Strange Behavior of battery

Thread Starter

abc14

Joined Oct 15, 2017
123
Hi Guys,

I am running battery life test on following battery.
https://www.batterystation.co.uk/saft-batteries/saft-ls33600-d-li-socl2-lithium-battery-1-pack

I expected the battery to last for 64 days. At the start of the test, battery voltage was 3.65V and it is 17000mAh battery. Currently am on day 34 of the test.

At times my test would stop, and I would take the readings on battery voltage and its still around 3.58V. And few seconds later, when I re-connect the battery everything works fine for another day before it stops.

Now few questions here.


1. Since the drop of voltage from 3.65 to 3.58V am I right to assume that the battery should have more than half of its capacity is still available ?
2. Battery cutting off is related to battery struggles to keep up providing .178mA for servo every 2 minutes ?
 

danadak

Joined Mar 10, 2018
4,057
What does the test bed look like, eg. what is measuring the battery ?

When you say it stops what stops ? The servo turning ?

When test is running you have no current for 2 Min, then 178 mA for how long ?

Regards, Dana.
 

OBW0549

Joined Mar 2, 2015
3,566
The data sheet for the battery shows a graph depicting a typical discharge profile:
Untitled.png

It looks to me like the battery voltage stays pretty constant until it is well over 50% discharged, so the voltage vs. time behavior you're observing would appear to be normal.
 

Thread Starter

abc14

Joined Oct 15, 2017
123
What does the test bed look like, eg. what is measuring the battery ?

When you say it stops what stops ? The servo turning ?

When test is running you have no current for 2 Min, then 178 mA for how long ?

Regards, Dana.
Measuring battery ?

I have RF module on the board, RF communications and servo stops when battery cuts off.
So my test circuit is sending RF comms every 30 secs which uses about 40mA, and servo actuation happens every 2 mins which uses 178mA and rest of the time systems goes to sleep during which it uses 2mA. I got these current readings by connecting multimeter as Ammeter in series with battery.
 

Thread Starter

abc14

Joined Oct 15, 2017
123
The data sheet for the battery shows a graph depicting a typical discharge profile:
View attachment 152901

It looks to me like the battery voltage stays pretty constant until it is well over 50% discharged, so the voltage vs. time behavior you're observing would appear to be normal.

Yes that is what I thought. Still doesn't explain battery stopping. I have 470uF cap for servo as well
 

MisterBill2

Joined Jan 23, 2018
9,851
Battery voltage versus percentage left is very non-linear with current batteries, and so predicting the remaining charge is a whole lot more complex. The voltage also depends a whole lot on both the load current and the load current history..
 

Thread Starter

abc14

Joined Oct 15, 2017
123
Battery voltage versus percentage left is very non-linear with current batteries, and so predicting the remaining charge is a whole lot more complex. The voltage also depends a whole lot on both the load current and the load current history..
Please for my understanding could you elaborate on predicting remaining charge. I am trying to figure this out for a while still cannot get my head around it.
 

danadak

Joined Mar 10, 2018
4,057
So is RF comm module no longer working at lower Vbattery ?

How about he servo, it has a PWM input, is either V too low for it to run
or the PWM source crapping out ?

You say you have RF on a board, is that UP LV detect shuting down the
com channel ?

Test that on a bench setup with a variable power supply.

Regards, Dana.
 

Thread Starter

abc14

Joined Oct 15, 2017
123
So is RF comm module no longer working at lower Vbattery ?

How about he servo, it has a PWM input, is either V too low for it to run
or the PWM source crapping out ?

You say you have RF on a board, is that UP LV detect shuting down the
com channel ?

Test that on a bench setup with a variable power supply.

Regards, Dana.
Servo is controlled via controlled pwm signal from Arduino. Power to servo is controlled via transistor.
 

BobTPH

Joined Jun 5, 2013
4,051
If you look at the green line, which is 200 mA, it lasts about 30 hours. That is a capacity of 6 Ah, nowhere near the 17 Ah claimed. At 3.5 mA, you get 4000 hours which is 14 Ah.

I think the battery is a bit overrated.

Bob
 

crutschow

Joined Mar 14, 2008
28,206
1. Since the drop of voltage from 3.65 to 3.58V am I right to assume that the battery should have more than half of its capacity is still available ?
No, you cannot predict the battery capacity left of a lithium battery from its voltage.
2. Battery cutting off is related to battery struggles to keep up providing .178mA for servo every 2 minutes ?
What do you mean "cutting off"?
 

ian field

Joined Oct 27, 2012
6,539
Hi Guys,

I am running battery life test on following battery.
https://www.batterystation.co.uk/saft-batteries/saft-ls33600-d-li-socl2-lithium-battery-1-pack

I expected the battery to last for 64 days. At the start of the test, battery voltage was 3.65V and it is 17000mAh battery. Currently am on day 34 of the test.

At times my test would stop, and I would take the readings on battery voltage and its still around 3.58V. And few seconds later, when I re-connect the battery everything works fine for another day before it stops.

Now few questions here.


1. Since the drop of voltage from 3.65 to 3.58V am I right to assume that the battery should have more than half of its capacity is still available ?
2. Battery cutting off is related to battery struggles to keep up providing .178mA for servo every 2 minutes ?
If you take the example of say; a 10Ah lead acid battery and hit it with a 10A test load - you won't get 1h out of it.

The Ah rate is usually specified over a 10h discharge period.

There are probably similar rules for other chemistries - but I've no idea what they are.
 

ArakelTheDragon

Joined Nov 18, 2016
1,353
I do not think the stopping is caused by the battery, perhaps you should check your RF module, which I am guessing is a development board and you are using its MCU?
 

Thread Starter

abc14

Joined Oct 15, 2017
123
That usually means the battery is clo0use to being discharged.
You could try adding a large capacitor across the battery, such a 5-10mF and see if that makes a difference.

That usually means the battery is close to being discharged.
You could try adding a large capacitor across the battery, such a 5-10mF and see if that makes a difference.

I have put a really large cap of 470 uF and it did improve the situation, battery only stopped once in last 24 hours
 

ArakelTheDragon

Joined Nov 18, 2016
1,353
The rulles for standard lead acid batteries are that if the battery is 10A/h, you can drain 1A for 10 hours. However you always have to check the data sheet, because the maximum current of discharge can be 0.5A. That means 20h by 0.5A.
 
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