Searching for engineer experienced in 24V vehicle electrical

[Tony Williams]

In article <1110583017.328079.206530@g14g2000cwa.googlegroups.com>,
GerberMultit00l <gerbermultit00l@yahoo.com> wrote:

7.) Fred Bloggs proposed a clever design idea. If I don't get
anywhere with my current design I'll surely try this. Heck, I
might just do it anyway for piece of mind. It performs a similar
function to the FET solution I was contemplating but will
probably be cheaper to implement.

I would have to reduce the size of my main relay in order to fit
a small secondary relay in my packaging space.

May be worth asking the relay mfrs if they can supply
a contactor with a main set of normal contacts and a
separate contact pair which is early-make_late-break.
Fred's solution could then be implemented with just
one extra resistor.

That also solves a minor problem on Fred's circuit,
K2 failing to de-energise if there is no load.

--
Tony Williams.

 

[Fred Bloggs]

Tony Williams wrote:

In article <1110583017.328079.206530@g14g2000cwa.googlegroups.com>,
GerberMultit00l <gerbermultit00l@yahoo.com> wrote:


7.) Fred Bloggs proposed a clever design idea. If I don't get
anywhere with my current design I'll surely try this. Heck, I
might just do it anyway for piece of mind. It performs a similar
function to the FET solution I was contemplating but will
probably be cheaper to implement.


I would have to reduce the size of my main relay in order to fit
a small secondary relay in my packaging space.


May be worth asking the relay mfrs if they can supply
a contactor with a main set of normal contacts and a
separate contact pair which is early-make_late-break.
Fred's solution could then be implemented with just
one extra resistor.

That also solves a minor problem on Fred's circuit,
K2 failing to de-energise if there is no load.

If he says that relay stays on for many minutes ( he wrote "2=2e5") then
replacing that bulk ceramic with an Epcos "switching" PTC varistor,
removing 12V zener, making K2 a subminiature 24V coil type with almost a
small signal current rating, would make for a long lasting configuration
with self-turn-off and absolutely *no* arcing on that big relay. The
drawback is can he tolerate possibly a few seconds latency at turn-off.

 

[Ge0rge Marutz]

My intentions were not to waste anyones time. If I did I sincerely
appologize. My original thoughts were that I would meet up with
someone and discuss this outside the forum. However, responses came in
quick and became overwhelming. So, I decided to carry on the
conversation here. Unfortunately I wasn't able to fill in the details
fast enough. That and I need to watch what I say. My company has a
new product coming to market and I do not want to give any of their
trade secrets away.

Back to the matter at hand. The BTS555 is truely a beast!!! I can't
believe they crammed such a device in that small of a package.

About reverse battery connection and this FET. Reverse current may not
damage this part. However, while reverse current flows, my 1 ohm load
will heat up considerably. It may be a few minutes before whomever
installed the product wrong to realize their mistake. By this time the
load could approach 150C. I hate to be so vague, but need to watch
what I say. I have protection mechanisms in place that will prevent
further heating. However, this is destructive. The device will not
recover and would become a warranty return. I would rather prevent
reverse current flow all together.

The good thing is that the BTS555 is packaged in such a small format
that I might be able to place a large body reverse current blocking
diode in series with the load and have some room to spare.

Anyone know of a high current, low forward voltage drop, Schottky diode
in a TO-220 or equivalent package?

George "Gerb" Marutz