Most efficient way to get 1.5 volts from 3.7 volts or less?

I have a digital height gauge that eats batteries. Not a cheap Chinese made one, but a fairly high quality Japanese made one. It uses one SR44 battery. For some reason it has started using batteries much faster than it used to. I have tried several different brands of batteries from several different sources and they all seem to last about the same. Because of the bulk of the sliding portion of the gauge I could easily attach a lithium coin cell holder and associated voltage dropping circuitry. Even a couple AA size batteries. I did try a typical alkaline AA cell but it didn't last much longer than a button cell. I think this is because the display starts flashing when the battey voltage drops to 1.45 volts or less. So what would be best for the longest battery life? Thanks, Eric

Reply to
etpm
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Take the battery out when not using the gauge. I have a set of calipers that "eat" batteries like that, because it's always drawing some current while waiting to "turn-on" when I turn the dial. ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Jim Thompson

Reply to
etpm

OK. If you have room to attach a battery holder, why not just add a switch? ...Jim Thompson

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| James E.Thompson                                 |    mens     | 
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Reply to
Jim Thompson

There's a silver-oxide battery type that's drop-in compatible with LR44, designated variously. Panasonic says LR44 is good for 120 mAh, sized 11.5mm diam, 5.1mm high, and the similar silver-oxide SR44 is 180 mAh, 11.6mm diam, 5.4mm high.

Other names for the silver-oxide are V76, AG13... and the names get applied loosely by online merchants of any-old-thing-that-might-fit.

It also might be possible to substitute a supercapacitor, there's some modest-sized ones that could take several minutes to droop from 1.8V to 1.0... you'd have to recharge it after a few minutes, but a charge stand or holster would't be TOO difficult for someone with machine tools

Reply to
whit3rd

Don't know if it's useful for you, but the cellphones that use low-voltage memory have opened a market for 1.5V regulator chips (that's the good news) which are almost always tiny (that's the bad news).

NCP170 is typical

Reply to
whit3rd

I have the same problem with mine, too. It's very common. You'd have thought the manufacturers would fit a switch in the first place. You could still have the auto-on feature but just have the switch disable it between sessions.

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Cursitor Doom

Greetings Jim, Every time I turn off the power I would then need to re-zero the gauge. This takes time and is something I don't want to do every time I use the gauge, which is several times a day. I could turn it off at night I suppose but then I would need to remember that. Eric

Reply to
etpm

Thanks, that chip or one similar looks like just what I need. Eric

Reply to
etpm

snipped-for-privacy@whidbey.com wrote on 9/23/2017 12:17 PM:

I think that is the only practical solution. I got tired of replacing the battery in my digital caliper, so I started removing it since I sometimes go a month or more without using it. Then I started using my old dial caliper and the digital hasn't been out of the box for a long time.

Switching to a slightly larger cell isn't going to do much for you. If an AA cell doesn't cut it I'm a bit at a loss. Cutting off at 1.45 volts says to me your gauge is dodgy. If you want to work around that with a regulator, you can get very small switching devices that will give you optimum efficiency or a small linear will allow you to use a lithium cell. Otherwise maybe a solar cell would do the job?

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Rick C 

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Reply to
rickman

If I was going to buck regulate, I'd use 9v battery to get significant watt-hours and a $0.99 from-China regulator. No screwing around with a PCB carrier.

Reply to
Bob Engelhardt

Could be there's moisture inside your gauge, dry it out!

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Reply to
Jasen Betts

No moisture. No corrosion even visible with magnification.

Reply to
etpm

You'd be surprised... With surface mount parts close together, low current high impedance circuits, a little moisture on some surface dirt is all it takes. To be safe(er) the boards should be baked for a time then coated with a suitable varnish while still hot and dry - then (if the pcb quality is up to snuff) you stand a pretty good chance of it working without phantom circuit losses.

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default

I don't even know how I would go about coating anything without ruining the read head. The read head is some sort of capacitive device. All the circuitry is located on one side of the circuit board that comprises the read head. There are a whole bunch of tiny holes that go through the circuit board. All of the capacitive type encoders are made the same way. So all the cheap electronic calipers look the same inside. Sylvac invented the device (if memory serves correctly) and more than one Japanese company made encoders under license. Mitutoyo was one. But now the patents have expired or have been pirated so you see these things everywhere. Any significant moisture will cause the read head to malfunction so I don't know if moisture is a problem. Thanks for the suggestion anyway. Eric

Reply to
etpm

Well, for sufficiently small values of "eats batteries". I'd vote for a damaged FET on an IC input someplace, perhaps due to ESD.

I just had the catch diode come loose on a SMPS proto, which caused the output voltage of the regulator to go from 6.2V to 4.5V. Took me awhile to figure out that the CMOS switcher chip was toast. It was an AOZ1282-1--quite a nice chip actually, as long as you don't blow it up.

Sort of a 1-MHz CMOS version of the LM2594 but more efficient and with a much more convenient enable pin, so that you can implement UVLO with just a zener and a resistor to ground.

Cheers

Phil Hobbs

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Phil Hobbs

Eric, I'd troll digikey looking for DC-DC converters.

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(A long link.. sorry)

George H.

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George Herold

snipped-for-privacy@whidbey.com wrote on 9/22/2017 2:15 PM:

There was a Kickstarter project for a clip on switching converter for AA cells that would provide a constant output voltage as the battery drained. It was barely larger than the AA cell so could be used in the same socket designed for the AA cell. The question is what voltage it would put out since your device seems to be abnormally sensitive to the voltage.

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Rick C 

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Reply to
rickman

Yeah, I'm not certain how high it can go. I know 5.5 volts is OK because that's what the silver oxide cells measure when new. It's too bad the display flashes when the voltage drops to 4.5. Eric

Reply to
etpm

I assume those are typos and you actually mean 1.55 or 1.5 volts and 1.45 volts?

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Rick C 

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rickman

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