Electronic & Hydraulic Shifting (Di2, Ui2, customisations)

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I'm far too clever for that.

I bought two 10cm male-female USB leads and plugged them into the D1. Weatherproof the D1 ends so even if the USB cables get filled with water and rust, you can just rip out the 10cm cables and replace them, no harm done to the device.

Initially I was running the D1 inside a bag but I was overheating it so it hangs under the aerobars now.

Oh and rust is usually just surface so you can usually clean it off and everything is fine. Maybe something else is wrong?

If you've the lights on, it's drawing current.
If you've the lights off, it's not drawing current.

If there is no current draw, the hub is not experiencing resistance.

Hold front wheel in air, spin with light on; then repeat with light off. You'll see the resistance your exposing the hub to by having light on all the time.

Turn the light off when not needed. It's stealing 4Watts, or around 3% of your power input.

A battery can't be charged more than 100%, so it will draw 1amp for short time, then stop. Most devices these days have some kind of trickle charging too I believe so that the amount of current they draw as they approach 100% lowers.

If you leave it plugged in all the time and the charger maintains the battery at 100% it'll draw 5v/1amp all the time.

No?

No. If the battery is fully charged, it would stop drawing power as there would be nowhere for it to go. The electricity needs somewhere to flow to, it can't just flow into the ether.

Every day's a school day!

I've tried spinning the wheel with the light on and off and I couldn't tell the difference.

Maybe irs too subtle for me to have noticed. I'll try it again.

Cheers for the electronics/physics lesson.

it's easier when the wheel is off the bicycle and on your hand.

It felt like a cup and cone hubs that have been overtighten drastically.

Ok so my list so far comprises of:
R785 STIs
Front Derailleur
Rear Derailleur
Battery (seatpost type)
Junction Box A (3 port)
Internal cableset (with Junction Box B included)
Di2 Grommet set
Charger

Is there anything i'm missing?
The only bit i'm confused about is whether all the cables i need are in the cableset (http://www.ribblecycles.co.uk/shimano-di2-cableset/#pid=19896) as there's no mention of the two STI-Junction A cables...i think you need these separately?

Dont get a cable 'set' just buy cables in individual lengths and junction box B.
You need 2 350mm cables from shifters to junction box A at stem.
A long cable from junction box A to B.
FD to Junction box B
RD to junction box B
Battery to junction box B
Small zip ties around cables to stop them rattle in the frame.
Shimano bleed kit and mineral oil.

Ah ok, i did wonder. So from a bit of measuring up i need

2 x 350mm (thanks @amey)
~750mm downtube a-b
~350 FD - Junction B
~550 RD -Junction B

Also do you need a significantly longer Battery - Junction B cable so you can remove the seat post?

Also do you need a significantly longer Battery - Junction B cable so you can remove the seat post?

I'd account for that yeah. I am guessing you already have shifters if so check box for this.

I've never ridden a dynamo hub, but I have a physics degree and know quite a bit about electrical engineering and resulting forces..

And no! Whether it's on all the time or not. It's the amount of charging done that results in a resistance in your dynamo. So when you plug it in occasionally, you get a higher resistance for a shorter time. Resulting in the same total resistance..

Plug it in at top of hill, unplug at bottom?

No, an iPhone charger is 0,5 amp if I remember correctly. It's the iPad charger that's 1 amp, but that's not relevant to your question.

In reality this means if you plug a battery in that's completely flat it's gonna charge at 5 volt and 1 amp for the first second of charging. It charges at 5 volt 0 amp when the battery is full (cause you can't charge a full battery). And in between your amperage (current) slowly drops, that's why your phone charges pretty quickly to 30%, but the closer you get to 100%, the slower it goes.

When you leave on your lights you are making it harder for yourself, when there is no connection between the 2 leads on your hub there is no current being drawn from your hub, there's only a voltage of 6 volt. Current*voltage=power so when your current is zero the power you need to put into your hub is zero.

When you put a 0,5 amp light on your hub and turn it on, your current is 0,5A and voltage 6V resulting in 3Watt (0,5*6=3) of power it uses, so you'll have to put out 3Watt of extra power through your legs.

Back to the iPhone (or di2) charger, when the battery is fully charged the power going to the battery is zero since there is no current, so leaving it plugged in doesn't result in extra Watts needed from your legs.

you'll have less speed at the bottom of the hill then when it's unplugged, leaving you to do more pedalling when you've reached the bottom ;)

I'm currently very fat, so my speed at the bottom of even a modest hill is around 700 mph.

so normally, a mile after you dropped down a hill you have to start pedalling. But when you plug in your charger at the top of the hill, you'll have to start pedalling after 0,8 mile

That's outrageous, I'll start carrying a car battery in my voluminous saddle bag in order to charge all the things.

There's a video at the bottom of this page showing difference:
http://www.sp-dynamo.com/8seriesdynamo%20hub.html

When riding, I don't notice anything. It'd have to be ~10W difference between on/off before it became obvious enough.

Well explained and makes perfect sense now. Ta.

Question... I have a bike with Ultegra Di2 on it. Can i switch it to flat bars (heresy!) and still operate the front derailleur?

yes

you need 2x climbing switches if you want a double or go 1x and 1x climbing switch .. or the alfine Di2 flat bar switch.

So i can just buy two of these: http://www.chainreactioncycles.com/shimano-ultegra-di2-r600-climbing-shifter-switch/rp-prod85146, one for front (left hand side of bar) and one for rear (right hand side of bar)?

yep and brake levers obv .. you still have Hylex? Might be keen ..

Nah, HY:RD which makes it easy

is it possible to charge a di2 external battery with the charger for internal batteries plugging into the junction box?

Also if i want to run 1x can i just not plug in a front derauillier?