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'[OT] Re: Reverse Polarity Protection for 3V PIC C'
1999\06\01@044722 by Windows-1252?Q?Sebasti=E1n_Dols?=

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The thread becomes philosophic, so.. I have added an [OT]

>>I don't agree with the statement that your product has failed.  Just the
>>contrary.

>No, the product has failed! A blow fuse is a failure it stops working!
>Hence FAILed
------
So, if your car runs out of fuel, and stop working, then the car is failed?
If the batteries are properly inserted and exhausted, then stop working,
then the product is failed? 'stop working' It seems to me a very hard
approach to the definition of 'failed'..
------
>>The user has preserved his/her investment in that product.  The failure is
>>in the user not following instructions in installing the batteries.

>There is some argument about service technicians not being able to change a
>set of torch batteries without an instructiion manual appicable here, be
>dammed if I can remember it :)
------
I always have supposed that a service technician has a 'little' knowledge
about 'something'.. and detect and make a correct replacement of a set of
batteries is something 'deductable', at least for me. That kind of
technicians will have *veryveryvery* high possibilities of been fired, at
least in my job environment. Except for graphite controlled nuclear
batteries, perhaps... :-)
------
>>If they would have been paying attention, they
>>wouldn't have put the batteries in backwards,
>>and they would not have had the inconvienence
>>of a blown fuse.  But they only lost a fuse
>>and a little time, not the whole unit.
>>
>Fuses in battery operated devices (Hand held) since when?
-----
Have you looked at your tester?
-----
>>As far as not being servicable by the user, how much education and
>>coordination does it take to change a fuse.

>An IQ or more than moron level perhaps?
-----
or perhaps to anybody not kidnapped from deep amazonia? I'm not sure,
because I've seen yanomamis using battery operated hanheld devices.. maybe
without fuses, but don't work if the batteries are wrong placed.. so are
failed? <g>
-----
>>It would have taken less time to pay
>>attention to the battery installation instructions
>>in the first place, thereby saving
>>time and trouble.
>
>If they can get the batteries wrong, then why do you assume that the
>operator can get a fuse correct?
>What is stopping the operator from changing it to a higher rating say a 3"
>nail?
----
Don't expect a secretary to do field care, but.. who in the hell uses a
secretary to do field care? And the secretaries I know are able to change a
toner in a laser or change a diskette in a PC.. I think they will be able to
change correctly a set of batteries that can be fitted in only *one* way, by
example.
----
>>The end choice is up to the designer.  I only offered a suggestion.  One
>>that has been used and proven by me.
>>It is there for you to consider.  Whether you use it
>>in your end
>product is totally up to you.
----
>All suggestions are open to comment. Sometimes there may be a better mouse
>trap out there, never hurts to check. (Snap!)

>>Whatever  failsafe method is chosen, as long
>>as it provides
>>the degree of safety necessary, and at a cost that is agreeable by
everyone
>>involved, is
>>the right choice for that product.

>Fuses and fuse holders are expesnsive, yet alone all the abuse that you cop
>when a fuse blows (Operator error or not)
----
Well, have you considered the possibility of Lithium batteries, and embed
your whole project in epoxy? Sure there is no wrong way to replace them.
Well, I know, if the batteries exhaust, the product is failed <g>.. but
maybe is a good way to assure your production too. Or the customer expects a
really cheap product and really longlife product and really userproof
product? Your customer it seems too clever to me. IMHO, of course.
----

Keep on PICing
/S

1999\06\01@092800 by Ernie Murphy

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My two cents on reverse polarity:

I do a lot of burn in and acceptance testing on boards designed for my
Mother to set-up (my Mom calls Dad when its time to program the VCR). I
*always* place a beefy diode across the power pins AND NOTHING ELSE, least
someone (namely me) blows up a burn in board filled with $40K of product. I
keep a drawer full of 1N4005's just for this. One amp you say? Well, my
power supplies put out a half amp max. That diode can short one out forever
and not fail. The problem becomes a no brainer and I sleep quite soundly
knowing I'll never loose a lot by applying power.

What does your battery do? Batteries can put out plenty. Just drop a wernch
across your car battery and watch the metal melt. (Kids, don't try this at
home.)

So if you want 100% fail safe, buy one set of very fresh batteries, and put
an ammeter across it and read its short output current. Buy a diode that
handles this current. Install in circuit and you too may sleep very soundly.

So endth the lesson.

1999\06\01@162116 by wwl

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On Tue, 1 Jun 1999 09:26:09 -0400, you wrote:

>My two cents on reverse polarity:
>
>I do a lot of burn in and acceptance testing on boards designed for my
>Mother to set-up (my Mom calls Dad when its time to program the VCR). I
>*always* place a beefy diode across the power pins AND NOTHING ELSE, least
>someone (namely me) blows up a burn in board filled with $40K of product. I
>keep a drawer full of 1N4005's just for this. One amp you say? Well, my
>power supplies put out a half amp max. That diode can short one out forever
>and not fail. The problem becomes a no brainer and I sleep quite soundly
>knowing I'll never loose a lot by applying power.
>
>What does your battery do? Batteries can put out plenty. Just drop a wernch
>across your car battery and watch the metal melt. (Kids, don't try this at
>home.)
>
>So if you want 100% fail safe, buy one set of very fresh batteries, and put
>an ammeter across it and read its short output current. Buy a diode that
>handles this current. Install in circuit and you too may sleep very soundly.
..And don't forget to measure how hot the BATTERIES get (before they
rupture!) This is probably the main hazard. Remember that if a user
mis-inserts them, he will probably spend enough time fiddling &
wondering why it doesn't work to let them nice and hot, ready to burn
when he finally figures out what he has done wrong & pulls them out -
OUCH!
I think N cells were mentioned at the start of this thread, so I guess
you're not pulling much power from them, and you could probably afford
to put a series resistor as well as the diode.

1999\06\02@065333 by Caisson

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> Van: Ernie Murphy <spam_OUTernieTakeThisOuTspamSURFREE.COM>
> Aan: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU
> Onderwerp: Re: [OT]  Re: Reverse Polarity Protection for 3V PIC Circuit.
> Datum: dinsdag 1 juni 1999 15:26

Hello Ernie

> My two cents on reverse polarity:

<Snip>

> So if you want 100% fail safe, buy one set of very fresh batteries, and
put
> an ammeter across it and read its short output current. Buy a diode that
> handles this current. Install in circuit and you too may sleep very
soundly.
>
> So endth the lesson.

Rule-of-thumb: The higher the Max-current, the higher the leakage current.
Not nice if your hardware takes up about 20uA, and your diode doubles that
(or triples, or multiplies by 500) ...

Greetz,
 Rudy Wieser

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