AA primary cell voltage through its life?

[ericmark]

My cat flap started flashing a red LED which is on the chart a signal of discharged batteries, so I changed them, 4 x AA cells, the flap has not been in use long so measured old batteries after changing, and 1.4 volt each.

So looked on internet and found

At what voltage should AA batteries be replaced?

Notice the voltage reading on the voltmeter. If the reading is more than 1.3V for alkaline battery (not rechargeable battery) then the battery still has some juice left in it, don't throw it away. Otherwise, properly discard of the battery.

There seems to be so odd ways to test them

Alkaline batteries bounce when they're going bad, so drop one on a hard surface to see whether or not it bounces.

and even seen some using the amp range, which seems dangerous to me.

But most seem to say "At 1.2-1.3V is typically when most 1.5V batteries start to become weak." and it does seem many bits of equipment report the battery being below useable voltage at around 1.3 volt so will not run on rechargeable cells. The Leclanché cell we taught about at school, and we have:-
– anode (oxidation of Zn): Zn → Zn2+ + 2e− | E0 = −0.76 volts
– cathode (reduction of Mn(IV)): 2 MnO2 + 2NH4+ + 2e− → 2 MnO(OH) + 2 NH3 | E0 = 1.23 volts
So producing a theoretical voltage of 1.99v of potential energy across the terminals. A variety of factors, such as internal resistance, lower this output value to the 1.4 volts measured from these cells in practice. But in that case my cat flap should have been working OK. But today cells are often not simple Leclanché so in real terms no idea what voltage I should be looking for?

Most of the instructions relate on cutting a hole in the door, bit on how it works is reduced to which is very little is says "Remove the battery cover, set aside the provided hardware pack, and install 4 high quality alkaline AA batteries (LR6). The green LED light will flash three (3) times which indicates that the cat flap is in Automatic Mode." I have looked and there seems to be a whole range of batteries which say they are alkaline AA cells, often with trade names like Duracell which it seems are designed for rabbit hatches not cat ones, but no details of how much energy is in them.

Five times what? I see statements like "The Leclanché battery wet cell was the forerunner of the modern zinc–carbon battery (a dry cell). The addition of zinc chloride to the electrolyte paste raises the e.m.f. to 1.5 volts. Later developments dispensed with the ammonium chloride completely, giving a cell that can endure more sustained discharge without its internal resistance rising as quickly (the zinc chloride cell)." every make seems to say they last longer, and price does not seem to help, Duracell Procell Constant AA LR6 PC1500 Batteries | Box of 10 for £3.29 and what seems to be same product £8 elsewhere. And Duracell +100% Plus Power Batteries AA at £6.50 for just 4, click on specifications and it says nothing of any use.

Some do say "for low drain devices" but nothing to say what is low drain, my TRV heads take 2 x AA cells and will last around 2 years, I normally swap every year, but the app shows 2.83 volt etc. and they seem to go to around 2.5 volt before it says change battery.

 

[Alec_t]

The cell voltage depends a lot on what current is being drawn. If you measured 1.4V with a DMM and no other load, then whatever peak current the cat flap draws may well take the voltage down below what is deemed acceptable for that device.

 

[big-all]

do what i do pepper grinder/blood pressure monitor what ever with a motor at the first sign off struggle remove into the clock/remote control/door bell or whaever box for further service

 

[Ragnar_AT]

New alkaline AA batteries are closer to 1.8 V (open circuit) in my experience, some even 1.9 V.

 

[Rodders53]

I have an ancient analogue meter with a battery test facility (load) for 1.5 V and 9 V cells that I keep in a drawer for such checks...
https://cpc.farnell.com/draper-tools/amm1/analogue-multimeter/dp/IN08777 is similar

One can get various Chinese battery check testers and multimeters with such a feature nowadays.

A new alkaline AA should be in excess of 1.5V with no load, though, surely?

You may wish to do some tests on the current drawn when locking/unlocking the flap to see if any alternative battery type would work better/longer and whether they'd be cost-effective? (e.g. the AA lithium usb rechargeables I have may hold voltage at 1.5V but are limited to a 2A current draw peak. Likely they'd also cut out with little or no warning when the charge runs out.).

An alternative power supply wired to the battery terminals might be another solution? (e.g. a 6V SLA).

 

[ericmark]

I am a little worried that our cats may not be able to get into the house, going out it does not need to read the chip in the cat, it only does that on return, I had heard them tapping on the flap, when it has picked up their chip it does show a green LED but where it is we only look when we hear them tapping at the flap, without grabbing a cat and sticking their head in the tube, it is hard to know if it is working. I read before fitting it failed safe, so discharged battery causes flap to unlatch, but now can't find where I read this so maybe it was another make of flap.

Says should last 12 months on a set of batteries but no where near 12 months, more like 3 months.

 

[JohnD]

For Alkaline batteries, Aldi own brand are best value.

You could get Lithium batteries, they hold a lot of power and have a slightly higher voltage.

More expensive, though.

I don't know if your device would work with rechargeables. If so you could just get in the habit of replacing them every week. Their voltage is only about 1.2

 

[Munroast]

for the rear LED flashing lights on my bike I replace them at 1.25v - that seems to be the point they loose brightness.

 

[ericmark]

With some thing like my TRV heads, if they become over discharged there is no real problem, but the cat flap saves them using the litter tray, so don't want it to fail.

 

[Harry Bloomfield]

With some thing like my TRV heads, if they become over discharged there is no real problem, but the cat flap saves them using the litter tray, so don't want it to fail.

Not really relevant, but....

My weather station transmits an updated set of data, back to the display console, in the house, every few seconds, and is designed to run on a pair of AA cells. The station resides on top of a mast, attached to the back of my workshop. Changing the cells, used to involve getting a ladder out, and climbing on the roof. A few years ago, I adapted it, by adding a cable down from the battery terminals in the transmitter, all the way down the mast, into my workshop, and to 4x AA holder, wired two in parallel.

Twice the battery capacity, means the cells last more than twice as long, and I can pull one pair of batties out to check/swap them, without disturbing the transmission. It also avoids a second problem, in that if power is removed from the unit, it can take an hour or two to regain data sync.

 

[Rodders53]

Shirley it is easy enough to test:

Remove batteries. Is flap locked shut or open?

Remove collar from cat and use collar/chip to actuate flap when performing tests (current drawn etc.,.)
{Surely it can't read the ID chip that is inserted by a vet under the skin?}

Sometimes you seem to overcomplicate things for the sheer joy of doing so

 

[DetlefSchmitz]

{Surely it can't read the ID chip that is inserted by a vet under the skin?}

It does exactly that, and works perfectly. What I do to check that it set up right is to scan the cat with my Flipper Zero, and then check that the flap unlocks when I pass the Flipper Zero through the portal. I realise that not everyone has one of these but our cat really hates being pushed through.
But I agree with the 'remove batteries' comment!

 

[ericmark]

Shirley it is easy enough to test:

Remove batteries. Is flap locked shut or open?

Remove collar from cat and use collar/chip to actuate flap when performing tests (current drawn etc.,.)
{Surely it can't read the ID chip that is inserted by a vet under the skin?}

Sometimes you seem to overcomplicate things for the sheer joy of doing so

I know with my TRV as the battery reaches a set point it opens the TRV, so to test cat flap the supply needs to slowly reduce in voltage, not simply take out batteries.

Cats do not have collars they are dangerous, look nice and shows people the cat is owned, that is if one ever really owns a cat, but the way they climb the apple trees, simply not safe, so it reads the ID chip that was inserted by the vet.

Getting a Flipper Zero to test a cat flap is a bit extreme. If the new batteries don't last I will look at a larger battery box, or battery eliminator, but cables will need to flex when the door is opened so not an ideal way. Problem is out is not chip controlled only in, so if battery fails they are locked out.

 

[Rodders53]

I know with my TRV as the battery reaches a set point it opens the TRV, so to test cat flap the supply needs to slowly reduce in voltage, not simply take out batteries.

If you know it all why the bleep ask for advice?

I will look at a larger battery box, or battery eliminator, but cables will need to flex when the door is opened so not an ideal way.

I believe there is a thing called flexible cable that might help with that "problem".
Or https://cpc.farnell.com/deedlock/alp135/door-loop-35cm-v-resistant/dp/SR06544 if you want to go a bit OTT.

 

[Harry Bloomfield]

Cats do not have collars they are dangerous, look nice and shows people the cat is owned, that is if one ever really owns a cat, but the way they climb the apple trees, simply not safe,

I didn't realise that, but not being a cat owner...

My dog is chipped, but a collar is only fitted when out of the house and garden. Obviously, when out for a walk, but also when in the car - just in case something were to happen, and the collar is easy to grab hold of.