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