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Forum Index : Microcontroller and PC projects : Cheap 30v 10A bench PSU...
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
I thought I would try out one of the cheap Chinese power supplies available on eBay and the like. Not expecting very much, I ordered THIS ONE. Supposedly capable of 30v and 10A, fully adjustable voltage and current limit. It arrived today, so the very first thing I did before even plugging it in, was to rip it open and give it a basic visual inspection. Mainly I wanted to evaluate it's mains-voltage compliance or lack of, before plugging in something that could actually be very dangerous.  Quite nice inside considering the price! Air-gap slots to separate the HV from the LV sides of the PCB, which is always nice to see with anything connecting to the mains. One thing they are doing, is that the main on/off switch is in the Neutral - naughty, naughty.  That along makes it non-compliant as the phase side of the AC is still present at any point on the HV side and earth, even with the switch off. I will be changing this to switch the phase as it should be. That's my only real complaint on the HV AC side. Quite good separation in the AC paths, and acceptable distances between phase and neutral on the PCB unlike some things I have seen. Nice grunty output wires, and inductive filtering on the main DC output. Component side is nice. Clean and tidy. All the SMD factory stuff is as good as anyone would expect. The hand-soldering is not too bad. Not super-duper cos they don't have any insulation over the HV wires(they are just exposed inside the case), but electrically functional and solid enough. I give that a pass, but would prefer to see insulation - but then, for the price of this thing.....  Mains input and voltage selector switch soldering.  Running with a gell-cell battery as a load. Currrent limited to 2A - seems to be working.   Load test. Shorted output. Can indeed supply 10A. That could make a big bang if you are not careful!  Voltage is adjustable from 0.00v to 32v. Voltage control knob is a multi-turn pot, so the control is nice, and you can easily adjust in 100mV steps. Adjustable voltage is nice and linear all the way from zero volts up to 32v across the entire range of the voltage control.  Current is adjustable via the other knob, and this is a standard pot not a multi-turn one. Adjustable current limit from zero right up to 10.5A in 100mA steps. This control is a little more coarse in adjustment then the voltage one, but still easy to use. I would still recommend this to anyone looking for bench power supply with full current limiting. The only thing that I really am frowning on is the fact they are switching the 230v(or 110v) neutral on the main on/off switch, so that needs changing to be compliant, but for the price of this thing - knowing you have to change that - it is still a great deal if you ask me - and you didn't....  I am considering buying another one, as I often need two voltages at the same time on my workbench. Smoke makes things work. When the smoke gets out, it stops! |
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Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
I bought a similar one off eBay a few months ago. It was a 30volt 5amp model, for $44 plus $1 delivery. Externally it looks identical. Like you I took the top off to check it was safe, and I was also impressed with the build quality. I've used it a few times since then, works a charm. Only issue I had was the current meter reads a little high, so 5 amps is actually about 4.2 amps, and that was the limit of its output current. But for my purposes, and for the price, I'm more than happy with it. Having built several variable power supplies in the past, in future I wont, I'll just buy another one of these Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Well, indeed. One of my main reasons for buying this one, was that I was watching Dave of EEVblog fame talk about cheap voltage regulator modules. But then I wondered how much more I would have to spend to get a fully built one, then I don't have to bother! I've just checked the bench PSU against my old-trusty multimeter, and the PSU output voltage is out by about 50mV - nothing of any significance. Current accuracy against my old-faithful is about 80mA out, but then, this is not a lab-certified PSU, and is close enough IMHO for the price. I always buy something like this with way more capacity then I need, so that it should be able to easily satisfy my needs. I was looking for 0-20v and 5A or so. This thing can do that easily. Smoke makes things work. When the smoke gets out, it stops! |
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| kg4pid Regular Member  Joined: 08/03/2015 Location: United StatesPosts: 50 |
One thing I noticed was the seperate Ground and Minus connection. I wonder if there would be any problem with powering something that was already grounded. Curious, take a multimeter and read the resistance between the two, unpowered of course. Then with it powered on read the voltage between the two. It would be nice to know if the two could be connected together. All of my fixed voltage power supplies ground the minus or negative connection. Max |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Your wish is my command. Resistance (PSU off) between negative(black) and ground(yellow) is infinite. There is no circuit even on 20Meg-ohm. Voltage between negative(black) and ground(yellow) with 12v output is zero. Voltage between positive(red) and ground(yellow) with 12v output is zero. Ground(yellow) is connected to mains earth inside the case. Smoke makes things work. When the smoke gets out, it stops! |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5119 |
This is the 5 amp model I bought. I took the photos when I had it apart, anything mains powered from China gets the once over.    Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Quazee137 Guru  Joined: 07/08/2016 Location: United StatesPosts: 593 |
Nice to see I am not the only one too take a look inside any thing major from China too. These are also good for gold plating with the pen. Easy way to add gold to pcb click triangle or conductive rubber push buttons and basic gold finger repair work. I opened up my bike controller and took a look around in it. Better than I expected. |
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CaptainBoing Guru Joined: 07/09/2016 Location: United KingdomPosts: 2170 |
LOL yeah you have to be careful what is inside stuff from china this guy though his $20 Punchbag was a fab buy, bet he felt like a boss when he smashed this bad boy open http://i.imgur.com/oRUzTNx.jpg "clean-up in isle 2" |
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| JohnS Guru Joined: 18/11/2011 Location: United KingdomPosts: 4044 |
Thanks for the info How good is the DC - any A/C ripple or HF noise? John |
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| kg4pid Regular Member Joined: 08/03/2015 Location: United StatesPosts: 50 |
How else are they going to get rid of all their garbage! |
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MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
In Europe the mains plugs can be rotated. This means equipment does not know which wire will be live. On/Off switches must disconnect both wires. Being compliant over the world is a major pain. Microblocks. Build with logic. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
Oh, that might explain the switch in the neutral then. America would have that issue, cos their power plugs will fit in either way around, so I see what you are talking about there.... I guess it does not matter for personal use - just so long as you don't on-sell it with anything in that configuration! Smoke makes things work. When the smoke gets out, it stops! |
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| MicroBlocks Guru Joined: 12/05/2012 Location: ThailandPosts: 2209 |
Most important wire is the ground especially in a enclosure from metal. If anything goes wrong the earth leak detector breaker (in the breaker box) will take care that the live wire is disconnected. Even if the on/off switch is on the neutral the effect will be the same. Without ground, well.... good luck. I even have seen some breaker boxes with the breakers on the neutral wire. Yeah i know..... Here in Thailand where the ground wire seems optional! you will have to be double carefull. Equipment here is sold with japanse plug, european plugs, English plugs etc. Sure they all fit into those two prongs but it will not be safe. In shops i stay away from metal doors, especially those on icecream freezers. Have gotten a little sting from those before and just to make sure i never touch them. Icecream is nice but not worth dying for. I always tell the owner, which then shrugs his shoulders and says 'mai pen rai'. The Thai 'no worries' equivalent. My procedure with new equipment is to make sure to find which one is live by opening the equipment (voiding warrenty often) and then make sure the plug is the same as the sockets i have in the house. If not then the plug comes of and a new one is mounted. I rewired every home in our family, and even did some neighbors houses. One other favorite is to extend wires by just connecting some more with tape. Doing things the right way does not win from doing it the easy. I also make sure to check the hotel showers water heater, seen a few wired wrong (even in 4-5* hotels!). I now just don't use them, Thailand has a hot climate anyway. :) Extension cords are another. Often they just have two core wires while the sockets are with three. So i make those myself too. I just bought the parts and make them the right length. Cheaper and more important safe. Microblocks. Build with logic. |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 10315 |
One problem with most cheap supplies (and I assume this one) is that you can't set/see the voltage and current with the output off. I bought a second hand Wayne Kerr (Farnell) LS30-10 off ebay for less than the price of this supply new. I can set the voltage I want and the current I want to limit at and then turn on the output at the selected voltage knowing it won't exceed the set current. It then reports the actual voltage/current when the output is on. Worth keeping a look for something quality second hand rather than cheap new IMHO  |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
What's wrong with setting the current-limit and voltage you want, and THEN connecting the banana plugs? Achieves the same result. You could also add a suitable isolating switch to the front panel of the ones I have posted here if you really wanted that ability. Smoke makes things work. When the smoke gets out, it stops! |
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| lizby Guru Joined: 17/05/2016 Location: United StatesPosts: 3378 |
Code-compliant U.S. outlets have one slot taller than the other. Most 2-promg appliances and extension cords will have one blade (hot) wider/taller, so the plug is polarized. Old plugs are not polarized, and I've seen some adapter plugs from China which are not. Grounded (3-prong) plugs are of course polarized. PicoMite, Armmite F4, SensorKits, MMBasic Hardware, Games, etc. on fruitoftheshed |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
That's nice to know. I always thought that the two-prong American plug and wall-socket used exactly the same size pins, so would plug in either way - even now.The newer plugs and sockets that are polarised is a good idea. Can you still plug the older plug into the newer sockets? Smoke makes things work. When the smoke gets out, it stops! |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Just another thought, after playing with the DPH3205 module I have. 2 or 3 of the similar DPS3203 or 3205's in a box could make a cheap front end to the 10A unit. Presume they could run in parallel off the 20-30V input & each can be programmed with 9 different outputs. 3 modules for under 100 bucks for a 3 output supply that's really easy to assemble sounds appealing. Not 10A, but the option of 3 or 5V modules as long as the input is not overloaded. Other thing slightly interesting, is that they boot up when input power is applied, and the On/Off switch below the Pot enables the output once the parameters are set. Set all parameters before output is enabled @matherp, No pulling out banana plugs @Grogster. Cheers.   |
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| Paul_L Guru Joined: 03/03/2016 Location: United StatesPosts: 769 |
Yep, the older same size blades will plug into the new polarized sockets. Really simple things like table lamps are still made with same size reversible blades. The polarized socket with different width blades was introduced way back about 1965. Here's a nema chart of some of the outlets available now. Paul in NY http://www.electrical-online.com/wp-content/uploads/2010/12/nema-config-1ph-250v.gif |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9610 |
@ Phil23 - Those things are exactly what Dave at EEVblog was reviewing. Nothing wrong with those, but I then was thinking: 'How about a complete PSU?' @ Paul_L - Do American regulations(electrical code) require that any AC mains switch be in the phase/hot/black wire? You guys need to be careful - The Towering Inferno(1974) started cos of dodgy wiring!!!! ...one of my all-time favourite movies. Smoke makes things work. When the smoke gets out, it stops! |
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