# Ionization Smoke Detector In Toddler's Room: How Safe ?

but the battery will "die" sooner.
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On Wednesday, October 1, 2014 11:58:24 AM UTC-4, Pico Rico wrote:

How so? The battery is rated at X amphours. Whether it delivers it through a diode or not is mostly insignificant. Only a very small amount of power is lost in the diode.
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On 10/01/2014 11:52 AM, trader_4 wrote: ...

But what's significant is what _fraction_ of the power consumption any portion might be...if the overall is also pretty small as one would expect/it must be to have a long battery life to begin with, that "very small amount" may still be a decent fraction of the total and then the decrease in lifetime is proportional to that fraction.
Again, this is all _purely_ hypothetical w/o any other data...but if the symptom exists that the battery life doesn't appear to be any longer w/ AC powered unit than non-, it's pretty clear there must not be any real power-saving circuitry inherent in the device design (or, the overall device power consumption is quite high and therefore drains the battery at about the same rate even though there is some extension over what it would have been w/o the AC).
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On Wednesday, October 1, 2014 1:09:40 PM UTC-4, dpb wrote:

Let's do the math. 9V battery. .6V drop across the diode. 8.4V goes to the load. That's 7% of the voltage across the diode and hence 7% of the power dissipated, because the same current is flowing through the load and the diode. And that 7% power dissipation would only come into play when the AC is out. The rest of the time, it would be zero. You'd have a design where if the AC is lost, the battery would diminish about 7% faster. But in return, you'd have a design where the battery lasts the shelf life, not just a year. I could come up with other designs that would perform better, but a diode is simple and cheap as an example.

What's apparent is that somehow they are using the battery power as well as the AC. I can't think of other battery/AC powered devices that do that. Sump pump backup? Emergency lighting? Battery banks at the phone company?
(or, the overall

The point is there is no good reason to be drawing down the battery at all. And why not put in rechargeables? Duh! That's what they do in those other examples.
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On 10/01/2014 12:28 PM, trader_4 wrote: ...

The answer as outlined above is more than likely "initial cost".
Again, if these bug you so much for that reason, the obvious alternative is to do some research and replace them with ones which do have an extended battery life and/or rechargeables.
Different device/design but the outdoor unit on the local weather station has started indicating "low battery" at night...it's got a solar charger and I replaced the initial battery just a month ago but it showed the missive the other night again already. I suppose the solar cell is now starting to fail/losing its "oomph" after 2-3 yr in the SW KS sun...
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On Wednesday, October 1, 2014 1:56:26 PM UTC-4, dpb wrote:

Yes, that explains why they didn't use rechargeables. It doesn't explain why they didn't use a 10 cent diode so that the alkaline battery is just there as standby and would last for years.

I agree, that's a possible solution. The comment was directed at why they didn't put in a 10c diode so I would not have to do that.

Does it have AC too?
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On 10/01/2014 1:04 PM, trader_4 wrote: ...

I still think it more than likely does... ...

See above... :)

...

Not the external station, no. The base in-house display unit does and it _does_ have pretty good battery life--seems I've changed them out once, maybe. But, this is a much higher-priced device (Davis Instruments VantageVUE) so the few pennies kinds of cost-cutting on mass-produced consumer devices isn't _quite_ so vicious.
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On 10/01/2014 1:22 PM, dpb wrote: ...

...
Actually, more precisely, I suspect the cut got made at the earlier "feature selection" level of what were/were not expected capabilities to meet the target market niche/pricing level for the device rather than being pared out on an individual component-level culling (altho that certainly occurs as well as the price/specific component alternative vendors/etc. evaluations that occur).
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On Wednesday, October 1, 2014 3:04:47 PM UTC-4, dpb wrote:

I can show you plenty of rechargeable, cheap, consumer products that sell for what a smoke detector sells for, or less that have battery "Backup" or rechargeable batteries, that don't draw the battery down along with using AC. Your argument about a 10 cent diode is silly.
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On 10/01/2014 4:15 PM, trader_4 wrote: ...

That the cost/feature analysis comes out at a different place on other products doesn't negate the general rule. And, in fact, the "feature set" on your device pretty much confirms it for your particular device.
As said, it isn't/wasn't that the particular one selected component got taken back out; the feature of which it might have been a key component wasn't included to begin with. The decision as to whether it was/was not to be included almost certainly included a consideration of the cost for the design/manufacture in comparison to the expected margin and potential increase/decrease in sales and was found lacking...
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On Wednesday, October 1, 2014 5:29:59 PM UTC-4, dpb wrote:

Pure conjecture on your part. You have no way of knowing what went into the design consideration or why anything was or wasn't done. For all you know it could be just a bad, dumb, design. I've seen battery backup on cheap consumer products where it doesnt' run the battery down in a year. The battery is only used if the AC goes down.
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On 10/01/2014 4:42 PM, trader_4 wrote: ...

Surely no more so than conjecture on your part, either,...I pointed that out some time ago upthread, as well, that we're both dealing in nothing but conjecture here (other than the fact that the design did _not_ include the feature I will submit leads to a higher likelihood that was done on purpose than not).
And, again, that other products have a different feature set and cost point has no particular bearing on the given one.
I'm bowing out of a futile and pointless subthread at this point...
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On Wednesday, October 1, 2014 5:48:22 PM UTC-4, dpb wrote:

I wasn't conjecturing on why they did it. Just pointing it out and that it's terribly inconvenient and dumb. Even if I buy your argument that it would make the product cost some tiny amount more, it doesn't make sense. They could charge \$2 more, point out that their design, unlike competitors doesn't draw the battery down unless the AC actually goes out and have a marketing advantage. They'd sell more and make more money.
..I pointed that

It does when they are cheap consumer electronics type stuff. And when we know how cheap semiconductors, like a diode are today. That diode could probably be integrated into an IC already in there, in which case it might not actually cost anything.

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On 10/01/2014 4:29 PM, dpb wrote: ...

You never followed up w/ the particular manufacturer/model so can't tell anything about who might have been but if it is a foreign knockoff it may well be that the entire engineering for the specific unit was "copy the model" in which case the feature set simply mimics that of the one chosen to ape.
Which if so simply pushes the original design choice of feature set/cost back to the previous manufacturer...
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On Wednesday, October 1, 2014 5:15:18 PM UTC-4, trader_4 wrote:

However the purchaser of a hardwired smoke detector is almost the end user; neither the manufacturer nor the purchaser/installer cares about features, only code compliance and cost.
nate
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On 10/1/2014 2:04 PM, dpb wrote:

Kind of like the Muntz TV. Way back when Mad Man Muntz was a car dealer in California. He branched into TV manufacturing by selling an extremely cheap TV set. The way he did it was to have his engineers go through the set and try what would happen if they left that out. One thing they left out was the IF stage. That reduced the sensitivity, but since they were mostly sold in the LA area they were close to the station and would still work, good enough so that people who couldn't afford a good TV would use them.
Bill
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On 10/1/2014 2:04 PM, trader_4 wrote:

--
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Christopher A. Young
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wrote:

Which, of course, has *never* been illegal. "Except by the consumer" and all. I remember being 7 or 8, hearing someone "joke" about that on TV, and being very confused because it was clear to me that the tags meant that the manufacturer and retailer couldn't remove them, but we as the final purchaser could.
This was in the late 70s/early 80s; perhaps sometime before then those words weren't on there? Or it just makes a better joke to pretend they aren't?
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The voltage without a diode can drop ..65v further and still power the unit.
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On Wednesday, October 1, 2014 2:02:54 PM UTC-4, Pico Rico wrote:

Wow, really? How very important. Let's see, we have a smoke detector that's primarily operated by AC. So, it can go forever on AC plus last about as long as a battery operated one if the power goes out. Power almost always goes out for hours or a few days, not a year or two. That voltage drop is important again, why?
I've also cited other common devices where they have battery plus AC and don't draw the battery down unless it's needed because the AC fails.
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