cheapo psu hack - Page 1
Forum section: electronics / projects

author: m3vuv
author_rank: Super Contributor
timestamp: January 12, 2022, 03:43:25 am
content: Hi all,ive ordered thishttps://www.aliexpress.com/item/1005003430889925.html?spm=a2g0o.9042311.0.0.15ab4c4dSSvyqFis there any reason why i cant have a switchable set of current sense resistors along with more pass transistors+ current shareing emitter resistors,along with a suitable transformer and filter caps to make this into a high power,circa 15a/0-30v lab psu with cc/cv capabilitys?

author: ledtester
author_rank: Super Contributor
timestamp: January 12, 2022, 04:29:39 am
content: Couple of notes...Found another listing for this item here:https://www.aliexpress.com/item/32986139693.htmland that listing includes a schematic:Also, the youtuber Steve Wagner just purchased one of these kits:https://youtu.be/zbC8YWBmsLg?t=530so I would expect him to make a video (or videos) about it.

author: strawberry
author_rank: Super Contributor
timestamp: January 12, 2022, 08:30:31 am
content: and new PCB that can withstand 15A

author: coromonadalix
author_rank: Super Contributor
timestamp: January 12, 2022, 12:10:41 pm
content: You need a more powerful xformer, recalculate all the power transistors section, the predriver section ... and yes stronger pcb traces etc ... oscillations problems may occur etc ..If you wanted a more powerful psu from start you should have bought one insteadYou can or could purchase the same models and put them in parallelBUT you wont get an efficient way to control them perfectlyThey use an already made current / voltage lcd kit Who will not be powerful enough to withstand an higher current load ......Lots of troubles aheadThe schematic look like some mastech already available schematics on the web

author: NiHaoMike
author_rank: Super Contributor
timestamp: January 12, 2022, 01:11:56 pm
content: Get a 48V "telecom rectifier" and a buck converter with adjustable current limit.

author: m3vuv
author_rank: Super Contributor
timestamp: January 13, 2022, 12:34:42 pm
content: I realise about the transfo etc,i have a big multitapped transfo,dont know the exact output but ive used it to power up 4x diesel engine heater plugs before for a few mins,must of been a 50+ amp load,also have a 15o amp bridge rectifier with bolt on stud diodes as well as a 50v dc rated cap and various 100 watt low value wirewound power resistors,just thinking as using this as a base for a high power adjustable psu,say 0-30v 0-30 amp,also have 8x npn to3 pass transistors,rated at 16 amp each,cant remember the number but was rated at 1 amp more than a 3055,so hoping to cobble something together,can switch tranfo taps if needed.,just wanted to use this kit as the controll unit.

author: m3vuv
author_rank: Super Contributor
timestamp: January 15, 2022, 09:20:45 am
content: Well this got delivered yesterday,on the paperwork next to the schematic is says 0-30v 0-50v adjustable constant current and constant volage power supply,so is it both or either?,the opamps are lm358 devices,should these opamps be swapped out for mc34071ap items?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 15, 2022, 09:57:44 am
content: The original board may work as 0-30 V or 0-50 V, but with the supplied transistors better only with a reduced current, like 4 A with 30 V max and maybe 2 A if the transformer can also deliver 50 V. Typically the Chinese supplies are a bit overly optimistic with the current ratings.The OPs are Ok - that is the part that can be resued. The OP does not see the full voltage and with a suitable output stage the OP part could also work for much higher output votlage (e.g. 500 V range).For higher power one would still need to change the whol pwer stage, rectifier and filters and also the relays (for higher contact rating).The realys may be the hardest part, as they may get quite some peak currents and they should be reasonable fast (limited break before make time).Chances are the current relays are already more on the small side and may suffer from contact wear from high peak currents (e.g. around 10 x the load current).A much higher power version would normally use a different type of circuit. More like a SMPS part first and than a similar regulator. The simple tap switching gets increasingly tricky.

author: m3vuv
author_rank: Super Contributor
timestamp: January 15, 2022, 10:22:42 am
content: i have a bunch of t03 16amp rated transitors on heat sinks,thought of using some auto heater plug relays for the tap switching,i have a big ex milatery transfo that has many required taps thats good for 40+ amps,its a beast.

author: m3vuv
author_rank: Super Contributor
timestamp: January 15, 2022, 10:27:01 am
content: would i need a better way of driving the pass transistors,ie a darlington?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 15, 2022, 12:17:32 pm
content: The driving transistor may also need an upgrade (for higher gain), possibly a darlington.The voltage regulator part seems to wholy rely on the limited speed of the LM358- this may tend to oscillate with different ouput transistors.It looks like there is also no really easy way to change that.So with the regulator part also a bit on the weak side, one may as well start from scratch and keep the PCB as intended, maybe a bit lower in current.

author: m3vuv
author_rank: Super Contributor
timestamp: January 15, 2022, 12:25:51 pm
content: Well i already have all the high powered bits in an old homebrew psu i built about 10yrs ago,732 based,just was unhappy with the cc mode not being adjustable enough for low currents,guess i will have to cobble sommat together and have a play.,just trying to make use of bits i already have,just thought that kit would be a handy way of controlling the output of my existing busted homebrew psu?