Checking electrical power consumptions

 

TL;DR you shouldn't let a Caterham battery unattended for over 2 months

 

Just out of curiosity and with some sunshine on an autumn holiday, I thought I could measure what kind of current the car uses when turned off.

Doing so was facilitated by the presence of the battery master switch : it was a simple matter of connecting the multimeter on each side of the switch before opening the circuit.

Using a set of probe wires with alligator clips, the Fluke was set to the 10A current mode.
The voltage was 13 Volts, the power calculation is based on that.

 

 

• Standby with the GKU D600 dashcams in time lapse surveillance mode : 240 mA = 3.12 Watts
• Cameras off (time lapse disabled) but still connected : 14 mA = 0.18 W
• Cameras disconnected from the power supply : 12 mA = 0.16 W
• Side lights on (LED units front DRL and tail lights) : 1.39 A = 18 W
• Dipped beams : 3.72 A (including the 1.39 from the DRL and rear lights) = 30 W from beam
• High beams : 3.74 A (also including the DRL and rear lights) = 30 W too
• Ignition on, dashcam on : 1.68 A = 19 W on top the the dashcams
• Brake lights (tail+3rd) : 0.4A = 5.2W as previously measured while installing the GSTOP 
  

 

 

First observations :

• As the Shido battery has a 8 Ah capacity, we can calculate that after the programmed 24 hours of time lapse, the dashcam will have consumed around 75% of the battery. Something I really did not suspect. In all fairness the app shows a serious warning message when the functionality is enabled. After that, the permanent 14mA will drain the battery in just about a week.
  Looking back at the post about the dashcam, I remember that the front camera is able to defrost the windshield and roof in its proximity, I could have guessed some serious power was at play.
  I have to re-check by making sure the camera was not woken up by the vibration induced by the removal of the bonnet and such.
• Even with the camera off, the battery is just able to endure 24 days of standby time.
• I really need to confirm that with the quiescent current of the dashcam power supply is negligible and close to 2mA. That is, that the immobilizer does sink around 10 mA, draining the full battery 33 days.
• You can multiply all those timing to around 3 to have an idea of what a 30Ah lead-acid battery can endure.
• Those LED front DRL and tail lights do consume some serious power, nearly as much as if they were old-school 5 W bulbs. Thinking it through, I think most of the measured 18W could come from the dashboard lights.
  

In conclusion (not final) :

• Equipped with a lead-acid battery, a battery cutoff switch is required if the car is left asleep for more than a month. On the long term, the battery would need to be maintained with a trickle charger.
  
• In my case, I definitely cannot afford over a week without disconnecting the battery. Or should at least turn off the parking monitoring of the dash-cam and know it can stay safe for maybe 2 weeks tops. Once disconnected, LiFePo4 can stay over a year without maintenance.
  
• If I ever leave the sidelights on over a work day, the battery will be dead by 3PM.