Favorite reverse bias protection for battery circuits

[Joerg]

Hi Joerg,


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.

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.

Very easy: Oscillator that is connected via a diode so it works only
when batteries are reversed, drives piezo. Battery inserted the wrong
way -> beep ... beep ... beep ...

If you want to also cover the case where only one of the batteries is
reversed use two of those, can drive the same piezo.

You don't need to be that extravagant. Just something in the
*normal* usage of the device that people can count on for
feedback/confirmation. E.g., if the device uses audio
output (synthetic speech or just "tones"), then design
the device so that immediately on turning on, it "chirps"
once.

[I don't recall what he has chosen for his output medium;
personally, I would opt for limited vocabulary speech as
it can be *very* small]

This gives a positive indication to the user in *normal*
operation (i.e., those times when you HAVEN'T just
changed batteries) that the device is, in fact, "on".
And, knowing to expect this, it can be used when replacing
batteries to act as a confirmation that the batteries
are, in fact, installed correctly, aren't "dead", etc.

Yes, that's usually good enough. No audio feedback -> something must be
wrong with the batteries.

 

[Martin Riddle]

That renders the unit dead and a blind or almost blind person will
have a hard time finding or buying the proper fuse and installing it.

Charlie: Solution #3 is the ticket (look on Hammy's link). But make
sure that the FET is guaranteed to be fully turned on at the lowest
allowed battery voltage, IOW the point where an UVLO comes on.

You can replace the fuse with a PTC, batteries might not like it, but it
would still function when the batteries are inserted correctly.

Cheers

 

[D Yuniskis]

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.

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? 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)

Will be looking for a good PMOS FET that will still conduct with two
low AA batteries, probably around 1.8VDC, if they make one! ;-)

If you go that route, consider how your design can tell the user
"yes, I am working" vs. absence of that indication so the user
can deduce "something is wrong with the batteries or their
installation" (or the device)

Very easy: Oscillator that is connected via a diode so it works only
when batteries are reversed, drives piezo. Battery inserted the wrong
way -> beep ... beep ... beep ...

If you want to also cover the case where only one of the batteries is
reversed use two of those, can drive the same piezo.

You don't need to be that extravagant. Just something in the
*normal* usage of the device that people can count on for
feedback/confirmation. E.g., if the device uses audio
output (synthetic speech or just "tones"), then design
the device so that immediately on turning on, it "chirps"
once.

[I don't recall what he has chosen for his output medium;
personally, I would opt for limited vocabulary speech as
it can be *very* small]

This gives a positive indication to the user in *normal*
operation (i.e., those times when you HAVEN'T just
changed batteries) that the device is, in fact, "on".
And, knowing to expect this, it can be used when replacing
batteries to act as a confirmation that the batteries
are, in fact, installed correctly, aren't "dead", etc.

Yes, that's usually good enough. No audio feedback -> something must be
wrong with the batteries.

*If* the audio feedback in normal operation is noticeable
enough. E.g., audio annunciators in most *cars* are
ineffective as: 1) there are too many of them 2) they
don't "complain" enough.

I.e., make the "chirp" something distinctive (a little
tune) so it's noticeable without being obnoxious -- and
"missed" when absent.

E.g., you could power up a Windows PC with your eyes closed
and would "notice" if their silly little tune didn't play...

 

[krw@att.bizzzzzzzzzzzz]

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.

A plastic slot that the '+' end of the battery fits nicely into but such that
the '-' end doesn't make contact?

 

[Joerg]

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

Are you sure? ...

Yup:

http://www.atbatt.com/product/14514.asp


... 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.

Will be looking for a good PMOS FET that will still conduct with two
low AA batteries, probably around 1.8VDC, if they make one! ;-)

If you go that route, consider how your design can tell the user
"yes, I am working" vs. absence of that indication so the user
can deduce "something is wrong with the batteries or their
installation" (or the device)

Very easy: Oscillator that is connected via a diode so it works only
when batteries are reversed, drives piezo. Battery inserted the
wrong way -> beep ... beep ... beep ...

If you want to also cover the case where only one of the batteries
is reversed use two of those, can drive the same piezo.

You don't need to be that extravagant. Just something in the
*normal* usage of the device that people can count on for
feedback/confirmation. E.g., if the device uses audio
output (synthetic speech or just "tones"), then design
the device so that immediately on turning on, it "chirps"
once.

[I don't recall what he has chosen for his output medium;
personally, I would opt for limited vocabulary speech as
it can be *very* small]

This gives a positive indication to the user in *normal*
operation (i.e., those times when you HAVEN'T just
changed batteries) that the device is, in fact, "on".
And, knowing to expect this, it can be used when replacing
batteries to act as a confirmation that the batteries
are, in fact, installed correctly, aren't "dead", etc.

Yes, that's usually good enough. No audio feedback -> something must
be wrong with the batteries.

*If* the audio feedback in normal operation is noticeable
enough. E.g., audio annunciators in most *cars* are
ineffective as: 1) there are too many of them 2) they
don't "complain" enough.

I.e., make the "chirp" something distinctive (a little
tune) so it's noticeable without being obnoxious -- and
"missed" when absent.

E.g., you could power up a Windows PC with your eyes closed
and would "notice" if their silly little tune didn't play...

It's the first thing I disable when I get a new PC

 

[D Yuniskis]

Hi Jan,

Use a bigger batteriy and a bridge rectifier,
then it does not matter how they are put in.

The device ends up larger. And weighs more, etc.

For *one* device, this is no big deal. But, folks with
disabilities tend to have *lots* of "special devices".
Each is typically larger than it's counterpart (for
the mainstream population).

 

[D Yuniskis]

Hi Joerg,

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)

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...

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.

 

[Joerg]

Hi Joerg,


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)

Yeah, their "datasheets" are not much to write home about.

No, that's not the same battery. I'll have to find one of mine
and see what size it claims to be...

But that's what you need when you want to replace two AA's. And you can
still reverse it.

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.

We have two of those as well. But I am afraid there's just a puny NiCd
in there which will die some day, plus it has very little runtime per
charge. The old D-cell lights can go for hours. Ok, they don't have a
built-in NOAA radio.

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.

I was (so far) rather disappointed by all this alternative stuff. It all
broke in due course. Nothing beats the old 2-cell $2.99 flashlight. Ok,
on the job I also carry a tiny MagLite Solitaire that needs only one
AAA. That has saved the day quite a few times. PHUT .. *BOOM* ... "S..t!
I can't see anything and somethin's glowing over here!" ... "Wait, I've
got a li'l lamp"

 

[Joerg]

Hi Joerg,

Joerg wrote:
[...]

Nothing beats the old 2-cell $2.99 flashlight. Ok, on the job I also
carry a tiny MagLite Solitaire that needs only one AAA. That has saved
the day quite a few times. PHUT .. *BOOM* ... "S..t! I can't see
anything and somethin's glowing over here!" ... "Wait, I've got a li'l
lamp"

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

Seriously, we religiously replace the smoke detector batteries twice a
year, my lab stuff is also done regularly, and so on. With flashlights
there are a few that always get exchanged when the regular-use one dims
out and their batteries get installed in the regular-use flashlight. So
there is a rotation scheme. Same with smoke detector batteries, they are
used up in the voltmeters, the radios I use for EMI work and so on. IOW
in gear where a low-bat situation is ok but used often enough that it
won't leak from old age. This way only depleted batteries are discarded,
nothing goes to waste.

 

[D Yuniskis]

Hi Joerg,

I was (so far) rather disappointed by all this alternative stuff. It all
broke in due course.

Yup. "Plastic". Designed to appeal as "impulse buys".

Nothing beats the old 2-cell $2.99 flashlight. Ok,
on the job I also carry a tiny MagLite Solitaire that needs only one
AAA. That has saved the day quite a few times. PHUT .. *BOOM* ... "S..t!
I can't see anything and somethin's glowing over here!" ... "Wait, I've
got a li'l lamp"

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?? :>

 

[Joerg]

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
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"

[...]

 

[D Yuniskis]

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)

Seriously, we religiously replace the smoke detector batteries twice a
year, my lab stuff is also done regularly, and so on. With flashlights

Aside from smoke detectors, we don't use anything with
replaceable batteries, here. No, I take that back,
the remote control for TV, etc.

Smoke/CO/Heat detectors are AC+DC. I think the battery is
not used -- though tested once a minute? -- in normal
operation. Replace on New Year's eve.

Anything else with a battery tends to be rechargeable
(iPods, PDAs, etc.). And, those batteries are silly to
replace as I can often rescue a replacement for the
entire device instead of paying as much for a "new"
battery :-/

 

[D Yuniskis]

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! :-/

 

[Grant]

Hi Joerg,


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)


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.

 

[Grant]

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.

 

[Don Lancaster]

Synchronous rectifier.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[E]

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

But you can solve that power problem with impulse relay. Connect coil thru
diode so that it gets power when polarity is wrong and another flyback diode
across coil to ensure it goes all way to another position. Then when
polarity is
wrong relay gets power and changes polarity.

Only problem is that you have to find someone how makes such relays...

schematic:
http://koti.mbnet.fi/erkkak/imp/imp.png

-ek

 

[Grant]

I tend to be designing things that are called "portable" and run from
a car
battery or the like. Right now I am doing the lowest powered product
ever
and that is 2.5W.


I have found that polyswitches can't be trusted if you have a
significant
battery to get hooked up backwards. They take too long to go open.

Bigger diode? Where I've seen them used was on 24V traction battery,
lots heating power available.

 

[Charlie E.]

You can replace the fuse with a PTC, batteries might not like it, but it
would still function when the batteries are inserted correctly.

Cheers

Presently looking at http://www.micrel.com/_PDF/mic94052-53.pdf which
seems to fit the bill. Any one used these, and know the gotchas?

Thanks,
Charlie

 

[Charlie E.]

LTC4358

Yikes! $4.50 each at digikey! ouch...

Charlie