Using old laptop chargers as PSUs: any caveats? - Page 1
Forum section: electronics / projects

author: bitwelder
author_rank: Super Contributor
timestamp: May 02, 2016, 05:20:58 pm
content: I found in my piles of old hardware several laptop chargers that I thought it would be possible to re-use together with a dc-dc converter to make some auxiliary lab power supply units (as they typically provide around 16-20V at 4-5A).Is there any caveat on using them in such a way, or do you have suggestions in how to choose the most suitable models?Thanks

author: stmdude
author_rank: Frequent Contributor
timestamp: May 02, 2016, 05:27:18 pm
content: I do it all the time to create bad-ass USB power-supplies.No caveats really. Just beware that the long cables can have a bit of inductance, so a little bit of bulk capacitance where you connect your LDO/SMPS will go a long way.

author: rob77
author_rank: Super Contributor
timestamp: May 02, 2016, 07:15:51 pm
content: using them too, add a Chinese buck converter module and you have a crude, but well usable bench supply.

author: dannyf
author_rank: Super Contributor
timestamp: May 02, 2016, 08:16:15 pm
content: I use them all the time. built a few solder stations with them.

author: jpittner
author_rank: Contributor
timestamp: May 03, 2016, 11:20:35 am
content: I used them quite often for 13.8V powered devices, just changing the voltage divider resistors in the control loop.

author: nowlan
author_rank: Frequent Contributor
timestamp: May 03, 2016, 11:27:17 am
content: The DC-DC converter is the weak point. You want to make sure it can deliver its rating, keep regulation, and has current limiting to be an effective lab supply. Otherwise just treat the same as the ATX psu hacks.

author: Fungus
author_rank: Super Contributor
timestamp: May 03, 2016, 12:05:19 pm
content: Quote from: bitwelder on May 02, 2016, 05:20:58 pmIt's a power supply, usually well designed and safety-certified. No problems there.The weak point will be the DC-DC converter. Make sure you get decent ones.

author: sleemanj
author_rank: Super Contributor
timestamp: May 03, 2016, 12:20:08 pm
content: My soldering iron is powered by an old laptop supply, works great.My bench LED lighting is powered by an old inkjet printer power supply (ripped out of a brother and encased in a homemade enclosure) - these are also good sources of power supplies, if you can deal with the about 32v that they usually put out.

author: Fortran
author_rank: Regular Contributor
timestamp: May 03, 2016, 12:32:23 pm
content: I like the Dell chargers.They have a 1-wire rom on the center pin that you can easily read to get the specs on it.HP chargers has a resistor to Vcc to determine the power.Been planning to make a portable lab supply using these and reading the center pin to set the max output.The connector is pretty cheap on eBay.

author: macboy
author_rank: Super Contributor
timestamp: May 03, 2016, 04:41:45 pm
content: Biggest caveat is that most will have thenegative terminal connected to earth groundfor safety. Thisarguablyisn't strictly necessary since there is galvanic (transformer) isolation between the line side and the output, but it is almost always there. This will make your life difficult if you want a +/- supply using two of these, or you could create a ground loop if you power a device that has another connection to ground.

author: bitwelder
author_rank: Super Contributor
timestamp: May 04, 2016, 05:13:27 am
content: Quote from: macboy on May 03, 2016, 04:41:45 pmYeah, I tested a few chargers and I did notice that.

author: station240
author_rank: Unknown
timestamp: May 04, 2016, 08:53:28 am
content: Quote from: nowlan on May 03, 2016, 11:27:17 amYes, some cheap DC-DC converters only have basic short circuit protection. It's dead short detection, still possible to draw enough current to destroy the circuit.Better off selecting something with adjustable current, as then you know it won't release magic smoke.