I've retired & I want to take up electronics as a hobby.

I'm wondering what I can use as a power supply. There are batteries, wall warts & modified PC power supply.

As you move along into electronics as a hobby I believe the bench power supplies you will use will really depend on where the hobby takes you. Figure in its most common denominator a power supply is about the voltage and current it can provide. Wall warts make for good starters in many but not all applications. I modified a 12 VDC 1.0 Amp wall wart to power my little uC (micro-controller) projects but it is hardly suitable for experiments requiring more current. Hacking home computer (ATX Form Factor) power supplies is another option and there are dozens of How To articles online. Finally there are a number of reasonably priced bench supplies available from China. These offer being adjustable and many are dual supplies which come in handy if you experiment with operational amplifiers. There are also bread boards available for building projects which have built in power supplies, usually +/- 15 Volts and 5 Volts.

I really don't think there is any one turn key single solution as to power supplies for the home electronics hobby type or enthusiast. Really depends on what you are experimenting with on any given day.

Ron

 

Wall warts make for good starters in many but not all applications.

When I started my electronics hobby, my first project was building a power supply. My second project was a crystal controlled oscillator with counters to give me a variable frequency square wave generator; it also included another power supply in the same box.

 

When I started my electronics hobby, my first project was building a power supply.

+1.

This was going to be my suggestion to get him started in electronics.

I was 7 or 8 y.o. when I built my first.

 

I've retired & I want to take up electronics as a hobby.

I'm wondering what I can use as a power supply. There are batteries, wall warts & modified PC power supply.

I have 4 spare wall warts. One is 12 volts DC & 3 are 5 volts DC. The 12 volt one has a coaxial connector. Two of the other 3 have mini-USB connectors. The 3rd has a I-don't-know-what-kind of connector. It's rectangular. I haven't bought a multimeter yet. I do have a battery tester. I set the tester on 22.5 volts. I stuck one of the test leads into the inner connector & quickly tapped the outer connector with the other lead. The needle didn't move. I reversed the leads & tried again. Same thing - the needle didn't move. I set the battery tester on 9 volts & tested a 9 volt battery & the needle moved.

It would seem to me that the battery tester would work since the wall wart outputs DC & the 9 volt battery outputs DC also. Other than the obvious possibility that the 12 volt wall wart is dead, why wouldn't the battery tester show 12 volts?

Wall warts are good for small projects and breadboards. Some are regulated, some not. I suspect the 5 V are regulated. The12 V, maybe. If it measuresb12 V with no load it is regulated. If it reads 16 V, or something it is probably unregulated. Is the12 V power supply cubical and heavy then it is probably unregulated. If it is light and thin it is probably regulated and a switching regulator.

 

Wall warts are good for small projects and breadboards. Some are regulated, some not. I suspect the 5 V are regulated. The12 V, maybe. If it measuresb12 V with no load it is regulated. If it reads 16 V, or something it is probably unregulated. Is the12 V power supply cubical and heavy then it is probably unregulated. If it is light and thin it is probably regulated and a switching regulator.

Yep, the 12V is cubical & heavy & the 5V are small & light.

You're probably right. The 12V is probably dead. I can get a 12V incandescent bulb at Radio Shack & test the 12V wall wart. If the bulb doesn't light, then I'll circular file the 12V. I can do the same with the 5V wall warts. I would think that a 12V bulb would light dimly at 5V.

Could I wire the three 5V wall warts together to get 15V? Of course, positive to positive to positive & ground to ground to ground. I don't want to short them out.

 

Could I wire the three 5V wall warts together to get 15V? Of course, positive to positive to positive & ground to ground to ground. I don't want to short them out.

To get 15V you need to connect the positive of one to the negative of the next.
The problem with doing this is what happens if you draw more current than they can supply or short circuit them. Then current can be driven backwards through one or two of them which may cause damage.

 

To get 15V you need to connect the positive of one to the negative of the next.
The problem with doing this is what happens if you draw more current than they can supply or short circuit them. Then current can be driven backwards through one or two of them which may cause damage.

I read about that on another post on this forum.

Here are the specs for each 5v wall wart:
5V at 1.8 A
5.1V at 0.7A
5V at 1A

If I connect positive to positive & ground to ground, do I get the average of 5 + 5 + 5.1 = 5.0333etc.? Do I get the average of the current 1.8 + 0.7 + 1 = 1.1666etc.?

Positive to positive to positive would be parallel & positive to negative would be series, right?

I reckon that it isn't a wise thing to do, is it?

 

If I connect positive to positive & ground to ground, do I get the average of 5 + 5 + 5.1 = 5.0333etc.? Do I get the average of the current 1.8 + 0.7 + 1 = 1.1666etc.?

Think of a water analogy. If you had a hoses capable of delivering gallons per minute of 1.8, 0.7, and 1.0 and you connected them in series; what flow rate could you get out of the combined hoses?

Whether you can connect them in series depends on whether the outputs are isolated from the input.

If you're serious about getting into electronics, buy or build a decent power supply. You can buy used. I've purchased good quality used digital supplies and DVM's on eBay for pennies to dimes on the dollar.

 

If you're serious about getting into electronics, buy or build a decent power supply. You can buy used. I've purchased good quality used digital supplies and DVM's on eBay for pennies to dimes on the dollar.

I agree, except I'd go even cheaper as long as you can. Over time I've moved to my favorite - the small power supply from an old hard drive enclosure. It has +12, +5 and -12 outputs. Not much current capacity (maybe 2A?) but that's plenty for most bench work. If I ever needed more current (like when I was using a peltier), I scavenged the PSU out of an old Mac, because it has no fan and is very quiet. Good to 6A or so at 5V. If I was looking for something today, I might start with a spare laptop power supply (small, free, quiet, plenty of power) and use a LM317 to give me whatever voltage I want.

Point is, you don't need to spend hardly anything to get going. But wall warts have issues (noise on the output, mostly) and I'd avoid them for bench work. They're fine to power finished projects.

 

DVM's are available for cheap - and decent ones at that at Lowe's & Home Depot. You can probably get one at an automotive parts store too but I'd suspect they may be higher priced. And by cheap I mean for around $20.00. I have a few different types.

Regarding coupling wall warts that are the switching type, I'd suspect that if you plug two of them in (I have never done this) and you take the positive lead of one of them and test the voltage from that to the negative lead of another, if you get the voltage of the first with the positive lead then I'd suspect that you can't connect them in series (5+)•••(5-5+)•••(5-5+)•••(5-) and get 15 volts out of it. However, if the outputs are independently isolated then yes, that can be done.

You posed the question about connecting the three of them in parallel (5+,5+,5+) and (5-,5-,5-) wanting to know what kind of amperage you can expect out of them. First, the final voltage would still be about 5 volts. However, you're combining the amperage capabilities of each. In general, you could expect to see 3.5 amps capacity. If you're drawing 2 amps and one of them fails then it's likely the other two will cascade into failure quicker than you can say "DARN-IT!"

I've converted an old computer power supply into a bench top supply. I have -12V @ 1A (to ground) +12V @ 18A (to ground), +5V @ 22A (to ground) and +3.3V @ 17A (to ground). From the supply I go to a distribution box with three banana plug sockets, one for ground, one for the -12V, one for ground and one for +12V. Two of the sockets are equipped with fuse holders. In the -12V socket I keep a 1 amp fuse. If I make a mistake I smoke the fuse and not the supply.

This distribution box can be plugged into the power supply with several different configurations. Plugging one lead (not the ground) into the +12 and the other into the +3.3 I can get a difference voltage of 8.7 volts. As for amperage I'd assume the lower value in every case just to be on the safe side. +12 and +5 gives me a difference of +7 volts. +5 & +3.3 gives me a difference of 1.8 volts. This arrangement is very useful. HOWEVER, I can not connect in a way to get (5+3.3) 8.3 volts. Since there is only ONE negative rail (-12V) I could go as high as 24V. -12 & +5 would give me 17V (at 1 amp since the -12 is only capable of 1 amp). 15.3V is the result of -12 & +3.3.

Since I'm not highly experienced (yet) with electronics I plan on eventually getting a dual variable power supply that can give varying voltages AND currents. I think the ability to limit current will be highly useful in troubleshooting something. Closest I've ever come to troubleshooting a current issue was when I had a TV with a shorted power supply. Plug it in, turn it on - replace the fuse. (yes, fuse) When I took it into the attic I plugged it in and turned it on. All the lights in the attic dimmed. That meant the wiring of the house could not handle the load I was placing on it. Had an electrical short occurred the house would have burned to the ground. Old "Tube & Knob" wiring. VERY old wiring. Couldn't discern colors of wires either. All you KNEW was "One was hot, one was neutral". Touch the wrong one and you found out quickly which was which. I ran a dedicated 12 gauge wire from the fuse panel to the attic. A run just under 50 feet. Put a 15 amp fuse in it, though I could have put a 20 amp fuse. The single outlet was rated for 15 amps and I didn't want to exceed that. Would have been different if I'd have had a string of outlets on it.

Anyway, back to the subject: Meters are readily available and not expensive. Power supplies are also readily available. If you're going to grow your hobby then you can start with wall warts. Sacrifice them if it comes to that (learning the hard way about smoke theory). OR you could build your own like I did; OR you could just get a decent power supply.

Also keep an eye out for a cheap oscilloscope. You'll learn a lot from just gazing at the wave forms.

 

I've retired & I want to take up electronics as a hobby.

I'm wondering what I can use as a power supply. There are batteries, wall warts & modified PC power supply.

I have 4 spare wall warts. One is 12 volts DC & 3 are 5 volts DC. The 12 volt one has a coaxial connector. Two of the other 3 have mini-USB connectors. The 3rd has a I-don't-know-what-kind of connector. It's rectangular. I haven't bought a multimeter yet. I do have a battery tester. I set the tester on 22.5 volts. I stuck one of the test leads into the inner connector & quickly tapped the outer connector with the other lead. The needle didn't move. I reversed the leads & tried again. Same thing - the needle didn't move. I set the battery tester on 9 volts & tested a 9 volt battery & the needle moved.

It would seem to me that the battery tester would work since the wall wart outputs DC & the 9 volt battery outputs DC also. Other than the obvious possibility that the 12 volt wall wart is dead, why wouldn't the battery tester show 12 volts?

The battery testers I'm thinking of have an internal load, most batteries fail because the internal resistance has increased - the unloaded terminal voltage may well appear normal. Such an internal load could overwhelm some low power wall warts. Its best to use a common or garden DMM for checking wall warts.

Side by side; its readily apparent that the ones that don't weigh much are SMPSU and the heavy ones are old iron-cored transformer. The SMPSU type usually have decent regulation and should read pretty much the voltage it says on the label, the old iron-cored ones can read a fair bit higher with no load. Some of the better iron-cored - particularly some selectable voltage types have an internal 3-terminl regulator.

 

Think of a water analogy. If you had a hoses capable of delivering gallons per minute of 1.8, 0.7, and 1.0 and you connected them in series; what flow rate could you get out of the combined hoses?

I assume that in series, the current would be summed & in parallel the current would be the average. Is my assumption correct?

Whether you can connect them in series depends on whether the outputs are isolated from the input.

So, bottom line, I'd say that you are not recommending connecting wall warts in series OR in parallel unless they are isolated from one another.

If you're serious about getting into electronics, buy or build a decent power supply. You can buy used. I've purchased good quality used digital supplies and DVM's on eBay for pennies to dimes on the dollar.

Think of a water analogy. If you had a hoses capable of delivering gallons per minute of 1.8, 0.7, and 1.0 and you connected them in series; what flow rate could you get out of the combined hoses?

Whether you can connect them in series depends on whether the outputs are isolated from the input.

If you're serious about getting into electronics, buy or build a decent power supply. You can buy used. I've purchased good quality used digital supplies and DVM's on eBay for pennies to dimes on the dollar.

 

On the Home Depot website, I found LED strip power supplies which could be adapted for breadboarding. That is, if I needed a 12V power supply. Interesting!
http://www.homedepot.com/s/LED%20power%20supply?NCNI-5
http://www.homedepot.com/s/LED%20power%20supply?NCNI-5

 

DVM's are available for cheap - and decent ones at that at Lowe's & Home Depot. You can probably get one at an automotive parts store too but I'd suspect they may be higher priced. And by cheap I mean for around $20.00. I have a few different types.

Regarding coupling wall warts that are the switching type, I'd suspect that if you plug two of them in (I have never done this) and you take the positive lead of one of them and test the voltage from that to the negative lead of another, if you get the voltage of the first with the positive lead then I'd suspect that you can't connect them in series (5+)•••(5-5+)•••(5-5+)•••(5-) and get 15 volts out of it. However, if the outputs are independently isolated then yes, that can be done.

You posed the question about connecting the three of them in parallel (5+,5+,5+) and (5-,5-,5-) wanting to know what kind of amperage you can expect out of them. First, the final voltage would still be about 5 volts. However, you're combining the amperage capabilities of each. In general, you could expect to see 3.5 amps capacity. If you're drawing 2 amps and one of them fails then it's likely the other two will cascade into failure quicker than you can say "DARN-IT!"

I've converted an old computer power supply into a bench top supply. I have -12V @ 1A (to ground) +12V @ 18A (to ground), +5V @ 22A (to ground) and +3.3V @ 17A (to ground). From the supply I go to a distribution box with three banana plug sockets, one for ground, one for the -12V, one for ground and one for +12V. Two of the sockets are equipped with fuse holders. In the -12V socket I keep a 1 amp fuse. If I make a mistake I smoke the fuse and not the supply.

This distribution box can be plugged into the power supply with several different configurations. Plugging one lead (not the ground) into the +12 and the other into the +3.3 I can get a difference voltage of 8.7 volts. As for amperage I'd assume the lower value in every case just to be on the safe side. +12 and +5 gives me a difference of +7 volts. +5 & +3.3 gives me a difference of 1.8 volts. This arrangement is very useful. HOWEVER, I can not connect in a way to get (5+3.3) 8.3 volts. Since there is only ONE negative rail (-12V) I could go as high as 24V. -12 & +5 would give me 17V (at 1 amp since the -12 is only capable of 1 amp). 15.3V is the result of -12 & +3.3.

Since I'm not highly experienced (yet) with electronics I plan on eventually getting a dual variable power supply that can give varying voltages AND currents. I think the ability to limit current will be highly useful in troubleshooting something. Closest I've ever come to troubleshooting a current issue was when I had a TV with a shorted power supply. Plug it in, turn it on - replace the fuse. (yes, fuse) When I took it into the attic I plugged it in and turned it on. All the lights in the attic dimmed. That meant the wiring of the house could not handle the load I was placing on it. Had an electrical short occurred the house would have burned to the ground. Old "Tube & Knob" wiring. VERY old wiring. Couldn't discern colors of wires either. All you KNEW was "One was hot, one was neutral". Touch the wrong one and you found out quickly which was which. I ran a dedicated 12 gauge wire from the fuse panel to the attic. A run just under 50 feet. Put a 15 amp fuse in it, though I could have put a 20 amp fuse. The single outlet was rated for 15 amps and I didn't want to exceed that. Would have been different if I'd have had a string of outlets on it.

Anyway, back to the subject: Meters are readily available and not expensive. Power supplies are also readily available. If you're going to grow your hobby then you can start with wall warts. Sacrifice them if it comes to that (learning the hard way about smoke theory). OR you could build your own like I did; OR you could just get a decent power supply.

Also keep an eye out for a cheap oscilloscope. You'll learn a lot from just gazing at the wave forms.
A cheap oscilloscope? There is such a thing?

 

"A cheap oscilloscope? There is such a thing?"

Even one of these would be a lot better than nothing.

 

Macnerd said: "Cheap oscilloscope? There is such a thing?"

Yes. I got mine on E-bay. Spent about $50 for it if I remember correctly. Not the greatest, but it does well enough. And since I struggle a little with understanding its readings sometimes, having one that doesn't do it all for you drives you to learn more about what you're doing. I also have a "Hantek" digital unit that connects to a PC. You need the PC to see the readout but you can use it to calculate, or should I say it calculates data for you. It has two traces and I think I got that for somewhere around $150.00 from Amazon (again, I THINK). Certainly no need for a beginner to buy a $9,000.oo scope. Sure, I'd LOVE a scope with a memory trace but with the Hantek I can review the trace millisecond by millisecond if need be.

 

one of these would be a lot better than nothing.

Can't open the link. Maybe you're editing it now.

 

Can't open the link. Maybe you're editing it now.

Sorry, I messed that up. I've changed it now.
http://www.ebay.co.uk/itm/Assembled...hash=item3f69e61f34:m:mjZcSP2a2MkrEB2q5ChkLcg

 

I assume that in series, the current would be summed & in parallel the current would be the average. Is my assumption correct?

No. In series, the lowest current would be the limiter. In parallel they add. Before you go much further with electronics, you should study the concepts of series and parallel.

So, bottom line, I'd say that you are not recommending connecting wall warts in series OR in parallel unless they are isolated from one another.

I'm recommending that you not do it at all. If you're serious about electronics, get something more appropriate so you don't need to stack supplies. Stacking would be okay if you needed a negative voltage and didn't have a dual supply. But to get a higher voltage, that screams kludge.

 

"A cheap oscilloscope? There is such a thing?"

Even one of these would be a lot better than nothing.

There might still be a few CROs being offloaded as people go digital.

Personally; I never use a scope for voltage measurements unless there's a peculiar waveform - but the TS might find it handy for comparing ripple.