How to Make a Super Long Life 9V Battery (Answer Inside)

RaceDriver205 · October 01, 2006, 01:34:22 AM

Im liking the look of this device though as well. I recon Ill start saving my old 9V batteries.
I do remember charging some button batteries once. I applied 12V straight to the battery, and the 'regulator' was me removing the power when the battery got red hot. I think I blew one up and sent scalding acid everywhere. Good times

stm · October 02, 2006, 02:59:38 PM

Paul, sorry for taking so long to reply--I didn't see your question until now.

The idea is to use any JFET whose Idss parameter lies between 4 and 10 mA. Good candidates that I know of are: BF245A, BF245B, 2N5458, 2N5459 and MPF102. An example of BAD candidates would be PN4329 or BF245C, since typical Idss is way above 10 mA.

The idea is to use a 12 Vdc wallwart (easy to get) whose typical output is indeed slightly higher, up to 16V. The JFET will take care of the rest and reduce the voltage applied to the battery as needed in order to keep current constant.

Paul Marossy · October 02, 2006, 03:08:32 PM

Thanks for the response. I built your circuit last night using a 2N5485, and it works - slowly. I estimate that it would take 48 hours to charge a battery from 7.5V to 9.5V. Maybe I need a different FET. Even at 10mA, I don't think it would be dangerous. Anyway, I am using a 9V 300mA wall wart for now which puts out ~12V unloaded, so I think I need to get a 12V wall wart and go from there. I'll just grab one from my thrift store wall wart pile!

stm · October 02, 2006, 03:22:30 PM

The 2N5485 looks like the perfect candidate!

Maybe your 9V walwart is just a little short of voltage for a proper charge. Also, it is possible that the zener diode is just limiting the maximum voltage too early. With the battery unplugged you should read at least 10V across the zener or 9.5V minimum at the series diode's output, otherwise you could add an extra diode in series with the zener to raise its voltage a bit, and/or change the series diode to a shottky type.

The bottom line is to have close to 9.6V at the output terminal when no battery is installed. If you have less, you should adjust the zener voltage and/or the series diode drop accordingly.

Cheers.

Paul Marossy · October 02, 2006, 03:39:50 PM

QuoteThe 2N5485 looks like the perfect candidate!

Yeah, I looked at the data sheet right after my last post and saw that it's right there where we want it to be. I just popped one in there because I had them right in front of me.

RaceDriver205 · November 16, 2006, 03:29:15 AM

Will this work well for an 8.4V rechargeable?

MetalUpYerEye · November 16, 2006, 06:26:53 AM

Going back to the battery "warming..."

I took my girlfriends car out to the family repair shop because she was having battery problems (the sucker was dying off every other day) and told the mechanic to park that car in a place where it'll be easily accessible for jump-starting because it might not start up the next day. He replied by telling me that batteries that are kept in a controlled, warmer temperature, will keep their charge. He also said that if a battery is cold, that warming it will release some kind of surface charge which should allow enough juice to get the car started and let the alternator take over from there.

He also scoffed at my foolishness saying "Come on, its basic physics.. Oh wait, you didn't finish school, did you?"

So maybe warming the batteries does have some kind of effect.

PS. Yes, I did finish school with more than acceptable grades (in case anyone cares...)

RaceDriver205 · November 16, 2006, 06:47:10 AM

Speaking of battery warming, that reminds me of an awesome aboriginal show called "bush mechanics" that used to be on.
I recall that amogst other things (including stuffing a flat tyre with leaves), they recharged a dead car battery by first making a fire, and then putting the battery INTO the fire! After a while of roasting the battery, they put it back in the car and drove off. Those guys were awesome!

brett · November 16, 2006, 07:05:00 AM

Hi
Supercaps and NiMH are cool.
Old wet batteries can often be zapped into life with an electric fence energiser. High voltage dissolves lead sulphate in the battery, which is the main reason for battery ordinariness and failure. Heat probably works by dissolving some sulphate. Surface charge discussion was probably rubbish IMO (my Masters included a lot of surface charge theory).

The bush mechanics are legends! One program had them resurface a clutch plate with some roadside wood (mulga?). Tools were a knife and spoon, or something like that.
cheers

Paul Perry (Frostwave) · November 16, 2006, 07:21:34 AM

Quote from: MetalUpYerEye on November 16, 2006, 06:26:53 AM
He replied by telling me that batteries that are kept in a controlled, warmer temperature, will keep their charge. He also said that if a battery is cold, that warming it will release some kind of surface charge which should allow enough juice to get the car started and let the alternator take over from there.

What a turkey!! and what an indictment of his teachers (if any).
I'm marking him 0 out of 2, and a demerit for rudeness. "Surface charge" my a$$.

One thing that can *sometimes* help, is to try the battery a couple of times, which warms it up (lowering the internal resistance!) then wait 5 minutes or so (hoping that diffusion will help).

I hope that mechanic uses monster cables on his hi-fi.

Paul Marossy · November 16, 2006, 07:32:19 AM

How funny, I was thinking about doing an update on this, and I saw several topic replies on my email this morning. I measured the battery voltage this morning to check how it's doing- it measures 8.83V after three months of playing it for a hour or so at least six days per week. Not too bad...

amz-fx · November 16, 2006, 07:34:01 AM

Temperature: If you heat a battery, the extra energy will enhance the chemical reaction in the cell that produces the voltage. This only works until the chemical components are depleted.

-Jack

Paul Marossy · January 14, 2007, 08:08:50 PM

Wow! I am really surprised at how long this battery has lasted thus far. Still measures 8.77V after about 6 months of (nearly) daily use for about an hour so each day!

Just an update for anyone who might be curious...

zjokka · February 08, 2007, 11:10:07 AM

I'm building this now after getting lucky and finding one 10V zener at the bottom of my box.

I don't have the fet specified, but as..

Quote from: stm on October 02, 2006, 02:59:38 PM
The idea is to use any JFET whose Idss parameter lies between 4 and 10 mA. Good candidates that I know of are: BF245A, BF245B, 2N5458, 2N5459 and MPF102. An example of BAD candidates would be PN4329 or BF245C, since typical Idss is way above 10 mA.

2N5457 which I do have around has typ Idss 3mA max 5mA, other are 10mA or over. But my question is -- will this work at all, or very slow?

zjokka · February 16, 2007, 04:24:29 PM

Quote from: Steve Newton on August 21, 2006, 11:54:23 AM
Anyone tried this for battery charging/recycling?
http://www.afrotechmods.com/reallycheap/batteries/batts.htm

I tried this circuit this week and it works great. First had a go at the circuit with the FET -- but didnt have one with the proper drain current. With a 2n5457 it took two days to get from 7.4v to 8.4v or something.

Afrotech's circuit works really fast and a 8.4V only takes an hour or two to get to 9.4V. Cannot tell exactly because when you take the battery off the clip it holds about 12V and drops very slowly. Out of the stack of fifteen, I blew one leaving it overnight. And guess what, no leaking, just one of the 6 baby batteries inside had popped, causing the bottom plate to lift up.

Now I have about 15 free 9V batteries, 10 duracells among them which cost about 6 EUR/piece in my country. This is amazing.

Paul Marossy · May 20, 2007, 03:15:10 PM

Just an update:

It's been about nine months now, and my first super long life battery is reading 8.6 volts. I think I can probably get one year out of that battery using the wah pedal that it's in been in for the last nine months, played at least 5 hours a week. Pretty cool, huh?

RaceDriver205 · May 21, 2007, 08:14:34 AM

Someone needs to make a pedal with 1 of these in: (1.3Ah)

Or 1 of these (18Ah):

"Yeah dude, the gains so high, it needs a battery -THIS BIG-!"

Paul Marossy · May 21, 2007, 09:48:47 AM

Yeah, but that won't fit in a wah pedal.

jakenold · May 21, 2007, 10:39:06 AM

Great work Paul. You get one MacGyver-point from me, as a reward. I own all 7 seasons on DVD, so take a quick guess at how my workshop looks like

I also find great humor in petemoore's ideas. I'll try to take my car battery to bed tonight and see if I get to work faster tomorrow

Paul Marossy · May 21, 2007, 02:51:05 PM

QuoteGreat work Paul. You get one MacGyver-point from me, as a reward. I own all 7 seasons on DVD, so take a quick guess at how my workshop looks like

I used to watch that show. He always figured out something with almost nothing to work with!

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How to Make a Super Long Life 9V Battery (Answer Inside)

jakenold