🚀 go-pugleaf

On 6 May 2003 18:10:14 -0700, the renowned ewgeneral@yahoo.com (Dale)
wrote:

>I need to measure the discharge from a 3V Lithium 'coin' cell,
>supplying current to some static ram and low power support circuitry.
>
>This battery is supposed to have a 10 yr backup capability, which i
>need to confirm, but I imagine the I to be in the very low uA to nA
>range
>
>Has anyone got any ideas on how to measure this reasonably accurately?

Assuming a typical circuit, well bypassed, a series resistor (to drop
say 50mV at full current) and an R-C filter to a high-Z voltmeter (eg.
10G) input. 

For example, if you're expecting 1uA, you might use a 49K9 1% resistor
and a 1M 5%/1uF film capacitor for the filter. Check it with a 3M
resistor in place of the circuit. The average current is the voltage
divided by the resistance of the 49K9 resistor. If you go really high
you might have to momentarily short the resistor to get your circuit
to start. 

Note that the highest drain (both the internal battery leakage, which
you can't measure and the external circuit leakage which you can
measure) by FAR will occur at high temperatures, so this testing
should be done in your environmental chamber. You'll also have to
account for differences from unit to unit (typical/maximum). 

Best regards, 
Spehro Pefhany
-- 
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