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6Instructables821,522Views226CommentsJoined December 8th, 2005
If you need to get in touch, please email me instead of sending an instructables message. matthew dot beckler at gmail dot com

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  • ATX to Lab Bench Power Supply Conversion

    Hi Frankie, great question. I think this is probably tripping the power supply's short-circuit protection. I have heard from other people's comments here and elsewhere that some power supplies will shut off if they experience a sudden increase in current draw. Perhaps you could use a capacitor in parallel with the light to help smooth-out the current spike?

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  • ATX to Lab Bench Power Supply Conversion

    Hello, good question! I hope you're learning a lot and having fun! It's a bit of an experimental process to determine the size and placement of a load resistor (or resistors) for this kind of project. Some power supplies have a shutdown system where they will turn off if nothing is drawing current, and the load resistor is used to ensure that at least a little current is always being drawn, to keep the power supply from turning itself off. If you'll always have a load connected to the power supply, like if you're using it to charge RC vehicle batteries or something like that, then you probably don't need a load resistor.From the comments on this Instructable over the past ten years, we've learned that some power supplies don't need any load resistor, some only need one on the 5v line, s...

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    Hello, good question! I hope you're learning a lot and having fun! It's a bit of an experimental process to determine the size and placement of a load resistor (or resistors) for this kind of project. Some power supplies have a shutdown system where they will turn off if nothing is drawing current, and the load resistor is used to ensure that at least a little current is always being drawn, to keep the power supply from turning itself off. If you'll always have a load connected to the power supply, like if you're using it to charge RC vehicle batteries or something like that, then you probably don't need a load resistor.From the comments on this Instructable over the past ten years, we've learned that some power supplies don't need any load resistor, some only need one on the 5v line, some only need one on the 3.3v line, and some need loads resistors on both. You'll have to experiment with it. I'd suggest trying it without any load resistor first, to see if it just works without. Then try adding it to the 5v line, then to the 3.3v line, then to the 12v line, then try adding one to both 5v and 3.3v, etc.To calculate how much current each resistor will draw, use Ohm's Law:Voltage = Current * ResistanceIf you put that 8 ohm resistor on the 5v line, we can re-arrange Ohm's Law to calculate the current:Current = Voltage / Resistance = 5 volts / 8 ohms = 0.625 amps of current (also called 625 milliamps).If you put that 50 ohm resistor on the 5v line:Current = Voltage / Resistance = 5 volts / 50 ohms = 0.1 amps of current = 100 milliamps of currentOnce you know the voltage across the resistor, and the current through the resistor, you can calculate the power that is burned in the resistor:Power = Current * VoltageFor 8 ohms at 5 volts, Power = 0.625 * 5 = 3.125 watts of powerFor 50 ohms at 5 volts, Power = 0.1 * 5 = 0.5 watts of powerSince the power burned is less than the power rating for each of those resistors, you don't have to worry about melting them or having them overheat, at least on the 5v line. Repeat the calculations above to determine the resistor current and power burned for the 3.3v line and the 12v line.I hope this helps, and good luck with your project!

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  • ATX to Lab Bench Power Supply Conversion

    Generally it's pretty difficult to do a good job making a higher voltage from a lower voltage, especially for a high-current application like battery charging. You're probably better off looking on ebay for a cheap 14v power supply.

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  • ATX to Lab Bench Power Supply Conversion

    Hello. I don't think it really is a good idea to make all those intermediate voltages by connecting different power rails. Each power rail is only designed to source current, providing it to a load, which returns the current to the common ground rail. I'm not sure it will work very well to draw current from one rail, only to return the current to a different power rail, which is expecting only to source current, not sink current provided to it.Most power rails are designed with a feedback circuit that detects when the output voltage droops too low and provides more current in that case. They don't really have any control system in place to handle the "voltage too high" situation, which is what you'd be doing by making it sink current from somewhere else. Imagine you have a bal...

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    Hello. I don't think it really is a good idea to make all those intermediate voltages by connecting different power rails. Each power rail is only designed to source current, providing it to a load, which returns the current to the common ground rail. I'm not sure it will work very well to draw current from one rail, only to return the current to a different power rail, which is expecting only to source current, not sink current provided to it.Most power rails are designed with a feedback circuit that detects when the output voltage droops too low and provides more current in that case. They don't really have any control system in place to handle the "voltage too high" situation, which is what you'd be doing by making it sink current from somewhere else. Imagine you have a balloon filled with regular air, so it will slowly sink but you can tap it upwards to make it higher. Your job is to keep the balloon at about 5 feet above the ground by detecting when it gets too low, and then giving it a little tap. This works great even if you start adding more weight to the balloon (equivalent drawing more current), but if you start adding an upward force (fan on the floor pointing up?) then your simple control algorithm doesn't have any way to bump it lower. I hope that strained analogy helps explain the situation.If you want different voltages than the standard voltages provided, I would strongly suggest buying or building an actual voltage regulator. It could be as simple as a LM317 regulator with a couple of resistors to set the desired current. You can even use a potentiometer (variable resistor) to make an adjustable voltage supply. The first circuit here is a good one http://www.circuitstoday.com/few-lm317-voltage-reg... but you can also look at the LM317 datasheet for other circuit ideas. Here's a cheap ($8) adjustable voltage regulator with voltage readout http://www.ebay.com/itm/LM317-AC-DC-Adjustable-Vol...It makes it a lot simpler too if all your circuits have a common ground voltage.Regarding switching 24v to a motor, don't forget that there are two ways to switch a circuit like that: high-side and low-side switching. Low-side switching is where your load (motor) is connected to the power supply voltage, through your switching device (a transistor, switch, or relay), and then to ground - The switch is below (on the low side of) the load (motor). A high-side switch is just the opposite. I attached a circuit schematic showing the difference.Transistors are very useful for many things, but let's talk about using them as a switch. Transistors have three connections: one connection that controls the switch, and two connections that either prevent or allow current to flow between them. There are two general types of transistors, and two general technologies of transistor. The two technologies are Bipolar Junction Transistors (BJTs) and Field Effect Transistors (FETs or MOSFETs), but for simple switching applications their difference isn't really that important. The two types of transistor are N-type and P-type. N-type transistors only turn on (conduct current) when the control input is a few volts higher than the bottom connection. P-type transistors only turn on (conduct current) when the control input is a few volts lower than the upper connection.If you are using a low-side transistor then you almost always want to use an N-type transistor, where the bottom connection is grounded and the control input just needs to be higher than a couple volts. If you are using a high-side transistor than you usually use a P-type transistor, where the top connector is connected to the power supply voltage, and the control input must be at least a few volts lower than that to turn it on.This can be used to allow a low-voltage microcontroller to turn on a higher voltage motor or light, but using a N-type transistor. While the microcontroller can only output maybe 3.3 or 5 volts as the control signal, this will be enough to turn on a N-type transistor connected as a low-side switch, which can then allow current to flow from, say, +12v through your motor, through the transistor, to ground. You may be able to do something similar with your 24v motor even if it doesn't have a true ground.Good luck, and I hope this reply was helpful.

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  • ATX to Lab Bench Power Supply Conversion

    The Power On (green) and Ground (black) wires need to be continuously connected to keep the power supply turned on. Most computers (even a mac mini) have a "momentary pushbutton" for the power button. The computer motherboard detects that momentary button press and then connects the green and black wires to turn on the power supply. You'll need to do the same, by holding the green and black wires connected for as long as you want the power supply turned on. I don't think the mac mini button will work very well for your power supply, unless you add some extra electronics. You could possibly use some sort of latch to turn the momentary pushbutton into a push-on/push-off sort of button, you know? https://en.wikipedia.org/wiki/Flip-flop_(electronics)It is not possibly to know how ...

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    The Power On (green) and Ground (black) wires need to be continuously connected to keep the power supply turned on. Most computers (even a mac mini) have a "momentary pushbutton" for the power button. The computer motherboard detects that momentary button press and then connects the green and black wires to turn on the power supply. You'll need to do the same, by holding the green and black wires connected for as long as you want the power supply turned on. I don't think the mac mini button will work very well for your power supply, unless you add some extra electronics. You could possibly use some sort of latch to turn the momentary pushbutton into a push-on/push-off sort of button, you know? https://en.wikipedia.org/wiki/Flip-flop_(electronics)It is not possibly to know how a switch works based on a photograph. You need to experiment to determine how the connections work. Are there only two connection points for that switch? Do you push the blue part directly in or does it slide or rotate in two directions? You don't need any resistors for the power supply on connection.

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  • matthewbeckler commented on matthewbeckler's instructable Laser cut desk name plate7 months ago
    Laser cut desk name plate

    There are a few in the Minneapolis area. I also have my own laser cutter now :-)

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  • ATX to Lab Bench Power Supply Conversion

    Hello, good questions!1. Placement of the power resistor is somewhat of an experimental process. Some power supplies don't need one at all, some need it on 5v, some need it on 3.3v. You will probably need to experiment to see where it is needed. If you turn on the added switch and the fan doesn't turn, or the fan turns off after a few turns, then you likely need to add a power resistor somewhere. I'd try 5v first, and then 3.3v, and if it still doesn't stay turned-on, maybe try both 5v and 3.3v? Good luck, and let us know what you find!2. The fuse is there to protect your circuit from a mistake, not to protect the power supply. I would expect most power supplies to have built-in over-current protection, either in the voltage regulators or even in a fuse inside the socket where you plug ...

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    Hello, good questions!1. Placement of the power resistor is somewhat of an experimental process. Some power supplies don't need one at all, some need it on 5v, some need it on 3.3v. You will probably need to experiment to see where it is needed. If you turn on the added switch and the fan doesn't turn, or the fan turns off after a few turns, then you likely need to add a power resistor somewhere. I'd try 5v first, and then 3.3v, and if it still doesn't stay turned-on, maybe try both 5v and 3.3v? Good luck, and let us know what you find!2. The fuse is there to protect your circuit from a mistake, not to protect the power supply. I would expect most power supplies to have built-in over-current protection, either in the voltage regulators or even in a fuse inside the socket where you plug it into the wall outlet. If you make a mistake in your circuit, such as an accidental short-circuit, this kind of big power supply will be able to provide amps and amps of current through that little wire, likely melting or causing other damage to your circuit. If you know your circuit will only need a few hundred milliamps (less than one amp in total) then adding a 1 amp fuse to the +5 or +3.3 or +12 line (which ever you are using) will help protect your circuit by having the fuse blow instead of dumping tons of current through your circuit. I would estimate the largest expected current use, then use a fuse with double the current.3. This is a very common (and very good) question, and the short answer is that you don't have to worry about the PSU having too many amps of current.This kind of power supply is more accurately described as a "voltage supply". It tries to supply a fixed voltage (like +5v or +12v) no matter the amount of current drawn. If you draw too much current (more than the rating) then the power supply will be unable to keep the voltage at the right level and the voltage supplied will droop down. If you draw less current than the rating, then everything should just work, there's no worry about it providing too much current.By way of analogy, the municipal water supply in your town probably supplies water at, say, 100 psi. A small bathroom sink will only draw a little bit of flow, while a garden hose will draw a lot of flow. Both are tapping into that 100 psi supply, but only draws as much flow as it needs. If you turned on all the faucets and hoses and taps in your house, you might draw so much flow that you exceed the flow capacity of your water supply, and so the provided pressure would drop a bit. I hope that makes sense.

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  • matthewbeckler commented on matthewbeckler's instructable Laser cut desk name plate7 months ago
    Laser cut desk name plate

    Sandpaper worked just fine for me, on this and other projects. A friend recently sent me this link, and I've been meaning to try it http://support.epiloglaser.com/article/8205/30190/easily-remove-engraving-residue-from-wood

    I had a membership to TechShop, and they give out free class coupons if you make an instructable based on something you make at TechShop. That is the entire reason I mentioned TechShop, this project would work on any other laser cutter. I don't belong to TechShop anymore since I moved to a city that doesn't have one, but I have never seen a better or more professional workshop than TechShop.

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  • ATX to Lab Bench Power Supply Conversion

    Hello Kokoro San. Be aware that many ATX power supplies have 12v split into 2 or more sub-supplies. Look at the sticker on the side of the ATX power supply for details. I would suggest using a battery charger to manage the charge process.I am not sure what you're asking about for diagrams?

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  • ATX to Lab Bench Power Supply Conversion

    Hello, good question!Using Voltage = Current * Resistance, we know that 12 volts across a 25 ohm resistor results in 12/25=0.48 amps of current flowing through the resistor. The other important formula to use is Power = Voltage * Current, so 12 volts * 0.48 amps = 5.76 watts of power, that becomes heat in the resistor. Since the resistor is rated for 10 watts, you're not going to melt the resistor but it may get warm over time.I wouldn't expect it to get too hot to touch, so perhaps the resistor has less resistance, and is therefore drawing more current? If I remember correctly, the wirewound resistors that can handle many watts usually have a large variance in the amount of resistance it actually has, compared to the "official" resistance. If you have a multimeter you can mea...

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    Hello, good question!Using Voltage = Current * Resistance, we know that 12 volts across a 25 ohm resistor results in 12/25=0.48 amps of current flowing through the resistor. The other important formula to use is Power = Voltage * Current, so 12 volts * 0.48 amps = 5.76 watts of power, that becomes heat in the resistor. Since the resistor is rated for 10 watts, you're not going to melt the resistor but it may get warm over time.I wouldn't expect it to get too hot to touch, so perhaps the resistor has less resistance, and is therefore drawing more current? If I remember correctly, the wirewound resistors that can handle many watts usually have a large variance in the amount of resistance it actually has, compared to the "official" resistance. If you have a multimeter you can measure the resistance of the resistor by itself, or you can put the meter in current measuring mode, and insert it in series with the resistor and measure the actual current. Let me know if you need more info about how to use a multimeter for this kind of investigation.If you could find a 100 ohm power resistor, that might work better. It would result in 0.12 amps of current instead of 0.48 amps. I really don't know how much current is needed for the minimum load, but I would guess that 0.1 amps would be enough. This would reduce the power burned as heat in the resistor down to 1.44 watts, so you could use a 5 watt power resistor instead of 10 watt.

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  • ATX to Lab Bench Power Supply Conversion

    Hello, good question! If you want to limit a specific binding post to only output a certain amount of current (1A, 2A, 5A, etc) then you need to use a fuse that will blow when the current limit is exceeded. Be aware that fuses are not very precise in terms of current limits, and there is usually a range where the fuse may or may not blow.Hope that helps, let me know if you have further questions, or if I didn't understand what you were asking.-Matthew

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