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From: Tom Gootee on 3 Jul 2010 15:52
We provide support for a number of systems installed in 24V vehicles.
When the vehicles are not in use, the users like to leave the system's
main power switch and circuit breaker both in the on position. If the
vehicle then needs to be jump started, the users often do not first
turn off the system's circuit breaker or power switch, despite
continuing attempts at training them. Jump starting under those
conditions tends to destroy a very expensive electronic module in the
system.

Modifying the systems themselves is not a viable option. And we do
not yet understand the exact failure mechanism that is occurring. We
do know that there is an internal SMPS upstream from the at-risk
module, but don't have schematics for the system. The system draws
about 35 Amps continuously, when operating.

Knowing only that, is there something that could be strapped across
the system's DC power terminals that would prevent damage from jump
starting? Something available off-the-shelf would be ideal. If
nothing already exists, what might work?
From: Nico Coesel on 3 Jul 2010 17:05
Tom Gootee <tomg(a)fullnet.com> wrote:

>We provide support for a number of systems installed in 24V vehicles.
>When the vehicles are not in use, the users like to leave the system's
>main power switch and circuit breaker both in the on position. If the
>vehicle then needs to be jump started, the users often do not first
>turn off the system's circuit breaker or power switch, despite
>continuing attempts at training them. Jump starting under those
>conditions tends to destroy a very expensive electronic module in the
>system.
>
>Modifying the systems themselves is not a viable option. And we do
>not yet understand the exact failure mechanism that is occurring. We
>do know that there is an internal SMPS upstream from the at-risk
>module, but don't have schematics for the system. The system draws
>about 35 Amps continuously, when operating.
>
>Knowing only that, is there something that could be strapped across
>the system's DC power terminals that would prevent damage from jump
>starting? Something available off-the-shelf would be ideal. If
>nothing already exists, what might work?

I recall a similar problem. It turned out an inductor in series with
the power was causing overshoots on the power supply rail big enough
to kill an opamp. A big capacitor solved the problem.

OTOH: in 12V automotive systems people usually design stuff to
withstand 60V (IIRC) spikes on the power rails.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico(a)nctdevpuntnl (punt=.)
--------------------------------------------------------------
From: Kevin McMurtrie on 3 Jul 2010 17:34
In article
<ad48d40d-5326-4bbd-b4bf-a7e2e9fbdc89(a)w31g2000yqb.googlegroups.com>,
Tom Gootee <tomg(a)fullnet.com> wrote:

> We provide support for a number of systems installed in 24V vehicles.
> When the vehicles are not in use, the users like to leave the system's
> main power switch and circuit breaker both in the on position. If the
> vehicle then needs to be jump started, the users often do not first
> turn off the system's circuit breaker or power switch, despite
> continuing attempts at training them. Jump starting under those
> conditions tends to destroy a very expensive electronic module in the
> system.
>
> Modifying the systems themselves is not a viable option. And we do
> not yet understand the exact failure mechanism that is occurring. We
> do know that there is an internal SMPS upstream from the at-risk
> module, but don't have schematics for the system. The system draws
> about 35 Amps continuously, when operating.
>
> Knowing only that, is there something that could be strapped across
> the system's DC power terminals that would prevent damage from jump
> starting? Something available off-the-shelf would be ideal. If
> nothing already exists, what might work?

I bet it's frying because a completely dead lead-acid battery becomes a
non-conducting bucket of water. There could easily be 20VAC power noise
until the battery starts conducting again. The downward cycle is
usually the fatal one because it draws power out of onboard capacitors
in a path that the semiconductors weren't designed to handle.
--
I won't see Google Groups replies because I must filter them as spam
From: Muzaffer Kal on 3 Jul 2010 18:05
On Sat, 3 Jul 2010 12:52:10 -0700 (PDT), Tom Gootee <tomg(a)fullnet.com>
wrote:

>We provide support for a number of systems installed in 24V vehicles.
>When the vehicles are not in use, the users like to leave the system's
>main power switch and circuit breaker both in the on position. If the
>vehicle then needs to be jump started, the users often do not first
>turn off the system's circuit breaker or power switch, despite
>continuing attempts at training them. Jump starting under those
>conditions tends to destroy a very expensive electronic module in the
>system.
>
>Modifying the systems themselves is not a viable option. And we do
>not yet understand the exact failure mechanism that is occurring. We
>do know that there is an internal SMPS upstream from the at-risk
>module, but don't have schematics for the system. The system draws
>about 35 Amps continuously, when operating.
>
>Knowing only that, is there something that could be strapped across
>the system's DC power terminals that would prevent damage from jump
>starting? Something available off-the-shelf would be ideal. If
>nothing already exists, what might work?

One solution would be to use a protection circuit at the input of the
system using an IC like LT4356 or a discrete implementation of the
same:
http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1142,C1029,P38400
--
Muzaffer Kal

DSPIA INC.
ASIC/FPGA Design Services

http://www.dspia.com
From: Tom Gootee on 3 Jul 2010 18:44
On Jul 3, 5:05 pm, Muzaffer Kal <k...(a)dspia.com> wrote:
> On Sat, 3 Jul 2010 12:52:10 -0700 (PDT), Tom Gootee <t...(a)fullnet.com>
> wrote:
>
>
>
>
>
> >We provide support for a number of systems installed in 24V vehicles.
> >When the vehicles are not in use, the users like to leave the system's
> >main power switch and circuit breaker both in the on position.  If the
> >vehicle then needs to be jump started, the users often do not first
> >turn off the system's circuit breaker or power switch, despite
> >continuing attempts at training them.  Jump starting under those
> >conditions tends to destroy a very expensive electronic module in the
> >system.
>
> >Modifying the systems themselves is not a viable option.  And we do
> >not yet understand the exact failure mechanism that is occurring.  We
> >do know that there is an internal SMPS upstream from the at-risk
> >module, but don't have schematics for the system.  The system draws
> >about 35 Amps continuously, when operating.
>
> >Knowing only that, is there something that could be strapped across
> >the system's DC power terminals that would prevent damage from jump
> >starting?  Something available off-the-shelf would be ideal.  If
> >nothing already exists, what might work?
>
> One solution would be to use a protection circuit at the input of the
> system using an IC like LT4356 or a discrete implementation of the
> same:http://www.linear.com/pc/productDetail.jsp?navId=H0,C1,C1003,C1142,C1...
> --
> Muzaffer Kal
>
> DSPIA INC.
> ASIC/FPGA Design Services
>
> http://www.dspia.com- Hide quoted text -
>
> - Show quoted text -

Yeah, that type of circuit would be nice. Jim Thompson also has one
that's similar in effect I think, but all discretes. And Maxim has a
discrete version schematic of something similar in some literature
about a similar IC they sell.

Does anyone know if there any COTS products (already available) that
use something like that?

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