DC PSU weirdness

  • Thread starter jamesson
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  • #1
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[warning: wall power issues ahead]

I had a friend send me an LED strip with a USA wall ac to 12v dc PSU, so I slapped a 3-pin wall cable on it and spliced a toggle button into it. Everything works fine buuuut...

If I put my finger here (assuming it's a resistor?)
resistor_a.JPG

I get some current, like so, even when the toggle's off

thumb.JPG



Either the toggle's crappy or I screwed up my solder work somehow (and I don't see how). Do I have a fire and/or shock hazard?

For sake of completeness, pics of solder work are below. Of course, critique of solder work is welcome and appreciated. The only thing I can't do is open up the toggle switch casing because it has some weird tamper proof screws.

joint_a.jpg one_tinned_a.jpg splice_a.jpg two_tinned_a.jpg
 

Answers and Replies

  • #2
phinds
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From what I can see of your totally out-of-focus pics of raw solder applications, they all look really bad ... as though not enough heat were applied so the solder didn't flow properly.
 
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  • #3
Twigg
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I'm going to second the above and say that solder technique could use a little work. But that wouldn't cause the issues you're seeing.

Do I have a fire and/or shock hazard?
Probably yes.

There's probably a loose copper trace in the strip that's moving around and touching the resistor's solder pad when you press on it.

What makes you think the toggle cause this problem on the strip? Didn't you put the toggle on the mains power cable?
 
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  • #4
DaveE
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not enough heat were applied so the solder didn't flow properly.
Yup. A "cold" solder joint. Although that's probably not your current leakage problem.

The right way to solder is to first align and hold the wires together so they won't move.
Then heat both wires together ( adding a bit of solder early can help with heat flow).
AFTER they are hot you add the solder and let it flow throughout the joint.
Then remove the heat and don't disturb it for a few seconds as it cools.

Good Mil/Industry practice would be to not splice wires this way without additional mechanical support (like a crimp connection, or heat shrink tubing & cable ties, for example). But you may not care about that.

You will want to make sure that you are putting the switch in the hot side, not the neutral side, assuming you are switching the AC HV side. If you don't know what this means, then you shouldn't be doing this sort of work without studying a bit more. Or, switch the low voltage DC side of the PS instead.

We aren't going to be able to tell you if you put the switch in the correct place without detailed documentation. Your pictures only show a solder joint, basically. I suspect the problem is more about the schematic or components. There are several ways to do this wrong, and we are not clairvoyant.

Finally, you ask if you have a fire/shock hazard. This appears to be a simple modification. If you don't already know (for sure) that it's been done safely, then my assumption is that it might not be safe. Never, ever, ever would I tell someone they've done this right without a complete description of what they actually did.

edit: I should add: How do you know if the wires are hot enough? You melt the solder by touching it to the wires, not the soldering iron. Your wires need to be hot enough to melt the solder you add. The soldering iron's job isn't just to melt solder, it's to heat the items you want to solder enough so that they can melt solder with out touching it to the iron.
 
Last edited:
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  • #5
Tom.G
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Here in the US, the wall power outlets have 3 holes.
  • The round one is Earth or Safety Ground.
  • Of the two slots, the wider one is the 'Low' side of the power connection. It is eventually connected to Ground at the power transormer on the pole and at the fuse/circuit-breaker box.
  • The smaller slot is the "Hot' or High' side of the supply. It has the line voltage connected to it, 120V here in the US.

A likely suspect to the action you are seeing is that the added switch is in the 'Low' side of the power connection. This leaves the 'High' side connected to your circuit even when the switch is Off.

When you touch the LED strip you are adding some capacitance from that point to everything else in your surroundings. Your body acts as one plate of a small valued capacitor (old term: condenser) to every conductor (including the Earth itself) that is within several feet of you. This allows a tiny amount of current to flow thru the LEDs and you, consequently the LEDs light up.

The safest way to cure this is to use a switch that opens both of the wires delivering wall power. This is called a Double Pole switch and has four terminals on it, two for the incoming power and two for whatever you are controlling.

In this image, the power line would connect to the terminals on one side and the device to control connects to the terminals on the other side. The dotted line shows that there is a mechanical connection between the two poles so that they operate at the same time.
--
DPST Switch.png

--
Hope this helps!

Cheers,
Tom

[EDIT] After looking at your photos, I see you are using a 3-wire power cord. The color coding is:
Green = Earth Ground, round pin
White = 'Low' side of incoming power, wide pin
Black = 'Hot' side of incoming power, narrow pin

If that is a manufactured cable with the plug already attached, it will be wired that way. If you wired the cable to a plug, make sure the wiring matches this description. Your existing switch should be in the Black wire.

By the way, your soldering job looks good to me, being out of focus it's just a little hard to inspect.

[2nd EDIT] Try this method for a neat inline splice, it's called a 'linesman splice'
--
Lines man splice.png

--
 
Last edited:
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  • #6
Baluncore
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How many modules are connected to the toggle switch?

That strip comes as parallel ±12V supply lines, running either side of modules having three LEDs and one current limiting resistor in series.
If when you touch that resistor, only one module of three LEDs is effected, then one of the conductors in that module has a break or a bad solder joint. Check and repair the solder joint, probably on the resistor.
The strip can be cut through the two bare copper patches, so you can cut out an unreliable module, and solder the two ends together using two thin wire links.

If modules on only one side are effected, then there is a break in one of the two parallel supply lines near that resistor.
 
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  • #7
Baluncore
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If the toggle switch does not turn on the LEDs, and if three LEDs only glow dimly when you touch the resistor, then you may have AC pickup through your body to the module. That is a worry because it means there is some live AC on the 12V DC supply rails. Maybe your DC supply is not isolated from the AC supply.

We need a more complete description of the fault condition.
 
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  • #8
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Thanks so much for the replies everyone. Since the consensus seems to be that the joints are bad, I'm going to redo them in the next few days and post new pics.

Thanks again

Joe
 
  • #9
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What makes you think the toggle cause this problem on the strip? Didn't you put the toggle on the mains power cable?
I think the toggle is the problem because, other than trimming for length, I made no changes to the strip whatsoever. And it's a solid state device with no moving parts.
 
  • #10
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If the toggle switch does not turn on the LEDs, and if three LEDs only glow dimly when you touch the resistor, then you may have AC pickup through your body to the module. That is a worry because it means there is some live AC on the 12V DC supply rails. Maybe your DC supply is not isolated from the AC supply.

We need a more complete description of the fault condition.

No, the toggle _does_ turn on the leds. Your theory seems sound because the construction of the supply is super crappy.
 
  • #11
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Could you please upload some pictures about that PSU and that how it is connected (to the LED strip, to the switch and so)?
 
  • #12
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Could you please upload some pictures about that PSU and that how it is connected (to the LED strip, to the switch and so)?

Here's the PSU terminal block. Green black and white cables are AC wall power, red and black are DC out (led strip). The label's buried, I don't want to disassemble it until I decide how I'm going to rewire the whole mess in a couple of days. The picture with the 5 wires in the first post shows how the switch is spliced in.
terminal_a.jpg
 
  • #13
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I see.

Some such PSUs has a symmetrized EMI filter on the input side, like here on the first page.
If by any reason the protective earth is not present or not good enough or has some localized issues, then such filter will generate a half-line voltage lingering around on device chassis. It's through high impedance so it's not dangerous, but it might be enough to light up some LEDs or create small sparks or prickle you.

This matter might involve the local safety code so at some point you might need to contact a qualified expert.
Or, you can simply move to a double-insulated PSU instead. That's expected to solve the issue.
 
Last edited:
  • #14
berkeman
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so I slapped a 3-pin wall cable on it and spliced a toggle button into it. Everything works fine buuuut...
Even I would not splice a switch into the middle of an AC Mains power cord. If it's a 2-prong plug, you can get little inline switches at the hardware store that clip onto the cord and use insulation displacement connections -- they generally work well.

For 3-prong power cords, I use switches like this one. They are inexpensive and reliable:

https://www.google.com/search?q=ac+...hUKEwjW9OzfhdrsAhVIGzQIHe9sAQ4Q_AUoAXoECAEQAQ

1603983089105.png
 
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  • #15
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Here in the US, the wall power outlets have 3 holes.
  • The round one is Earth or Safety Ground.
  • Of the two slots, the wider one is the 'Low' side of the power connection. It is eventually connected to Ground at the power transormer on the pole and at the fuse/circuit-breaker box.
  • The smaller slot is the "Hot' or High' side of the supply. It has the line voltage connected to it, 120V here in the US.

A likely suspect to the action you are seeing is that the added switch is in the 'Low' side of the power connection. This leaves the 'High' side connected to your circuit even when the switch is Off.

When you touch the LED strip you are adding some capacitance from that point to everything else in your surroundings. Your body acts as one plate of a small valued capacitor (old term: condenser) to every conductor (including the Earth itself) that is within several feet of you. This allows a tiny amount of current to flow thru the LEDs and you, consequently the LEDs light up.

The safest way to cure this is to use a switch that opens both of the wires delivering wall power. This is called a Double Pole switch and has four terminals on it, two for the incoming power and two for whatever you are controlling.

In this image, the power line would connect to the terminals on one side and the device to control connects to the terminals on the other side. The dotted line shows that there is a mechanical connection between the two poles so that they operate at the same time.
--
View attachment 271772
--
Hope this helps!

Cheers,
Tom

[EDIT] After looking at your photos, I see you are using a 3-wire power cord. The color coding is:
Green = Earth Ground, round pin
White = 'Low' side of incoming power, wide pin
Black = 'Hot' side of incoming power, narrow pin

If that is a manufactured cable with the plug already attached, it will be wired that way. If you wired the cable to a plug, make sure the wiring matches this description. Your existing switch should be in the Black wire.
Here in the US, the wall power outlets have 3 holes.
  • The round one is Earth or Safety Ground.
  • Of the two slots, the wider one is the 'Low' side of the power connection. It is eventually connected to Ground at the power transormer on the pole and at the fuse/circuit-breaker box.
  • The smaller slot is the "Hot' or High' side of the supply. It has the line voltage connected to it, 120V here in the US.

A likely suspect to the action you are seeing is that the added switch is in the 'Low' side of the power connection. This leaves the 'High' side connected to your circuit even when the switch is Off.

When you touch the LED strip you are adding some capacitance from that point to everything else in your surroundings. Your body acts as one plate of a small valued capacitor (old term: condenser) to every conductor (including the Earth itself) that is within several feet of you. This allows a tiny amount of current to flow thru the LEDs and you, consequently the LEDs light up.

The safest way to cure this is to use a switch that opens both of the wires delivering wall power. This is called a Double Pole switch and has four terminals on it, two for the incoming power and two for whatever you are controlling.

In this image, the power line would connect to the terminals on one side and the device to control connects to the terminals on the other side. The dotted line shows that there is a mechanical connection between the two poles so that they operate at the same time.
--
View attachment 271772
--
Hope this helps!

Cheers,
Tom

[EDIT] After looking at your photos, I see you are using a 3-wire power cord. The color coding is:
Green = Earth Ground, round pin
White = 'Low' side of incoming power, wide pin
Black = 'Hot' side of incoming power, narrow pin

If that is a manufactured cable with the plug already attached, it will be wired that way. If you wired the cable to a plug, make sure the wiring matches this description. Your existing switch should be in the Black wire.

By the way, your soldering job looks good to me, being out of focus it's just a little hard to inspect.

[2nd EDIT] Try this method for a neat inline splice, it's called a 'linesman splice'
--
View attachment 271773
--

[2nd EDIT] Try this method for a neat inline splice, it's called a 'linesman splice'
--
View attachment 271773
--

I
Even I would not splice a switch into the middle of an AC Mains power cord. If it's a 2-prong plug, you can get little inline switches at the hardware store that clip onto the cord and use insulation displacement connections -- they generally work well.

For 3-prong power cords, I use switches like this one. They are inexpensive and reliable:

https://www.google.com/search?q=ac+...hUKEwjW9OzfhdrsAhVIGzQIHe9sAQ4Q_AUoAXoECAEQAQ

View attachment 271795

I would have gone this route, but I'm semi trying to do this for a living and I didn't really have any pictures of my solderwork. I may rethink that.
 
  • #16
berkeman
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I'm semi trying to do this for a living
To do what for a living? Soldering or splicing switches into the middle of AC Line cords? Hopefully the former and not the latter.

If you are wanting to improve your soldering, what are you using for your soldering equipment? The gold standard AFAIK is the Metcal line of solder stations. They use RF heating and sensing of the soldering tip(s), which helps you to deliver a wide range of power to the workpieces.

1603989232908.png
 
  • #17
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3
To do what for a living? Soldering or splicing switches into the middle of AC Line cords? Hopefully the former and not the latter.

If you are wanting to improve your soldering, what are you using for your soldering equipment? The gold standard AFAIK is the Metcal line of solder stations. They use RF heating and sensing of the soldering tip(s), which helps you to deliver a wide range of power to the workpieces.

View attachment 271802

I've never actually heard of this brand (I've been on Weller as far back as I can remember) and I thank you for the reference. I'm coming into some decent cash very shortly and I'll be looking to build a full bench. However, I'm trying to strike a balance between the "gold standard" as you call it and the kind of thing I'll expect to find on a job site. On the one hand, some things will still be out of my price range. On the other hand, I think building some things from scratch/parts is a good test of my skills. I'll be posting a separate question(s) regarding assembling a bench in the next few days.

For this project, I'm on a pot-regulated loaner iron. I think it's reasonable for me to achieve some minimally respectable results with it before I go buying anything else.
 
  • #18
berkeman
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You will probably mention this in the new thread about assembling your new soldering workbench, but what kinds of things are you planning on soldering? If you will be soldering a range of sizes of components (from wires and switches to through-hole components to SMT parts), then an RF regulated iron is pretty much needed, IMO. And if you will be doing fine-pitch SMT parts, you should look at getting an inexpensive binocular microscope -- they are pretty standard for industry rework solder stations.
 
  • #19
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You will probably mention this in the new thread about assembling your new soldering workbench, but what kinds of things are you planning on soldering? If you will be soldering a range of sizes of components (from wires and switches to through-hole components to SMT parts), then an RF regulated iron is pretty much needed, IMO. And if you will be doing fine-pitch SMT parts, you should look at getting an inexpensive binocular microscope -- they are pretty standard for industry rework solder stations.

Yeah, it'll all be covered there. Like I said, I have a decent budget, but not an amazing one, and my strategic policy has always been to get as good as I can get with suboptimal tools before buying the blue chip stuff.
 
  • #20
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You will probably mention this in the new thread about assembling your new soldering workbench, but what kinds of things are you planning on soldering? If you will be soldering a range of sizes of components (from wires and switches to through-hole components to SMT parts), then an RF regulated iron is pretty much needed, IMO. And if you will be doing fine-pitch SMT parts, you should look at getting an inexpensive binocular microscope -- they are pretty standard for industry rework solder stations.
To give you a better idea, the kinds of prices Metcal seems to charge are reeeeeally pushing it. Like, I might be argued into it but it's a hard sell.
 
  • #21
berkeman
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To give you a better idea, the kinds of prices Metcal seems to charge is are reeeeeally pushing it. Like, I might be argued into it but it's a hard sell.
That's why I posted one of the least expensive ones. :wink:

Honestly, though, once you've used one, you never want to go back to a simple iron. They are amazing at putting down just the right amount of heat for big stuff and teenie little SMT joints. If you are only going to be soldering wires and big stuff, you can probably get away with a simple (and big) iron. The adjustable ones can be a good intermediate choice, if you get used to the adjustments you need to make for different size workpieces.
 
  • #22
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That's why I posted one of the least expensive ones. :wink:

Honestly, though, once you've used one, you never want to go back to a simple iron. They are amazing at putting down just the right amount of heat for big stuff and teenie little SMT joints. If you are only going to be soldering wires and big stuff, you can probably get away with a simple (and big) iron. The adjustable ones can be a good intermediate choice, if you get used to the adjustments you need to make for different size workpieces.
I'll probably decide to start with the chunkier stuff and buy something for detail work later. Besides, I think it's a good opportunity to build a PID regulated thermal system.
 
  • #23
Twigg
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Is it just me or does that PSU look like overkill? How many feet long is that LED strip and how many watts is that PSU good for? If you can get away with a wall wart it will make this project much simpler (and significantly cheaper / more profitable). If you're going to do projects like this for a living, not having to mess around with AC power cables will reduce your costs and spare you a metric crudton of liability. Not saying you shouldn't learn, but knowing what you need is important too

I'm restraining myself from ranting about tools here and waiting for your new workbench thread :nb)
 
  • #24
58
3
Is it just me or does that PSU look like overkill? How many feet long is that LED strip and how many watts is that PSU good for? If you can get away with a wall wart it will make this project much simpler (and significantly cheaper / more profitable). If you're going to do projects like this for a living, not having to mess around with AC power cables will reduce your costs and spare you a metric crudton of liability. Not saying you shouldn't learn, but knowing what you need is important too

I'm restraining myself from ranting about tools here and waiting for your new workbench thread :nb)

No, the LED strip is rated for 12v, I checked - it's super bright, I had to cover it to keep from frying my eyeballs. Although, running it at a lower voltage may be worth a shot.
 
  • #25
Twigg
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No, the LED strip is rated for 12v, I checked - it's super bright, I had to cover it to keep from frying my eyeballs. Although, running it at a lower voltage may be worth a shot.
No don't do that. Typing my full reply up now.

Edit:
I'm asking you about the power the strip consumes, not the voltage. The strip takes 12V, but how many watts? If it doesn't say the watts anywhere, does it indicate the amps? If you don't know, try seeing if the LED strip has a part number and googling it. The manufacturer absolutely should provide this information in their specs. Usually they give a spec that's watts per foot. Multiply that by the length of your strip and that gives you the total power consumption.

Edit edit:
If you want to dim the LEDs you need a PWM controller.
 
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