Just checking batteries with my multi-meter when doorbell ceased to work.
Got a shock (surprise, not electrical) to get a NEGATIVE reading.
Thought at first must be a problem with meter, but worked fine when testing the new batteries.
Online search soon revealed that such polarity reversal does occur, but is a rare phenomena. Never come across this before in more than seventy years!
Anyone else ever experienced this?
Also, the putative cause, that a battery in series with a stronger cell is driven by the latter into polarity reversal. Well, fine. But this occasion BOTH of the 'in-series' cells had reversed!
So, a rare event within a rare event! How about that!
Wish my Premium Bonds would catch on to this behaviour.
Started: 6th Dec 2019 at 21:14
I understood your advice earlier about shrubs for hedging, Priscus, but you’ve lost me with this one!
Replied: 7th Dec 2019 at 01:34
Mind you I have had a small Jack Daniel’s or two so maybe I’m looking at it wrong!
Replied: 7th Dec 2019 at 01:36
It threw me when I first encountered it.
Took an AA alkaline battery, and put leads from digital multimeter to its terminals.
Nominally a 1.5 Volt battery, but is not new.
So, I was expecting to see reading of maybe 1.2V if the cell was OK,
and perhaps something circa 700 milliVolt if cell had expired.
What I read was MINUS 150 millivolts.
And a similar negative reading for the other cell!
Turning them round the wrong way yielded similar readings in positive territory, so at first, I thought perhaps my meter's 'polarity reverse' function was misoperating. Not so: new batteries tested OK, and tried another meter, which yielded similar results!
Replied: 7th Dec 2019 at 02:46
Does anyone understand this? I'm afraid it is well away from my knowledge.
Replied: 7th Dec 2019 at 04:59
Testing the voltage of a battery tells you nothing.
Oh, and by the way electrons flow from negative to positive.
Replied: 7th Dec 2019 at 09:48
Test the battery under load.Testing the voltage with s multimeter does not give a true reading of the state of a battery.You can buy a multi purpose battery checker which tests a range of battery sizes for a few pounds
Replied: 7th Dec 2019 at 16:16
A bad battery can give a misleading high voltage reading, but be unable to source adequate current if polarised, or otherwise high internal resistance.
A BATTERY WHICH DOES NOT YIELD A USEFUL VOLTAGE even on no load test, then YOU KNOW IT IS SPENT!
The reason I test them rather than just swap them is because occasionally, it is not the battery in the chime unit, but the battery in the bell push (cordless) that requires swapping.
The latter last much longer, as only deliver current when the bell push is actually pressed. (They last about seven years)
My question was NOT about testing batteries. I asked if anyone else had come across the rare phenomena of polarity inversion.
Replied: 7th Dec 2019 at 17:30
Replied: 7th Dec 2019 at 18:03
"only deliver current when the bell push is actually pressed"
I bet the bell only sounds when the bell push is actually pressed, too?
Have you checked it's tyre pressures!
Replied: 8th Dec 2019 at 22:37
Well, yes tonker BUT the transmitter draws current when the bell push is activated, and the receiver draws current ALL THE TIME, as it is in standby mode awaiting to detect a signal from the transmitter.
So the transmitter batteries last about seven years.
The receiver batteries last about eighteen months.
A change to cold weather tends to prompt a failure of the former batteries, so it would not have been unexpected a few days ago, though test revealed it to be the receiver's batteries expired once again.
Replied: 9th Dec 2019 at 00:18
Batteries this week equivalent to £5 for 24 AA or 16 AAA. Any problem at all no testing skimmed in the recycling.
Replied: 9th Dec 2019 at 04:50
Which is of no help whatsoever, if you need to determine whether battery, or battery which powers the related equipment is causing the malfunction.
Replied: 9th Dec 2019 at 05:45
Change both. Easy Peasy.
Replied: 9th Dec 2019 at 13:48
But not as easy as changing just the one which requires changing!
THERE IS ABSOLUTELY NO PROBLEM TESTING THE BATTERIES.
It takes me all of three seconds to do it.
I have only described the process to illustrate how I had come to encounter the phenomenon of polarity inversion.
It is something I have never previously encountered! Or, even heard of prior online search in response to what I found.
(changing the A23 Battery in bell push a bit more involved: I am sure that I could find one locally, but it is not worth the trailing around the shops to find one. Easiest just to order online. As I will get around seven years out of it, it is not one that I will have in stock.)
Anyway, as my post has drawn no response from any of the techie folk on these boards, I guess no one has owt to say on the topic of polarity inversion.
Replied: 9th Dec 2019 at 14:54
There is an Irish joke about 'phenomenon', but is in rather poor taste, so I will refrain from posting.
Replied: 9th Dec 2019 at 17:35
Now then, your use of the word "current" is somewhat debatable, as current is neither drawn or delivered.
Would you like a five minute argument or the full half-hour?
Replied: 9th Dec 2019 at 17:56
Now then tonks, you know very well that current draw is fairly usual terminology to use in these circumstances!
And when it comes to electronic active elements, they frequently are rated with respect to the current they can source (or sink)
Just because you like to try to impose your notion of what language people may or may not use, does not mean that anyone has to comply with your imposition.
Replied: 9th Dec 2019 at 18:46
Well, many (most) people don't know what current actually is. It's easy to get mixed up in current (Amps) and power (Watts).
You see, 'power' is what is drawn and delivered, current is resultant of that power-draw, relative to the P.D. (in Volts).
Current is non-existent in a circuit until power is drawn.
Replied: 9th Dec 2019 at 19:06
I am quite clear.
I am sorry if you are mixed up.
And in superconductors current IS existent, even though no power is dissipated.
Replied: 9th Dec 2019 at 19:12
Replied: 9th Dec 2019 at 19:17
Tha knows nowt thee Tonker, what with you only being a time served electrician.
You should leave things like this to the experts.
Replied: 9th Dec 2019 at 19:26
And I thought you were trying to claim some familiarity with Ohm's law.
Replied: 9th Dec 2019 at 19:27
Last edited by priscus: 9th Dec 2019 at 19:32:40
Let me put it another way.
What is I Squared multiplied by R, when R=0?
Replied: 9th Dec 2019 at 19:35