Carefull when recharging 9V alkalines on your workbench

[RaceDriver205]

Now, recharging these 9V "alkalines" or "zinc-carbons" is all well and good, but just don't stuff it up like me.
I left one charging with a constant-current supply, and it seems I may have told it to charge at 650mA instead of 65mA. I come back to it in the morning and its exploded charcoal-like black powder all over everything. No wonder they recommend don't try to charge. It seems 9Vs have 6 small silver cylinder batteries in them, and one had completely blasted its entire contents out the bottom of the casing.
And this powder doesn't clean off in a hurry. 

[Mark Hammer]

NEVER....EVER...leave them untended for more than an hour.  You need to be able to feel whether they are getting warm.  If they are, shut-r-down, wait until they feel room temperature and then charge some more if need be.

This is precisely why battery companies provide not even the slightest hint that alkalines and carbon-zincs can be rejuvenated by rechargers.  Somebody's gonna get it or do it wrong.

Glad you're okay, though.

[stm]

I succeeded recharging 9V alkalines overnight with a modest 5mA current.  The battery didn't even got warm and I raised its voltage from around 8.2V to 9.5V in around 14 hrs.

Since they are not intended to be recharged, they don't handle gas buildup, which means you have to recharge them veeeryyyyy sloooooowllllllyyy.

[dschwartz]

How do yo feed constant current to a battery? is there a schematic for that???

Months ago, i did something similar with the "afroman" circuit, but it suddenly stopped working, as it seems that the transistor was burnt....
i have a lot of 9v alkaline laying around ant it woulkd be great to recharge them!

does anyone have a verified schematic ??

[Mark Hammer]

Alkalines and carbon-zincs can be "rejuvenated" but not "recharged" in the traditional sense.  My lengthy experience with hundreds and hundreds of 9v alkaline and carbon-zinc is that once they drop below 7v or so, you're going to have a tough time bringing them back up to 9v.  If it read 7.8v, then there is an excellent chance you can pump an alkaline up to 9.5v.  If it reads 6v, then it's a candidate for recycling the battery top as a DIY battery connector (http://hammer.ampage.org/files/DIY-snaps.pdf).  This is in contrast to Ni-Cad and other true rechargeables where dropping even further down (e.g., 3v) bodes well for a nice robust recharge, while attempting a recharge at 7v will result in the "memory effect" creating less than a full charge back up to 9v. 

Note that rejuvenated alkalines and carbon-zinc will not retain the full voltage as long after a "recharge" as they did fresh.  I have a whole stack of pedals with such 9v batteries sitting in them in what is essentially standby mode.  That is, the pedal rarely gets used, but when it does, there is something in it that can hold up for a demonstration over the course of an hour when someone comes over to the house.  I would NOT consider these reliable or robust enough to be gig-worthy unless it is a really low current-drain pedal.  A good 9v alkaline rejuvenated from 7.8 back up to 9.6v for the first time is probably going to be robust enough to hold out for an evening or two of normal conscientious gig use.  A carbon-zinc that has fallen to 7.2v and been resuscitated to 8.7v for the 3rd time (which IS possible)...not so much.

Quite frankly, it is hard to know in advance what sort of charging current is suitable for a set-and-forget charge of such batteries.  That's why I'm going to berate you and insist that, regardless of what you use to rejuvenate the battery, DON'T LEAVE IT UNATTENDED OR UNMONITORED FOR MORE THAN AN HOUR.

[petemoore]

  Right *before applying power to a non rechargable battery, I'll set the timer, this way I won't have a distraction between the time the battery goes into charger and when the timer doesn't get set...yupp...messy, I still have a messy looking [but cleaned up enough to work, and be handle-able] 1.5v slot in my charger from when that happened.

[MetalUpYerEye]

Don't you guys cover your work with something when you're done? If I leave the work bench for the night and don't want to put everything away i'll always drape an old t-shirt or equally drab rag over my stuff to cover it.

[Mark Hammer]

Oh, you mean like something that can catch fire in your absence?

Nope.  Best practice is to either monitor closely so nothing bad happens, or don't do it at all.  Draping something over so that it probably won't make a mess if a catastrophe happens in some specific way is considerably less than a best practice IMHO, and quite possibly NOT "better than nothing".

Play safe.  I like seeing the number of members go up.  I hate seeing it go down, especially on account of preventable tragedies.

[RaceDriver205]

Months ago, i did something similar with the "afroman" circuit, but it suddenly stopped working, as it seems that the transistor was burnt....
i have a lot of 9v alkaline laying around ant it woulkd be great to recharge them!

does anyone have a verified schematic ??

I used the afroman circuit, it works fine (unless you set the current wrong!). Maybe use a fatter transistor.

[Torchy]

50mA Constant Current Battery Charger

LM317T has built in protection against over-voltage, over-current and over-heating. Vin is 12 - 24V DC 200mA wallwart.

[alextheian-alex]

Yeah, a LM317 is simple to rig up as a current regulator, just one resistor is all you need.  set the current by using picking a resistor value using this formula that I got by switching around the variables posted in the data sheet: (1/current)*1.25, where current is in millamps and resistance is in ohms.

[petemoore]

  Suitable metal container ?
  I think in a coffee can would be good, as long as it's dry in there, an open glass coffee decanter would be even better for insulation, heat reasons, worse for durability.
  If for some reason could the internal resistance go up and cause a problem?
  Not that I'm going to do any testing beyond the time limiting and heat detection, just warming seems to be reliable, I was repeatedly testing the voltage, marking time anyway, with a 'RS' charger doing alkaline, 20 minutes...then I'd run 'em to like...between <8v and ~9v, pushing the charge time up by charge, rest, charge again sometimes.
  Carbon re-charged FF mojo.
 

[R.G.]

Hmmm....

thermistor; PIC with A-D sensing voltage, current, and temp, and setting current levels.

[Torchy]

No modify/edit button again ?

Here's the schematic, thought the i-hacked site allowed direct linking  ... 

[dschwartz]

wow! that´s even simpler that afroman´s circuit..and it looks more reliable...i´m gonna make it...

is the 24ohm resistor setting the current?

[zjokka]

Months ago, i did something similar with the "afroman" circuit, but it suddenly stopped working, as it seems that the transistor was burnt....
i have a lot of 9v alkaline laying around ant it woulkd be great to recharge them!

does anyone have a verified schematic ??

I used the afroman circuit, it works fine (unless you set the current wrong!). Maybe use a fatter transistor.

http://www.afrotechmods.com/reallycheap/batteries/batts.htm

I used the Afroman circuit with mixed results.
- After you charge them for some time they start dropping in voltage longer than I have the time to wait.
- 7V and higher recharged fine, in some hours
- batteries under 7V never stopped dropping back to lower than acceptable levels (like 8.5V to go easy)
- now after storing the recharged batteries (9V - 9.8V) for about a week and a half, they all started dropping way under 9V again.

btw, there a article on WIKI on alkaline recharging that seems to discourage it:
http://en.wikipedia.org/wiki/Rechargeable_alkaline_battery

zj

[Mark Hammer]

I suppose one could summarize the usefulness of rejuvenating 9v batteries in the following ways:

1) They require a battery that still has SOME fight left in it.
2) They are not able to "come back" nearly as many times as true rechargeables.
3) Recharged voltage is an increasing function of pre-recharge voltage (i.e., the higher before recharge, the better the outcome)
4) Stability of recharged current levels is less than that of a fresh battery; they will drain (though not back to pre-recharge voltage) over time.
5) Current drain is faster than a new battery hence recharged 9v should be used where higher sustained current capability is not required.
6) In general, the better the battery to start with, the more they benefit from rejuvenation.  An industrial "pro" Duracell alkaline will charge up higher and more often, with more juice, than will a bargain store two-fer-a-dollar 9v carbon-zinc.

[zjokka]

(careful: only 'full' is not full enough without a second L - but I saw my English linguistics professor make this mistake once. she never forgave herself  ) sorry I started teaching again today...I'm sorry.


Mark, you mean your personal findings confirm mine?

I suppose one could summarize the usefulness of rejuvenating 9v batteries in the following ways:

1) They require a battery that still has SOME fight left in it.
2) They are not able to "come back" nearly as many times as true rechargeables.
3) Recharged voltage is an increasing function of pre-recharge voltage (i.e., the higher before recharge, the better the outcome)
4) Stability of recharged current levels is less than that of a fresh battery; they will drain (though not back to pre-recharge voltage) over time.
5) Current drain is faster than a new battery hence recharged 9v should be used where higher sustained current capability is not required.
6) In general, the better the battery to start with, the more they benefit from rejuvenation.  An industrial "pro" Duracell alkaline will charge up higher and more often, with more juice, than will a bargain store two-fer-a-dollar 9v carbon-zinc.

I used the Afroman circuit and if you read his page he discharged the batteries completely before successfully recharging them again. Also seem to vaguely remember comments in the ealier thread that the recharged alkalines lasted longer with the number of recharges.

The 15 9VS I got from a friend were put in a bag for dead in the course of 6 months, but about 4 of them measured 8.8V or higher (highest 9.4V). He might have tossed them in by mistake, but I doubt it.


The best thing would be a Wah in which an internal dynamo recharges a second battery. By the time the first is empty, the spare one is recharged 

completely impossible probably 

zj

[petemoore]

  Some circuits work great on an old battery, like FF, which doesn't draw too much current and sounds different at a lower voltage operation, adjusting bias or volume.
  Other circuits, like clean-ish sounding ones, may become less than clean in an undesirable way when voltage drops below a certain level where bias or rail hitting problems begin. 

[Mark Hammer]

Absolutely.

I think it's simply a sensible thing to try and recycle batteries as much as is safely and fruitfully possible.  There is enough harmful waste material out there already.  At the same time, it should be seen as an adjunct to use of wallwarts and new batteries, not a replacement for them.  Have reasonable expectations, and make prudent choices, and there is a viable place for rejuvenated carbon-zinc and alkaline batteries in this world.

I will still put in a vote for hanging out in cardiac wards and tech services at university.  Cardiac patients and anyone else who has to wear portable monitoring devices frequently depend on 9v industrial strength alkalines for the telemetric pack.  Hospital policy is often to leave them in for a fixed period and then toss them long before there is any risk of the telemtric data being iffy or intermittent.  You can frequently find heaps of $4 batteries at 8.4v sitting in cardiac wards.

Same goes for any tech service that provides support for lecture halls where profs wear wireless mic packs.  The transmitter runs off a Duracell, usually, and the tech folks are not going to risk having a mic go on the fritz in front of 900 people, or where a similar sized crowd is listening in on a remote teleconference.  So, when things start to sink below 9v, they toss 'em.

Both these freebies will rejuvenate VERY nicely for at least 5 or 6 times.  So, make friends with the techs and the ICU nurses!