Whats wrong with this freaking rectifier part II

[Noah]

As was the general consensus of this forum I traded my Variac autotransformer for a very expensive toroidal isolation transformer. I am now having the same problem as before. The circuit draws tons of current and resets my house breakers. The new transformer is wired in parallel for 40 VAC at 37.5 Amps. I checked the AC voltage off the leads to ensure I soldered up the transformer properly. I have checked out the connections on that lexan plate again and again and can't find any short circuits. Does any one know whats wrong now? Thanks

[Noah]

Pic 2

[ESjaavik]

Hi Noah,

Take this in steps.
1. Connect only the transformer primary. Make sure the secondary leads don't touch.
2. Connect secondary to the rectifier. The secondary fuses goes in between them.
3. Connect rectifier to the Capacitors. Make sure polarity is right. Measure volts if you have a meter.
4. Connect breakout board if you have that.
5. Connect the Geckos, one at a time. Leave them disconnected from the indexer/PC, but connected to the motors.
6. Then connect your vice. (Just joking).

During this, when your house breaker blows, the last component you connected is probably the one that is faulty or improperly connected. If this happens at any point other than 1. your secondary fuses have too high rating or your secondary fuse block is faulty. Make sure that the screws fastening the leads to it don't extend down and touch the metallic plate underneath.

If you use red for positive and black for negative, the right capacitor on your picture is connected the wrong way around.
And what's that box standing on it's side in front of the capacitors, I cannot read the label.

One thing very positive about your setup: You have securely fastened all the components and used shrink tube to extend the insulation over the terminals.

[arvidb]

Toroidals are known to have a huge inrush current at switch-on. If this thing is rated 40 VAC @ 37.5 A, thats 1500 VA. It's a big transformer!

You should probably use a soft-start circuit that limits the current when you turn it on. More info here: http://sound.westhost.com/project39.htm

Also, make sure you have parallelled the windings correctly. You say you measured the AC voltage across them, but this is not enough to make sure you have connected them correctly.

Try this:

Hook the secondary windings up in series. Measure the voltage across both. You will either get 40+40=80 VAC or 40-40=0 VAC. If you get 80 VAC, turn one winding around and make sure you now measure 0 VAC across the series connected windings. Connect the two leads together (the two between which you have 0 volts). The windings are now connected in parallel correctly.

Arvid

[ESjaavik]

Toroids are harder on the fuses, but this also depends on the windings. Norwegian practice is to wind it "hard". This makes it tougher on the fuses. But you can ask the winder do make it "softer". And what the common practice is in USA, I don't know. But Noah, call the supplier of your toroid. Give him the rating of your main fuses and ask him if there should be a problem. And of course check that you don't have other load(s) on these fuses that already have "eaten up" much of their capacity.

Oh, one other point: If your fuse blows in my point 3. above, try hooking up just one capacitor (Assuming they are in parallel, if they are in series because of low voltage rating, then don't leave out one). That will make the inrush current lower.

[balsaman]

Can you make a drawing of how it's all hooked up and post it?

Eric

[Noah]

Thanks for all the suggestions. I am going to try my hand at a couple of these today. In response to some of your questions....
Those two capacitors are supposed to be connected in parallel. Isn' that how they are connected? The box standing on end is a 15v DC-DC transformer for a fan that will be on top of the box. I think we can rule that out as the fan is not even connected. Also the transformer leads were the first thing I was going to test. The label reads as follows

Primaries: Black/ White Brown/Orange
Secondaries: Red/ Blue Gray/ Yellow

I took this to mean that white and black were one set of primaries and Brown and Orange was the other. To test before I connected anything I did a resistance check on the black and white leads and found them to be continuous. I think this procedure would have the same results as measuring voltage on the secondaries, just its a whole lot safer.

[Noah]

You also talked about transformers having a big start up. I know this is the case, but all I have connected is the geckos and those capacitors. Would this really draw >20 Amps of house current at start up? Usually the house breaker will not trip immediately, it takes a couple seconds. Also even after a couple seconds you can hear that buzz that occurs in transformers when large amounts of current are flowing. One thing I did notice is that the EIC power cords got really hot. These are 16 AWG wire wheras the cords on the plate are 12 AWG (pointless I know, but it looks cool right?). Is 16 AWG to small for this transformer?

[Noah]

Oh and one last thing. Maybe I was thinking poorly when doing this, but those fuses are rated at 20 Amps each. They are not connected after the rectifier, not before. Each gecko has its own fuse. My goal was to have these fuses blow when an axis stalled. Is there a problem with this? Thanks.

[Noah]

Now I see what you mean about the capacitor. Capacitors are bipolar though right? So long as thy are in parallel which they are, the circuit should work the same either way.

[ESjaavik]

Noah:
The capacitors are not bipolar! On one side you have a stripe with large "-" signs on them. That's the side of the negative terminal. My guess is you have the capacitors connected wrong polarity. The current then may have blown the rectifier. I don't know what the peak current capability is for the rectifier but probably much less than what a 37A toroid will deliver into a short. The only thing that does not look right with this theory is that your capacitors should then have left this world with a huge bang! But if the rectifier failed fast enough, it may have protected them from being subject to wrong polarity long enough to leave. My stepwise procedure will then fail at point 2.

If it does, I would check the caps using a current limited power supply before risking a new rectifier.

Move the fuses to be before the rectifier. Often the rectifier shorts out if overloaded. If it does, there should be a fuse protecting the transformer. Actually the fuse should be before the transformer too. If you do this, use slow-blow fuses.

If it takes a couple of seconds before the house fuse blows, it's not the inrush current. It lasts only for a fraction of a second. This is also the case with the charge current for the capacitors.

And you said you checked the voltage, so I didn't put that in. You'd better do that in point 1. as it seems to me you are not quite sure.

And please be sure the polarity of those caps are correct! They are big, so they will leave a dent in your wallet if connected wrong way. They may also cause a need for a new set of underwear. And of course dangerous too. They usually spit their internals out in the direction of the terminals. If they have a "Y" punched in the other end, this is so they will open in that direction too. Yours are secured, so the can won't leave the board.

If you want to know how I know, it's because I got a batch of bad caps (free) when I was younger, and had great fun blowing them off at safe distance using a long cable. BOOM!! :-)

[arvidb]

Electrolytic capacitors are usually NOT bipolar, and can explode spewing boiling/burning electrolytics all around if you are not careful. Always connect them correctly with regards to polarity, and never exceed their voltage rating.

"Primaries: Black/ White Brown/Orange
Secondaries: Red/ Blue Gray/ Yellow"

How did you connect the secondaries together? If you parallell them, you can do it two ways: Red+Gray/Blue+Yellow or Red+Yellow/Blue+Gray. One will work as expected, the other will produce a short circuit that will trip your house breakers for sure!

Arvid