# Low Voltage High Current power supply

I am going to start off by saying I have no electrical backround, I can solder and am very mechanically inclined. I am wanting to use these as a laser power supply. I have a 24v 50a, a 48v 25a , and am getting a 5v 175a power supplies. I would like to do the voltages and amps adjustable with a potentiometer to go from 0- to their rated output. I see voltage regulators all over but they arent made for high current and usually dont make the current adjustable. How could I do this? Most laser diodes these would be used for are 2.2-3.5 volts.

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Jack A Lopez5 years ago
In a general sense, a regulator is a control system which measures some physical quantity (like voltage, or current, or temperature, or pressure, or angular speed, or pH, or whatever), and then uses that signal as negative feedback in an attempt to keep that quantity constant in time.

You've probably heard the legends of control theory, of systems with inputs and outputs. http://en.wikipedia.org/wiki/Control_theory
Watch the output using a sensor.  Use this signal as feedback to control to the input to the system.

For example the cruise control of a car has a speed sensor. If the speed sensor says the car's speed is too slow, then it opens the throttle a little bit in, an attempt to make the car go faster.  If the speed sensor says the car's speed is too fast, then it closes the throttle a little bit, in an attempt to reduce the speed of the car.

For a DC power supply, it is possible to regulate voltage or current.  That is to say, it is possible to regulate the voltage across the load, or the current flowing through the load, depending on which one of those you choose to use as the feedback signal.

The input to the system in either case is the same. There's this big switch, usually a transistor of some kind, and its function is analogous to the car's throttle. Turn the big switch "on", and both voltage and current to the load tend to increase. Turn the big switch "off", and both voltage and current to the load tend to decrease.

For those bench power supplies with two knobs on them, one for a voltage limit and one for a current limit, the actual regulation you get depends on which limit the load sort of "bumps up against" first.  If the current is hitting the current limit, but the voltage is still less than the voltage limit, then you're getting constant current regulation.  If the voltage is hitting the voltage limit, but the current is still less than the current limit, then you're getting constant voltage regulation.

Often this kind of power supply will also have two little indicator LEDs labeled CC and CV, which stand for "constant current" and "constant voltage" respectively.  The CC indicator turns on when the current flowing through the load is hitting the current limit. The CV indicator turns on when the voltage across the load is hitting the voltage limit.

Laser diodes and LEDs like constant current. In contrast, trying to feed constant voltage to a LED or laser diode is a good way to let the magic smoke out.  Also for  a LED or  laser diode, the brightness, the quantity of light emitted per unit time, tends to be proportional to the current flowing through it.  So basically you set the brightness by setting the current, and you do this with a constant current regulator.

There exist inexpensive adjustable switching regulators in module form, that I think would be suitable for driving laser diodes.  For example:

The prudent thing to do when setting up such a regulator is to test it with some load other than your expensive laser diode, like say a resistor, to make sure its working in constant current mode, and at the current you want it to.  Once you're confident the module really and truly is regulating the way you want it to, then it's safe to swap in the laser diode.
wby300 (author)  Jack A Lopez5 years ago
24v 50a, 48v 25a , 5v 175a The 2 you have linked to are 2 and 3 amp. The one diode I have now operates on 2.2v at 56A I appreciate the explanation and the links but the links dont help. And yes, I even tested my Sorensen before hooking up the diode.
5 years ago
Wow! That's a beefy laser diode!  Do you have have a link to the data sheet?  I ask just because I am curious, not because I'm incredulous.

I have seen a 30 A constant current supply here:
http://www.powerstream.com/dc-hydrogen.htm
That gizmo is actually intended for electrolyzing water into hydrogen and oxygen.  It is expecting a voltage across the load of about 4 volts, so I am guessing it could run comfortably at 2.2V and 30A, since that's less power than it is designed for.

Actually, since that company, PowerStream, makes things similar to what you are looking for, you might ask them about this 50A laser diode supply you are seeking.

iceng5 years ago
I didn't know laser diodes capable of such current were readily available.
That kind of input power, even at poor efficiency can still do serious work.

I have been wanting to put holes into  rock 1/2" dia  3/4" deep.

Where does one acquire such diodes ?

If I had some Laser diodes like that,  you can bet there would be
interesting circuit supply designs unfolding from this rocky Sierra
mountain state engineer.

A
5 years ago
The largest I've seen on Ebay ('cos I just looked) is a 15W diode unit, made for cutting applications, and about 1300 USD, complete - from a supplier in Turkey.

Double that and its comparable to a CO2 laser and becoming tempting. What I'd like to see is a fibre laser kit ;-)
wby300 (author)  steveastrouk5 years ago
Not exactly sure where you looked but there are more powerful lasers than that on ebay. Also a CO2 and Diode laser are completely different even though the power output may seem the same. A CO2 laser 10,600nm will not cut certain metals as well as a 1064nm even though it may have 10w in power over the lower spectrum laser.

Also some lasers wont travel through liquids well 2000nm-2900nm these are used for medical more because they are easier to control when cutting on the human body. The lower on the spectrum the laser is, the better it is as far as the quality of the beam and how fine the dot is. UV and X-ray spectrum lasers are the future of lasers.

No laser should be viewed without the proper eyewear, although the CO2 is not absorbed by the cornea. As long as the beam isnt directly shined in the eye it is considered eye safe.

If you are considering getting into lasers, I reccomend doing a lot of research before hand, Also purchase a complete laser because you will get everything, including the cooling system, and safety switches.
5 years ago
I already have a laser cutter, and a lot of experience with diode lasers for optical research applications.
wby300 (author)  iceng5 years ago
I have one diode that puts out 40w at 2.2v 36a. I also have a co2 that is 50w but these take a special supply that puts out up to 40kv at very little current, usually less than 5a. I was looking at getting 2 100w diode bars to use as add on pump diodes for a 150w flash pump laser I have. These are readily available to anyone, you just need to know where to look. Ebay is a good site for these, you can look on several used laser equipment sites also. These can be purchased brand new from manufacturers also, although they are usually more than double the used cost. I have an argon I paid 100.00 for and it sells new for 12k, mine is about 4 years old. My co2 was 300.00 with shipping, the tube alone usually starts at 3k for a name brand one.
5 years ago
Since 40kV x 5A = 200 kW, I think there should be a mA there.
wby300 (author)  steveastrouk5 years ago
Yes, sorry, most are in the mah range.
Vyger5 years ago
Arc welders are adjustable. Low voltage and super high amps for melting welding rod to steal.
5 years ago
What do you steal with melted welding rods? Or do you use them to threaten the cashier at the Kwik-I-Mart?

(Yes, I know, but it was too good an opportunity to waste :-)
5 years ago
I Know, I no. English as my only language and I all too, two, to often confuse the spell checker. I always wondered about the whole, hole, idea of looking it up when you don't know how to spell it to begin with. But, or butt, I at least know how to pronounce aluminum.
kelseymh5 years ago
Current should not be "adjusted." Power supplies are rated according to the maximum current they can deliver to a load. The load will attempt to draw whatever current it needs to do its job.

Usually, high-current supplies as you describe are already voltage adjustable, as part of their design. If yours aren't, then you'll need to buy or build an appropriate circuit, which can handle at least the maximum current for which the supply is rated.

You should also expect to build such a circuit with active cooling, since you'll be trying to dissipate several hundred watts of heat.
wby300 (author)  kelseymh5 years ago
Why do companies like Sorensen make high end power supplies with adjustable voltage and current? Either way there still arent any voltage regulators that will work at 175A. I have 2 radiators with dual fans and high volume water pumps from a couple lasers, so cooling wont really be a big problem.
5 years ago
See mpilch's comment. The current is not adjustable; it is determined by the load (Ohm's law: I = V/R). Those supplies have a maximum current limit, and a circuit which automatically reduces the voltage when that limit is reached, limiting the current draw by the load.

We used exactly this kind of high-voltage supply (from CAEN) on the BaBar drift chamber. The supplies could deliver up to 2 kV per channel with a software selectable current limit up to 200 uA.
wby300 (author)  kelseymh5 years ago
OK, so I want to be able to adjust the limit of the current. Setting a maximum or making it adjustable sound exactly the same to me. What is it called when its made so you can ADJUST the maximum output of current?
5 years ago
That's called a "current-limiting" power supply. If your load can safely handle a reduced voltage, but may attempt to draw more current than it can handle, then a current-limiting supply is what you want.

See also Steve's comment above. You cannot simultaneously control both the current and the voltage, since the two are constrained by the load, via Ohm's law.
5 years ago
They are not INDEPENDENT variables, you can control one, and the other is free. So a constant voltage supply delivers a constant voltage in a certain range of loads with a variable, finite range of output current, so a constant current supply delivers a constant current over a certain range of loads and finite range of output VOLTAGES.
5 years ago
5 years ago
It's delivering the constant current by moving the voltage up and down, right? Okay, I see your point. If the voltage is actively varied, and the current-limit setpoint is tunable, then you end up with an adjustable-current supply.
5 years ago
+1.
It actually works by controlling the voltage across the loop between pin 2 and 1. The device aims to set the voltage between 1 and 2 to be 1.22 Volts BUT here, the source of that voltage is derived from the voltage across the TOP horizontal resistor, so effectively we are fixing THAT. If the voltage across a fixed resistor is fixed, so is the current through it.
5 years ago
No, it is perfectly reasonable to make a current mode PSU.
Re-design5 years ago
To use a voltage regulator on very high current, you have to use transistors to carry the load. Something like 3055 IIRC. You put several of them in parrellel and put them in heavy heatsinks amd maybe a fan or two and they carry the load.

Check out this link.  It uses different transistors but a similar principle.
wby300 (author)  Re-design5 years ago
Thank you, I was looking at something like this yesterday. I figured you could just keep adding transistors until I get to the current I need. This is exactly what I was looking for, I just need to look around for some values to get the voltages I need.
mpilchfamily5 years ago
Many companies make bench top power supplies where you can set the current limit of the power supply. Your not adjusting the current just setting the max it will allow so you don't burn up whatever circuit your testing.

Trying to engineer the added circuits needed to convert those power supplies to adjustable supplies with adjustable current limiting takes some electronics know how.

If you really want to learn it then check out this videos below. If your interested then look up the full series. Now he isn't converting a PSU, he's building one from scratch. But he goes over all the design aspects and principles involved in making a lab power supply. Everything he shows you can be used to run your PSUs. You may have to add a bit more in order to handle the amount of current you think you'll need.

wby300 (author)  mpilchfamily5 years ago
Thanks for your info, I will look into this. I have been getting a lot of books on learning electronics, just never seem to get the time to read.