12VDC Wall Charger/Converter Box

[ArcWindsor]

I recently acquired two AC converter boxes that plug into the wall and output lower DC voltages. I have a few questions about each. I posted pictures of the specs (stickers) on the boxes at the bottom of this post.

The first one is a wall charger that converts 100-120VAC to 3-12VDC. It has a 1200mA output max and is meant for being a universal charger. I can select different voltages, but I'm typically going to use 12V. My point is to use it for several purposes...

1) testing some 12VDC car things (such as LEDs and relay coils) to make sure they work before wiring them into the car. This makes it so that I can test stuff right in the house in the winter instead of freezing outside to use the car battery

2) to power some LEDs (with some switches) for home lighting. This is just for lighting up some small areas for seeing or decoration... hobby

3) to charge peripheral devices whose wall chargers are lost/broken or didn't even come with a wall charger. For a lot of my devices, I have car chargers but no wall chargers. So using the converter box, I can avoid finding/buying wall chargers and going outside to the car just to charge it.

So I have a few questions about using this:

- First is the fusing safety. I'm assuming that since its 12VDC, I would select the wire gauge/fuse value in the same manner as if I was in the car installing something. So I plan to use 24AWG with a 500mA fuse (probably much smaller than necessary). I feel safe with this. What do you think?

- Secondly, the box has an output-voltage selector switch. I can select 3V, 4.5V, 6V, 7.5V, 9V, and 12V DC. So my question is that since I'm not used to voltages other than 12V, if I was to use 9V (or something less than 12V), then would the fusing be the same? For ex, assume the max fuse size for 24AWG is 3A on 12V, but what would be the max fuse size for 24AWG on 9V? Would it go up or down? I'm typically going to use the 12V setting only, but I'm asking this just in case I ever decide to use a lower one. Would I be safe using the 500mA fuse on 24AWG for all the voltages?

- Using this box on the 12VDC setting, is it okay to test 12VDC relay coils (the kind I plan to use in the car) to make sure the relay works properly? I always test my relays before installing them in the car. The box wasn't really designed to power relay coils, so that's why I'm asking. I don't know much about inductive spikes and whether or not they can mess with the box. Of course the coil's current will be under the max limit.

That's all for the 12V box.


The second box I have converts the wall outlet to an 18.5VDC output. I wanted to power some LEDs with this box too. I know its not okay to power LEDs rated at 12VDC (they have resistors for 12V car 'plug n play') using the 18.5V box, but what if I add extra resistance OR put two LEDs (with their resistors) in series? After putting two LEDs in series, I measured 9V or so across each LED, and the whole series runs something like 14mA (measured). So I'm assuming this won't kill the LEDs or pose a safety risk. Can you let me know what you think about this?

And lastly, how should I fuse 22AWG on 18.5V?

Thanks a lot in advance. I know I asked a lot of questions, sorry.

Here are pictures of the specs for the 3-12VDC box (the first one I talked about):
**broken link removed**

And here's the specs of the 18.5V box (it says 12VDC, but it measures 18.5VDC):
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[Sceadwian]

1.) Yes should work fine for testing lower power car components. 1.2 amps is not a lot in the car world though so you could have problems with anything that uses more power than an indicator light. You should be okay with testing relays and what not, but test full scale before installing to be sure, the general failure would be that your adapter can't provide true 12 volts at your desired current where your car would have no trouble, so if it fails on the test setup it may work in the real world, so if it doesn't work when you think it should you run out to the car to test it.

Or use a PC power supply, they provide rock solid 12 volt rails that are close to what is needed by even high powered audio amplifiers.

2) Will work great, go with a higher voltage than the LED is rated for and use balance resistors to make up the rest.

3) Should work fine for that purpose as well, but be very careful here. These types of supplies are tap switched selectable brute force rectifiers typically. On the 3V setting the no or low load voltage may be too high for the device you're trying to replace it's charger. I'd be more worried the lower the voltage you go.

Fusing should be rated for the max current, plus enough overhead to prevent false trips if you intend on loading it, but this will only protect the SUPPLY not the devices plugged into it. Considering it's rated for 1.2amps you should use an additional fuse for devices lower current requirements. Aside from the slight voltage drop piggy backing a .1 amp fuse to protect the devices is really something you HAVE to do. In the case of a failure of the device with it's rated supply you could be talking about enough extra current allowance where if the device fails and goes up in flames the supply might not even notice. The device ratings are typically only with rated charges for that particular device, using a power supply with the extra amps capability means you really should be second fusing the devices.

I'm sure I missed a bunch of information, but that's a start.

 

[ArcWindsor]

Thanks

With the fusing, I'm most worried about the wires burning up during an overload and catching fire. I can't use a 0.1A fuse for some of the devices, for ex, my GPS draws about 300mA (on 12V) when charging according to the DMM. So to 'second fuse' them, you mean add another smaller fuse just before the socket?

What do you have to say about the 18.5V box? I plan to take two 5mm LEDs, each is already pre-wired with resistor for "12VDC" (cars), and put them in series. The series would consist of two 5mm LEDs and two of the resistors they're already prewired with. When I tested this with the 18.5V box, I measured about 15mA through the whole series, and each LED is seeing about 9V. The LEDs alone on 12V would draw 20mA. So I assume the series on 18.5V is okay?

thanks again

 

[Sceadwian]

Yes that's what I mean, rate the main fuse for the power supplies limit, that should actually be on the AC side of the power supply as well. The output from the power supply should have the fuse rated for whatever load you'll be using it for. Since you want an adjustable trip current you might want to see if you can find a small breaker that has an adjustable trip current.

The LED's can't be seeing 9 volts they'd be in flames at that point you must be measuring across the drop resistor as well. As long as the LED's are bright enough the series string you're using will work fine, and since you're 5ma under it's normal output they should last forever. If you put enough of those modules in series you could actually plug it directly into the electrical outlet in your home (I've done this before) however you get flicker because they only conduct during one half of the AC cycle.

 

[#12]

I say, use a 1 amp, fast fuse and wires at least 20 gauge (American). The fuse protects the wires.
Then you can use a smaller fuse if you want to.

 

[ArcWindsor]

Thanks for the help so far everyone. A few more questions have come up though.

First Question:
What is this black thing in this below picture (not the plug, but the thing with the holes in it)? Should I put the main fuse before or after it? That is, should I put the fuse between the wall-plug-in box and the black thing, or should I put the fuse between the black thing and the output plug (the plug in the below pic)? I'm guessing this component handles the conversion to DC?.. possibly, in my best guess. But let me know for sure. My main concern here is the fuse placement.
**broken link removed**

Second Question:
I found another wall wart today for this old HomeMedics chair back massager thing that collects dust. Its 12VDC and 1000mA max. When I cut the wires, I noticed that besides copper braid, there is this white/gray fur looking stuff too. You can see it in the below picture. Its soft like hair or fur (possibly fiber glass?) More details... the chair pad has some kind of vibrator/massager thing for your back, and it also heats up if you press the heat button. So...

1) Does anyone know why there's "fur" in the wire?
2) My main concern is... can I still use this wall wart to power LEDs (only LEDs, no peripheral devices or relays)? Also, can I still solder because obviously that 'fur' will burn up. I'm guessing it'll be fine because the LEDs don't need the fur. Whatever was inside the chair pad needs it, not my LEDs. So will it be okay to use for LEDs and to solder?
**broken link removed**


Third Question:
The 12VDC chair pad has a control-pad with 4 separate switches to operate the massager and heater. I chopped it off, tested all the wires with the continuity/beeper setting, and found the power input and all the outputs for the switch pad. Since a) its 12VDC, and since b) LEDs draw a relatively small amount of current, then would it be safe to use this switch-pad to switch my LEDs? I can post a picture of the switch pad if you want, but its just simply 4 switches contained on a single control pad. The reason is because it'll save me from buying 4 switches, and it'll also save me from having to mount 4 separate switches.

Thanks a lot,

 

[MikeMl]

First: Ferrite choke used to prevent the DC charger cord from radiating RFI eminating from inside the original thingy that the DC charger powered. It can be cut off and discarded.

Second: The fiber is to make the cord strong, flexible, and less prone to kinking. Has no electrical significance.

Third: Most little switches, including membrane switches are good for ~1A DC.

 

[ArcWindsor]

Thanks for the advice. I got some LEDs powered from a few different power supplies... thanks to your help

Here's something else I want to ask... Can I use my computer's power supply to power LEDs? I'm talking about my current working computer. I noticed people do 'case mods' with LEDs, so obviously they tap into the computer's internal circuitry. Can I tap the same place but run the wires out to light up the desk/shelves nearby?

Has anyone done something like this?

 

[Sceadwian]

Yes, you can do that easily. You can take the molex connector from a spliter and cut the wires on one split to tap the power. Yellow is +12 volts, Red is +5 volts, black is GND.

 

[ArcWindsor]

Thanks,

I keep seeing this 'molex' word. Do I need the molex connector, or can I just splice the LED into the voltage source?

If not, where do I find a molex connector? And how much are they typically?

 

[Sceadwian]

Molex is a brand name, the connectors themselves don't really have a proper name. It's the four pin connector you see coming off of power supplies that go to most hard drives and CDROM's. You can get splitters to go from one source to two destinations.
**broken link removed**

 

[ArcWindsor]

But do I have to use the Molex connector? Can't I just splice into the wires on the original (stock) plug to accomplish this?

Actually, I might grab the connector anyway if its more convenient and conventional.

Also, where do I access this inside the computer? Roughly, how much stuff needs taken apart? If its complex, then I don't need a full description. Just let me know about how difficult this task is.

Thanks,

edit: is this the one?
http://www.xoxide.com/4pinsplitter.html

 

[Sceadwian]

Plug it in....
Nothing needs to be taken apart at all, that's why I recommended using a Y connector, even if you don't have an available power connection inside you can use the Y to tap from some other device without having to modify anything on the PC side at all. It's hard to get simpler.

 

[ArcWindsor]

Oh, there's a plug on the outside of the computer for it? Okay, I'll look into it further myself.

Another thing... Others have told me that powering LEDs like this will slow down the computer. What's up with this? Will it hurt my computer's speed in doing things like moving through the Windows Explorer (normal use)? Will it slow down the start up speed possibly? I never turn mine off anyway.

 

[Sceadwian]

No, there's no plug on the outside of the computer.. They're on the inside... nothing has to be modified though except for the Y connector your pop into place.

As long as the LED's don't draw more power than the system needs to run it won't effect anything, whoever told you it would slow down your computer was trying to sound smart when they had no clue what they were talking about.

Drawing an extra amp or two from the 12 volt rail shouldn't cause any major power overhead on the power supply, most are rated past what the system actually needs.

 

[ArcWindsor]

Weird project alert! I have some '12VDC' LED brake/turn bulbs that are meant for retrofitting into my rear incand assemblies on my car. Because that's highly dangerous (optics), I decided to find a safe use for these otherwise useless and dangerous car bulbs.

Before starting, I thank you guys here for the advice... for being in part responsible for me being able to accomplish projects like this. This project is powered by a wall wart like the ones we've been talking about. So I thought I'd show you guys what kind of stuff I've been messing with lately in terms of this topic. There's still more to come.

I started with a regular house lamp that takes the std 120VAC Edison-base bulbs. The lamp has a damaged push-switch. It doesn't turn on/off without fiddling with it 10 times, so most normal non-light-obsessed people would just throw it away. The way I look at it is the only thing that's broken is the switch/socket piece, so that's the only piece I should discard of.

materials: 7440 socket, 7440 LED tower bulb, fuse, connector, switch, wall wart, and one broken lamp
**broken link removed**
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socket and bulb
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Test fit... fits perfectly in the lamp's tip.
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So then I soldered it on and mounted it in there. The lamp uses its 'stock' wires still... except for the socket and the plug-in ends where I had to cut/solder.
**broken link removed**
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thumbwheel switch... I thought this switch was a pain to solder with... until I realized that its just a crimp-type thing.
**broken link removed**
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Test run
**broken link removed**

Its final resting place. Of course its not as bright as when it was a 120V lamp, but it gives a decent amount... decorative for the most part. Works great at night though. Let me know what you think of my little project.
**broken link removed**

 

[Reloadron]

Interesting project and seems to work fine. Something worth watching is I noticed you used a little thumb wheel switch. Those switches are generally rated for AC current. Since you are using a resistive load (DC Incandescent Lamp) and the load likely draws little current this is not a problem. However, when using switches always make sure the switch is rated for your application to insure a long and safe switch life.

Noticed you are in NE Ohio. I am in the Cleveland SE suburbs myself. If you ever need simple parts or computer related parts feel free to PM me. I have piles of junk I have accumulated over the decades.

Ron

 

[ArcWindsor]

well, the load is an LED bulb that draws like 70mA on about 12-14V. Considering its rated at 3A on 120V, I figured it'd be fine.

Is DC bad for AC rated stuff? In other words, if you ran 1A DC through something that's rated at 1A AC (hold voltage constant), than is that worse?

Thanks for the post by the way... I'll let you know if I need any parts.

 

[Reloadron]

Is DC bad for AC rated stuff? In other words, if you ran 1A DC through something that's rated at 1A AC (hold voltage constant), than is that worse?

Yes, it can be. However, there are times it is not a problem also.

For example let's use a light bulb as in everyday incandescent lamp like an automotive lamp. A lamp with a filament is a resistive load. That 12 volt lamp could care less if it is AC or DC current used to illuminate it. For this application 12 VDC is the same as 12 VAC RMS. The DC is the AC RMS equivalent.

However, if we use your wall wart as another example there is a big problem. The wall wart is designed to run on AC current. The first thing the incoming voltage sees is a transformer to reduce your 120 VAC mains to a lower level AC before it rectifies and filters it to DC. The transformer in there is an inductive load designed for an input current that is constantly changing direction, in your case 60 times per second. Devices like this would not work on DC current.

In conclusion without listing thousands of devices, feed them what they want.

Have a god day.

Ron