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Convert 0-30V 3A PSU to 5A or more


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I have built dual output 3A PSU - the original chematic. When not used on extremas it's ok. Now that I'm trying to build the 5A PSU I need really large heatsinks since I want it to be as stable as possible. Now the trouble is that this kind of heatsinks aren't easy to find. I was planning to use 2 of those instead on 2 walls of the box, so basically those h/s will be as part of the box. I'm interested in 2 flat h/s sized 150x250mm or more. Any suggestions where I could purchase something similar or same? I live in California, US btw. If samples are available from somewhere I would really appreciate it ;D

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Hi Kain,
Don't worry about stability, if your heatsinks don't work well then the output transistors will be destroyed!
If the project is powering a low voltage or accidently shorted load at 5A, the output transistors must dissipate about 200W.
You were talking about using a flat heatsink. But it must have big, exposed fins like the picture in the article, and even bigger.

My Newarkinone catalog has 11 pages of heatsinks, some with power ratings and temperature rise. Digikey is another large supplier. Order on the web or by phone.

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Ante, I've been thinking about this but it's kind of pointless to put water cooling system considering that the air cooling h/s with large enough surface area would do it fine. I have built water cooling for my PC though, but the reason is overclock, noise and staility. It has been working for 1.5 years so far with no leaks and problems (crosses fingers). About the immortality of the project - if I make a water cooled setup and it happens to leak somewhere it will be extremely mortal ;D Oh, btw here is a picture of the front pannel of my PSU - almost finished. Only the writings and knobs for the potentiometers are missing :)

post-2662-14279141889689_thumb.jpg

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Hi Bohda,
A TL431 is much better than a zener diode with an ordinary resistor. Since D8 is operating inside the constant current feedback loop of U1 in our project, this combination is approximately equal to the performance of a TL431, when the zener and resistor are the parts as discussed before.

A few people have made a new PCB but have not reported back again.

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  • 3 weeks later...
  • 3 weeks later...

Ok, since nobody posted any PCB for this project, I decided to finish the job. The board I have worked on so far would be double layer board since I was trying to make it smaller, I really hope you don't mind. I can do single layer too but it would be about the same size as the original. The one I am about to finish is 100/60 mm.

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I would use 2 monting bolts x 3mm so this is not a big deal. The real thing is that I took the 15W resistor off the board - it will be way better if it's attached on the box and link with short wires to the board since it will allow it to cool better i believe. This is why the board can be that small ;D

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Thank you Kain, for taking on the job of designing the PCB :). Double layer board, that will be a new challenge for me I'll be looking forward to giving that a go ;D. I was planning on putting this project together some time after Christmas, to add to the original PSU that I put together, with a couple of modifications and works very well 8).

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Do I understand this right, I can use this power supply to recharge rechargeable batteries, by setting the voltage and current limit to suit the requirements of the battery to be charged. Is it possible to add a circuit that can be adjusted that will sense when the battery is fully charged, then disconnect the power or maybe shut down the PSU.

If it can be done I think it would be very handy :).

Sorry if this isn't the appropriate place to ask this question.
I was thinking it may be a handy optional add-on for this project.

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Dazza, I think the application you are talking about can be achieved pretty easy - I mean the self turn off. In fact, you almost have it built in already ;D. If you noticed the LED that is used for indication would light up if the current limiter is working. However, as far as I understand the current is still there, but cannot exceed the given value. So, if you battery is the load in the circuit, while it's being charged it would become lighter load thus the circuit protection would stop working and the LED would turn off. If you invert this signal for the LED you can have a circuit that goes on when the LED turns off, such as something that breaks the circuit and so on, such as thyristor in combination with reley or something else. Use your imagination ;D. If I am right your shut off is as easy adjustable as the curent limiting is. I hope I'm right thoough hehe

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Hi Guys,
A battery that is charged from a regulated current supply does not become a lighter load.
It will continue to draw the same amount of regulated current that you have set for maximum, but after it is fully charged will convert the entire charging power to heat and gasses. If the charging current is high the heat will damage the battery or the gasses cause it to vent or explode. If the battery is a lithium rechargeable, it will probably catch fire.

Depending on the battery's chemistry type and temperature, you can charge it through a current-limiting resistor (or current regulator) for a fixed amount of time. If the charging current is high, a high temperature cutoff circuit should also be used in case the charging battery was not completely discharged.

IC manufacturers make battery charger IC's for each chemistry type.
Good explanations about charging batteries are in our Articles section.

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Hi Kain, are you trying to make me blow up my batteries :o, just kidding I don't have any yet ;D ;D ;D. Lucky ;D.

Hi audioguru, from what you have explained, it won't be easy to allow for different battery types to be charged.
Maybe I should just try for battery types that I will mostly use :).

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Dazza, I almost got you though, huh? ;D Just kidding. The blow off thing hasn't happened to me before but for I always use resistor to limit the curent down as audioguru suggested. Audioguru, doesn't the current protection limit the current down so it will serve the same purpose as resistor in this case?

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Hi Dazza,
I wouldn't use a supply with adjustable voltage and current controls to charge a battery. A kid comes along and fiddles with it or you accidently bump it and you have a very dangerous situation.

The charging characteristics of each battery type is different, although a Ni-Cad and a Ni-MH are similar. Aren't you using a good old lead-acid battery? At room temperature, just limit the current to a reasonable amount with a resistor and limit the voltage to 13.8V for a 12V battery. When it becomes fully charged, it won't over-charge like the other types will.

Hi Kain,
That's good that you use current limiting resistors to avoid explosions! You are correct, current regulation serves the same purpose as a current limiting resistor, except it automatically changes its resistance to keep the current at the same value when the load voltage or source voltage changes.

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Hi Audioguru,

This is not entirely true, I have charged many batterys in this way and never caused any damage. If you just do it right there is no problems as I see it. For example to charge a car battery, set the voltage to 13.75Volts then connect the battery and set any current up to 5% of the capacity. For a 60Ah battery this will be 3A, and leave it. There will be no destruction or gassing or explosion, what will happen is the voltage is now lower (current foldback) than the 13.75V set but the current will stay at 3A. Slowly the voltage will rise to 13.75V but not more, then the current will start to fall. Gassing will only occur in a lead acid cell if the voltage exceeds 2.38Volts (14.28V) so there is no gassing here. The voltage set at the start is the maximum for the charge that

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Hi Ante,
You charge your batteries at a very low safe current and use voltage limiting.
I was cautioning Kain because he didn't understand that a current regulator will increase its output voltage to maintain the set current.
He also misunderstood that a fully charged battery would automatically reduce its charging current which certainly is not true if the charger's voltage is not limited.

Did you notice that car amps are rated with a 14.4V supply?
It must be the battery's gasses that create the extra output power!

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