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Forum Index : Electronics : I fell for a trap, that those more experienced avoid no doubt

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poida

Guru

Joined: 02/02/2017
Location: Australia
Posts: 1418
Posted: 11:03pm 27 Sep 2019
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I discovered that little yellow components are not all the same.
I needed 1uF ceramic or monolithic caps, for the nanoverter #3 board

Jaycar frequently has an empty little box, "labelled 1uF monolithic" when
I visit. But not last week. Beauty, I'm always needing these. So I got some.

I spent about 4 hours destroying things and discovering #3 nanoverter had a short, across one of the 1uF caps that are located in the charge pump area. (C9)
A short that brings 15V supply straight to Vs, being one of the transformer's primary winding connections. Not a good thing as it happens.

I blew my unbreakable test inverer board, taking 16 high quality and costly IR3808
out. Why did the 1uf mono go short?

Eyesight, even with spex nowadays is not good for me.
Close examination showed the 1uF mono was in fact 1uF 35V Tantalum.
Tants don't like reverse polarity much and it was 50/50 chance which way I placed them on the board since I "knew" they were mono/ceramic and so unipolar.
Except they were NOT mono/ceramics.

I had placed 6 of these on nano #3 and all had to come out.

One thing I saw with the Tant caps in this application was the nanoverter's
AC voltage reading on the LCD dropped, and dropped, continually at about a -2V/second rate. The DVM showed a steady 230V output. I had a Tant cap stuffing up the ADC reference voltage too.
wronger than a phone book full of wrong phone numbers
 
Solar Mike
Guru

Joined: 08/02/2015
Location: New Zealand
Posts: 1138
Posted: 11:38pm 27 Sep 2019
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Tough luck there Poida, I gave up using tant caps anywhere near power supplies years ago, they have such a low impedance that current surges destroy them and in doing so they short circuit the power supply. Polypropylene film caps are the ones to use for current discharge applications as in mosfet drivers, they self heal.

Cheers
Mike
 
noneyabussiness
Guru

Joined: 31/07/2017
Location: Australia
Posts: 513
Posted: 09:36pm 28 Sep 2019
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And regularly catch fire if damaged.... personal experience, similar to you poida...
I think it works !!
 
Warpspeed
Guru

Joined: 09/08/2007
Location: Australia
Posts: 4406
Posted: 10:32pm 28 Sep 2019
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Same here, very frustrating.  
A while back I bought a huge quantity of Chinese low esr electrolytics, 1uF and 10uF, and have had zero failures since.
Cheers,  Tony.
 
tinyt
Guru

Joined: 12/11/2017
Location: United States
Posts: 438
Posted: 03:57am 29 Sep 2019
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Got used to aluminums with bar markings for negative terminal. Had one of those surface mount tants soldered in reverse, because the bar marking is for the positive terminal. It did not explode, it smoked first then glowed red hot and popped from the PCB, almost hit me in the face.
 
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