How to test a low current RTC work time with a 12mAh battery?

[wangdi]

Dear Professionals,
I have a RTC with backup battery switch function.
If the Vcc is remove, the RTC will switch to Vbat to power.
Now I have a choice to use a small 12mAH battery to be a backup battery.
So, I can calculate the theory work time of the RTC.
That is:
12mAH / 150nA = 80,000Hrs = 9.13 Years.

The Question is HOW CAN I TEST THE ACTUAL WORK TIME OF THE RTC ?

Thank you for your answer, wish you happy.8O

 

[ckshivaram]

First use external power and write routine to write the value into RTC.... then display it on LCD and see if time is running....

later disconnect the power supply and check if RTC is working from the time of disconnect without getting reset....

do you mean this or HOW CAN I TEST THE ACTUAL WORK TIME OF THE RTC ??? can you explain the correct meaning

 

[wangdi]

that is , i want to use a multimeter to test the current of the RTC Vbat pin.
So , I can estimate how long the 12mAh battery can be used by the RTC.

i.e, if I get the current of Vbat is 300nA, I can suppose the battery will be used for 1.5 years.

That is still an estimated value. So, I want a more exact value.
And I can't wait for 3 years to see if the circuit is OK or not?

 

[leo_o2]

How about connecting 1000 RTC circuit to the battery? The test time is shortened to 1/1000.

 

[wangdi]

it's impossible i think , can you give me an advice?thank you!

 

[keith1200rs]

I don't understand the problem. You know the battery capacity. You can measure the current consumption (I assume). So you can calculate the lifetime.

What have I missed?

Keith

 

[wangdi]

∑√
Dear Professional,
Yes, your meaning is OK, but I think the situation is not so optimistic.
Because I think the battery will leak current when stay in air, or connect to the metal or something,
and I don't know the battery 's capacity if will be changed when supply 500nA, which is a small current.

Or I need check some parameter of battery ? Thank!

 

[keith1200rs]

What type of battery? You need to find the self discharge characteristics of the battery. NiMH are not great so I doubt you will get 6 months. Lithium are far better but you need to check the specifications.

Keith

 

[FvM]

If you think about the problem thoroughly, you'll see, that part of the questions can be easily answered by measurements, others can't.

RTC current consumption of one exemplar - easy
Temperature dependence of the same - almost easy
Variation between lots - can be only answered by the manufacturer
Battery capacity at nominal current (e.g. 10 uA - 1 mA) - almost easy
Temperature dependence of the same - special equipment needed
Long term capacity and self discharge - nearly impossible to determine within acceptable periods
Temperature dependence of the same - even more complicated
Variation between lots - a matter of faith

In addition, I can report, that manufacturers sometimes feel a need to correct their long term performance assumptions...