Rechargeable batteries (for my Fluke DMM)

[PRNDL]

I seem to be having issues with rechargeable batteries.

My Fluke bench meter has four D NiCad batteries and two are measuring zero volts.
The meter, unfortunately, doesn't work until the batteries have sufficient charge.

My phone headset uses two rechargeable AAA's. I put in two new duracell NimH a few months back.
They are no longer charging!

Harbor Freight has some really good deals on batteries - four NiMH for $6

Does anyone have experience with rechargeable batteries?
(I have a feeling my issue is fairly common).

Now the issue with the Fluke is they have solder tabs. Mouser has them at very high prices ($15 each or so). The meter is usually connected to AC when in use, and not used when stored.

A friend mentioned their technique for reforming rechargeable batteries is to connect them to his 30 amp welder. I'm considering this because of the price, but my question is whether it will work.
It's not the craziest thing I've heard, but it's up there.

Thanks!!

[sluckey]

You are experiencing a down side of NiCads. If they just sit under a constant charge and rarely have to carry the load, they will lose their 'memory' and their charge will slowly dwindle. NiCads work best and give longest life when they are charged to max, then discharged deeply. Repeat, repeat, repeat. I would not replace nicads in a 'bench' meter, especially if I had a battery operated meter too. I'd just remove them.

HF has lots of good deals on their cheap stuff. Deals ain't so good on quality name brands though.

[jjasilli]

I detest batteries of all types.  I think the best rechargeable battery is a wallwart or a power supply.  I just rigged a 5.3V obsolete phone charger wallwart to power my Itty Bitty Book Light, which is my bench work light.

Just spent $8 for two mini 12 volt batteries to power my $19 DVM's!!!  I'm gonno drill a hole in the darn things and power them off a wall wart also.  Eventually, I've got 2 computer power supplies lying around which I'll build into a variable bench power supply (as soon as I finish 12 other projects).

Anyway, I feel your pain!

[PRNDL]

Bad news ... without batteries, the Fluke goes into to some kind of manic calculation mode. The same thing occurs when the batteries are dead.

The wall wart idea is very good, except in this case where the Fluke will try to recharge the wall wart.

Harbor Freight has inexpensive NiCd D's, so I'm going to put them in.

As for the phone, it seems that I didn't put the battery cover back in correctly, which stopped it from being recharged in the cradle.

Who thought that batteries would be such a drama!

[PRR]

> connect them to his 30 amp welder.

For an instant!!

A battery will EXPLODE fairly quickly at 30A.

The usual trick is to charge a couple thousand uFd to 6V or 12V, and dump that into the cell.

The problem is that if you have several ni-cads in series, with any load, and let them go "flat", one will go to zero before the others. After that it gets -reverse- charge. In this mode, the chemistry forms icicles or stalactites which eventually grow across the cell and short it out.

The icicles are skinny. A BIG blast of current will vaporize the tip off the icicle, removing the short. For a while.

A big prolonged current will heat the cell until it bursts, a nasty and somewhat toxic event.

Replace the cells. It isn't worth the effort to de-short them over and over.

Tab-cells could be replaced with a battery holder, if you can find space.

I suspect the DVM will work with the ni-cads removed, as wart-power only. Since you can get a functional battery-portable $13 DVM, as cheap as $4, this may be a better plan than re-celling the bench Fluke.

[jjasilli]

Just spent $8 for two mini 12 volt batteries to power my $19 DVM's!!!  I'm gonno drill a hole in the darn things and power them off a wall wart. . .

Nevermind:  I've since discovered that eBay sellers carry these mini 12 volt batteries REAL cheap!