Step up DC-DC charger repair

Darren2018

100 W
Joined
Aug 18, 2018
Messages
223
Recently I have been using the DPX800S modules to charge batteries. I used to use the common 1200W/1800W "house brick" step up converters but the DPX800S is much more refined so I have swapped over to these. I have a faulty module and I wondered if you could replace the main FET with something that is better or add another one in parallel? I took one apart and it uses a 055N15A and I was thinking of changing it to a IRFP4568. The transistors are really expensive when you consider that the modules only cost £23 delivered but I can get 2 used IRFP4568 for £6. The modules get quite hot when ran at ~60% of their current or power specifications but just by adding a higher powered 6W fan I found I could run at ~85% without it getting too hot. I was wondering if an upgrade to the FET, its thermal path or the heatsink would compound these gains further? I have found 40x40x18mm heatsinks which could be placed vertically so the added area would not make the footprint any larger. This would also allow the FET and diode to be directly connected with thermal paste or a graphene thermal pad to the heatsink as they would be isolated. The total for these upgrades would be £16 which would bring the cost to £39 but it could potentially allow you to use 1 module reliably instead of 2 which is half the footprint, half the cabling and half the time to set it all up to charge a battery. Plus when I do eventually break a module I can rebuild them easily as I will keep those parts as spares. Anyone know of any better adjustable step up converters which do not need modifying and are not too expensive?
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I bought two of dpx800s from drok on amazon. Both of them failed almost immediately. They both overheated due to a failure of the fan. The mosfet controlling the fan is hiding under the cooling fan next to fan power plug. It is labeled d4184. This appears to be a 40v mosfet. The mosfet that shuts off the output is on the bottom of the board right next to the output and it is a 045n10n mosfet. Both are to-252 but a to-220 will work. Just trim the middle leg off. I have had a minghe bst-900w for several years now and it has been reliable. I have a juntek bst-900w and it failed some time ago.

I have managed to repair both of the dpx800s units. I ran a 12v wall wart directly to the fan. I may upgrade the mosfet but I need to know what chip is driving it first. I don't want to over tax the mcu or the driver mosfet.

This guy starts speaking english after the first 30 seconds and it is easy to find comparable mosfets with his instructions. https://www.youtube.com/watch?v=LqP-G68SyFg.

I really enjoy watching this guys videos. "learn electronics repair"; His practical approach to troubleshooting has helped me tremendously. Search his videos for "all you need to know" and you will find several videos that go into great detail. https://www.youtube.com/watch?v=LNu00nMBaaQ
 
According this guy https://github.com/delboy711/BST900 the bst900w uses a ucc3803 pwm controller. I think I will try the serial connection on the dpx800s to see if I can query the controller.

here is a forum for the bst-900w on eevblog: http://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/

Here's a pic of what's underneath the top controller board on the DPX 800S.
PXL_20230207_055944442.MP.jpg

Here's a pick up the rest of the board
PXL_20230207_061021696.jpg

This seems useful
https://www.ti.com/product/UCC3803#features

The user guide has a different part # but it is probably identical.
https://www.ti.com/lit/ug/sluu176/sluu176.pdf?ts=1675753233922&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUCC3803
 
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