I respectfully disagree. What you said would be true IF your PS was a constant current device. With a CC device you get varying voltages designed to maintain the current. Cell phone chargers are not CC, they're CV (Constant Voltage). If the rated output current is exceeded the voltage WILL drop. But since the TS wants to drive some LED's at less than 30mA, a cell phone charger should be well equipped to handle that load.

Sorry. The "load resistor" I'm talking about came up in post #2, where is it said a load resistor rated at 2 or 3 watts must be placed across the wall wart output so that it will apply the nameplate voltage. This is true for non-regulated power supplies consisting of a line frequency transformer, bridge rectifier and smoothing capacitor. It is not true for most modern day switching power supplies commonly used to power most everything electronic.

A switching power supply does not need a "load resistor" as described in post #2 to supply the rated voltage; most of them are well regulated and it's rare to find one that's not.

The "load resistor" to which I referred is quite apart from the series current-limiting resistor REQUIRED when using an LED from a constant voltage source. Sorry for the confusion, but I would not call the series resistor a load resistor.

 

That's a cable. A charger has a voltage regulator in it:
View attachment 272802

If you strip down the USB cord on the non USB end, exposing the red and black wires, and test them, its 5v and that's a thing of beauty.

The wires are frayed....any tricks to binding them up? I am using a breadboard with binding posts, with very limited success.

 

Sorry. The "load resistor" I'm talking about came up in post #2, where is it said a load resistor rated at 2 or 3 watts must be placed across the wall wart output so that it will apply the nameplate voltage. This is true for non-regulated power supplies consisting of a line frequency transformer, bridge rectifier and smoothing capacitor. It is not true for most modern day switching power supplies commonly used to power most everything electronic.

A switching power supply does not need a "load resistor" as described in post #2 to supply the rated voltage; most of them are well regulated and it's rare to find one that's not.

The "load resistor" to which I referred is quite apart from the series current-limiting resistor REQUIRED when using an LED from a constant voltage source. Sorry for the confusion, but I would not call the series resistor a load resistor.

On the topic of power supplies, I've started looking at 5V wall charger. My question is two fold: (1) the output (in ma) of the wall wart is used only by what the circuit needs or "draws from" (2) if I have a 100ma circuit what difference does it make if that current coverage is by a 5v Wall wart at 500ma or a 5v wall wart at 1.5A?

 

As several people have already said, a circuit will only draw the current it needs.

Consider plugging a light bulb into an outlet. You can plug a nightlight that draws 4 watts into an outlet. The same outlet can power a 60 watt bulb or a 100 watt bulb without a problem and without somehow adjusting something.

In fact, that same outlet can supply up to 1800 watts (US 15 amp circuit) or even 2400 watts (20 amp circuit). But plug in something that draws 3000 watts or a fork across the outlet, and the circuit breaker or fuse will blow.

A switching DC supply works the same way, only supplying the current needed.* Shorting or overloading a switching DC supply will usually be a little different (over the short term). They (mostly) just respond by reducing the output voltage and thus current is reduced. Disconnect the short, and they'll do their thing again.


* This discussion concerns constant voltage power supplies. Constant current supplies are a separate topic for somewhat specialized applications. Discussing them here only confuses the issue.

 

The wires are frayed....any tricks to binding them up?

Do you mean stranded? You can twist and tin them, or solder the wires to 0.025" square male header pins, or attach male DuPont-style male crimp pins.

 

Do you mean stranded? You can twist and tin them, or solder the wires to 0.025" square male header pins, or attach male DuPont-style male crimp pins.

Thanks, sorry for being a bit vague. Thanks for that info. I was also able to find USB cords with one end's 4 wires already exposed and made into female jumpers each -- red, black, white and green. My understanding is the white and green are data. Ive got the male pins already to breadboard.

 

I'm not exactly understanding what you're trying to do. It appears you have an LED and resistors in series to power.

A DC power supply has positive and negative (or common) connections. If you have a power supply like this picture (available cheaply at thrift stores), you can cut off the barrel plug, strip back the insulation and you'll find either 2 wires with separate insulation or a center wire with a layer of wire wrapped around it. One of these wires is positive, the other negative but the color of the wires may be meaningless.

View attachment 272847


A USB power supply usually has a USB A connector.

View attachment 272848

You'll need a USB cable to use on of these. Presuming your breadboard doesn't have provision to plug in a USB cable, you'll have to cut off the 'wrong' end of the cable. You'll find 4 or 5 conductors in the USB cable. With a little luck, there will be red and black conductors, often heavier than the other conductors, along with green and wires. The red and black are probably power, with green and white being data. But again, there is no guarantee and colors may be different or even switched.

View attachment 272852

I ordered some USB cables with the black and red wires attached to some female jumpers better suited for the for the breadboard than the frayed ends I was dealing with. I checked it out - 5V. As for the current supply I have a barrel plug receptacle that seems to work well with a 15v wallwart. This was the issue b/c someone not in the forum remarked that it had dangerous current. Hence the discussion about which wall wart to use. You guys cleared up the issues -- appreciate that.

 

Here's a video I did on parallel LED's. Not germane to the topic of this thread. But the point I'm making HERE (not in the video) is that my rig was drawing 45mA even though the wall wart (not shown) was capable of providing 1000mA (1A). As for the wires going into my breadboard, they are stranded wires that were tinned with solder. Enough tinning to keep the wires together and straight, and strong enough to be pushed into the breadboard.

As has been explained by others, if you have a supply that is capable of providing a million amps and you put something that only draws half an amp then that's all the current that will flow, regardless of the size of the supply. Conversely, if you have a supply capable of providing 100mA and you try to use it to power something that draws1000mA, it's not going to work because the supply is too small for the job. Kind of like fighting a forest fire with a garden hose. Sure, you get water out of the end but it's not capable of supplying enough water (current) to put out the fire.

The video:

 

Thanks, sorry for being a bit vague.

Don't make up your own terminology. Wire is in two general categories: solid and stranded. Frayed implies something that is worn or unraveling.

I was also able to find USB cords with one end's 4 wires already exposed and made into female jumpers

You must have many USB cables available for modification. If you're serious about electronics, you need to be able to make up things like this yourself.

You can use something like this if you still want to be able to use them for their intended purpose:

The price seems to have doubled since I bought some from Ali Express a couple years ago...

 

Don't make up your own terminology. Wire is in two general categories: solid and stranded. Frayed implies something that is worn or unraveling.
You must have many USB cables available for modification. If you're serious about electronics, you need to be able to make up things like this yourself.

You can use something like this if you still want to be able to use them for their intended purpose:
View attachment 272954
The price seems to have doubled since I bought some from Ali Express a couple years ago...

Dennis this looks awesome and yes I feel like upping my game. I found it on Ali Express as you pointed out. Ship date 3 Oct. Ill try again.

How do I integrate this board to supply with another PCB (a very simple one with LEDs?) I don't want all the answers spelled out but just a few.

 

A 15 volt supply is not hazardous. For driving LEDs, it will work fine, but the LED's series resistors will need to be changed.

 

I have found the opposite that modern/current Wall Warts are now SMPS and quite accurate at the output and under load, The older version that were simple linear supplies and were quite high at open circuit/no load..

Indeed current wall warts are mostly switcher supplies and some of them are well regulated, and some are not so well regulated. But I have many that have transformers and the are mostly not regulated at all. So don't assume that the TS has a current production wall wart. At 15 volts it could be anything.

 

But I have many that have transformers and the are mostly not regulated at all.

As I said, many of the older ones were linear supply i.e. Unregulated.

 

How do I integrate this board to supply with another PCB (a very simple one with LEDs?)

If you're referring to the board that I referenced, you can install 0.025" square headers on the board; male or female.

I usually install male header pins on the board. In that case, your USB cables with female pins would work well.

You can buy DuPont-style pins and a crimper on Ali Express (and other places).

If you're the careless type, you can get polarized connectors in other styles.

 

If you're referring to the board that I referenced, you can install 0.025" square headers on the board; male or female.

I usually install male header pins on the board. In that case, your USB cables with female pins would work well.

You can buy DuPont-style pins and a crimper on Ali Express (and other places).
View attachment 272968
If you're the careless type, you can get polarized connectors in other styles.

That's pretty nifty the (Weibily product). I wish I had known about this product much earlier.

So for the following photo this appears to have a lot of potential use to me however Id like some advice on which level to integrate it? Bread board? PCB? And what are the large holes for? What stage in development do I introduce this thing.

 

Bread board? PCB?

Either or both.

And what are the large holes for?

I suspect they're for mounting in cases where you want to use wires instead of headers for power and data connections. Note that the pads on either side of the connector are connected to the shield on the connector, and both are isolated from the GND pad.

What stage in development do I introduce this thing.

It would be best to design for it early, but it could also be to address something you forgot to consider.

I anticipated a need for the ones that I ordered more than 2 years ago and still haven't used one. When I bought it was $2.19 for 20 with free shipping.

 

Either or both.
I suspect they're for mounting in cases where you want to use wires instead of headers for power and data connections. Note that the pads on either side of the connector are connected to the shield on the connector, and both are isolated from the GND pad.
It would be best to design for it early, but it could also be to address something you forgot to consider.

I anticipated a need for the ones that I ordered more than 2 years ago and still haven't used one. When I bought it was $2.19 for 20 with free shipping.

does this appear to be the same item?
crimping kit

 

does this appear to be the same item?

Similar. The one I referenced didn't include a crimping tool or male header pins.

A word of caution. Some items on Amazon are identical to those on Ali Express, but you pay more on Amazon. You can find unscrupulous sellers and counterfeit product on both sites.

I don't know why Ali Express is showing October delivery dates for a lot of items. Shipping time for recent orders was on the order of 2-4 weeks. I only had a couple items take months.

 

I found it on Ali Express as you pointed out. Ship date 3 Oct. Ill try again.

FWIW, I ordered some step-up regulators that gave a 10/4 delivery date in the listing. After I ordered, the order status says estimated delivery is 8/31.

 

FWIW, I ordered some step-up regulators that gave a 10/4 delivery date in the listing. After I ordered, the order status says estimated delivery is 8/31.

I want to invest in a crimping set like the photo you had posted. Do you think the one I posted would do the same job as what you had posted?