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From: "Luis de Arquer (ldearquer AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com>
Date: Tue, 27 Nov 2018 23:55:09 +0100
Message-ID: <CAGqyy=ZnzCZm+=Yxe=Et0zqsPVHCG9TmyGtZnrFQfy8UiWknyQ@mail.gmail.com>
Subject: Re: [geda-user] [off-topic] 24V automotive (truck) design issues
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Richard,

I looked up the truck specs, and the TVS spec is indeed close to low.
I got a bit misguided when you said the electronics survived 50V on
the bench, but my guess is either you were not using the TVS there, or
the power supply was limited in current.

ISO-16750-2 (2012) specifies 32V as max continuous operating voltage
for trucks, and 36V for up to 60 min, which is very close to the TVS
breakdown voltage already -in the best case, it will warm up the TVS,
which reduces its peak pulse absorbing capacity. Is there a trade-off
for you to go for a higher voltage TVS?

Hope you find the fix!

Luis



2018-11-27 19:13 GMT+01:00, Richard Rasker (rasker AT linetec DOT nl) [via
geda-user AT delorie DOT com] <geda-user AT delorie DOT com>:
> Hello Luis,
>
> Op 27-11-18 om 16:54 schreef Luis de Arquer (ldearquer AT gmail DOT com) [via
> geda-user AT delorie DOT com]:
>> Hi Richard,
>>
>> On car, we normally use a TVS with a high enough value so that
>> supressed load dump doesn't affect it, yet the other pulses can be
>> drained through -so 36V to 40V. 33V TVS showed to burn on load dumps.
>>
>> Anyway, let us know what you find out! I am curious to see why it failed
>> :)
>
> I just got the boards in, and sure enough, the TVS diode was obliterated
> in the broken ones.
>
> This Friday, I'll go to the truck company with a DSO for measurements on
> the actual vehicles, both in the workshop and 'live' on the road.
>
> I'll let you know what I find!
>
> Thanks again,
>
> Best regards,
>
> Richard Rasker
>