DC power supply? Then work from there.

When I was young one of my transformer projects was messing with a 15 KV neon light transformer, 15 KV but only 30 mA. Built a few Tesla coil projects using that damn thing.

Again, be careful!

Ron