Favorite reverse bias protection for battery circuits

Anything other than AA cells is expensive. And as Charlie wrote AA cells are difficult to key without going to precision molding or milling.

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.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

Why PMOS?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

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.

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)

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.

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 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.

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

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

See...

Newsgroups: alt.binaries.schematics.electronic Subject: Battery Reversal Protection (from SED) - BatteryReversalProtection.pdf Date: Tue, 16 Mar 2010 15:32:36 -0700 Message-ID:

But pick a better transistor, with lower saturation. I don't store discrete transistor data in my head like I do ASIC processes :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
      The only thing bipartisan in this country is hypocrisy

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

Of course, if you can get that proverbial PMOS with VT=0.7V, as I can in ASIC's, you'd do this...

Newsgroups: alt.binaries.schematics.electronic Subject: Re: Battery Reversal Protection (from SED) - BatteryReversalProtection.pdf - BatteryReversalProtection-2.pdf Date: Tue, 16 Mar 2010 15:51:15 -0700 Message-ID: ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
      The only thing bipartisan in this country is hypocrisy

I like LTC4358.

They took care of a lot of problems typical for trivial DIY reverse battery protection circuits.

Vladimir Vassilevsky DSP and Mixed Signal Design Consultant

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.

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)

*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...

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

On a sunny day (Tue, 16 Mar 2010 14:32:50 -0700) it happened Joerg wrote in :

Clever.

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

Their battery holders don't look particularly well keyed either:

Yup:

That's why everyone here knows where the spares are. There are also spare flashlights.

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

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

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).

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...

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.

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

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

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 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"

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

[...]

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.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

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

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?? :>

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" :-) [...]

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.

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