Variable and fixed output power supply build from laptop charger - Page 1
Forum section: electronics / projects

author: aiq25
author_rank: Regular Contributor
timestamp: April 13, 2015, 12:40:20 am
content: Hello. I'm planning on building a variable and fixed output power supply using an ATX case and a 3rd party Toshiba laptop charger (it's for an older model laptop I think). I had a new ATX power supply I was going to use for this project but decided not to because I don't need that much power and I felt it if I did something wrong I might be in a of trouble.I took out all the circuitry from the ATX supply to use the case, switch and fan. The laptop charger I'm planning on using seems like is good quality (Chinese made). Its 15V output at about 7.33A (110W max power). I have tested the charger but not at max capacity. The charger is long and won't fit into the ATX case unless I put it on it's side (see attached picture). I'm planning on using some LM2596 voltage regulators for this. I was going to buy some modules from eBay but I don't feel like I can trust those modules. Does anyone know where I can find them for a reasonable price? I don't mind paying extra if the build quality is better.I'm planning on having 2 or 3 5V outputs at 1.5A max for all of them (in the case it will be one regulator but will have separate connectors for banana plugs). Also planning on have 3.3V, 12V and the variable output all at 0.75 or 1 A max. I'm thinking of using cheap volt/amp meter combination from eBay. I don't know how accurate these should be. One problem I think I Will have is with heatsinking. I'm planning on using at least 2 heatsinks and I'm not sure if I will be able to fit them all in the case because the long power supply.I think the first step would be test the charger and see if anything smokes when I try to get it to output high current. I'm planning on building a constant current dummy load to test this. I have access to some equipment that I can use to test the dummy load and build it.The point of this project is to learn and built something, not necessarily to save money but saving money doesn't hurt.Any feedback would be appreciated.

author: smjcuk
author_rank: Frequent Contributor
timestamp: April 13, 2015, 09:43:02 am
content: The ones on ebay/aliexpress are probably fine. Might get a bit hot so consider ventilation.Watch out for cheap laptop switch modes. They're noisy, potentially dangerous and tend to melt or break if you push them. I've had some quite interesting failure modes including dumping mains live straight down the output cable.I am however wondering if a second hand bench supply with current limiter would be a better investment.

author: Rick Law
author_rank: Super Contributor
timestamp: April 14, 2015, 08:54:48 pm
content: Quote from: aiq25 on April 13, 2015, 12:40:20 amThose cheap Chinese ready-made Buck modules works pretty well. Each costs around $2 USD (LM2596). The Chinese compatible XL6009 (instead of LM2596) ones are even cheaper. I used a number of LM2596 buck for over a year. They are not bad at all. I've not used the XL6009 but I have used an XL4051 (high current version).Since laying out good buck circuit is difficult to do well - too dense and too sensitive, I think using those modules is a good idea.You said want volt display, some of these modules are equipped with Volt display (starts around $3 USD). You should also consider modules equipped with current limit (starts around $4 USD). The ones with current limit, volt and current display LED are a good bit more expensive.Since you are making 5 of them at least, why not order one first, try it out. If it works, then get another 4 from the same seller.

author: edavid
author_rank: Super Contributor
timestamp: April 14, 2015, 09:04:19 pm
content: Quote from: Rick Law on April 14, 2015, 08:54:48 pmThe XL6009 modules are boost modules.Here is a cheap source of LM2596 modules, if you are not in a hurry:http://www.malloom.com/led-driver-power-supply-adapter-ac-100-240v-to-dc-24-40v-waterproof-40w

author: aiq25
author_rank: Regular Contributor
timestamp: April 14, 2015, 09:08:51 pm
content: Quote from: edavid on April 14, 2015, 09:04:19 pmHoly moly those are cheap!! Do you think these will be the same quality as eBay ones? I don't mind waiting because I just thought of another project I would like to before this.

author: edavid
author_rank: Super Contributor
timestamp: April 14, 2015, 09:29:22 pm
content: Quote from: aiq25 on April 14, 2015, 09:08:51 pmI could not see any difference.

author: Rick Law
author_rank: Super Contributor
timestamp: April 14, 2015, 10:33:31 pm
content: Quote from: edavid on April 14, 2015, 09:04:19 pmHoly macro... I got all those numbers mixed up - I just had it in my mind XL6009 is the Buck also. Good that you point it out.

author: ez24
author_rank: Super Contributor
timestamp: May 03, 2015, 03:45:40 am
content: To aiq25 (the op)I think we are working on the same project. Would you be interested in my progress? I have put out lots of posts that maybe you could track by searching on my name.I would not mind joining forces.Roger in San Diego

author: paulie
author_rank: Frequent Contributor
timestamp: May 03, 2015, 04:15:29 am
content: Quote from: Rick Law on April 14, 2015, 10:33:31 pmActually that part is functional as a buck converter too. Unfortunately the cheap chinese modules are configured as boost but some liars list it as buck. I ordered a few based on this incorrect info but it did eventually work in my favor with full refund. No need for more boost modules but the price was right.

author: Rick Law
author_rank: Super Contributor
timestamp: May 03, 2015, 05:52:00 am
content: Quote from: paulie on May 03, 2015, 04:15:29 amGood that it worked out for you.I rarely trust the eBay description alone. I have seen the other way around. Item description said boost, but item detail has Vout < Vin+3V. I like to inspect the item photo carefully to see if it indeed is what it is suppose to be.Even when photo, description, and details all matched, I recently got some CD32 inductors instead of the CD54 listed/sold - exactly alike but very much smaller than the CD54. Very annoying.Well, eBay/AliExpress Chinese stuff are cheap, so the occasional hassle is part of the price of cheap, I suppose.