I have a 120 volt transformer with a 300 mA 12 secondary I put a diode and a cap as shown

The solder melts off the cap as soon as i power it up

 

The solder melts off the cap as soon as i power it up

Wow. Do you mean the soldered connections to the cap or "solder" coming out of the cap?

It sounds like the cap is installed in reversed polarity. But, I would think the cap would explode way before any solder flows.

The only experience I have even similar to this was with computer grade caps (the ones with screw terminals) mounted onto a PCB. Once the caps were mounted you could no longer see the polarity marking which was only on the top of the cap.

One test technician would look at some power resistors that were in series with the caps. If they were glowing a dull red then a cap was in backwards. Surprisingly, I never heard of of one exploding.


p.s. The solution to this problem was drawing a polarity stripe along the side of the cap before bolting it to the board.


p.p.s. I just remembered that I _have_ seen power resistors melt the solder causing them to open the connection to the PCB.

 

A transformer rated for a third of a watt melts solder?
Odd. I need about a hundred times that much power for a small soldering iron.
You're doing something wrong.

 

A transformer rated for a third of a watt melts solder?
Odd. I need about a hundred times that much power for a small soldering iron.
You're doing something wrong.

I calculate about 4 watts. I have some small soldering irons at that low wattage. But... I doubt that they could deliver a high enough temperature into a cap to cause solder melting.

Definitely an enigma. I expect to learn something new when the solution is revealed.

 

I'm stumped forreal here I tried 2 caps 1000 uf and 100 volt rating the solder melts off at the point where I soldered it to the diode.
The output is 19 volts AC unloaded I used a bridge at first no problems but the voltage was too high for the regulator so I figured what the heck
I'll use a half wave and I big cap but without nothing but a diode and cap and 100 ma load resistor it get's hot.

Fast I never had this happen before.

It's just like the circuit I posted I've made a few of these there the supply for the relay then after the relay I add 2 10uf and regulator I always test the relay power before add the rest I tested as shown

 

Could this be the problem I looked up the number on the diode there Transient Voltage Suppressor diode I thought I was in the right cookie jar.

Guess there some more stuff to throw out I can't see good to read numbers anymore.
I try to keep stuff where I no what I have well I didn't no I had these I guess there the problem. I thought I had some 1N4003 I have 1N6274A

 

I can't see good to read numbers anymore.

I buy drugstore (3.5 diopter) cheaters @ $12 for a 3 pack and a few sets of (3) jewelers loupes, 2x, 5x, and 10x.
I only use the 10x but I keep one in the shop, one in the truck, and one in the shed.
Many a part number has tried to sneak past me, but they can't sneak past a jewelers loupe.

 

I was just thinking it was likely an issue with the diode when I read #6.

I know what you mean about not being able to see to read part numbers. I used to be very near sighted & could read really tiny stuff. Then I lost a lot of my accommodation but got by quite well with bifocals. Then I had my meat lenses ultrasonically liquefied and sucked out & replaced with plastic & now I have NO near vision. With the right glasses I can read fine print as long as it positioned within a millimetre or two of the right distance. I don't do electronics at all any more.

I've blowed up some caps. Blowed 'em up real good! I blew up one about about 35 x 70 mm. It was like firing a shotgun in my lab. Spoils one's concentration for a bit.
I had a big computer grade, probably about 3/4 of a litre, pee its electrolyte all over the floor under a mag tape drive. No serious consequences, fortunately. I never determined why it failed or had a failure in the replacement. I've seen large film capacitors blown in two by lightning strike.
My "favorite" was a cap blown up by a client, because they didn't do what I carefully told them to. It was about 35 x 60 mm, and blew from overvoltage. When you looked at the circuit board around it, you could tell from what direction the blast had come because there were little bits of the spacer paper from the cap winding stuck all over the other components. Sometimes idiot clients do have amusement value.

 

Has anyone here ever seen clip-on auxiliary lenses for glasses that can be flipped up like some clip-on sunglasses? I've often thought they might be quite useful. I have a flip-up headset magnifier, but it is kind of big and clunky.
I sometimes resort to two pairs of glasses. Looks bloody strange but works quite well.

 

The output is 19 volts AC unloaded I used a bridge at first no problems but the voltage was too high for the regulator so I figured what the heck
I'll use a half wave and I big cap but without nothing but a diode and cap and 100 ma load resistor it get's hot.

Pardon me but doesn't a full wave rectifier drop more voltage than a single diode?

And what's the time frame at which the solder melts? If it's nearly instantaneously then it's far more than a few watts of power. If it takes five minutes - yeah, I could see that being sufficient time to heat a low temp solder such as tin/lead. Silver solder takes a higher temperature (lead free solder). They even make a "High Temp" solder for harsh environments. But why your solder goes molten at all with that low power - either your wires going to the cap are very small gauge or you're getting more current in the system than you're aware of. From your diagram I don't see how that could happen. So what would happen if you just put a quarter watt resistor in the circuit? What would happen if you put a half watt; or a full watt - or a 5 watt resistor?

Maybe you've tapped into the force. Using it you are, beyond the caps ability I think.

 

Has anyone here ever seen clip-on auxiliary lenses for glasses that can be flipped up like some clip-on sunglasses? I've often thought they might be quite useful. I have a flip-up headset magnifier, but it is kind of big and clunky.
I sometimes resort to two pairs of glasses. Looks bloody strange but works quite well.

I used to have one of those side clipped magnifiers. Held two lenses, one low power, one medium power. flip them both down and you get high power magnification. Maybe I'll see if I can find something like that on e-Bay or Amazon. They're very handy and they clip to one side of your glasses.

I've also admired my dentist's micro-binoculars. however, those things are damed expensive, and I can't justify the cost.

[edit] See! Ask and ye shall receive: https://www.ebay.com/itm/16-5X-Jewe...729207?hash=item211942cdb7:g:ZO8AAOSwn7JYDCn2

Here's one like what you describe: https://www.ebay.com/itm/Clip-on-Eye-Glasses-Binocular-Magnifier-Eyeglasses-With-1-5X-2-5X-3-5X-3-Lens-HW/122795117114?_trkparms=aid=555019&algo=PL.BANDIT&ao=1&asc=20150817211709&meid=c11d9f8b116f46dfaa7d43f24337d767&pid=100506&rk=1&rkt=1&&itm=122795117114&_trksid=p2045573.c100506.m3226

This one might help you "Geeter Done": https://www.ebay.com/itm/Carson-Optical-Visormag-Clip-On-Magnifying-Lens-For-Hats/112804199438?_trkparms=aid=555019&algo=PL.BANDIT&ao=1&asc=20170221125811&meid=ee56e00154ab44c1a68e9ee066c1de39&pid=100753&rk=1&rkt=1&&itm=112804199438&_trksid=p2045573.c100753.m4841

OK, now lets get back on topic.

 

Thanks Tony. The clip-on-flip-up isn't quite what I envisioned, but it's certainly worth a try.

I seriously considered the micro binoculars in the past, but since I've packed in doing electronics, I'll probably never acquire any. My fixed-focus eyes would still be an issue, but the working distance of those things is a great boon.

 

Pardon me but doesn't a full wave rectifier drop more voltage than a single diode?

Nope you only get half Of the AC with one diode with the bridge you get both.
The problem here was I thought I had a diode that blocked 100 volts I had one that only blocked 10 or so maybe less. Have to read up on this been a long time. But from what I remember the diode has to be able to block haft the output AC the thing I had was made to stunt it to ground fast before the rest of stuff got hurt.

Haft wave it's 8.98 volts
Bridge it's 17.86 volts

Oh and I guess I should dig the transformer out of the trash LOL

 

Looking at your diagram; I see a capacitor (assumably its voltage at startup is zero volts) and a diode. 12 volts with no resistance other than that of the ESR of the capacitor, which may be rather low, with the forward voltage of the diode, assuming 12 VAC RMS, the output of which should be 12 x 1.414, = 16.968 VDC pulsed, (assuming no resistance we'd assume infinite current. Well, in a real world - - - . So what is the ESR of your capacitor? Typically, at 16 VDC a 1000 µF cap would be 0.16Ω. At those values, (assuming an infinite wattage from your transformer) 100 amps (1600 watts). I'm sure your diode can't handle that much current, nor can your transformer likely put out that kind of power. So there MUST be some serious voltage drop going on due to excessive loading (at startup). Once the cap is charged the ESR goes way up. But its initial startup current (theoretically speaking) will be 100 amps. However, that shouldn't last more than a few dozen milliseconds at most. Oh, wait - I forgot the Vf. OK, at 15.3 VDC is 95.6 amps.

If your solder is still melting - something is presumably not correct in your setup.

 

Nope you only get half Of the AC with one diode

Yes, that's true. So I suppose my numbers are a bit extreme. But still, half of 95 amps is still a lot of amperage at startup. Again, assuming infinite capabilities of your transformer. How many amps is your transformer capable of? Do you know that info?

[edit] half the voltage? No - wait! isn't it 12 volts peak? Not peak to peak? Awe geez. Now you got my head spinning. Think I'll go shovel some snow.

 

I just told you what happen the diode I use was not a diode for What I needed.

Now the transformer is 300 ma at 12.6 volts the diode should of blocked haft of the AC

With nothing hooked Up but the diode You get 8.98 volts hook the cap to that and You get lots of heat LOL

From What I understand the Transient Voltage Suppressor diode passes any voltage above it cutoff to ground

Where as the 1N4003 will block one haft up to a 100 volts

So the cap became a big load and I did't stick my dvm to see what voltage I was at with the cap the solder was dripping on my table LOL

 

Well, honestly, I'm at a loss to offer any other ideas. Good luck.

 

It was the Transient Voltage Suppressor I thought I had a 1n4003 the suppressor looks like a diode it don't act like one tho
I just never seen the solder melt off the wires going to a cap like that before. I've made 100's of these

I'm not being hard here #12 had it nailed on the head there something wrong I got one of them and installed it for a diode.

I'm using them in this to get the 12 volts for the relay and then dropping it down for the esp
But that one went crazy on me Lol

 

It was the Transient Voltage Suppressor I thought I had a 1n4003 the suppressor looks like a diode it don't act like one tho
I just never seen the solder melt off the wires going to a cap like that before. I've made 100's of these

I'm not being hard here #12 had it nailed on the head there something wrong I got one of them and installed it for a diode.

I'm using them in this to get the 12 volts for the relay and then dropping it down for the esp
But that one went crazy on me Lol

The current rating of a transformer is based on the acceptable temperature rise, not on the maximum current that it can deliver. So if it is good for 0.3 amps at a 100% duty cycle it is probably able to deliver a lot more current for a few seconds. THAT would explain the solder melting. And then having the wrong kind of diode would explain why the excessive current. I use a good magnifier because most part numbers are way to small for me to read any other way. Verification is often VITAL.

 

The suppressor diodes I am familiar with act like Zener diodes. Some suppressor diodes are like two Zeners in series so they can work on ac instead of DC voltages.

Zeners and suppressors are specified differently so I am not sure of all of the differences. I have, on occasion, used a suppressor diode in place of a Zener but never the other way around.


For magnification, I use an Optivisor. I don't know what power lenses are installed. They are pricey but have good lenses and flip up and down. Up for looking at the scope and down for looking at the circuit.


When I do surface mount I use a stereo microscope having both 10 and 20 power.