Favorite reverse bias protection for battery circuits [Design]

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From: MooseFET on 16 Mar 2010 21:41

On Mar 16, 11:03 am, Hammy <s...(a)spam.com> wrote:
> On Tue, 16 Mar 2010 10:56:46 -0700, Charlie E. <edmond...(a)ieee.org>
> wrote:
>
>
>
> >Hi All,
> >Still working on my color reader, and getting close. Biggest problem
> >is that now I have almost TOO much drive on my LEDs, but that I can
> >deal with!
>
> >Now, to the latest problem. My system is for the visually impaired. I
> >just put the batteries in one of my prototypes backwards, and it
> >didn't last very long. While I expect this device to have very long
> >battery life, since it normally doesn't operate but for a second or
> >two, it looks like the MC1253's don't like getting reversed biased
> >very long. So, for my design question of the day - What is your
> >favorite circuit for preventing reverse bias from the batteries? The
> >old diode trick drops too much voltage, so wondered if there are any
> >clever FET tricks to block backwards voltages.
>
> >Thanks!
>
> >Charlie
>
> I usually use #2 on this page a shorting shottky.
>
> http://www.recom-international.com/press/Reverse%20Polarity%20Protect...

I never use the shorting diode method. A blown fuse makes the
equipment
"DOA" and gets it sent back.

From: MooseFET on 16 Mar 2010 21:43

On Mar 16, 10:56 am, Charlie E. <edmond...(a)ieee.org> wrote:
> Hi All,
> Still working on my color reader, and getting close. Biggest problem
> is that now I have almost TOO much drive on my LEDs, but that I can
> deal with!
>
> Now, to the latest problem. My system is for the visually impaired. I
> just put the batteries in one of my prototypes backwards, and it
> didn't last very long. While I expect this device to have very long
> battery life, since it normally doesn't operate but for a second or
> two, it looks like the MC1253's don't like getting reversed biased
> very long. So, for my design question of the day - What is your
> favorite circuit for preventing reverse bias from the batteries? The
> old diode trick drops too much voltage, so wondered if there are any
> clever FET tricks to block backwards voltages.
>

I did a quick check and nobody mentioned the idea of a diode in
series
with a relay coil.

> Thanks!
>
> Charlie

From: D Yuniskis on 16 Mar 2010 22:01

Joerg wrote:
> D Yuniskis wrote:
>> Joerg wrote:
>>>> I just want something for my bugout-bag that I can rely on
>>>> *without* having to worry that some component (e.g., a
>>>> battery *buried* inside the "emergency light") has died
>>>> because it's been in storage for 10 years... I *think*
>>>> this thing will work good as there are no "components"
>>>> that I'd have to worry about crapping out (just the little
>>>> DC "motor/generator" and a bunch of mechanical bits)
>>>>
>>>> What good are emergency devices if you can't rely on
>>>> them in an emergency?? :>
>>>
>>> That's what preventive maintenance is for :-)
>>
>> Bug out bag isn't something that sits in a prominent
>> position in the house. I.e., you've got to go *looking*
>> for it. And, hopefully, *never* need it. (out of sight,
>> out of mind)
>
> Ahm, what about the food items in there? Just imagine, you and your

No food items. Keep canned goods in the cupboard
and *remember* to take some on your way out the door :>

Of course, the whole purpose is *not* to need these things!
Otherwise, one should *invest* properly in them! :-/

> family have successfully evacuated. Now dad does the manly thing and
> starts the fire. Mom pulls out a can of Progresso, says 'Best before
> 1998' on there, puts in can opener ... *POOF* .. *SPLAT* ... a horrid
> stench wafts through the area ... "Oh, maybe that's why the can was
> bulging" :-)

From: Grant on 16 Mar 2010 22:09

On Tue, 16 Mar 2010 17:28:42 -0700, D Yuniskis <not.going.to.be(a)seen.com> wrote:

>Hi Joerg,
>
>Joerg wrote:
>>>>>>> I take it you aren't making a custom (molded) case?
>>>>>>> Why not purchase COTS battery holder that *is* "keyed"?
>>>>>>
>>>>>> Anything other than AA cells is expensive. And as Charlie wrote AA
>>>>>> cells are difficult to key without going to precision molding or
>>>>>> milling.
>>>>>
>>>>> Yes. Find a battery holder that someone *else* has incurred
>>>>> the cost of that molding! Preferably, something that lets
>>>>> the user access the "battery compartment" without having
>>>>> to disassemble the device itself.
>>>>
>>>> Very tough. I had tried that at times in the past and there ain't
>>>> much out there. Even the ready-to-go enclosures with built-in
>>>> compartment that I came across aren't really good in that respect.
>>>
>>> I've been eying the Bulgin products. MPD and Keystone
>>> tend to be bottom feeder designs which haven't impressed
>>> me. But, I'm currently designing for much higher power
>>> requirements so batteries (at least standard cells)
>>> aren't an option.
>>
>> Their battery holders don't look particularly well keyed either:
>>
>> http://www.bulgin.co.uk/Products/BatteryHolders/BatteryHolders.html
>
>I've been through their site and haven't been able to find
>any mechanical drawings *or* photos that show enough detail
>to decide. I have a few on my next Digikey order just to
>"evaluate" -- though it would be hard to come to a conclusive
>decision for *all* of their products based on a sampling of
>a few... (if I like the quality -- touch and feel -- I will
>followup with a call to the manufacturer)
>
>>>>> OTOH, if he is making "one off", a bit of plastic glued on either
>>>>> side of the '+' holder terminal can do the trick.
>>>>>
>>>>> I'd also look for those (camera?) batteries (two cells side
>>>>> by side... 3V?) as I think that is keyed (at the very
>>>>> least, it eliminates the problem of putting one cell in
>>>>> correct and one backwards)
>>>>
>>>> I have one, in case of a trip way into the boonies (those are Li
>>>> batteries so they'll last longer). Very expensive, not really an
>>>> option for everyday use.
>>>
>>> Are you sure? ...
>>
>> Yup:
>>
>> http://www.atbatt.com/product/14514.asp
>
>No, that's not the same battery. I'll have to find one of mine
>and see what size it claims to be...

Kodak had a camera powered by a pair of AA NiMH cells glued into a plastic
holder.
>
>>> ... The ones I have are made by Duracell (though
>>> none of them are in convenient places for me to examine).
>>> I would imagine a "colorimeter" sees infrequent use so
>>> you would want a battery that's going to be "there for you"...
>>> (My pet peeve re: flashlights is you use them so infrequently
>>> that the batteries are *always* dead when you need them)
>>
>> That's why everyone here knows where the spares are. There are also
>> spare flashlights.
>
>We now use "emergency flashlights". I've disciplined myself
>to give each one a "quick wind" whenever I come across one
>just to keep the battery fresh.
>
>I recently came across one of these "emergency" devices
>that stores energy *mechanically* -- no more dependence
>on Li cells (going bad from lack of use). I need to
>see what other offerings they have.

From: Grant on 16 Mar 2010 22:13

On Tue, 16 Mar 2010 18:43:58 -0700 (PDT), MooseFET <kensmith(a)rahul.net> wrote:

>On Mar 16, 10:56 am, Charlie E. <edmond...(a)ieee.org> wrote:
>> Hi All,
>> Still working on my color reader, and getting close. Biggest problem
>> is that now I have almost TOO much drive on my LEDs, but that I can
>> deal with!
>>
>> Now, to the latest problem. My system is for the visually impaired. I
>> just put the batteries in one of my prototypes backwards, and it
>> didn't last very long. While I expect this device to have very long
>> battery life, since it normally doesn't operate but for a second or
>> two, it looks like the MC1253's don't like getting reversed biased
>> very long. So, for my design question of the day - What is your
>> favorite circuit for preventing reverse bias from the batteries? The
>> old diode trick drops too much voltage, so wondered if there are any
>> clever FET tricks to block backwards voltages.
>>
>
>I did a quick check and nobody mentioned the idea of a diode in
>series
>with a relay coil.

That's because a relay coil likely draws more power than the circuit you're
trying to protect ;)

I like diode and polyswitch, or MOSFET circuit.

Grant.