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Old 01-02-2023, 09:59 PM   #1
JC173
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Default Benchtop Power Supply Question

Hey all,

Relatively new to the hobby, and I'm looking to purchase a benchtop power supply unit.

I'm looking at this range of units, but I don't understand what voltage and amp range I should shoot for. Also, why would the 120v unit only produce 3 amps?

https://amzn.to/3ZiQqvd
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Old 01-02-2023, 10:02 PM   #2
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Default Re: Benchtop Power Supply Question

cant answer the question unless we know what you want it for.
maybe you only need 30v - maybe you need upto 200
maybe you only need 3A - maybe you need 60A

it all depends on your use of it.
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Old 01-02-2023, 10:05 PM   #3
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Default Re: Benchtop Power Supply Question

That's a fair point

Point is I'm not really sure what I need. I intend to do mainly smaller projects, but I want to test salvaged circuits or LED strips at the moment.
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Old 01-02-2023, 10:36 PM   #4
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Default Re: Benchtop Power Supply Question

led strips from tv's = pretty high voltage
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Old 01-02-2023, 10:41 PM   #5
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Default Re: Benchtop Power Supply Question

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Originally Posted by stj View Post
led strips from tv's = pretty high voltage
Somewhere between 27 and 29 volt given the ones I have now. It's roughly 3.3v per LED right?
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Old 01-03-2023, 12:11 AM   #6
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Default Re: Benchtop Power Supply Question

no,
the leds often have multiple chips in them and the strips use around 80v
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Old 01-03-2023, 12:40 AM   #7
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Default Re: Benchtop Power Supply Question

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Originally Posted by stj View Post
no,
the leds often have multiple chips in them and the strips use around 80v
Reeeally... how do I know if there are multiple chips?

Would the 120V supply be adequate given that it only supplies 3A?
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Old 01-03-2023, 08:37 AM   #8
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Default Re: Benchtop Power Supply Question

look for info in the tv section
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Old 01-03-2023, 01:31 PM   #9
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Default Re: Benchtop Power Supply Question

A TV that uses 120V to power LED strips at 3A would mean it's a very big TV since it means it's drawing 360W, that's very very bright, my 40" LED TV is less than 60W...

And it's a switching PSU, it's wattage limited - more volts means less amps.

I wouldn't trust a 120V switching PSU for low voltages...so if you really need low voltages more than high voltages, I'd stay away from it especially if you need more current.

Again back to what you are going to do with it... and one size won't fit all.
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Old 01-03-2023, 03:10 PM   #10
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Default Re: Benchtop Power Supply Question

Maybe it's worth mentioning about basic security, when talking about power supplies?
What current protection devices do you use in your workshops?

https://www.youtube.com/watch?v=wRFRwOnLsZI&t=1s
Great simple thing.
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Old 01-03-2023, 06:34 PM   #11
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Default Re: Benchtop Power Supply Question

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Originally Posted by eccerr0r View Post
Again back to what you are going to do with it... and one size won't fit all.
The problem is, I don't know enough about the hobby yet to know exactly what I need or what I might end up using it for.

Quote:
Originally Posted by UNITRAX View Post
Maybe it's worth mentioning about basic security, when talking about power supplies?
What current protection devices do you use in your workshops?

https://www.youtube.com/watch?v=wRFRwOnLsZI&t=1s
Great simple thing.
I'm working on building one right now actually
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Old 01-04-2023, 09:54 PM   #12
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Default Re: Benchtop Power Supply Question

I'd say if you're just starting with learning electronics, 0-30V and up to 5-6 Amps should cover plenty of ground. If you plan on doing experiments with many "heavy duty" DC motors (i.e. anything size 540 and up), consider dropping the voltage requirement a little (down to 24V, perhaps) to get more current: 10-15A for such motors. Even then, that might not be too cheap, considering 10 Amps at 24V is already a 240 Watt PSU, and that can be expensive.

IMO, best way is to get several different PSUs, and not necessarily bench type. In fact, I *still* don't have a (working) bench PSU, despite experimenting with projects quite often. Majority of small breadboard projects I power with small plug-in power adapters (5V, 9V, 12V, 15V, etc.) And when I need more heavy current with low voltage, that's where my ATX PSUs come in. For higher voltage, I've used various contraptions - from non-isolated resistive mains droppers (light bulbs, soldering irons, countertop ovens, and etc.) to AC dimmer-controlled transformers.

It's certainly more cumbersome to do it my way, but it's also been cheaper (and I find it more rewarding, since I sometimes have to *actively* think about how I want to power something, rather than just dial in a number on a bench PSU and hope it all works fine.)

That said, there have been times where I did wish I bought or made an adjustable PSU. Most of these were when I needed low voltages (3.3V or less) at medium to high currents (more than 2-3 Amps) and good regulation. But again, I think 0-24V or 0-30V @ up to 3-5 Amps should work well enough for you to get into electronics. That along with a computer ATX PSU and a 60-90 Watt 19-20V laptop adapter should cover a good deal of projects.

Last edited by momaka; 01-04-2023 at 09:58 PM..
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Old 01-05-2023, 02:50 AM   #13
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Default Re: Benchtop Power Supply Question

Quote:
Originally Posted by momaka View Post
I'd say if you're just starting with learning electronics, 0-30V and up to 5-6 Amps should cover plenty of ground. If you plan on doing experiments with many "heavy duty" DC motors (i.e. anything size 540 and up), consider dropping the voltage requirement a little (down to 24V, perhaps) to get more current: 10-15A for such motors. Even then, that might not be too cheap, considering 10 Amps at 24V is already a 240 Watt PSU, and that can be expensive.

IMO, best way is to get several different PSUs, and not necessarily bench type. In fact, I *still* don't have a (working) bench PSU, despite experimenting with projects quite often. Majority of small breadboard projects I power with small plug-in power adapters (5V, 9V, 12V, 15V, etc.) And when I need more heavy current with low voltage, that's where my ATX PSUs come in. For higher voltage, I've used various contraptions - from non-isolated resistive mains droppers (light bulbs, soldering irons, countertop ovens, and etc.) to AC dimmer-controlled transformers.

It's certainly more cumbersome to do it my way, but it's also been cheaper (and I find it more rewarding, since I sometimes have to *actively* think about how I want to power something, rather than just dial in a number on a bench PSU and hope it all works fine.)

That said, there have been times where I did wish I bought or made an adjustable PSU. Most of these were when I needed low voltages (3.3V or less) at medium to high currents (more than 2-3 Amps) and good regulation. But again, I think 0-24V or 0-30V @ up to 3-5 Amps should work well enough for you to get into electronics. That along with a computer ATX PSU and a 60-90 Watt 19-20V laptop adapter should cover a good deal of projects.

Right to the point !! ... I have all kinds and for all purposes . Lately , I had to repair a car stereo at home . I needed something 12v with powerful amperage . 10 minutes of thinking and opening whole boxes and then I grabbed an old computer PSU which did the job fairly well . When I finished the repair and On testing CD's , i had to limit the sound volume to not more than 50% , or else , the PSU would cut off .
Yet , In a room , I have like 5 or six laptops on a one huge table , and I've got sick of adapters and cables , inlets and outlets , so I decided to build one powerful unit to replace all the adapters . I'm now checking my old electronic schematics to choose the convenient one .
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Old 01-05-2023, 03:25 AM   #14
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Default Re: Benchtop Power Supply Question

I use my 30v 3A power supply for the majority of my power supply use.
I have a device for injecting low voltage and high current for help with detecting shorts and I have a 900W boost converter for the occasions I need more than 30V.
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Old 01-06-2023, 07:10 AM   #15
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Default Re: Benchtop Power Supply Question

Quote:
Originally Posted by jiroy View Post
Right to the point !!
Yet , In a room , I have like 5 or six laptops on a one huge table , and I've got sick of adapters and cables , inlets and outlets , so I decided to build one powerful unit to replace all the adapters .
I want to know how you did this when some laptop computer switching power supply have a third wire on the outside a lot of them will not work with out it
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Old 01-06-2023, 08:47 AM   #16
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Default Re: Benchtop Power Supply Question

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I want to know how you did this when some laptop computer switching power supply have a third wire on the outside a lot of them will not work with out it
I didn't do it yet , and if you continued reading the whole post ,you would know that ..I'm still searching my old schematics .

Do you mean the Ground wire as the third wire ?
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Old 01-06-2023, 10:42 AM   #17
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Default Re: Benchtop Power Supply Question

Quote:
Originally Posted by jiroy View Post
Yet , In a room , I have like 5 or six laptops on a one huge table , and I've got sick of adapters and cables , inlets and outlets , so I decided to build one powerful unit to replace all the adapters . I'm now checking my old electronic schematics to choose the convenient one .
Sounds like an interesting project. I suppose just one big 19-20V PSU to power it all with lots of laptop plugs. The only thing is, you have to make sure each output is current-limited to what a regular laptop power adapter would normally be (60-90W, typically, aside from a few high-end / gaming machines.) Otherwise, you may get some "interesting" fireworks, should a laptop go faulty with shorted silicon somewhere.

Also sam_x3 brings a valid point about the 3rd / ID wire. Don't know how Dell and HP are these days, but a few years back and more, Dell were still very picky about having a genuine adapter. Can't tell you how many I've seen with dead / discharged batteries or running in low performance because the ID wire on the original adapter went bad at some point and so made the laptop perform in lowest state and/or not charge battery.
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Old 01-06-2023, 10:59 AM   #18
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Default Re: Benchtop Power Supply Question

Quote:
Originally Posted by momaka View Post
Sounds like an interesting project. I suppose just one big 19-20V PSU to power it all with lots of laptop plugs. The only thing is, you have to make sure each output is current-limited to what a regular laptop power adapter would normally be (60-90W, typically, aside from a few high-end / gaming machines.) Otherwise, you may get some "interesting" fireworks, should a laptop go faulty with shorted silicon somewhere.

Also sam_x3 brings a valid point about the 3rd / ID wire. Don't know how Dell and HP are these days, but a few years back and more, Dell were still very picky about having a genuine adapter. Can't tell you how many I've seen with dead / discharged batteries or running in low performance because the ID wire on the original adapter went bad at some point and so made the laptop perform in lowest state and/or not charge battery.
Ah , okay ..The DC third wire of Hp and Compaq mostly ..Well , if you remember Momaka , some years ago , I talked about my loss (app. 5000$) when I bought some laptops affected with the Nvidia problem . I talked also about how they refused to fund money back , and instead , to grow my frustration , they offered cheap compaq something with no Nvidia inside . I thought back then , what da hell , the rotating and touch screens of my Hps were more expensive than their offer .. In other words , another treachery .
Eventually , I stopped buying ANY HPs ! . Same recommendations to friends and customers ..
Right now , I have only Asus (Republic of games,770GTX 16GB) as primary set , and 3 Acers Icore 3 , one mini Asus for nightly purposes and one Toshiba 8GB DDR2 (Yes , believe it or not , unique ,and needs more posts later), so basically i'm in no need to a third wire .

By the way , i laughed at (Sam x3) , lol ..

Last edited by jiroy; 01-06-2023 at 11:06 AM..
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Old 01-06-2023, 01:18 PM   #19
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Default Re: Benchtop Power Supply Question

we can fake the 1wire eeprom with an arduino or a pic to fool those laptops
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Old 01-06-2023, 01:21 PM   #20
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Default Re: Benchtop Power Supply Question

Quote:
Originally Posted by momaka View Post
Sounds like an interesting project. I suppose just one big 19-20V PSU to power it all with lots of laptop plugs. The only thing is, you have to make sure each output is current-limited to what a regular laptop power adapter would normally be (60-90W, typically, aside from a few high-end / gaming machines.) Otherwise, you may get some "interesting" fireworks, should a laptop go faulty with shorted silicon somewhere.

Also sam_x3 brings a valid point about the 3rd / ID wire. Don't know how Dell and HP are these days, but a few years back and more, Dell were still very picky about having a genuine adapter. Can't tell you how many I've seen with dead / discharged batteries or running in low performance because the ID wire on the original adapter went bad at some point and so made the laptop perform in lowest state and/or not charge battery.
Yes, Dell still does this, and it detects the wattage of the connected supply. Aftermarket power supplies can fake it, so they don't need to be genuine.

Thing is, if for any reason it can't detect the wattage, it'll totally nerf your laptop. Either it won't charge the battery, or your CPU will be stuck at some stupid low clock speed and the computer will be unusable.
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