Can you recomend an adjustible current limiter? - Page 1
Forum section: electronics / projects

author: pcm81
author_rank: Regular Contributor
timestamp: June 08, 2023, 02:34:04 am
content: I am building a resistance soldering unit. Got a 7.5VDC 200A power supply for the job. Would like to add an adjustable current limiter to the output. Can someone recommend an off the shelf part? My other, 12V resistance solderer has a 50A 12VDC power supply and i am regulating that one with a 600W light dimmer on its AC input. For this 1500W model (7.5V @200A psu) i am looking for a adjustable current limiter, rather than just input power limiter like a light bulb dimmer would be. Can anyone recommend an off the shelf part, so that i don't have to try to cobble one together with high power diodes.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 10, 2023, 09:47:38 am
content: Regulating high currents is a pita, and you do not do that "behind the power supply".Adjusting input power with a light dimmer (alike) in front of the power supply is a common way with manageable loss, maybe you can modify the power supply to have an internal current limit.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 10, 2023, 01:08:08 pm
content: brand model of your psu, photos, internals etc ...we can just guesstimate things

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 10, 2023, 02:10:42 pm
content: Also, when the output is some resistance wire, then controlling the output voltage instead of the current may be adequate, or even preferential.As usually resistance increases with temperature, feeding it with a constant voltage will reduce the current at higher temperatures, and this (partially) stabilizes the temperature. This is quite common in self limiting PTC heating elements.

author: pcm81
author_rank: Regular Contributor
timestamp: June 11, 2023, 01:42:44 am
content: Thanks for replies, after a couple of days i thought there wont be any...The power supply is Cosel 7.5V 200A power supply PBA1500F-7R5Spec sheet:https://www.mouser.com/datasheet/2/622/coel_s_a0001320608_1-2288971.pdfThe intended use is as a current source for resistance solderer so a straight up resistive load.

author: coromonadalix
author_rank: Super Contributor
timestamp: June 11, 2023, 03:00:40 pm
content: sadly in theses psu, you would need reverse schemtaics etc .. to learn and know how it worksthe priciple of current sensing resistors, coils transformers etc ... are still the same, but implementation(s) differs a lot between brands

author: Terry Bites
author_rank: Super Contributor
timestamp: June 11, 2023, 06:44:21 pm
content: Off the shelf, I doubt it.It's a switch mode supply so current/voltage limiting on the input side isn't going to work.Dimmers, bulbs motor controllers etc -nopeModding the psu is frought with problems including difficult conversations with your insurers.

author: inse
author_rank: Super Contributor
timestamp: June 11, 2023, 07:17:51 pm
content: I have modded a lot of simple small scale SMPS‘s up to notebook power bricks.Those are mostly straightforward and there are chances to modify the output voltage in a limited range.I also played around with server power supplies, delivering 60 or 80A at 12V and I must say they are doing some crazy stuff in there, no chance for me to achieve anything without instructions.The 1500W supply you are using is most probably more than a pumped-up wall wart as well.It will also have PFC, so the DC link caps will be charged to ouchy 400V.How about current control via PWM on the low voltage side?You are going to need some capable MOSFETs and metalworking as 200A is getting difficult on standard PCB substrate.