Perhaps subtle electronics issue

[Muse]

I left the Computemp Plus on the AC adapter for a few weeks. I removed my home-made filter because it didn't seem to be helping the problem, then left it so-connected for a few weeks. Problems! The temperature shown for the outside temperature probe (which is connected by wire) was not infrequently off, and many times off by more than 5 degrees F. I don't recall that happening when I had the unit on 9v battery power.

So, over 3 days ago I removed the AC-->DC power source and reattached the terminal clip for 9v battery, put in a good alkaline 9v battery and it's been behaving perfectly ever since AFAIK. No anomalous behavior whatsoever. So, I guess I give up unless I can maybe buy an AC affair that supplies power that the unit works with OK. Maybe a proper filter would work, but I don't know where I'd get either of those, so for now, it's 9v batteries. I ordered 4 Energizer Ultimate Lithium cells off of ebay, so I'm hopeful that the unit will work OK with those and maybe get at least 2 years service from one. If it doesn't work with them, I'll use those Energizer cells in my smoke alarms and CO detector. I think the Lithium 9v batteries supply a different voltage, around 8.1v and the thermometer unit could conceivably not work OK with them.

 

[Rubycon]

9V Lithiums use three lithium manganese dioxide cells in series providing an open terminal voltage in excess of 9VDC so that should not be an issue at all. Anomalies from running on shore power through a wall wart are either due to a ground loop or amplified electromagnetic interference from the leads, coupling potentials or a combination of both. With a low power device I'd recommend running off a primary lithium or alkaline 9V battery as designed.

Alternatively, there are numerous sensor and controller designs that are practically turnkey, accurate, and have logging capabilities, etc.

 

[SOFTengCOMPelec]

One solution, is to buy the following:
N.B. Get one with the 9V battery clip adapter built into it. As shown.
Also make sure it is EXACTLY 6 AA batteries in size.
AA Alkaline batteries, have a massively bigger capacity, compared to small 9V batteries.

Get quality (slightly expensive) AA alkalines with a VERY long shelf life left. E.g. Eight years in the future, like 2025 or similar.
You should be able to get at least 5 years shelf life ones.
You can even get special long life lithium AA's, but probably no need.

So now you should be able to get something like 5 years battery life (because AA's have about 4 or 5 times the capacity of 9V batteries), so replacing them is much less bad.

As already mentioned, replacing it with a mains adapter is electrically problematic. You really would have needed one with a built in regulator. These are hard to get hold of and can be expensive. They could also break, BEFORE AA alkalines even run out.
Because the capacitors (especially in cheap units), wear out over time.
It could be that the leads and mains connection are interfering with the temperature unit. If so it can be extremely difficult to solve. Even an expert in electronics may have difficulty solving it.

The 16V you originally mentioned, can cause terrible harm to your unit, as that is way too much.
EDIT: Also 16V may also be the cause of your malfunctions.

 

[Muse]

I like that idea. However, I think that device, the 6xAA shell, has to be quite a bit bigger than a 9v battery, so there wouldn't be room in the unit for that and I'd have to attach it. Doable. Well, the unit seems to behave just fine with the Lithium 9v in there. Presumably I'll get 2x the life out of that battery than the alkalines I used to put in there. Big improvement!

 

[SOFTengCOMPelec]

I like that idea. However, I think that device, the 6xAA shell, has to be quite a bit bigger than a 9v battery, so there wouldn't be room in the unit for that and I'd have to attach it. Doable. Well, the unit seems to behave just fine with the Lithium 9v in there. Presumably I'll get 2x the life out of that battery than the alkalines I used to put in there. Big improvement!

I also had a temperature meter with a similar problem. The batteries (pair of AAA), only lasted about 3 months. So I put the external AA battery holder behind the temperature meter, by using a PP3 battery clip, with wires. I connected the wires inside the unit.
It then lasted considerably longer.
With a bit of luck, the lithium solution (you have now gone for) may last more than twice as long.

But you are right, it would be too big to fit inside the case. But so was the AC adapter solution.

With a pair of these (connected together in the right way, take care of polarity, best to check with a meter afterwords), you can make an extension cable. Allowing it to be put by the side of the meter, a bit like the AC adapter.

You might also be able to use velcro sticky things, so it sticks on the back of the meter.

 

[Hugo Drax]

Speaking of smoke alarms, we recently upgraded to Roost and I love it.

https://www.kickstarter.com/project...battery-smarten-your-smoke-alarms/description

https://www.amazon.com/dp/B00ZWQHVP4/

Ummmmmmmmmmmm. NO.

 

[SOFTengCOMPelec]

If there is room on the back, you can stick the flat type of battery holder on to it. Maybe with velcro sticky things.
Anyway, you have solved the problem for about 2 years now. With the lithium PP3.

 

[Muse]

I also had a temperature meter with a similar problem. The batteries (pair of AAA), only lasted about 3 months. So I put the external AA battery holder behind the temperature meter, by using a PP3 battery clip, with wires. I connected the wires inside the unit.
It then lasted considerably longer.
With a bit of luck, the lithium solution (you have now gone for) may last more than twice as long.

But you are right, it would be too big to fit inside the case. But so was the AC adapter solution.

With a pair of these (connected together in the right way, take care of polarity, best to check with a meter afterwords), you can make an extension cable. Allowing it to be put by the side of the meter, a bit like the AC adapter.

Yeah, a couple of those in parallel or even three would give 2x or 3x the life, not counting for shelf life. I had the AC adapter under my bed and plugged into an extension cord that is there. It worked some days, but too often I'd look at the unit and realize that the temperature shown was for sure wrong, too high, sometimes by 5 degrees, even more. I've had this thing for almost 12 years and I've gotten really good at guessing. I have indoor temperature sensors in various places in the house and I can usually guess the temperature within a degree. Of course, I'd have to go outside to sense the temperature out there and my guesses for that are nowhere near as good. Still, when the unit is off by several degrees I have suspicions. The giveaway that the reading on the unit was erroneous was the fact that hitting the "High" button (which reveals for a few seconds what the highest temperature was since midnight), caused the present temperature (which is what it otherwise displays) to change (i.e. go lower) when it was false. Seems that when it was false, it said the outside temperature was higher than it actually was. I'd never seen that behavior when running on a battery. I just hoped that when I put the unit back on battery power after being on 2 different AC adapters for something like a month, that it would again work OK. It seems to be working OK again and I've given up on the AC adapter idea for it. Seemed like a great idea but it just wasn't!

 

[SOFTengCOMPelec]

The pair of battery clips when electrically connected together. Can plug inside the unit (as if it was a battery), AND onto the external battery holder. Hence why I said it was a sort of extension lead. Sorry if I was not clear, originally.

You can parallel up further battery packs, to extend the life. But it is not such a good idea, as the batteries might fight each other, if it goes faulty.
That is why items designed to allow it, may have diodes designed in, to stop that from happening.

 

[Muse]

The pair of battery clips when electrically connected together. Can plug inside the unit (as if it was a battery), AND onto the external battery holder. Hence why I said it was a sort of extension lead. Sorry if I was not clear, originally.

You can parallel up further battery packs, to extend the life. But it is not such a good idea, as the batteries might fight each other, if it goes faulty.
That is why items designed to allow it, may have diodes designed in, to stop that from happening.

OK, I think what you mean is that with those two clips, one can go on the 6x AA affair and the other can go inside the unit and attach to the clip in there. Yeah, that's obviously what you meant. I didn't read it carefully to begin with. Sensible setup.