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# Help figuring out discharge current and voltage?

## Help figuring out discharge current and voltage?

(OP)
Hi, I'm trying to figure out how to find the maximum specified discharge current (mA) and the end of discharge voltage (V) for this battery.

http://www.varta-microbattery.com/applications/mb_...

I'm looking to make a pack and get it tested and need to know that information. Just starting out learning about all this and it's a little confusing. Can anyone help me out or point me in the right direction?

Thanks

Mark

### RE: Help figuring out discharge current and voltage?

Looking at the capacity verses discharge graph the maximum "reasonable" current would be around 1mA.

The maximum unreasonable current would be 10mA. Things are going pretty non-linear at 10mA and that can cause more issues in a 'pack'. That 10mA should be treated like when a device wakes up and transmits for a second then stops drawing that much current. Consider it for pulse loading. If you need more than 10mA you must us a capacitor that will support the entire pulse/momentary load leaving the battery to recharge the cap over time at a more leisurely draw.

The data sheet state "End Voltage" as 2.0V - believe it.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Help figuring out discharge current and voltage?

What is your objective for this particular test. By way of comparison, a standard AA cell can easily dump 10[edited] amp and last for about 15 minutes at that discharge rate. Your datasheet seems to imply about the same[edited], but would be limited by its internal resistance.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

### RE: Help figuring out discharge current and voltage?

IR; About the same what? Size? It doesn't look to me like it can deliver an amp, not even close.

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Help figuring out discharge current and voltage?

How do you figure that? It's specified for 2000 mAh, while a standard AA cell is typically around 2400 mAh

The unknown is the internal resistance.

I mis-wrote above, the standard AA cell can actually dump around 10A when shorted.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

### RE: Help figuring out discharge current and voltage?

#### Quote:

How do you figure that?

Well, none of the graphs allow for more than about 12mA draw. I think this battery is strictly for memory backup.??

Keith Cress
kcress - http://www.flaminsystems.com

### RE: Help figuring out discharge current and voltage?

From the bottom left figure, "capacity vs load resistance" it shows capacity dropping quickly as current draw approaches 10mA and if you draw 20mA the capacity is down to half of the max capacity. Drawing more than 10mA would be inefficient use of the battery and you might find a more suitable fit if you want to draw more. It's like driving a car at 200km/h, you are not going to get the same mileage as you would driving at 60km/h.

For example:
If you draw a constant 1mA at 23°C then capacity is 1900mAh meaning you can draw 1mA for 1900mAh/1mA = 1900 hours until the voltage is about 2V.

If you draw a constant 10mA at 23°C then capacity is 1400mAh meaning you can draw 10mA for 1400mAh/10mA = 140 hours until voltage is about 2V.

Be careful with batteries that advertise long shelf life. Not sure about these batteries but some manufacturers of Lithium Thionyl Chloride batteries advertise long shelf life but underestimate the effect of the passivation that helps provide the long shelf life.

### RE: Help figuring out discharge current and voltage?

Note also that the discharge curves for constant current and constant resistance are different. The is further complicated by the fact some loads are neither constant current nor constant resistance

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers

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