Quote:
Originally Posted by Harley Dave
My concern is that the terminal voltage falls away overnight down to 80% ish on a frequent basis - (in steps it looks like) - what causes this? (obviously alarm etc contributes...) but why the steps...
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The discharge when the car is not running is completely normal for any car with a wet lead acid battery.
The charge slowly drops because
a) constant power drain from the car: clock, alarm, central locking, Volvo OnCall, and any other device using a memory: all use power all the time
b) self discharge in the battery, which increases at lower temperatures
c) chemical age of the battery: older batteries are less capable of holding a charge than newer batteries, due to the chemistry involved
The CTEK Battery Sense takes some time to properly reflect the battery's state of charge.
However you have had the CTEK Battery Sense connected for over a month, and me now for also about 2 months.
So our CTEK Battery Senses should both have "learned" the charge cycles and be accurate (as can be).
The fact that the battery drops about 1% state of charge a day was something I was not aware of, and never noticed, until I connected the Battery Sense. With measurements comes knowledge and insight.
The Battery Sense does a great job of informing you as to the current state of charge, and when you should make the decision to connect a battery charger.
As you can see, the battery sense estimates the time taken to recharge the battery (this is based on battery size which you configure in the app, as well as current temperature and charge voltage.).
The time to fully charge the battery is actually much longer than you think!
We used to say "drive for 30 min after starting a car from a flat battery to charge it up enough" but that would never have brought a 100% charge.
It simple brings "enough" charge to keep you going.
I saw my battery was at 80% on Friday night, so I put my 5A battery charger on the car at 21:30
The Battery Sense reported that the battery was fully charged at around 05:00, which is a charge time of 7.5 hours
At 5A charger capacity, 5 x 7.5 = 37.5Ah added to my 90Ah battery.
But the calculation is not that simple because the charge current and voltage is regulated, it is not a constant 5A. The CTEK charger reduces the charge current as the voltage increases.
Assuming it is on average about 50%, that means the charger loaded about 18.75Ah to my 90Ah battery.
Battery Sense reported the battery as being 80% before charging, which would be 72Ah (90 x 0.8 = 72)
72Ah + 18.75Ah = 90.75 Ah
At which point I must congratulate myself on my math and my assumptions, because the results are perfect
And as for the steps: you are simply seeing the charge time (engine running, charge state increasing) vs discharge time (engine not running).
You should be able to correlate the data to your drive cycles.
If you can, put the charger on for 24hrs to bring the battery back to 100% charge. Then monitor how it holds it's charge.