1500W inverter repair - Page 1
Forum section: electronics / repair

author: SonOfGod
author_rank: Newbie
timestamp: October 20, 2023, 08:14:30 am
content: Can anyone help me with replacement MOSFET?. I’ve replaced the Mosfets and it just blows up again cause I don’t think I have the correct voltage and AMP value. There’s 4 MOSFETS next to each other on the heatsink 2 are earthed to the heatsink and 2 are insulated from the heatsink. The data sheet shows 55v but this 1000w inverter puts out 220v so not sure if each Mosfet takes part of the load

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 20, 2023, 12:35:56 pm
content: I guess you have to check all passive components near those MOSFETs. e.g. gate resistors etc. Then, if everything is fine you have to check gate signals if drivers are fine (preferably with oscilloscope). After all this tests you may more safely solder MOSFETs. After soldering MOSFETS you have to check gate signals with oscilloscope again.

author: Kwakerman
author_rank: Regular Contributor
timestamp: October 31, 2023, 04:43:49 pm
content: Can't help with the MOSFETS but it is unlikely they will be providing the 220v. More likely they are switching the primary of a step-up transformer and it is the secondary of the transformer that is providing the 220v output. Stick with the original type of MOSFET as they obviously work, just need to figure out what else is dead. Try starting it up on a current limited power supply to prevent them being damaged again

author: watl0611
author_rank: Newbie
timestamp: November 09, 2023, 08:42:35 am
content: First use an oscilloscope to check whether the MOS gate drive is normal and the PWM dead time, then check whether there is a short circuit in the subsequent stage, and finally install the MOS

author: fzabkar
author_rank: Super Contributor
timestamp: November 09, 2023, 09:43:12 pm
content: You should also be wary of fakes, if you are buying from Chinese sources.

author: Jwillis
author_rank: Super Contributor
timestamp: November 11, 2023, 05:30:08 pm
content: Most likely the PWM driver has failed. When they go, a new Mosfet won't last long. Many simple inverters and switching power supplies don't have very good over load protection. Theirs not much to prevent the PWM from going to full 100% duty cycle under over load conditions. That puts the MOSFET in a full linear condition and they burn up catastrophically. This usually shorts the gate as well,which kills the PWM.Another thing that will damage a high frequency inverter are heavy inductive loads. The inrush current over loads the output MOSFETs. Some have a large output inductor and are less prone to this problem. Many cheaper models may have too small or no output inductor at all.

author: fmashockie
author_rank: Frequent Contributor
timestamp: November 11, 2023, 07:03:37 pm
content: I once had a similar problem with a APC BR1500MS. It is APC's 'economy' pure-sine wave UPS. So the large transformer handles the inverter and the AVR functions simultaneously.This APC UPS kept blowing the large inverter MOSFETs everytime the unit would switch from battery to mains or vis versa. I looked into everything, but could not find the source of the issue.Turns out the large transformer had some internal breakdown of some kind that was causing leakage current/short between windings. I performed a HI-POT test on it and it failed miserably. I replaced the transformer and the issue was resolved.I'm not sure what make/model UPS you have here, but checking the large transformer is worth it (I can see one in the background of your photo). Especially if it is part of the inverter circuit. A simple resistivity test will not catch any internal breakdown issues. A HI-POT test is probably necessary to verify it's condition.