lithium primary coin cell in parallel?

[Bob Minchin]

I have just purchased a commercial device from the far east which is powered by two CR2032 lithium coin cells connected in parallel.

I can see no positive reason for this at all and some negative ones

The operating current is 60uA and 16uA on standby which it reverts to after 5mins in activity. I have sometimes seen these cells paralleled up to meet a peak current requirement but there is nothing like that sort of current being drawn by a couple of chips and a LCD display

Each cell is rated at 230mAh which should give around 3800 hours normal operation and 14000 in standby so well over a year with mixed duty cycle.

SO why on earth are there two cells fitted??

Any clues?

Bob

PS it is a digital readout scale - a bit like the cheapo verniers but a lot longer.

[Graham.]

two CR2032 lithium coin cells connected in

5mins in activity.

requirement but there is nothing like that sort of current

operation and 14000 in standby so well over a year with

Does it have any settings or calibration data stored in volatile memory?

Perhaps the idea is you replace the cells one at a time before either is exhausted.

[Bob Minchin]

by two CR2032 lithium coin cells connected in

5mins in activity.

requirement but there is nothing like that sort of current

operation and 14000 in standby so well over a year with

Good call! That would enable the current position to be retained but if that were the design idea, they have not bothered to mention it in the instructions. The only indication of low battery is a flashing display and as the cells are hardwired together, they would be no indication of which had failed. Indeed connecting them that way means their terminal voltages are identical and so possibly have similar remaining charge in each.

Bob

[Harry Bloomfield]

on 28/07/2011, Bob Minchin supposed :

Usually the minimum voltage required for memory retention requirements is much lower than the minimum required for operation.

[John]

Sounds feasible. I've had instructions on a big programmable calculator warning you to change the batteries one at a time so as not to lose memory contents.

rusty