Battery for a vintage VOM

hman

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Well, ya see, I've had this-here vintage Hewlett-Packard 427A volt-ohmmeter for quite some time.
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Had it stored away for a few years, finally unearthed it a couple weeks ago. Unfortunately, the battery (an Eveready 763, 22.5 volts) had died of old age (originally installed in 1999). So I went searching. Several sellers on Amazon and eBay must have thought the battery chemistry was platinum-iridium or something, judging by the prices they wanted. Among the lowest prices was one on eBay for a bit under $70 ... sold by Lowes, of all places. Gritted my teeth and placed the order.

When the "Exell" battery arrived, I was taken aback by the weight - about half that of the old Eveready! How could such a lightweight have anywhere near the milliamp hours capacity of the original?
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It seemed far from right. I didn't even try connecting it ... figured it would be easier to return if still in the original shrink wrap. Luckily, the local Lowes store was willing to handle the return.

So what to do? AHA!!! I did a bit of figgering and tried dividing 22.5 by 1.5. Got 15. Stacked up 15 AA cells, and found they would easily fit within the same volume as the 763 battery. Luckily, I'd not discarded the old 763. Cut open the cardboard "wrapper" and removed the cell stacks - three parallel stacks of 15 chicklet-sized cells.
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I soldered the AA cells together in series, wrapped them with electrical tape, re-connected and re-sealed them in the original battery wrapper, and checked the voltage - right on.
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Loaded the "refurbished" battery in the meter, and by golly, it's happy!
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I now have a very good mirrored scale analog meter. True, even with the mirrored scale it doesn't give as many decimals of precision as a digital meter. But nothing beats an analog meter for time-varying signals! Furthermore, I have a nice, inexpensive source of replacement batteries! Assuming 50¢ a cell, that's just $7.50 ... instead of $70.00 for a "new" battery!
 
Nice save John- I wonder why HP didn't just provide a 15-cell holder- Maybe some sort of sweetheart deal with Eveready?;)
 
I had a similar experience with a Triplett VOM that I acquired recently. The battery for the high resistance scale was still available at but great cost. The battery was a NEDA 210, 30 volts, 180 mah, and 16 x 26 x 65mm.

We have several appliances that use CR2032 lithium batteries that crap out when the voltage drops to about 2.8 volts. I made a carrier from a piece of PVC tubing and loaded it with a dozen used CR2032 batteries. Some button contacts on the ends and I had a 30 volt battery at essentially no cost. At 23mm, the new battery fit neatly within the small allotted space.

Should I run out of used batteries, the cost of ten fresh CR2032's is still only about a fifth of the cost of an OEM replacement battery. Lithium batteries are compact enough that they make a good choice for a substitute for some of the more exotic batteries.
 
Batteries are a pain...but there are ways around as you've done.
My daughter had a battery (one D-cell) chiming clock that ate batteries. So, we made a substitute out of a PVC pipe, a 5V wall wart, and an LM317 voltage regulator. Attached
I found a niced 3/8" craftsman rechargeable drill in our company's junk box. No battery and no charger. So I turned it into a "corded" drill with a discarded computer monitor power supply brick. Attached
 

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Nice, make the next one out of rechargeable batteries and you'll never have to worry about it again :encourage:
John
Thanks, John! I've actually started replacing single-use cells with Eneloop type rechargeables, and do have a bunch of AA and AAA cells on hand. I'd seriously considered using them for the meter. What kept me from doing so was the need to wire the 15 cells in series. Soldering was the only way I could come up with to do the job, so rechgarging would have meant unsoldering and later resoldering the whole pile :(

Nice save John- I wonder why HP didn't just provide a 15-cell holder- Maybe some sort of sweetheart deal with Eveready?;)
Thanks, Mark! My guess is that "back in the day" there was a goodly number of pretty popular high voltage battery packs ... "B" batteries for portable radios, etc. So HP just designed around a useful size.

And of course, not all cell stack batteries are amenable to this trick. During graduate school, one of the labs I worked at was using a 300 volt "bias" battery as a super low noise DC power supply. That one would have required 200 flashlight cells for a substitute! PS - learned something the day I had to replace the battery with a fresh one: a battery has no "off" switch, and 300 volts HURTS!

I had a similar experience with a Triplett VOM that I acquired recently. The battery for the high resistance scale was still available at but great cost. The battery was a NEDA 210, 30 volts, 180 mah, and 16 x 26 x 65mm.

We have several appliances that use CR2032 lithium batteries that crap out when the voltage drops to about 2.8 volts. I made a carrier from a piece of PVC tubing and loaded it with a dozen used CR2032 batteries. Some button contacts on the ends and I had a 30 volt battery at essentially no cost. At 23mm, the new battery fit neatly within the small allotted space.

Should I run out of used batteries, the cost of ten fresh CR2032's is still only about a fifth of the cost of an OEM replacement battery. Lithium batteries are compact enough that they make a good choice for a substitute for some of the more exotic batteries.
Likewise, a great save! Those CR cells pack a lot of volts into a small space.

Batteries are a pain...but there are ways around as you've done.
My daughter had a battery (one D-cell) chiming clock that ate batteries. So, we made a substitute out of a PVC pipe, a 5V wall wart, and an LM317 voltage regulator. Attached
I found a niced 3/8" craftsman rechargeable drill in our company's junk box. No battery and no charger. So I turned it into a "corded" drill with a discarded computer monitor power supply brick. Attached
Both great saves! Did your daughter participate in the build?
 
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Another strategy for reclaiming old cordless power tools is connect to a newer style battery via a cord. It seems that there is no common style for battery packs among manufacturers or even for a given manufacturer over the years. I have used the connectors from a defunct battery for a cordless tool to make a plug for the tool. With a cable attached and the other end connected to a rechargeable battery from a more current tool and the battery either hooked on my belt, I had a usable semi-cordless tool again.
 
You can easily charge series nimh packs. It's not as healthy for them as a balance charger would be, but it's possible. They are far more forgiving than lithium. 15 cells though, ugh.
 
Another strategy for reclaiming old cordless power tools is connect to a newer style battery via a cord. It seems that there is no common style for battery packs among manufacturers or even for a given manufacturer over the years. I have used the connectors from a defunct battery for a cordless tool to make a plug for the tool. With a cable attached and the other end connected to a rechargeable battery from a more current tool and the battery either hooked on my belt, I had a usable semi-cordless tool again.
Good idea to use part of a battery pack as a plug. But durn! Don't ya just hate the proliferation of styles?!?!? Like a lot of other folks, I've made an "executive decision" to go with just two brands of battery tools. Got rid of several others that were yet another style.

You can easily charge series nimh packs. It's not as healthy for them as a balance charger would be, but it's possible. They are far more forgiving than lithium. 15 cells though, ugh.
Battery and charger technology is getting pretty wild out there. I've seen a lot of battery packs with extra contacts (temperature overload and/or monitoring individual cell voltages???). The Eneloop charger I have will take any number (up to 4) AA or AAA cells, in any combination, but won't do series. For all I know, it may well have 4 separate charging circuits. I'm not much of an electronics whiz, so I haven't tried delving into modern chargers.
 
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nice save hman!

i like the other way of skinnin' cats when the alternative is ridiculously expensive.

i wasgunna' suggest using a 115vac transformer with a 24vac secondary.
if you add a bridge rectifier, the result would be a right about 22vdc
if you ever wanted to go that route
 
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