Introduction: Variable Bench Power Supply

This is a simple adjustable bench power supply I built to help me in my instructables. 8 )

Some time ago I build another using a computer (ATX) power supply, but this kind of solution provides fixed values: 3.3, 5 and 12 volts. This is the less expensive solution you will find (just if you have an ATX as spare), and is useful if you will work just with these values, but this is not my case.

This project works with around 0.8V-29.4V ~ 5A.

Let’s do this…

Step 1: Materials

Here is a list of materials I used for this project:

Ebay:

- 1 x LTC 3780: http://www.ebay.com/itm/LTC3780-DC-5V-32V-to-1V-3...

Price: US $14.20

- 1 x 12V 5A Power Supply: http://www.ebay.com/itm/12-24V-Universal-2-3-5-10...

Price: US $9.40 (if you decide to go with 12V 2A 24W price is US $ 4.89)

- 1 x Voltage/Current Display: http://www.ebay.com/itm/DC-100V-10A-Voltmeter-Amm...

Price: US $ 3.99

- 1 x 500kΩ Potentiometer: http://www.ebay.com/itm/Cosmos-Tocos-Potentiomete...

Price: US $ 2.49

- 2 x Binding post: http://www.ebay.com/itm/10-PCS-4mm-Banana-socket-...

Price: US $ 0.38

- 1 x AC Switch: http://www.ebay.com/itm/New-Heavy-Duty-2-Pin-Car-...

Price: US $ 0.99

Of course you will need cables, weld iron, AC plug, Heat Shrink Tubing or isolate tape and miscellaneous that all Maker has.... ;

Step 2: CASE

If you have a plastic or metal case to use, it’s up to you. I prefer use wood and build it by my own.

I will not enter in details regarding the case dimensions because I believe that it is not important, and the size will be different if you decide to use different components. So, find a case that fits your project and let’s go!!

As you can see I decided to use a PC cooler fan just because I had one, but it is not necessary. It is so cheap that I recommend using. I used black paint in the wood (fan entrance) to provide a better finishing. Using a drill (8mm) I opened 5 holes to the air exhaust.

I am a Maker, so I have lots of electronic parts that I use in my project. I like to use metal 5mm LED Mount Bezel Holder as the cable holder in the case, it gives a professional touch in the project…. 8 )

Step 3: CIRCUIT

You just need to wire the components as showed in the electric diagram. Piece of cake.... ;

Some people are afraid with no protection of the original circuit, so I decided to improve the safety adding one fuse and grounding the circuit. Safety First!!!

Step 4: Wiring Everithing...

To install the potentiometer to control the voltage output you will need to remove the original mini potentiometer welded in the LTC board. Just use the soldering iron to remove this item and weld the cables as showed in the diagram.

Step 5: Testing

All cables connected its time to test the PS.

Bingo!! First project without any problems!!!!

Step 6: Knob.... ?

When I was concluding he project I noticed that I did not have a potentiometer knob! No problem, that’s the reason God gave us creativity…. 8 )

Using wine cork, a beer bottle cap and super glue I improvised one knob (MacGyver is my master…. Hahahaha)

Step 7: Final Touches

With everything inside the case, I applied a finishing to protect the wood case (wax) .

It is possible to install another potentiometer to control the current too, but to me this is not necessary.

Just it!!!!

See you soon!

Comments

author

VERY FUNNY TECHNICAL POWER SUPPLY. : D

author
Mayur BK (author)2017-05-19

what is the minimum output current ?

author
BADyoyo2 (author)2016-12-11

What AWG wire should I use for this project as I have no idea if my 16 gauge spool would work.

author
djdessert (author)BADyoyo22017-02-21

http://www.powerstream.com/Wire_Size.htm
For a circuit carrying ~5A, the wire gauge should be 14 or lower (thicker).

author
Sergiy18 made it! (author)2016-07-24

I have made a similar one. First of all, I've found the LTC3780 module schematic @ http://wiki.beyondlogic.org/index.php?title=WD2002SJ_LTC3780_Synchronous_Buck_Boost_Converter_Ebay_Automatic_lifting_pressure

Here are some suggestions for improvement:

- to regulate an output current replace a medium 200k potentiometer, pull it to a front panel in the same way it is shown for the voltage regulator.

- add 50k potntiometer in sequence with 500k as it is shown at the below circuit for coarse and fine voltage regulation

- add a Constant Current (CC) Mode Indicator: I've added a simple CC Indicator based on one transistor (any low power NPN transistor). It works just fine.
Schematic:https://drive.google.com/file/d/0ByNQSJffKH-NcmhMZ...

Indicator is connected to anode of D2 / output (leg #1) of LM358 op-amp that
controls current.
+5 rail is available at the module - generated by a LM7805 linear
regulator. CC Indicator can be also connected to an input voltage that
feeds the module. Then the value of R1 should be changed accordingly.

So, I wold highly recommend it to improve your bench power supply!

Enjoy.

CC Mode Indicator.JPG
author
javicarrera (author)Sergiy182016-10-26

Hello! nice solution for the constant current mode indicator. I have tried to make the same circuit but, somehow is not working. I get the +5v and ground directly from the 78L05, and the indicator is connected to leg 1 of LM358 as you show us.

The problem comes when the led should turn on, is not bright enough because is getting only 1.8V, where could be the problem?

Thanks in advance.

author
neblin7 (author)2016-08-04

Question. So, as I turn the knob, the pot, the display will slowly rise in both voltage and amps until I get the desired amount? Since voltage and resistance are directly proportional, those numbers ( V and R) will always be related since 12 Volts = 1 Ampere? I'm still learning on my own and don't want to toast any tests I decide to try. Thanks! =)

author
leomiranda (author)neblin72016-08-29

In the way I wired you just control the voltage (0,8 to 29,4 Volts is the range I have). Just select the desired voltage and when you connect the load, the actual current will be displayed.

author
neblin7 (author)2016-08-04

One more question. What's the lowest voltage that I can dial in with this power supply? Thanks.

author
leomiranda (author)neblin72016-08-29

0,8 Volts is the lowest.

author
MMKaresz (author)neblin72016-08-14

According to LTC3780 psu, 5V.

author
luismoro (author)2016-08-14

Muito legal o projeto!
E a knob com a tampa da Invicta ficou bem diferente! Hahahaha

author
leomiranda (author)luismoro2016-08-29

Obrigado (Thank you)

author
deluges (author)2016-07-24

Grat project ! I especially like the safety lion :)

author
leomiranda (author)deluges2016-07-28

hahaha.... thank you!

author
bl10 (author)2016-07-24

I see your fan for cooling but I only see one vent in the box. The box should have two vents if heat is a concern.

B.

author
leomiranda (author)bl102016-07-28

As I explained in the article, it is not necessary to install one because heat is not a concern. I just installed one because I have a lot of fan spares.

author
celiosantos (author)2016-07-25

Nice instructable! Very usefull for a small electronics shop i intend to make one.

author
leomiranda (author)celiosantos2016-07-28

Thank you!

author
acastrofly (author)2016-07-26

Porque o colega não postou seu projeto em portugues?

author
leomiranda (author)acastrofly2016-07-28

Por vários motivos. O principal: Porque talvez menos de 1% dos que
frequentam o site falem Português. Além disso, o site é em Inglês. Meu objetivo
é que o maior número de pessoas no mundo tenham acesso aos meus projetos. Desta
forma.... os faço em Inglês. Se notar as pessoas que comentaram este artigo vai
encontrar Franceses, alemães, americanos, indianos.... logo não faria sentido escrever
em outro idioma, muito menos em Português. E se tem algum brasileiro lendo meus artigos e que não entenda
Inglês... que sirva de incentivo para começar!

Thank you, Dank, Takk e pra você... muito obrigado. rs

author
CLTYD (author)2016-07-22

Excuse me, but… If I want to put a knob for the current… where I must to do it? By the way, when you turn on the switch, the voltimeter starts to work?

Anyway, I liked a lot your project! Thanks for share it with us.

author
Sergiy18 (author)CLTYD2016-07-26

Please, refer to my comment below RE recommended improvements...

author
leomiranda (author)CLTYD2016-07-22

Hi! See this video:

author
rhughes19 (author)leomiranda2016-07-24

Video doesn't play.

author
CLTYD (author)leomiranda2016-07-22

Thanks for reply me… but I can't see de video :S

author
leomiranda (author)CLTYD2016-07-22

Try this: https://www.instructables.com/id/Build-your-own-Variable-Lab-Bench-Power-Supply/

author
CLTYD (author)leomiranda2016-07-22

Wow! Amazing. Thanks for reply me. I like it!

author
pdavis19 (author)CLTYD2016-07-24

Current depends on voltage & load: I = V/R. So if your voltage is 12V and your load is 1K ohms, then your current is 12 milliamps.

So you adjust the current by adjusting either the load or the voltage.

author
443300889588 (author)2016-07-21

Metal mains toggle switch. No earth. Not for me!

author

I think that your concerns are unwarranted.

Like most toggle switches the one that the author used does not have any of its terminals connected to the metal toggle handle and is perfectly safe. However if you’re still paranoid then simply substitute another SPST switch with a similar current rating and a plastic handle.

As for the Earth connection (which we refer to as “ground” in North America) the 12V power supply has a ground connection that you can bring out to a third terminal on the power supply.

You could also put this project in a metal chassis and connect the chassis to ground, this would have the benefit of reducing the noise emissions from the coils on the voltage convertor (which might be an issue if you’re working with low-level audio circuits).

Personally I think it’s a very nice project and would like to congratulate the author on producing a great and useful Instructable.

author

Not paranoid. Catastrophic failure of the switch could lead to it becoming live. In a workbench/maker environment where I'm very likely to do something silly, I would far rather be safe than sorry. It would be a simple job to earth (sorry, I'm not in North America) the switch and 12v supply - little more is required than using three core cable. Alternatively, as you suggest, a different switch could be used.
I too think it's a good instructable, although a bit more commentry on replacing the pot (which one, why and what with) may have been interesting.

author
leomiranda (author)4433008895882016-07-22

Hi all! I will not enter in this discussion, but I would like to thank the comments. As electrical engineer I know what I am doing, but I have to consider the people who do not have this knowledge. Based on this, I added a photo including a fuse and grounding circuit. Please, comment if you have time.

Regards

author
RaymondR6 (author)leomiranda2016-07-25

I believe the comment comes from someone who has 230 VAC as their "mains' voltages, not just 120 VAC and "neutral" as we have. So this application may leave one live wire on the supply as the SPST toggle switch just opens one line. For better safety and prevent any voltage on any supply line, use a DPDT toggle switch to open and control both lines, leave the unused switch contacts open, and insulated the switch in a plastic enclosure. Adding the "ground" or "earth" is a good safety option.

author
JeffM15 (author)2016-07-24

Very kool. I like the voltage display. Good Idea!

Check this one out too. Use that old ATX PS laying around to make this.

http://www.tinginc.com/projects/atxpowersupply/ind...

Cheers,
Jeff

author
hamjudo (author)2016-07-22

I built something which is electrically similar, but the case was not nearly as nice. The case I used is too embarrassing for a photo here.

I happened to have some laptop power supplies with bad connectors. I chose an old Dell 90 watt supply. It provides 4.7 Amps at 19.5 volts, which is well within the specs of the LTC3780. I had to solder on a new barrel connector and mating connector on my powersupply box. I put in a current limit potentiometer.

I got my LTC3780 from a different provider. The circuit board looks the same, and the capacitors look the same. The capacitors have a maximum voltage of 35 volts. The LTC3780 and the other components can all go up somewhat higher.

I replaced the internal current limit potentiometer with one that was accessible. The minimum value for the current limit is almost an amp on mine, so that feature ins't quite as useful as I had hoped.

My power brick is unswitched, so I plugged it into a switched power strip. The switch on the power strip is not as convenient, but it means I didn't have to do any mains level wiring.

At low output voltages it can put out more than 10 amps. Next time I will go for a 20 amp meter instead of 10 amps.

author
rafununu (author)2016-07-22

Clean concept and well doing. Have you any idea of the remaining high frequencies from the converter ?

author
leomiranda (author)rafununu2016-07-22

Sorry, no idea.

author
plouc (author)2016-07-21

The knob is particularly cool!

author
leomiranda (author)plouc2016-07-22

Hahaha.... thanks

author
vsolymossy (author)plouc2016-07-21

Agreed!

author
deki (author)2016-07-21

suggest fusing it as well

author
leomiranda (author)deki2016-07-22

Thanks for your suggestion. If you take a look you will see the modification.

author
MayukhN2 (author)2016-07-21

This is a bit of a generic question, but for these dc boost or step down circuits which come with the small blue trim pots, can we replace them with a potentiometer of any (reasonable) value, or do they have to be a certain value? Thanks

author
rafununu (author)MayukhN22016-07-22

Yes of course but they should have the same value.

author
leomiranda (author)rafununu2016-07-22

Yes, agreed. thanks for your comment.