Hi Stefan, Steve,
I read this thread with interest and I had been meaning to write down some observations and try to make some rough estimates of where non-motor power goes. Despite wanting to figure this out and being a bit obsessed with wanting to maximise battery capacity when I first got the bike, 7.5months and 3500km in, I am with generally happy that the lights on the bike are alway on. I felt a bit self conscious cycling in broad daylight with the lights at first, but I don't give it a second thought now. I think it's a nice touch from a safely perspective - even if not perfect.
However I have also done a few multiday rides, camping on route, where I have not taken my charger or a spare battery. For these I generally ride with the TCU powered, but without assistance, unless I feel I need it - usually when I'm either feeling a bit tired/lazy, a big hill where I run out of gears to keep a good cadence, or an annoying headwind.
From doing several rides like this I believe the the lights/tcu/sensors/etc are consuming not insignificant power. I just measured the current flowing through the front and rear lighting circuits, using both a relatively new Hall effect DC current clamp and a very old Fluke multimeter in series with the circuits.
Both indicated around 80-90mA for the rear light and around 400-470mA for the front. The closed circuit voltage across the lighting terminals was about 11.67V and the internal battery had just been fully charged. This would indicate my lights are operating a bit below Lezyne's rated consumptions @12V of 1.2W (rear) and 6W (front). This seems fine to me making allowances for manufacturing, temperature and supply variations.
Theoretical lighting consumption:
Using the nominal rated power for both lights (7.2W) it would seem the lights alone could drain a fully charged SL1-320 battery in around 44-45hours excluding other variables.
320Wh / 7.2W = 44.4h
7.2Wh/ 320Wh = 2.25% of capacity per hour)
Ride based stats:
I did a 100mile non-competitive event last month that used 27% of my battery according to the specialized app. I only used ECO assistance for 15mins over the ride and the App said average motor power over the ride was 1W. Elapsed time was 10 hours but the bike was powered up for no more than 8.5 to 9 hours. Moving time was 7h40m.
Optimistic non-motor/light consumption:
To make these calculations conservative I'm going to assume the average motor power and nominal lighting power were consumed over the entire elapsed time of the ride - rather than the moving and bike powered up times respectively.
Total consumption = 0.27% * 320Wh = 84.4Wh
Total motor consumption = 1W * 10h = 10Wh
Total lights consumption(rated) = 7.2W * 10h = 72Wh
Total non-motor/lights consumption = 84.4 - 10 -72 = 2.4Wh (optimistic)
This would indicate the power consumed by the TCU, it's display, bike sensors (cadence, speed, power meters etc), Blutooth comms with Specialized App on Iphone & ANT+ chest HRM is actually very low over a long journey.
Pessimistic non-motor/light consumption:
If I use my lighting power measurements rather than the nominal rated ones, along with the actual times the lights and motor would have been used over then I get:
Total consumption = 0.27% * 320Wh = 84.4Wh
Total motor consumption = 1W * 7.66h = 7.66Wh
Total lights consumption(measured) = 6.5W * 8.5h = 65Wh
Total non-motor/light consumption = 84.4Wh - (7.66 + 65)Wh = 11.74Wh (pessimistic)
Even this more pessimistic number still seems low over a long day of riding when we consider how much data gets logged. (maybe around 1.3W/h). I think we could ride 8hours a day for 30 days and have every ride fully logged if the motor and lights were off and one could keep the phone charged.
Final thoughts
While I still like the "always on" nature of the lights for daily use I would still welcome the ability to override them on long journeys where I felt their benefit was negligable.
I could of course, just ride with the bike powered off completely - which it entirely feasible - but I like all the data I get. I'm not banking on Specialized doing a TDU firmware update that would allow us to turn the lights off but I might one day try a DIY solution with a switch if I find something elegant enough. I've seen at least one posted only but I thought the switch was too clunky. It would be interesting to know if the TCU hardware is capable of isolating the lighting supply circuits. Has anyone done a teardown on the Mastermind TCU?
