Battery substitution question

I have a bathroom scale that uses three AAA cells, which need replacing. Since I don't have any non Li-Ion cells handy I was wondering if I could use one 10440 and two dummy cells instead. Obviously this is not a high drain situation, so there shouldn't be any voltage drop issues on either side. Any opinions?

Timothybil said:

I have a bathroom scale that uses three AAA cells, which need replacing. Since I don't have any non Li-Ion cells handy I was wondering if I could use one 10440 and two dummy cells instead. Obviously this is not a high drain situation, so there shouldn't be any voltage drop issues on either side. Any opinions?

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The scale is probably wired in series, so I guess you could do that, but how far are you away from the store?

I'd just head down to the gas station/7-11, or ChinaMart and buy some real AAAs.

Chris

ChrisGarrett said:

The scale is probably wired in series, so I guess you could do that, but how far are you away from the store?

I'd just head down to the gas station/7-11, or ChinaMart and buy some real AAAs.

Chris

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The point being I would rather use rechargeables whenever I can, and the scale doesn't seem to like three NiMH. If I have to use primary cells, they will be lithium. I don't buy alkalines any more.

If the scale doesn't like NiMh cells, than it probably doesn't like the fact that you are offering it 3.75 volts instead of 4.5 volts. Generally scales end up using highly regulated voltage internally, so they need 'headroom' on the supplied voltage. When fully charged a 4.2 volt Li-Ion may offer enough 'headroom' for the regulator, with key being the word 'may', 4.35 is more likely to work, but neither is likely to work for very long since somewhere r before 3.75 volts it will stop working, and 3.75 volts is well above complete discharge voltage on a Li-ion cell voltage. The scales are often not very high current applicatrs. Some of them will run on CR2032's, which is a 3volt low current battery, but obvious not your scale.

Buy the Energizer Lithium Ultimates, or Advanced. They will last a long time and don't leak.

Of course, you can fiddle with this stuff until you're blue in the face, no bother to me, but I think you're over thinking things.

How many times do you weigh yourself during a week?

Chris

IMO, if something won't work with Eneloops, I won't buy it (or I'll return it). If it requires almost-full alkalines, you'll be feeding it new alkalines way too often, because it will only use a bit of their capacity before their voltage falls to the level of NiMH.

WalkIntoTheLight said:

IMO, if something won't work with Eneloops, I won't buy it (or I'll return it). If it requires almost-full alkalines, you'll be feeding it new alkalines way too often, because it will only use a bit of their capacity before their voltage falls to the level of NiMH.

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Well, the original cheap alkalines that came with it lasted for six months, so using all the capacity shouldn't be a problem. I finally broke down and dropped in some lithium primaries, because I won't by alkalines anymore.

Timothybil said:

I was wondering if I could use one 10440 and two dummy cells instead.

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I have tested single 14500 plus two AA dummies in a clock and it works fine. Pretty much same situation.
If each alkaline cell provide 0.9 volt at end of it's life then I don't understand why shouldn't work with 1.2V NiMH. You may try another set of fully recharged NiMH.
BTW, Lithium Primaries are excellent choice for low current devices.

Timothybil said:

Well, the original cheap alkalines that came with it lasted for six months, so using all the capacity shouldn't be a problem.

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Did you measure their voltage after that? Unless they're under 1.0v, you haven't used all the useful capacity out of an alkaline cell.

IMO, 6 months doesn't sound like a very long time for an occasional-use device like a scale. If you're going to feed it with lithium primaries, they'll last a lot longer, since most of their run-time is spent at greater than 1.4v.

WalkIntoTheLight said:

Did you measure their voltage after that? Unless they're under 1.0v, you haven't used all the useful capacity out of an alkaline cell.

IMO, 6 months doesn't sound like a very long time for an occasional-use device like a scale. If you're going to feed it with lithium primaries, they'll last a lot longer, since most of their run-time is spent at greater than 1.4v.

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I believe you are right. I took the cells from the scale and tried them in one of my AAA lights. They worked just fine. The light may be just a little bit dimmer than with fresh lithiums, but the light just sits by my keyboard to help me find the occasional item that has fallen on the floor, so if it suddenly stops, no harm done.