Author Topic: Cheap bench power supply?  (Read 11420 times)

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Offline slybundaTopic starter

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Cheap bench power supply?
« on: January 28, 2024, 01:37:29 pm »
Looking fora cheapo bench power supply, one of those 0-30v things. Seen a few on AliExpress but not sure which one to go with. I dont want to cheapo out to the point i end up with something dangerous so just need it to be safe and reliable.
Any suggestions?
 

Online Aldo22

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Re: Cheap bench power supply?
« Reply #1 on: January 28, 2024, 01:54:49 pm »
I recently bought the cheapest one and wrote about it here.
 

Online nctnico

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Re: Cheap bench power supply?
« Reply #2 on: January 28, 2024, 02:12:06 pm »
I recently bought the cheapest one and wrote about it here.
For your primary bench power supply, you'll want a linear one. Not a switcher like yours. Way too much noise on the output; you can't make decent measurements in circuits. Korad sells decent linear bench power supplies. I'd go that route when on a budget.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Online Aldo22

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Re: Cheap bench power supply?
« Reply #3 on: January 28, 2024, 02:21:22 pm »
For your primary bench power supply, you'll want a linear one. Not a switcher like yours. Way too much noise on the output; you can't make decent measurements in circuits. Korad sells decent linear bench power supplies. I'd go that route when on a budget.
Yes, that's right.
I still have an old linear one, which is usually sufficient for electronics experiments.
But it doesn't deliver more than 10 watts.
The new one can deliver up to 300 watts.
It just depends on the intended use.
 

Offline madires

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Re: Cheap bench power supply?
« Reply #4 on: January 28, 2024, 02:22:33 pm »
Cheap, AliExpress, safe and reliable in one sentence sounds like an oxymoron. Or in other words, anything with a mains plug you buy from AliExpress requires a safety inspection before plugging in. Back to your question. Are you looking for a linear or switching mode PSU? How many amps?
 

Offline audiotubes

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Re: Cheap bench power supply?
« Reply #5 on: January 28, 2024, 02:51:56 pm »
The Korad KA3005PS is supposed to be an update on the prior "P model. I just got the new one for 100 euros to use for some radios while I check out my main POS supply I was using. Seems pretty ok, especially for the price.
I have taken apart more gear than many people. But I have put less gear back together than most people. So there is still room for improvement.
 

Offline slybundaTopic starter

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Re: Cheap bench power supply?
« Reply #6 on: January 28, 2024, 03:00:12 pm »
Doesnt need to be much on amps maybe 5amp. Can use it to charge batteries and inject voltage here and there and pop a few old capacitors now and then lol.
 

Online bdunham7

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Re: Cheap bench power supply?
« Reply #7 on: January 28, 2024, 03:14:42 pm »
Doesnt need to be much on amps maybe 5amp. Can use it to charge batteries and inject voltage here and there and pop a few old capacitors now and then lol.

Many otherwise OK power supplies are at risk of blowing up if you charge batteries.  You either need one that won't do that (good luck and lots of money, these are typically vintage units) or you can get one with a remote sense feature and use a large diode for battery charging.  The Korad KA3005PEA from Eleshop in the UK has the remote sense option, you'd need to read the manual to see if it will perform properly charging a battery through a diode.  Some PSUs have significant limitations on the sense voltage differential and won't work with this setup.
A 3.5 digit 4.5 digit 5 digit 5.5 digit 6.5 digit 7.5 digit DMM is good enough for most people.
 

Offline slybundaTopic starter

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Re: Cheap bench power supply?
« Reply #8 on: January 28, 2024, 03:29:31 pm »
Ahh i see. Mostly want to charge up some lead acid batteries like the ones you get in ups 6v and 12v batts. What sort of power supply am i looking at then for this sort of job? Im in the uk so ebay, amazon and mouser etc are available to me. Cheapest power supply at rs components seems to be well over priced.
 

Offline andersthuresson

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Re: Cheap bench power supply?
« Reply #9 on: January 28, 2024, 03:34:26 pm »
I have 4 power supplies. 2 of them are linear and the other 2 are switching type. Which ones I use depends on what type of work I will do. For audio work I always choose linear supplies because I want to keep the noise low. One of my supplies is a switching power supply from Aliexpress and it's branded "Nice-Power". It outputs 60VDC/5A and so far it's been working fine. They have a bunch of different versions with various outputs.
 

Offline madires

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Re: Cheap bench power supply?
« Reply #10 on: January 28, 2024, 03:48:51 pm »
Ahh i see. Mostly want to charge up some lead acid batteries like the ones you get in ups 6v and 12v batts. What sort of power supply am i looking at then for this sort of job?

You can find good lead acid battery chargers for 50 bucks (supporting 6 and 12V).
 

Online DaneLaw

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Re: Cheap bench power supply?
« Reply #11 on: January 28, 2024, 05:57:40 pm »
A cheap linear bench PSU, here Korad has been the obvious choice for many over the last decade, simply because of the price.
Korad KA3005D / 31V / 5.1A is around 70 euros and up from European resellers incl. VAT but the Korad KA300X series control scheme is problematic, as you control the output "on/off" by one of the two main knobs by holding it in for a given time, here the KD300X series is preferred, with its dedicated on/off buttons.. - if you control it from PC then you don't have these issues.

Also, the path I went a little over a handful of years back, I purchased one from Europe KA3005P, and one from China KD3003P both with PC control interface (=P).

A look inside..http://tinyurl.com/28upwfre
http://tinyurl.com/5h636f4c

Went with linear to circumvent the noise from switching when working with delicate laser diodes but nowadays, I really don't use them a lot, I primarily use these small switching PSUs like below that can run on fx powerbanks - as the diodes don't seem to mind and it is way easier to manage when your setup are based on mobility in lack of a dedicated bench, here these 4½ kg AC PSU's gets quite cumbersome.
You can obviously daisy chain them to get a higher voltage or amps than the 5.1A or 31V as most linear PSUs are limited at 3A or 5A.

If I were in the market for a linear PSU in 2024, I would pursue one with a graphical interface, as these 7-segmented displays can be a limiting factor, when trying to maintain an overview of your settings etc.
 
« Last Edit: January 29, 2024, 04:26:51 pm by DaneLaw »
 

Online KungFuJosh

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Re: Cheap bench power supply?
« Reply #12 on: January 28, 2024, 06:02:40 pm »
I have a Tekpower TP3005P I got on Amazon for $100 7 years ago, and it's been great. Seems generally clean and stable.
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Online csuhi17

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Re: Cheap bench power supply?
« Reply #13 on: January 28, 2024, 06:12:03 pm »
To charge the battery, only use a charger or through a charging circuit, do not use a PSU directly.

Even battery chargers can cause problems, I know someone who burned down his shed with a battery charger because he overloaded the charger...

Buy two separate units for charging and feeding.
For charging, there are a couple of RC battery chargers that can charge several types, and they have a variety of protections and parameters.

You have to pay close attention to the setting, because you have to set the number of cells (voltage) separately, not all of them are automatic.

I do not recommend the HTRC T400 duo series because they measure inaccurately.
Fnirsi oscilloscope = waste&regret
 

Offline bingo600

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Re: Cheap bench power supply?
« Reply #14 on: January 28, 2024, 06:19:40 pm »
The Korad KA3005PS is supposed to be an update on the prior "P model. I just got the new one for 100 euros to use for some radios while I check out my main POS supply I was using. Seems pretty ok, especially for the price.

Arrghhhh  |O
NOT NICE to reveal that (fine) price  :scared:

One Korad KA3005PS on the way from eleshop.eu  :palm:
Ended up in 122€ incl shipping to DK

/Bingo
 

Offline slybundaTopic starter

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Re: Cheap bench power supply?
« Reply #15 on: January 28, 2024, 09:43:05 pm »
any options for powering small stuff like mosfets and led's and microcontrollers for a little while on a breadboard? usb powerbank and some sort of buck/boost converter possible?
 

Offline shapirus

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Re: Cheap bench power supply?
« Reply #16 on: January 28, 2024, 10:30:02 pm »
any options for powering small stuff like mosfets and led's and microcontrollers for a little while on a breadboard? usb powerbank and some sort of buck/boost converter possible?
I got one of these ~3 years ago: https://www.aliexpress.com/item/1005005145280146.html and coupled it with an old school transformer+bridge+caps AC/DC PSU (I thought I needed this kind of galvanic isolation at the time).
It works fine.
I charged batteries with it many times, because nobody told me it was a bad idea. Just as expected, no issues whatsoever (though it does consume a little bit of current, like few mA, when it's off and you apply voltage to its terminals).
Voltage regulation is off by ~10 mV. Current regulation struggles to work correctly up to about 25-35 mA, but it glitches on the safe side: sometimes it goes into CC mode and lowers voltage when it's not yet necessary. Higher than that, it works well.

One caveat in this configuration: because of the capacitive coupling between the transformer's windings, there is considerable AC voltage between either of the terminals and mains earth or a human. Of course they are in phase, so it's proper DC between the two of them, and it's a very high impedance source, but I did kill a few MOSFETs with this voltage (connect source to one of the PSU terminals, touch gate, bingo). It would make sense to add a PE connection to optionally tie one of the terminals (negative) to mains earth to avoid these issues.

The only scenario so far when I needed anything else has been when more than one power rail was required. In these cases a proper multi-channel (2 or better 3) lab PSU would be much more convenient.




Noise at 15V output with a 1.2k resistor as load, 5us/div horizontal, 10mV/div vertical:



« Last Edit: January 28, 2024, 10:56:19 pm by shapirus »
 

Online KungFuJosh

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Re: Cheap bench power supply?
« Reply #17 on: January 28, 2024, 10:40:20 pm »
I got one of these ~3 years ago:

Those are great. I use one of those in my FUtracer curve tracers. I usually get this version: https://www.amazon.com/gp/product/B01LWXAC5E/

I haven't tried this one yet, but it looks interesting for people that need more voltage: https://www.amazon.com/dp/B0C89F4XJY/
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Offline shapirus

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Re: Cheap bench power supply?
« Reply #18 on: January 28, 2024, 10:42:32 pm »
BTW, speaking of noise, you should not necessarily rely on power being clean. If the circuit you develop requires very clean power, then adding filters is on you. If your device will be powered by e.g. a USB port, then you can expect any sort of noise in power input, and you need to filter it anyway.

If you need to test some components etc. and make precise measurements that can be affected by the PSU's switching noise, then it's easy to add filtering between the PSU and the circuit, including, if necessary, a linear regulator. I really see no point in requiring that your bench PSU should necessarily be a linear one. Switching converters, even cheap ones, should be fine for most cases.
 

Offline shapirus

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Re: Cheap bench power supply?
« Reply #19 on: January 28, 2024, 10:52:04 pm »
I haven't tried this one yet, but it looks interesting for people that need more voltage: https://www.amazon.com/dp/B0C89F4XJY/
Yeah it looks quite good, and it's btw a lot cheaper (about $35) on Ali. I might build a second unit to serve as a second channel, will see. However when you add the price of an AC/DC PSU... it may well be that getting the ready made one (I am sure they make ones already with a case and AC/DC supply) will cost the same, if not less, not to mention that it's easier. Building my first one was fun, but it was just enough of that particular kind of fun for me :).
« Last Edit: January 28, 2024, 10:59:32 pm by shapirus »
 

Online KungFuJosh

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Re: Cheap bench power supply?
« Reply #20 on: January 28, 2024, 11:04:50 pm »
Yeah it looks quite good, and it's btw a lot cheaper (about $35) on Ali. I might build a second unit to serve as a second channel, will see. However when you add the price of an AC/DC PSU... it may well be that getting the ready made one (I am sure they make ones already with a case and AC/DC supply) will cost the same, if not less, not to mention that it's easier. Building my first one was fun, but it was just enough of that particular kind of fun for me :).

Yes, I've seen it on Ali, and they do have readymade versions. There's also the RD6024 you can look for on there that has more power. The assembled version isn't that cheap though.
"Right now I’m having amnesia and déjà vu at the same time. I think I’ve forgotten this before." - Steven Wright
 

Offline Wallace Gasiewicz

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Re: Cheap bench power supply?
« Reply #21 on: January 28, 2024, 11:39:10 pm »
It is possible to filter switching PS. But I have found it to be very difficult. In a switching PS there is both line noise and radiated noise. It is very hard to get rid of the radiated noise.  Putting filters on the output of a PS (line noise) can decrease the volts and amps from that indicated on the PS meters  They also inject noise into your house wiring.. Besides that the switching of the PS changes with amp demands of the circuit so the freq of the interference changes.  The higher the power of the PS the louder the noise. It is a lot easier to get a  quiet PS than to deal with all that. 
If you are dealing with RF. there is already enough interference caused by your household appliances and computer stuff.  The high power switching stuff in electric cars can make AM radio unusable.

There are many very good switching PS built for specific equipment. The harmonics or noise from these PS is such that it does not interfere with the intended load.    An example would be radios like HAM transceivers. The PS are built so that there is no interference with any freq used in the radio.   

If you are not going to deal with any radio stuff then I guess this is not as important, but for RF Hobbyist it is very important.
 
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Online Aldo22

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Re: Cheap bench power supply?
« Reply #22 on: January 29, 2024, 10:03:48 am »
What do you think of the measures shown in this video to reduce the noise?
He has almost the same device as me, so I would like to do the same if there are no objections.  ;)

 
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Offline shapirus

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Re: Cheap bench power supply?
« Reply #23 on: January 29, 2024, 10:22:46 am »
What do you think of the measures shown in this video to reduce the noise?
I loved his way of using the probe as a contactless sensor to find the source of EMI. Sweet! Live and learn.
 
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Online BeBuLamar

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Re: Cheap bench power supply?
« Reply #24 on: January 29, 2024, 10:58:28 am »
I don't know much but I bought the Matrix MPS-3605LP for $129 from Amazon and I am very happy with it. However, now i check the price is up to $250.
 


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