running di2 from an eBike battery
has anyone successfully removed the di2 battery from 12 speed di2, and run the system permanently from one of the auxiliary outputs from an eBike battery?
obviously, the eBike battery is orders of magnitude larger than the 7.4v, .5 Ah di2 battery in the seatpost. assuming an always output is available and an appropriate step-up or step-down regulator is used, can anyone think of reasons why this is a bad idea? obviously running the battery completely down to zip would leave you without shifting as well, but nobody should ever do that on an e-bike anyway. i'm thinking about a little project to hardwire lights and a varia to a bike that didn't come with those things, and it got me thinking about the di2 battery as well. why ride with four separate batteries, one of which is 10x the size of the others combined. garmin varia battery - 3.7v, 1400 mAh = 5.2wh knog pwr road 700 - 3.7v, 5000mAh = 18wh shimano di2 battery - 7.4v, 500mAh = 3.7wh ebike battery - ±36v, 242wh. assuming the auxiliary output from the battery can handle the current of lights, it seems like it would not have any problem with di2, right? the accessory cable by the motor/battery manufacturer is a dead simple y cable splitting from the small proprietary connector to two pairs of bare wires, which certainly suggests they designed it to be wired directly up to simple DC loads.... |
I'm pretty sure that the battery holds the Di2 setup configuration. (I'm familiar with 11 speed Di2, not 12 speed.) I don't think it can be substituted with a generic battery source.
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Originally Posted by mschwett
(Post 23123821)
obviously, the eBike battery is orders of magnitude larger than the 7.4v, .5 Ah di2 battery in the seatpost. assuming an always output is available and an appropriate step-up or step-down regulator is used, can anyone think of reasons why this is a bad idea?
I suggest you do some research into Di2 system operation before you go any further. |
Originally Posted by Bald Paul
(Post 23123995)
I think there are a lot of people that can find reasons this is a bad idea. In fact, a VERY bad idea.
I suggest you do some research into Di2 system operation before you go any further. ang suggested technical sources other than bettershifting or shimano’s manuals? at some point inside the BT-DN300, whatever brains it has receives power from a dumb battery… |
Originally Posted by mschwett
(Post 23124039)
i thought i had read that with 12 speed, shimano moved all the brains into the rear derailleur from the battery, but i infer from your reply that this isn’t the case.
ang suggested technical sources other than bettershifting or shimano’s manuals? at some point inside the BT-DN300, whatever brains it has receives power from a dumb battery… When using the product, be sure to connect the electric wires to the center E-TUBE port. The product will not operate normally if nothing is connected to the center E-TUBE port. and: Be sure to attach the dummy plugs to any E-TUBE ports that do not have electric wires connected to them. The product will not operate normally if the dummy plugs are not attached. |
Instead of replacing the Di2 battery with the e-bike battery, why don't you just charge the Di2 battery from the e-bike battery? Voltage on your e-bike is likely different for the motor than it's accessories. So make sure you know what voltage you are tapping into. Although I'd tap into the main voltage and use a power supply (transformer) that is appropriately rated for that input voltage and produces the correct output voltage and amperage for the Di2 charging. If you tap into the other e-bike voltage that might be the same as your Di2. Then you need to know it can supply the needed amperage.
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Originally Posted by Iride01
(Post 23124094)
Instead of replacing the Di2 battery with the e-bike battery, why don't you just charge the Di2 battery from the e-bike battery? Voltage on your e-bike is likely different for the motor than it's accessories. So make sure you know what voltage you are tapping into. Although I'd tap into the main voltage and use a power supply (transformer) that is appropriately rated for that input voltage and produces the correct output voltage and amperage for the Di2 charging. If you tap into the other e-bike voltage that might be the same as your Di2. Then you need to know it can supply the needed amperage.
since the big battery has 5v accessory ports, that’s a safe way to charge or power accessories rather than stepping down the 36v again… |
Originally Posted by Bald Paul
(Post 23124078)
Although my experience is with the 11 speed Di2 system, it still sounds like there is some type of 'black magic' inside the 12 speed battery. If it was just a 'dumb' battery, why would the dummy plugs be needed? This is what the manuals say:
When using the product, be sure to connect the electric wires to the center E-TUBE port. The product will not operate normally if nothing is connected to the center E-TUBE port. and: Be sure to attach the dummy plugs to any E-TUBE ports that do not have electric wires connected to them. The product will not operate normally if the dummy plugs are not attached. |
it might also be worth looking at how shimano does it themselves, although i’m guessing their main battery is heavily customized/designed to do all the other di2 functions.
”Utilizing SHIMANO e-bike’s centralized battery power source and integrated smart systems, SHIMANO CUES Di2 ” |
FWIW, the number of times my Di2 battery has required a charge just wouldn't justify all the modifications to the wiring of an e-bike. They last a pretty long time. If you're really wanting electronic shifting, just install it as a stock system. At least that's what I would do.
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Originally Posted by Bald Paul
(Post 23124221)
FWIW, the number of times my Di2 battery has required a charge just wouldn't justify all the modifications to the wiring of an e-bike. They last a pretty long time. If you're really wanting electronic shifting, just install it as a stock system. At least that's what I would do.
given that the lights need charging very often, i'll start with hard-wiring those. |
You change the seat post often? I wouldn't let one little frustration with that set you up for even more frustration with doing something the is essentially going to be a one off thing with no engineers behind it to say that it's going to perform perfectly and not leave you endlessly troubleshooting issues.
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Originally Posted by Iride01
(Post 23124346)
You change the seat post often? I wouldn't let one little frustration with that set you up for even more frustration with doing something the is essentially going to be a one off thing with no engineers behind it to say that it's going to perform perfectly and not leave you endlessly troubleshooting issues.
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Originally Posted by mschwett
(Post 23124375)
no, i don’t imagine i’ll ever need to change the seat post again! i just think one battery is better than two, especially given that it gets charged fairly regularly.
What if you took a longer than expected ride, and your e-bike battery died? Yes, you can still pedal, but now you wouldn't be able to change gears. |
Originally Posted by Bald Paul
(Post 23124411)
But....
What if you took a longer than expected ride, and your e-bike battery died? Yes, you can still pedal, but now you wouldn't be able to change gears. |
I ride Di2 on one of my bikes. I do love it, but it doesn't lead me to avoid the other bike with campy record, I'm quite happy on either one. But I'm not sure I'd make the investment to carry Di2 on an e-bike. Somehow seems "outta spec" to me.
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