Cheap Chinese Boost Converters? - Page 1
Forum section: electronics / projects

author: sourcecharge
author_rank: Regular Contributor
timestamp: May 24, 2020, 10:08:20 pm
content: So, I've got a home project for a tool that requires 60v to 90v at about 2 to 3 amps, but I want to use an old pc ps unit that has been modified to turn on with the back switch. So, I need a boost converter, and I figured I would look for something cheap and pre-made before making my own.I found some cheap boost converters, and I found one that is sold as a 1200w, 1500w, and a 1800w.Here is an excellent review of the 1200w version:https://robojax.com/learn/arduino/?vid=robojax_1200W_20A_boost_converterThe website includes all of the pdf datasheet files except the diodes and opamp which after doing a digikey search, I was able to find their datasheets and I've included them below.I bought the 1500w version and now I'm having second thoughts as I'm still waiting for it to arive.The question is, what do you think can be done (other than putting a bigger heatsink and higher cfm fan) on it to make it more relieable or should I just return it?

author: trobbins
author_rank: Frequent Contributor
timestamp: May 25, 2020, 01:09:17 am
content: Why would you think you need to make it more reliable as you indicate your load is no more than about 270W? Are you planning on using a low input voltage where the input current would get close to input current limits? Is your tool a resistive load, or do you know for sure its input requirements (especially at turn on and during operation)?It is just a dc/dc converter module, so you do need to know how it operates, especially if you are going to approach any limits, and then work through ways to manage the operation.The sales blurb identifies a 20A input limit, so if you want to watch a video that operates the unit above 20A then you have to ask yourself whether the video person knew about the 20A limit (or didn't appreciate that there would be a limit capability especially given a 15A fuse rating), or whether the sales blurb spec has changed since then to highlight that aspect. Operating a unit to failure due to operation above limit levels does not really provide a good view of 'reliability' imho.

author: wraper
author_rank: Unknown
timestamp: May 25, 2020, 01:17:05 am
content: You could replace electrolytic capacitors with higher quality ones if you plan for long term frequent use (over 2-3 years). Otherwise I don't think you should do anything about it given your load.

author: wraper
author_rank: Unknown
timestamp: May 25, 2020, 01:23:55 am
content: Quote from: trobbins on May 25, 2020, 01:09:17 amAccording to review of 1200W unit, 270W is likely about the max power you would comfortably run 1500W model.

author: sourcecharge
author_rank: Regular Contributor
timestamp: May 25, 2020, 03:09:18 am
content: Quote from: trobbins on May 25, 2020, 01:09:17 amForgive me for not adding that I have read many reviews on amazon about these boost converters and that the reviews say it's hit and miss on the quality, and that even if the converter comes working, it fails after 1 or 2 years.Also, something about it failing if you have it connected to a load while it is powering up.Quote from: trobbins on May 25, 2020, 01:09:17 amThe PC PS is 11.6V+, so with a 80% efficiency, it would be pulling about 29A, but remember I got the 1500w model which has a 90V output with a 30A input max.Quote from: trobbins on May 25, 2020, 01:09:17 amThe load(s) are steppermotor controllers that ultimately drive steppermotors, so the load is inductive and I'm not sure if this boost converter will work with inductive loads with only a 11.6v input.Quote from: trobbins on May 25, 2020, 01:09:17 amI was going to try to spice operation but it seems B2 does not have the TL494, and I'm not sure how to make one without the logic. It would be nice if I could figure out how to convert LT spice models into B2 spice models.This would be great to see if I could use different part that I have like the irfp260n or some other high voltage, high current, low Rd(on).Quote from: trobbins on May 25, 2020, 01:09:17 amThe 1500x unit has a 90v output max with a 30A input max, so it's a little different but relatively the same because if you do search for the 1500w 90v version, there is 2 15A fuses instead of 1.I think what the reviewer was doing was trying to make the point that the circuits (fuse) that were ment to save the unit, didn't work, so it's up to the user to limit the input or output in order for the unit not to fail.Maybe the fuse should be changed to a quick instead of slow blow?Quote from: wraper on May 25, 2020, 01:17:05 amWhat would be your manufacturer recommendation for electrolytic caps?Quote from: wraper on May 25, 2020, 01:23:55 amWhat I'm really worried about is ESD because if you look at the Vdsmax of the main regulator of the 80V 1200w version, it's 85v.This seems like it maybe a reason for failure long term wise. The 1500w version supposidly is 90v output max so I'm guessing the mosfet would be about 100v.The question really is whether using a mosfet with a higher Vdsmax is going to help even if the Rdon is 10 higher.The reason why I'm asking is that the irfp260n has 250V Vdsmax and has 45mohms, vs the one on there estimated to be between 95 and 100V Vds and 3-5 mohms.I'm thinking that if I just use a bigger heat sink, with a 120cfm 12v fan that it would then become bullet proof?

author: trobbins
author_rank: Frequent Contributor
timestamp: May 25, 2020, 03:09:29 am
content: Quote from: wraper on May 25, 2020, 01:23:55 amThe output power capability is directly related to the input and output voltages used. If a regulated 12V supply is the input, then yes with a 15-20A input current capability, the output power capability should be constrained to below circa 240W. That may or may not meet the user's application, and like any power converter, the operating temperature of devices and parts are at the mercy of how the user sets up the cooling management.

author: trobbins
author_rank: Frequent Contributor
timestamp: May 25, 2020, 03:34:23 am
content: The fuse appears to be a standard auto fuse - they have sort of defined operate times versus current - the user should become aware of what time it takes for such a fuse to blow with a certain % of over-current. Fuses do not save semiconductors when levels are pushed above ratings - the fuse saves the cable to the input and hopefully the pcb tracks.Any and all reviews should be taken with a large grain of salt - I would suggest that youtube reviewers are far more suspect than the equipment they review, especially the linked reviewer and how he tested the module and the conclusions he came to.If you have determined that your application exceeds or gets close to the nominal current ratings/limits of the module then the simplest way forward is to use two modules in parallel. If you wanted to run your system for years then you have to consider spare parts - even industrial users get caught not being able to buy a part after warranty finishes and have to effectively replace the whole power system through either oversight or not having enough budget.The only way to assess your load is to measure its voltage and current requirements, both at startup and under worst-case use or loading conditions. Assumptions at the start may well lead to stress, head-scratching and throwing everything out later on.Certainly worth the caution in assessing the part specs being used and then applying your own 'derating', such as for how close you go in output voltage compared to the FET's spec ratings. It can get quite technical to measure and assess whether a particular part is 'good enough' for its use, or changing to another part will have any consequences (such as achieved switching speed and the switching loss difference between parts). Electrolytics may well be operating towards their ripple current limit, but you need to measure that, or deduce it from nearby measurements and simulation - until that is done then a cap may not really be being stressed, and you may not have any other technical concerns such as the affect of ripple on supply or load or EMI or the control of the module.

author: sourcecharge
author_rank: Regular Contributor
timestamp: June 09, 2020, 09:47:24 pm
content: So I got my boost converter, and it turns out 50V and about 1/2 an amp was all that was needed, and it works great for for my DIY toroid winder.It came in soft packaging, but was bubble wrapped 2 times. It didn't seem to have any damage and it fired up right of way. I never even changed any of the settings as it came preset at 50V. The PC PS works great for it and I got it now running a 5V, 11.6V, and a 50V output (variable up to possibly 90V) using the boost converter.Before I had multiple DC PS running my toroid winder, but now, it plugs right into the wall.