On Thu, 12 Oct 2017 15:15:25 -0700, mike wrote:


Since I need this badly, for medical needs, I decided to just buy a new
one . I got a 400W, and thought that would work fine. However, that one
has a built in buzzer which is loud and extremely annoying. As soon as I
plug it in, it "screams" at me until it's "settled". Besides annoying, I
often use these inverters when I go camping, with a portable 12V
battery, and having this think scream in the middle of the night is not
acceptable. Needless to say, I'm returning it for a refund.

So, until I am able to find one without that annoying buzzer, I need to
use my old one. All I can think is to leave it out of the original case,
mount some heat sinks to the transistors and put it into a
non-conductive case, made of plastic or wood.

I am posting this because I wonder if anyone knows what else could cause
it to fail to work inside the case, yet work perfectly outside. The
amount of work and cost of another case is almost not worth all the
trouble to re-case it, but it seems that most of the new ones have those
annoying buzzers. Why they have that, is beyond me, but I refuse to have
to cope with that noise.


The transistors are likely insulated from the case. Check for insulator
failure.

That's a good idea. I did not think to check that....

Painting the board to insulate it from the slots in the case is unlikely
to last for long. Use something more robust like Kapton tape.

I sort of think that paint would not last long, unless I applied it real
thick. What is "Kapton" tape? I never heard of that.

Although I do my best to keep stuff like this inverter from getting
abused, anything that sits around between the car seats tends to get
tossed around and fall off the seat, and so on. The case is a heavy
aluminum, and it's not dented or anything, but it could have been
pressed tighter to that board, and thus shorted over time.
\
Although inverters are fairly cheap, I hate to toss this one that works
fine outside the case and was always dependable in the past. Not ot
mention it lacks them damn noisy buzzers. Instead a red LED lights if
the battery power gets low. (A much better design).