Battery life

Rickharris

Senior Member
Using an 08 and running a program to flash 3 LEDs (about 10 MA load) every 20 seconds or so for just 10 milli secs how long is my 3 cell alkaline battery pack going to last?

My back of the envelope calc seem to suggests a lot longer than the supposed shelf life of the battery.

Code:
start:
high 2
pause 10
low 2
sleep 10
goto start
Just looking for conformation it will be a long tome before I need to get the ladder out again to change the battery.
 

manuka

Senior Member
Select new ultrabright LEDs & they'll probably still be near blinding at just ~1mA total draw!

As the PICAXE itself will however draw a few mA,this may be the limiting factor. Even SLEEP can be 100 µA range unless the BOD (brown out disable) command is used, giving hibernating ( SLEEP/NAP) currents at around a fraction of this.
 

Andrew Cowan

Senior Member
PIC: ~1mA
LEDs (average): 3*(0.01/20)*10: ~0.015mA

Total: ~1mA

Capacity of pound-store-style AA cell: 1100mAh
Capacity of average AA cell: 2200mAh
Capacity of duracell AA cell: 2900mAh

Life with pound-store-style AA cell: ~1000 hours = just over a month
Life with of average AA cell: ~2000 hours = almost three months
Life with of duracell AA cell: ~3000 hours = just over four months

As Stan says, reduce the 'Axe's consumption, and those times will increase massively.

A
 

BeanieBots

Moderator
As long as your peek current is within about C/10, you can assume the duty of the pulse to represent the average of the current. Hence, I expect your calculations will be quite accurate. As Stan points out, the PICAXE current is likley to be a significant factor.
 

Dippy

Moderator
10 Mega Amps!? Blimey! Let's assume 10mA.

My quick calcs indicate a lot longer than Andrew calculates. With I estimate ~2 years - assuming the impossible situation of no battery degradation or self-discharge.

I'm basing that on:-
100 microAmps in Sleep - could well be lots less if you switch off all peripherals.
And 3 x 10mA LEDs, plus 2mA for PICAXE whilst clocking.
And 'perfect' PROPER make (no cheap crap) AA alkalines.
And a 'perfect' circuit.
And PICAXE happy at <3V.
And 10mS flash with 4500 flashes per day.
And at room temp - freezing conditions can cut this.

But, what size cells? AA, C, D ?

If important and in long term < 5 oC consider those lithium batts.
Yes, more expensive, but will last longer when in cold.
This is the territory for lithiums.
And if you break your leg falling off the ladder ...
 

jaka

Member
Just a quick one.

How do you know the rated capacity of a AA cell and at what point do you decide they are discharged.

Jim
 

BeanieBots

Moderator
Just a quick one.

How do you know the rated capacity of a AA cell and at what point do you decide they are discharged.

Jim
From the datasheet.
What, no datasheet!
Typical AA these days (eg duracel) is ~3Ahr.
Cheapos can be as small as 500mAhr.
You get what you pay for.
Weight is a good indicator when in doubt.

EDIT:
"Flat" is typically taken as 0.7v but varies from manufacturer to manufacturer.
In practice, the available capacity between 1.4v and 0.7v is very little. Hence, 'flat' can often be taken as simply when the 'equipment' stops working.
 
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techElder

Well-known member
I'm thinking your battery pack contacts will have to be cleaned of corrosion long before you need to change batteries.

And while you are there, you will decide to change out the batteries anyway!
 

jaka

Member
I'm thinking your battery pack contacts will have to be cleaned of corrosion long before you need to change batteries.

And while you are there, you will decide to change out the batteries anyway!
TC. Agreed, but we pay silly prices for our batteries over here, so we like to squeeze out the last volt.

BB. B & Q don't issue data sheets.

In work we use bucket loads of AA's. We have found the the cheapo's last the same time as the black and golds.

But not Zinc Chloride. They are a no no.

Jim
 

Rickharris

Senior Member
Batterys at present are 3 x almost new AA Duracells (or rather the industry brand of the same) - I think I will order a 3 cell C pack - this is flashing an LED in a dummy burglar alarm so plenty of room.

Before you think of coming round I moved the real box to the back of the house as it is solar powered and will get more sun there and save me having to remove every 6 months to top up the battery.

The dummy is just there to tell possible nere do wells There is an alarm.

Thanks to all you mathematicians.
 

BeanieBots

Moderator
B & Q don't issue data sheets.
Ha, Ha, no they don't.
They (and many other outlets) do something much worse. They make rediculous claims like "last up to ten times longer" with no backing data or mention of circumstances.

A 100mAH lithium backup battery will probably last 100 times longer than a 5000mAh zinc chloride battery doing the same 'backup' function but I wouldn't bet the same if they were used to drive a toy car pulling a few amps.

As with ICs and other electronic components, all reputable manufactureres will produce datasheets for their products. As pointed out by IP, Duracell are one of those who produce good information. My golden rule is that if there is no published datasheet, then they are obvioulsy ashamed of its performance and you should avoid using the product for that obvious reason.

When it comes to batteries, IMHO there should be law making the manufacturer state nominal capacity on the packet. After all, it has been law on all other products to state volume (or similar) on other packages for years.
 

Dippy

Moderator
Is Rick scared to say "Procell" ? :)

I also wish there was a universal agreement on capacity testing and that it was printed on the packet.
In fairness a couple of the Big Brands do have similar schemes, but you can only find this with the data sheets.

A friend of mine (OK, it was me) accidentally got some cheap CH anonymous batteries.
After they failed after 10 minutes I weighed them. Half the weight of proper makes.
Moral. Don't buy cheap unheard-of-make Chinese made crappo batteries.
(I know many tightfists will continue to do so).

Sadly, people don't realise that batteries are Horses for Courses too.
Drawing current in big lumps can really knock certain batteries.
Sub <5 oC temperature can really affect alkalines but it's sometimes tricky to get data.

Battery clips and holders are another thing.
99% of people buy the cheapest on the Planet. In many cases that's fine. e.g. schoolboy/novice level projects.
I've done the same - and learnt the lesson.
Compare Maplin Chinese stuff with Bulgin.
Come on Rick, get decent stuff... yes it costs!
Thicker plastic, better plastic, sprung at both ends, better metal, better plating , better everything.
If you want something to last and that you can trust to leave unattended for long periods then you need QUALITY.

Yes, apparently the word "quality" is still in some dictionaries.
 

Rickharris

Senior Member
Scared me? Might have been the bit in the data sheet that says "not available retail" I seem to have collected quite a few of these form who kknows where (looks innocent) although they must have been in the garage for at least a year.
battery box We used to buy a lot from rapid - mainly because they were Rapid and with their educational discount reasonably priced when buying in 10's or 100's

OK i will confess how my back of the envelope calc went.

The data sheet says the battery will give upwards of 150 hours of service into 75 ohms down to 1 volt - assumes the 08 will operate to 3 3olts. this represents 16 Ma according to duracell.

150 hours is 540000 seconds - The unit is asleep for 21 seconds so 540000 * 21=11340000 disregarding the few micro amps the 08 draws when asleep for now.

The LEds draw current for 10 mill sec - 1/100 of a second so 11340000*100=1134000000 sec /60=min /80=hours/24=days/365=years = 35.95890410958904 years - Now even halving that to account for optimism and the 08 current and any incorrect assumptions re LEDS will give 17.97945205479452 YEARS long outside the shelf life of most batteries.

Although I did until recently have 4 NiFe cells that were in steam engines as a power backup and they still held a charge. Went to the dump in a mad clear out a few months ago - I instantly regretted it.

I am most than likely WAY out of line with my thinking here hence the question in the first place.
 
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Dippy

Moderator
"16 Ma according to duracell" - eh?

You can't ignore the sleep current.
The current could be 10 to 150 microAmps, depending on your code and PCB.
My calcs integtrate quiescent and transient and duration and how many per day.
This gives an aH figure.
All I will say is that this methd fairly accurately predicted battery lifes of half a dozen people-counting devices i did some years ago.
I'm only suggesting ballpark figures and not claiming anything rash. My estimate at 100 microAmps etc is 2 years for AA assuming 2aH because of unknown-to-me-operating-temperatures and rotting.


Aha!!
I guess the supply has dried up now you've retired? ;)

A member of the local Constabulary:-
"Good evening Sir, I seem to have found some Procells in your cupboard. You realise you can't buy these in the shops?"

Rick: "Yes officer, I know that , but a kindly and mysterious stranger at the local Pub bought them for me from Farnell".:)

If that fails I'll come and visit you inside.
Wednesdays are good for me.


Oh Dear, Oh Dear, Oh Dear. Cheapo battery holders with cheapo switches in long-term-unattended and awkward to-get-to-possibly-damp places. You may regret being a skinflint Rick , but I hope not. Keep supporting the Chinese Empire mate ;)


The problem I had with battery holders was in a commercial outdoor app.
Version 1 used the cheap 6xD holders from Maplin.
- One device got dropped and the sheer intertia of the mass of batteries broke the end of holder clean off - crap cheapo plastic.
- In another device , regular vibration momentarily moved the battery away from the pip (again inertia of battery sliding).
Moving over to QUALITY holders with spring contacts at BOTH ends got rid of the problem.
Result:
ChCh 0 Bulgin 2 (an away win).
You get what you pay for.


PS. Or simply design it better and use a single C 3.6V Lithium and solder some wires onto the axial leads. Will you worry about a tenner in 10years time? I don't think so.
 
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manuka

Senior Member
Now look what you "back of an envelope" Asian AA madmen have done- our Dippy has near lost his marbles. Dippy- tablets in the bathroom cupboard remember- top shelf behind the toothpaste.
 

1dgjctgmln1

New Member
lithium

I put 3 off the shelf "AA" (1.5V each) lithium batteries in a battery holder. All together, the measured voltage is 5.4V brand new. Would that damage a picaxe chip much if it was used to power the chip directly? I'm only asking because I'm building a device that I plan to use out in the cold a lot.
 

eclectic

Moderator
I put 3 off the shelf "AA" (1.5V each) lithium batteries in a battery holder. All together, the measured voltage is 5.4V brand new. Would that damage a picaxe chip much if it was used to power the chip directly? I'm only asking because I'm building a device that I plan to use out in the cold a lot.
Which Picaxe?

e
 

john2051

New Member
All this info on batteries, and I dont think there has been any mention that when flat most of these cells leak! including duracell. Does anyone know what the fluid is? it sure makes a mess of chrome plated spring contacts, and it burns if you get it on your fingers. I also had som nicads leak, what would the white crystals be?

regards john
 

manuka

Senior Member
John: Time you checked electrochemical basics- it's a huge topic so Google ! However classic zinc-carbon (Leclanché) batteries have an electrolyte of ammonium chloride, while alkaline (& NiCd/NiMH) cells use potassium hydroxide. Sodium Hydroxide (NaOH) of course can form a white powder with carbon dioxide from the air, so no doubt KOH does similar. The white crystals are hence probably Potassium Carbonate.
 

eclectic

Moderator
I put 3 off the shelf "AA" (1.5V each) lithium batteries in a battery holder. All together, the measured voltage is 5.4V brand new. Would that damage a picaxe chip much if it was used to power the chip directly? I'm only asking because I'm building a device that I plan to use out in the cold a lot.
From Manual 1, page 25

PICAXE Power Supply
All PICAXE chips will run programs at voltages between 3 and 5.5V DC.
The later generation parts (M2 and X2 parts) will also run down to 1.9V.

e
 

srnet

Senior Member
I put 3 off the shelf "AA" (1.5V each) lithium batteries in a battery holder. All together, the measured voltage is 5.4V brand new. Would that damage a picaxe chip much if it was used to power the chip directly? I'm only asking because I'm building a device that I plan to use out in the cold a lot.
Curious as to the reasons for the choice of Lithium cells, what will be the current load from the 'device' ?
 

Dippy

Moderator
I would guess the answer is , perhaps, in the word "cold"....?

Check out the performance of normal alkaline cells below 5oC.
I've done micropower circuits for prolonged sub-zero (Celcius) and lithium based cells were far,far superior.
 

srnet

Senior Member
Should have remembered.

Years back a climbing friend asked for advice on batteries for headtorches on Everest (where its jolly cold), I did recommend Lithium as I recall.

This was an Irish team, and they took a lot of potatoes, but thats a bit of topic.
 

BeanieBots

Moderator
Also, don't forget that Cadmium and most of its compounds are EXTREMELY poisonous even in minute quantities.

Always remove batteries from equipment that is not going to be used for long periods.
If you have a Duracell battery that has leaked, take pictures and send them to Duracell. They will compensate you even for consequencial losses as long as the battery was not abused. (ie put in the wrong way round or attempted to re-charge etc).
 
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