diy 6870/9070 Di2 internal battery

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weastman
Posts: 32
Joined: Sat Apr 16, 2016 3:06 pm

by weastman

I have looked through a few threads and found that on the previous di2 series quite a few people made diy internal battery's from lithium battery packs.
I haven't seen anything like this done for the newer 6870/9070 series of di2 that uses e-tubes and can bus protocol communication. Is it possible and if so, has anybody got any relevant threads/site/tips.

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motorapido
Posts: 332
Joined: Fri Jul 30, 2010 7:08 pm

by motorapido

Hi Yepp,
i have done it on a few battery packs, its pretty easy but involves cutting up the battery casing, and a bit of soldering. I will try to post up a how too over the weekend as i've just done a pack for a new build.
I keep the existing electronics from the battery holder as well and drop it in the down tube then run wires and a plug up the seat tube, it means you need to pull the battery to charge it but thats no big deal.

the battery mount electronics are fully potted and are removed from the battery mount by first unscrewing the 2 shallow cap-heads on the underside of the mount to separate the battery pack clamp and electronics from the mounting plate. Then flip up the battery pack locking lever to expose 2 grub screws, back these off and the electronics drops out.

the positive terminal is the one furthest away from the mounting plate.

more info and photos to follow

weastman
Posts: 32
Joined: Sat Apr 16, 2016 3:06 pm

by weastman

Thanks that'd be great, so guessing this mod is more to clear up the bike than weight saving as you are using the same battery.
Am I correct in thinking all the brains of the battery are in the mount therefore I could hack up a mount and then use some custom battery's?
Pictures would be great, thanks

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motorapido
Posts: 332
Joined: Fri Jul 30, 2010 7:08 pm

by motorapido

There are already a few writes ups on how to strip a battery down, but here's how i've done it.

You can either drill the heads of the three black screws in the contact end of the battery pack, or simply saw through the plastic corners where they are located, you can tell by the change in noise from the saw blade or cutter when you are through.

next you need to saw through the casing, hold the saw flat to the casing and go slow as its not very thick, once you are partially through you can use a screw driver to pry it apart. note the ends of the battery are potted into the end of the casing, but it comes away pretty cleanly leaving you with a pack like this.
ImageImageImageImage

the last photo also shows the the electronics pack from the battery mount.

Next is to cut through or desolder the 3 metal tags securing the battery electronics to the plastic moulding and contacts. and solder on your desired plug or socket to the three pads. the pin outs are in text on the electronics pcb B+ B- etc

All three contacts must be used as the centre pin is the balance for charging the battery pack, it is only not advisable to miss this out but the Shimano charger will not charge it if you miss this contact.

i use 4 pin extension plugs for PC cooling fans and remove the unused pin.

depending on your seat post size the next stage may not be required. if you cut away the white plastic holder from the battery, the remaining pack size with a layer of heat-shrink sleeve or tape will fit inside a 30.9 or larger seat-tube as is, so its just a case of cutting up a suitable piece of foam etc to secure it into the seat post.

if your seatpost is smaller say 27.2 you will need to desolder the battery cells and bend them end on end leaving the balance plate contact in place on the batteries so that at the end it will run from between the 2 end to end cells, you can then run wires to all three pcb battery contacts +, - and the balance.
With the electronics inline with the cells the whole lot will slide inside some 22mm plastic conduit. with some thin plastic plates as caps, you end up with this a 49gram battery pack instead of 70grams.

Image

To get the electronics out of the battery mount, first remove the frame mounting plate, the 2 silver thin cap heads, flip up the locking catch and unscrew the 2 grubscrews, the electronics which are potted can then be removed.

Image

solder 2 wires only to the positive and negative terminals on the battery mount pins that match with your positive and negative wires on the battery plug. with enough wire to fit the electronics module in remotely for example in your down tube at the bottom bracket.
You can then use a standard plug Di2 cable to hook it up to your junction B.

Image

You will end up with a battery and electronics weighing about 70grams instead of 125grams and its internal.

For charging, take another of the plug / sockets you've used in your system and some long wires and solder it up to the 3 contacts of the battery casing in the correct order, you must use the balance 3rd wire to charge the system. Glue/ tape the rest of the plastics of the pack together and you have a charging interface to use the standard external battery charger.
Image

sorry if this is incomplete or a bit rushed, trying to write it whilst looking after/be referee for my 4 year old twin boys.

message me if you are unclear of anything and i will do my best to clarify.
Last edited by motorapido on Fri Aug 04, 2017 9:50 pm, edited 1 time in total.

weastman
Posts: 32
Joined: Sat Apr 16, 2016 3:06 pm

by weastman

Thank you very much for posting this, very helpful. I think I really need to do this.
I have got a couple of questions just to make sure I understand this:
-I am able to run the battery pack without its plastic mouldings and contacts, therefore I could feasibly just buy some appropriate batteries rather than buying the Shimano one and ripping it apart.
-What electronics are in the battery mount, is this simply an etube to two pin connector or are there more complex electronic involved that control the battery, ie, can I also make this myself or do I need to hack up a shimano one?
Thanks again, really great to see this along with photos.

motorapido
Posts: 332
Joined: Fri Jul 30, 2010 7:08 pm

by motorapido

Yes you can run the battery pack with out its mouldings and contacts, however i have never tried it without the electronics that are on the battery, the electronics looks a bit more complex than a simple thermal fuse and Li-Po fuses but i'm no expert so it may have other battery management functions.

in the battery mount there are more complex e-tube electronics, as this is often one of the elements that needs updates to firmware. if you run an 10speed front mech with 11 speed rear mech if you update the battery mount firmware it kills the system and it won't work for example. Also there is no way to go back a level of firmware.

Personally i would stick with hacking a Shimano pack, Merlin cycles are doing them for £28 ea, or 2 for £50 for example and they often come up on ebay for about £20.

weastman
Posts: 32
Joined: Sat Apr 16, 2016 3:06 pm

by weastman

Sounds like the safest bet yes. I would prefer to keep hold of my own original stuff just incase so will keep an eye out for some deals. Mine will be going in a Scott Foil aero seatpost so should be plenty of room. Thanks

goodboyr
Posts: 1483
Joined: Wed Jan 10, 2007 10:56 pm
Location: Canada

by goodboyr

It's a good idea to retain the electronics. Li pos if not charge managed properly can overheat and do very bad things.......

weastman
Posts: 32
Joined: Sat Apr 16, 2016 3:06 pm

by weastman

Iv finally taken the plunge and caring or some mods, namely fully hidden di2 wiring with battery in seat tube. Today I hacked up the battery wiring it back up to the battery mount so I can still plug a etube wire into it. I am then going to relocate this to the seattube when some more etube wires arrive. I will add some pictures when possible, thanks for all the advice @goodboyr very helpful!

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Joostt
Posts: 1
Joined: Sun Oct 16, 2016 3:46 am

by Joostt

Hi all I did this yesterday as per your directions and its works a treat. Thank you very much goodboyr

VengeSWrks
Posts: 43
Joined: Wed Jan 27, 2016 7:29 am

by VengeSWrks

I just did this mod last night after reading it that morning.:)

Very easy to do and fits perfectly inside of my F8 seat tube. Thanks guys!

superkatsu
Posts: 2
Joined: Mon Mar 11, 2013 10:15 am

by superkatsu

Hi, nice post and as I see many interesting projects, maybe you can aswer my question for Dura Ace 7970, I open up the battery mount and it seems that there is no electronics at all inside, means I can fit any battery?

So my 2nd question, I have a 7.4v 1500ma helicopter battery with 3 pin charging port, I like to make a terminal in the frame where I plug in the charger, is it possible to charge inline without damaging the elctronic?

by Weenie


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