High current Regulator? - Page 1
Forum section: electronics / beginners

author: wby300
author_rank: Newbie
timestamp: December 11, 2013, 03:31:44 pm
content: I have 2 old power supplies that are 5v 150A output, I want to make these both adjustable so I can control the voltage and current down to 0v. I also have a couple other power supplies that are 24v 50A and 48v 25A that I would like to make adjustable also. I am definately a begginer at electronics, is this going to be something too hard to build? Thanks everyone, I am new to this forum and appreciate any help anyone offers.

author: mariush
author_rank: Super Contributor
timestamp: December 11, 2013, 03:36:36 pm
content: I think you should start with something smaller and simpler. 150 A is stupid high current, you can weld metals with that. It wouldn't be easy to implement current limiting at those currents.

author: wby300
author_rank: Newbie
timestamp: December 11, 2013, 03:55:23 pm
content: Yes, I know the risks. I am trying to do this project for lasers, I have several diodes that max at around 25A each but voltage is 2.2v_2.8v

author: Dave
author_rank: Super Contributor
timestamp: December 11, 2013, 03:59:43 pm
content: Let me guess, old computer ATX supplies? You are probably better off building a power supply from scratch than trying to modify one of these into a decent lab supply.Btw, laser diodes need a regulated current, not voltage.Edit: I just read the topic again.

author: RossK
author_rank: Contributor
timestamp: December 11, 2013, 05:11:34 pm
content: http://www.mouser.com/Search/ProductDetail.aspx?R=STP80PF55virtualkey51120000virtualkey511-STP80PF55These MOSFET's are capable of acting as your regulators. While the SOA (safe operating area) graph does not include their DC characteristics they do operate quite well and reliably in their linear region. The architecture of these FET's is ideal for linear mode operation. When looking at the SOA graph realize that the x-axis (voltage) is the voltage dropped across the MOSFET and that if you were to graph the power curve over the full voltage range (assuming a resistive load) the maximum power which will need to be dissipated (via heat) by the device is at 50% voltage as the power dissipated by the load and the FET's are equal.I would suggest designing the regulator for the loads you expect to drive through it, not the maximum the power supply is capable of. In any case use a PTC (or several in parallel if needed) to protect the mosfets from over current conditions and a TVS to protect against voltage spikes, esp. for the 48V supply.Assuming max current here is a starting point of estimates of the number of FET's that would be needed - assuming adequate heat sinking and forced air5v 150A - 3 to 5 fets24v 50A - 5 to 8 fets48v 25A - 5 to 8 fetsAnd yes, i have successfully built and used adjustable voltage supply based around these FETS

author: codeboy2k
author_rank: Super Contributor
timestamp: December 11, 2013, 07:01:49 pm
content: What is it about this forum that attracts people that have little to no experience with electronics, but want to start with 100's of amps and/or 1000's of volts?No offense intended to the poster, but you're not the first person to come here claiming they have little experience, yet want to start doing something with power levels that put fear in even the most seasoned engineers...Then when we point it out, suggest that maybe you should start smaller, they're like "yah, yah, I know all the risks, don't worry I'll be careful... how do I do it?"You do realize those lasers at even 60% efficiency are going to emit a 30W beam !!You will need one of Mike's stickers, included below for your pleasure:http://www.electricstuff.co.uk/scarylaser.gifAnd read Mike's pages on his work with lasers, and the power supply mods he had to make. It's not as simple as it seems.Start herehttp://www.electricstuff.co.uk/argonlaser.htmlGood luck, and be careful.

author: tszaboo
author_rank: Super Contributor
timestamp: December 11, 2013, 07:13:59 pm
content: Assuming, that you use the MOSFETs above, 0.5K/W, ten in paralel, 125 degrees junction temperature, 25 degrees room temperature. Tell us, when you have the 0.05-0.07 K/W heatsink required, and we will tell you how to proceed. (Get a BFH)

author: wby300
author_rank: Newbie
timestamp: December 12, 2013, 11:26:30 pm
content: Thanks to RossK, who actually provided information. I came to the BEGINNER part of this place asking for information so I can become a non beginner, not so people could whine about what I am wanting to do. I have plenty of experience with lasers, not even sure why laser safety was mentioned but that is covered and not related to the real question. I also am not wanting to build a massive power supply, just add adjustability to an existing one. I have never heard of an ATX power supply for a computer pushing 150A. I also have several lasers, a couple 150W, 9-25W a 50W Co2. I have a mill and lathe for metal with tons of aluminum and steel for things like heat sinks, also have parts for about 3 liquid cooling systems if I happen to need one. I didnt realize adding a dial for current and voltage to an existing power supply was rocket science. Just a thaught, but if you dont want to hear newbie questions on "how to build a powersubstation in my living room", dont hang out in the newb section.

author: senso
author_rank: Frequent Contributor
timestamp: December 13, 2013, 12:04:25 am
content: 5v is a bit low, but TIG and arc welders can work all right with 20v, 150A with a 3mm stick will CUT right through 2mm steel.For someone with lath and milling machines, not knowing anything about welding is a bit strange.And yes, limiting 150A to 0A outside the regulation loop of the supply will involve dissipating massive amounts of energy.

author: IanB
author_rank: Super Contributor
timestamp: December 13, 2013, 01:15:51 am
content: Quote from: wby300 on December 11, 2013, 03:31:44 pmYes, it is.If power supplies were not designed to be adjustable to begin with, you can't make them adjustable. The voltage and current regulating loops of adjustable supplies are "inside" the power supply and usually make the design much more complicated. If they are not there to begin with you can't add them. All you can really do is add secondary voltage and current regulating circuits on the outside, and this is hard to do for currents greater than about 5 A.

author: wby300
author_rank: Newbie
timestamp: December 13, 2013, 10:58:21 am
content: Well thanks for actually explaining that, it makes a little sense when it is explained and not just stated that it is a crazy insane idea. I had considered the welder idea also but like you say, 5v is seriously low. I got these for 20.00 each and they are in great shape, so I couldnt really pass them up.