ATX power supply conversion Videos on You tube - Page 1
Forum section: electronics / beginners

author: SteveLuck
author_rank: Newbie
timestamp: December 29, 2011, 04:27:54 am
content: Hi GentsI'm a complete novice - I've followed instructions built a few kits with no bother. I wanted a power supply for a few different voltages so i don't have to muck around with lots of different battery combinations. There's a whole bunch of videos on you tube showing how to convert old computer power supplies. So I drilled some holes cut some wires and soldered up a bunch of terminals and insulated everything!After getting one belt off it (my fault for doing silly shit late into one evening!) I've double checked everything it all works including the case being earthed properly.Question is what have I built?2.8 amps on a 3.4v terminal, 7.5amp on 5.2v, 0.03 on a 9 volt terminal made by putting a voltage regulator on a 12v supply and finally up to 15amp on the 12volt terminalDoubled checked my cheap Chinese multimeter its only rated to 10 amps oops! no wonder the leads where getting a little warmI wasn't expecting 15amps i've used 240volt welding sets that could handle a huge duty cycle and only just blow a 13 amp fuse!Video I followed was by jumper oneHave i built something useful or something dangerous?

author: McMonster
author_rank: Frequent Contributor
timestamp: December 29, 2011, 04:41:50 am
content: You never measure current by just setting the meter to amps and sticking the probes into terminals or some points in the circuit! If you'd do that with some LiIon cells or worse a car battery or mains socket you'd likely got hurt or killed, especially with those cheap chinese meters. Voltage is measured that way, current is measuredfor the given loadby breaking the circuit and putting the meter in series with the load. That way you can tell what current that load draws.To test how much current a supply or a battery provides you would need a special device called dummy load, but you don't need one at this level.

author: SteveLuck
author_rank: Newbie
timestamp: December 29, 2011, 04:55:09 am
content: I see - thanksMostly i just intend to play with Arduino's and stuff with low voltages and low currents where i can make mistakes safely? whilst learning.Any other novice mistakes to avoid?Cheers StevePS Two half decent meters on order as per Dave's recommendations.

author: IanB
author_rank: Super Contributor
timestamp: December 29, 2011, 08:23:02 am
content: It's a really good idea to use batteries for powering electronics while learning. When I am experimenting on a breadboard I have a battery holder with an on/off switch that I use to power my circuit. It is then very convenient to switch off the power while configuring the circuit and switch it on for testing without having to unplug any wires.I could use a mains regulated power supply for this, but power supplies are usually much bigger, take up lots of space on the bench, and of course are expensive. An ATX power supply is not a good substitute as it can provide dangerous currents if you make a mistake. You really want a proper regulated supply with a low current limit so it won't make any wires hot in the event of an accidental short circuit.

author: gxti
author_rank: Frequent Contributor
timestamp: December 29, 2011, 04:13:45 pm
content: Seconded on using some sort of isolated supply. Having a really beefy ATX supply is nice when you need to bring the amps, but computer power supplies are earth-referenced (ground is tied to mains earth) which means you have to think about ground loops before you connect a device powered by one of those to another device powered by something else. With an isolated mains supply or a battery you can connect power supplies in series to get multiple voltages for a circuit, for example. For a cheap isolated supply, most "plug packs" are isolated and will supply a few watts. 12 volts is common, 5 volt one exist too. To check for isolation, with the device unplugged use your multimeter in resistance (ohms) mode to measure between each input terminal and the output ground. If you see > 1000 ohms on all terminals then you're good, if you see < 10 ohms then it's not isolated. This is just a suggestion though, you can certainly get stuff done with a earth-referenced supply but you need to make sure you don't connect a circuit on that power supply to another circuit with a voltage potential between their grounds. You should also look into some sort of current limiting circuit so you don't blow up boards with 15 amps if you make a mistake.With regards to measuring current, like McMonster said you're lucky you didn't blow up your meterandyour power supply. A meter in current mode should be treated like a short circuit, and never connected "across" anything, only in series. As for 15 amps, remember that's 15 ampsat 12 volts-- your 240V welding set is fused for 3120 watts (240 * 13), but the power supply is only 180 watts (12 * 15).

author: phil_jp1
author_rank: Regular Contributor
timestamp: December 29, 2011, 07:46:51 pm
content: Quote from: SteveLuck on December 29, 2011, 04:27:54 amIt's definitely something useful, but as everyone said - you should be aware of GND to earth ground connection.And for overcurrent protection you can put some fuses on power rails (according to your needs, of course).Quote from: gxti on December 29, 2011, 04:13:45 pmNot in this case. ATX power supplies have overcurrent protection. It just shuts down on overcurrent event. But, there's a pretty real chance to destroy your meter and/or get meter test leads on fire if your meter doesn't have fused current high range.

author: fmaimon
author_rank: Unknown
timestamp: December 30, 2011, 12:59:25 am
content: Quote from: phil_jp1 on December 29, 2011, 07:46:51 pmThe biggest problems is that your circuit will probably be destroyed before the protection kicks in.