ohm meter battery

Hi Lenny,

I can't imagine that the 1.5V battery provided that much current for the low ohms scale. Otherwise you would burn them out pretty quickly and leakage would have been a real risk.

Of course you could simply put an ammeter in series with a battery and see what is drawn, I suspect it will be under 100ma, which means you won't need much of a heat sink - if any. 500ma would be a small finned clip on heatsink.

If you have the schematics and remember ohms law you can figure out what the maximum current draw is for the battery...

John :-#)#

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Only if you use a carbon-zinc cell. An alkaline cell should be fine.

Sadly, I see corrosion, often severe, with alkaline types as well.

Mark Z.

Years ago, Duracell UK used to have an offer to repair/replace? any item damaged by their batteries leaking. That's now gone.

Duracells leak, had to throw away a perfectly good camera :-(

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Adrian C

+1

On Thursday, March 20, 2014 12:16:03 AM UTC-4, snipped-for-privacy@gmail.com wrote :

lt battery in a VTVM. I have an RCA WV98C Senior Voltohmyst VTVM that is in perfect condition but doesn't get used very often. This battery retrofit c ircuit takes power from the 6.30 volt filament transformer and is built aro und an LM317. With a trim pot you set it for 1.55 volts and you never have to change a battery again. It also needs to occupy an area no larger than t he battery presently does.

s going to leak and rot the inside of the unit. I was going to build the ci rcuit but it occurred to me that I should probably be concerned about the c urrent that the LM317 will be dissipating when the meter is used on the low ohms range. Does anyone have a feel for the size that an adequate sized he at sink should be in order to handle this? Thanks, Lenny

That's correct. I've seen Energizer's and Duracell's leak. In fact I've fou nd that Rayovac's, (the Batteries Plus house brand) are one of the worst. A nd along with the current crop of crap out there I find it very interesting that it's been many years since I've seen the "leak proof" guarantee print ed on the batteries, and have gotten a free flashlight, or "other device" r eplaced because a battery leaked and ruined it. I suspect that they didn't just "forget" to put that guarantee on there....

I think that I'll try that idea of measuring the current. I suppose that I can use the chassis with an insulator as a heat sink if I determine that th e device doesn't have to dissipate that much extra current. Lenny

The cell needs to be checked periodically, regardless. The mess caused by alkaline cells is /rarely/ severe, and can /almost/ always be cleaned up. That from a lead-acid cell destroys the metal.

We've had the Duracell/Energizer argument before. I've never had trouble with Energizers. The only alkalines I've ever had leak were Duracells. And those were all AAs. I've never had Duracell C or D leak.

Devices don't dissipate current. They dissipate power. In the case of an ohm meter, measurements are usually short term so when averaged over a longer period of time, there isn't much power to dissipate via heat sinks or whatever. I have never heard anyone discuss damage to a meter caused by high currents when measuring low resistances.

Pat

So how to clean up? Flashlight with alkaline batteries permanetly now glued to aluminum case. No solvent I have tried works. Even after cleaning the threads on the cap and screwing the cap back on (batteries seemed dry but still glued in place) and leaving the flashlight for a week or two, the cap is glued back on again. A pipe wrench and vice will not turn it.

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Duracell is just as bad as any other. Expensive Mamiya camera motor drive corroded, flashlight ruined, Nikon flash corroded, etc (as they say much much more) ... Also true for 9V duracells. They all leak! corrode! Impossible to clean! I had to grind off corrosion with a diamond tip rotary tool where I could get at it. The flashlight was a total loss since I could not get the batteries out! no solvent worked! Tried CLR, straight white vinegar, etc.

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Yes.

I put alkaline in a radio, and left them there, and they leaked too. I was certainly surprised, since it was precisely the situation I was trying to avoid.

Michael

That sounds like pathologically bad leakage.

You need something alkaline to dissolve the electrolyte. Household ammonia usually works. It will also /at least/ discolor the aluminum.

Actually considering that the battery leaks an Alkaline, I can only imagine that using additional alkaline will only make matters worse.

May I suggest that you try a mild ACID - vineger (clear, not malt) works a treat for neutralizing the alkaline leakage. You may want to dilute the viniger 50:50 with distilled (or Vancouver, BC, tap) water.

John :-#)#

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(Please post followups or tech inquiries to the newsgroup) 
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."

Also true for 9V duracells. They all leak! corrode! Impossible to clean! I had to grind off corrosion with a diamond tip rotary tool where I could get at it. The flashlight was a total loss since I could not get the batteries out! no solvent worked! Tried CLR, straight white vinegar, etc.

I've been using alkaline batteries for decades (including nicads and NiMHs, which are also alkaline), and have not had these sorts of problems. Yes, I have had leakage. But it's been uncommon, and in only one case was the contact badly damaged.

I have a Sony TFM-117WB with four Duracell C cells in it. They've been there over a year. I checked them the other day, and they were fine.

I have never seen a 9V battery, of any chemistry, from any manufacturer, leak.

Duracell used to guarantee that their cells wouldn't leak, and would replace or repaire damaged products. In one case, a dictating machine was cosmetically damaged by leakage, and Duracell made good on the guarantee.

He's trying to unstick the battery. You want something that will dissolve an alkalai -- another alkali. You don't want something that might cause an acid/base reaction.

Ammonia has always worked for me.

Ditto. The batteries just leaked in my p-touch printer and the gunk weakened the battery terminals causing some to just break off where they were bent to act as springs. The cells were energizer, and not the fake ones from the dollar store.

high drain devices always seem more prone to leakage for some reason.

Alas, I've seen leakage from pretty much every size of alkaline.

One thing I have read, is that alkalines are quite unlikely to leak if they haven't yet been used... but that discharging them triggers an electrochemical process that starts the leakage syndrome (swelling and/or corrosion).

So, if you have a device which is mostly kept around as a standby (e.g. an emergency flashlight or radio), and isn't actually being used, then the batteries will probably be OK up through their published shelf-life date. However, once you use the device and start drawing the batteries down, it's best to replace them relatively soon after the first-discharge date (e.g. a year or so).

The devices I've had which have been crudded up or damaged by alkaline leakage all seem to be of the "light or occasional use" variety, where the batteries are neither left in an "unused, on the shelf" state,

*or* used up and thus replaced within a couple of months.

For some history - back around 2004/5 I was selling some New Old Stock Williams brand pinball and video games that had been sealed in their factory boxes since 1980. In about 50% of the cases one or more of the three AA alkaline batteries had leaked enough to damage the battery holder and in a couple of cases enough to damage the logic board slightly. These were EverReady or DuraCell batteries (both used by the same game manufacturers).

Later I had a few more of these games (still sealed) that I sold around

2010 and 2011 - again the batteries either had or had not leaked, and again the damage was minimal.

In a few cases the 3 batteries still held full charge - 1.56VDC!

I think the reason batteries leak is because of current flow through the battery, in other words is the battery is sitting on a shelf it is less likely to leak than if it is a circuit where a tiny bit of current may flow. If batteries are damp that can lead to self conduction and leakage too.

I have these old still charged batteries still (somewhere buried in my shop) in a plastic bag to see how long they will last...

John :-#)#

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(Please post followups or tech inquiries to the newsgroup) 
John's  Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games) 
                      www.flippers.com 
        "Old pinballers never die, they just flip out."

Yes, he will. A VTVM has a 1 Meg resistor in the probe for DC measurements, to keep it from affecting the circuit being tested. The capacitance of a set of meter leads on a DVM will screw up a lot of high impedance circuits.

Here is one of many simple conversions to replace the battery with a regulated DC supply. You only need a few mA for the Ohm meter function in a VTVM. I did this to several VTVMs back in the '70s.

View in a fixed-width font such as Courier.

+---+ 1N4001 TIP29 | | +-----++ C E 1.5VDC | +---+ |+---+-----+-----\ /---------+-------o | | +-----++ | | \ / | 6.3VAC| |+ +++ --+-- | | | -+- | | B | | | | 50uF -+- | | +-----+ | | +---+ | | |1k | | |+ | | | -+- +++ | | -+- +---+ | Gnd | | | -+- -+- +--------+ | | 10uF Gnd | |+ | | -+- | +++ -+- | | | | 10uF | 1N4001 | | | | +-+ | -+- +++ | Gnd | | +-+ | | | -+- 1N4001 | | Gnd +-+ +++ | -+- Gnd

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