Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old March 20th 14, 05:16 AM posted to sci.electronics.repair
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Default ohm meter battery

I found this circuit somewhere, (I can't remember) to replace the 1.50 volt 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 circuit takes power from the 6.30 volt filament transformer and is built around 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 the battery presently does.

As much as I like keeping things original, I'm worried that the battery is going to leak and rot the inside of the unit. I was going to build the circuit but it occurred to me that I should probably be concerned about the current 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 heat sink should be in order to handle this? Thanks, Lenny

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Old March 20th 14, 07:26 AM posted to sci.electronics.repair
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Default ohm meter battery

On 03/19/2014 9:16 PM, wrote:
I found this circuit somewhere, (I can't remember) to replace the 1.50 volt 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 circuit takes power from the 6.30 volt filament transformer and is built around 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 the battery presently does.

As much as I like keeping things original, I'm worried that the battery is going to leak and rot the inside of the unit. I was going to build the circuit but it occurred to me that I should probably be concerned about the current 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 heat sink should be in order to handle this? Thanks, Lenny


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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Old March 20th 14, 09:30 AM posted to sci.electronics.repair
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Default ohm meter battery

wrote in message ...

As much as I like keeping things original, I'm worried that
the battery is going to leak and rot the inside of the unit.


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

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Old March 20th 14, 11:21 AM posted to sci.electronics.repair
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Default ohm meter battery

"William Sommerwerck" wrote in message
...
wrote in message
...

As much as I like keeping things original, I'm worried that
the battery is going to leak and rot the inside of the unit.


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.

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Old March 20th 14, 01:12 PM posted to sci.electronics.repair
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Default ohm meter battery

On 20/03/2014 10:21, Mark Zacharias wrote:
"William Sommerwerck" wrote in message
...
wrote in message
...

As much as I like keeping things original, I'm worried that
the battery is going to leak and rot the inside of the unit.


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.


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 :-(

--
Adrian C



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Old March 20th 14, 01:13 PM posted to sci.electronics.repair
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Default ohm meter battery

On Thu, 20 Mar 2014 05:21:54 -0500, Mark Zacharias wrote:
"William Sommerwerck" wrote in message
...
wrote in message
...

As much as I like keeping things original, I'm worried that
the battery is going to leak and rot the inside of the unit.


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.


+1


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Old March 20th 14, 01:17 PM posted to sci.electronics.repair
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Default ohm meter battery

On Thursday, March 20, 2014 12:16:03 AM UTC-4, wrote:
I found this circuit somewhere, (I can't remember) to replace the 1.50 volt 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 circuit takes power from the 6.30 volt filament transformer and is built around 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 the battery presently does.



As much as I like keeping things original, I'm worried that the battery is going to leak and rot the inside of the unit. I was going to build the circuit but it occurred to me that I should probably be concerned about the current 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 heat 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 found that Rayovac's, (the Batteries Plus house brand) are one of the worst. And 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 printed on the batteries, and have gotten a free flashlight, or "other device" replaced 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 the device doesn't have to dissipate that much extra current. Lenny
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Old March 20th 14, 01:23 PM posted to sci.electronics.repair
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Default ohm meter battery

"Mark Zacharias" wrote in message
.com...
"William Sommerwerck" wrote in message
...
wrote in message
...


As much as I like keeping things original, I'm worried that
the battery is going to leak and rot the inside of the unit.


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.


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.

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Old March 20th 14, 05:48 PM posted to sci.electronics.repair
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Default ohm meter battery

"Mark Zacharias" wrote in message
.com...
"William Sommerwerck" wrote in message
...
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.


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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