Creating an in-bar battery pack

[Discodan]

Hi All,

I'm going to spawn a new thread here rather than taking the Aldi Bike Lights thread http://www.bicycles.net.au/forums/viewt ... 12&t=91977 too far off topic.

In short I want to create a new battery pack for the Aldi light, one that can live inside the drops of my handlebars. I'd then connect it to the head unit which is mounted under my Garmin for a very subtle but effective package. I'm not an electrical engineer so am starting to get out of my depth on some of this stuff, thus the thread to try and tap into the expertise in the forum.

Here's how the head unit mounts up at the moment https://1drv.ms/i/s!AlR9KEiul8ImtFHyFCf0Znu3vU7j

Considerations:

Capacity - the current Aldi light uses two 18650S22 in parallel which gives 3.7V and I'm guessing 4400 mAh capacity. To replicate that and fit inside the bars I'll probably use 4 x 1.2V 900 mAh AAA cells in series giving 4.8V & 3600 mAh whilst being narrow enough to fit in the bars

Charging - ideally I'd put a charging plug in the bar-end (I have a spare plug for some old dead batteries) but can just unplug the head unit and charge it from there if need be. What I'm unsure of is the battery management smarts; this is the board that is on the Aldi battery pack https://1drv.ms/i/s!AlR9KEiul8ImtFSQeKk7Fyu8j2nC. Does anyone know if I can re-use this or do I need to source another one; what does it even do?

Packaging - the plan is to create a sausage of the 4 batteries (or 8 if I go high capacity) and seal them in heat shrink with 1 cm between them. That should be able to be fed up the bar and around the drops although it's a bit of a pain as I use Cinnelli Neo-Morphe bars that have a funny reverse bend at the end and a pinch point under the levers. Worst case I'll need to go back to my other normal bars but I'd rather not. I'll need to drill a hole for the wire to come out, if I use the Neo-Morphe's that will be fine as they have triple layer of carbon over the external cable tunnel.

So, is this doable or a folly? Any suggestions, ideas, or obvious things I've missed in my ignorance?

cheers
d

[eeksll]

oh snap! I just looked at doing this recently.

However, you are going to have issues charging your batteries with 1 charger port if the batteries are still connected to each other.

My solution works as I am using 3x18650 batteries in series and I can get off the shelf RC battery chargers which charge/balance the series batteries while they are still connected up together.

edit: do you have any spare di2 holes out front of your frame? if so you could shove 2x18650 batteries in a seat tube, use exsiting circuit and have the wire come out near the front.

[Discodan]

Interesting pickup. At the moment the charger works for two cells connected in parallel to create an effective battery of 3.7V & 4400 mAh. I was working on the assumption that four cells in series to create an effective battery of 4.8V & 3600 mAh would be much the same.

Of course I could just give it a shot, worst case I kill a few cells which only cost $4 each right? It would be a lot easier if the Aldi light was 8.4V like most lights on the market as I could steal the board from another battery pack. As it's a 3.7V system there's not many of them out there.

[Trevtassie]

Why not stick the two 18650s inside your steerer tube? You can drill a hole in a spacer and run the wires past the star nut and out near the top of the stem.

[Discodan]

Why not stick the two 18650s inside your steerer tube? You can drill a hole in a spacer and run the wires past the star nut and out near the top of the stem.

That could be genius, a lot simpler both for packaging and the electronics side and no need to change the bars. I'll have a fiddle in the shed tonight and see if it could fly.

[eeksll]

Interesting pickup. At the moment the charger works for two cells connected in parallel to create an effective battery of 3.7V & 4400 mAh. I was working on the assumption that four cells in series to create an effective battery of 4.8V & 3600 mAh would be much the same.

Of course I could just give it a shot, worst case I kill a few cells which only cost $4 each right? It would be a lot easier if the Aldi light was 8.4V like most lights on the market as I could steal the board from another battery pack. As it's a 3.7V system there's not many of them out there.

4x1.2v battery in series will give you the 4.8v but you won't be able to sum the capacity. So it would be 4.8v at capacity of a single cell (not sure what they are 900mAh?)

I got a circuit board off ebay, the more important number to know is the current required to supply that light? Voltage isn't the most important factor here (although you dont want that going too high).

[eeksll]

Why not stick the two 18650s inside your steerer tube? You can drill a hole in a spacer and run the wires past the star nut and out near the top of the stem.

That could be genius, a lot simpler both for packaging and the electronics side and no need to change the bars. I'll have a fiddle in the shed tonight and see if it could fly.

I wonder if that would work for me .... I already went to plan B as the 18650 wont fit in my handlebar either.

[Discodan]

The in-steerer idea can work.

Because it's a carbon steerer it doesn't have a star nut but uses an expansion plug so there's no way to get the cable past. It will be a lot more elegant to punch the cable out the front of the steerer and through a spacer below the expansion plug. It just means I'll need to put some very small bullet connectors (4-5mm diameter) on the cable so I can feed the cable in from outside through a small hole rather than pulling the whole charging connecter through which is closer to 8-9mm diameter.

I've got a race this weekend so I'm not going to start screwing with this right now but will have a play next week. As I see it I'll need to:
- hack the wiring so the two cells are still in parallel but now above each other and not next to each other
- add bullet connectors for the charging/power cable to allow the plug head to be removed for access
- find the right diameter packaging to hold them in place and to stop any rattling, maybe a section of inner tube or some foam wrapping
- drill through the carbon steerer and a stem spacer with a 5mm bit for the cable, this is above the top bearing so I'm not worried structurally
- put it together
- have beer
- start doing more early morning rides to justify it

Any thoughts team?

[find_bruce]

I like the idea of integrated cells, but there are a few issues as you have discovered. I briefly thought about putting a cell in a stem, but decided I didn't want to ride a bike with holes drilled in the stem. Another place to think about is inside the seat tube. Wires would need to be a bit longer though.

18650 cells are 18 mm in diameter x nominally 65 mm long (0 at the end means cylindrical). In reality closer 70mm long- they are too wide to fit side by side in your steerer, so you will need at least 140mm of space in your steerer. Some forks go straight through at the bottom while others have a narrower opening at the bottom. You can also get star nuts with a hollow bolt to run the wires through - may work for you depending on the diameter of the bolt your expansion plug uses.

Will need to be nice and waterproof though.

I wouldn't bother with NiMh batteries

Li-ion batteries come in different sizes. 26650 are too big to wide to fit in a 1 1/8" steerer, but may do if you have 1.5". 14500 are the same size as AA but the few I have seen are only ~600 mAh. Tesla is apparently using 21700 which would be good, but unobtanium.

Are 16650 narrow enough for you?

[eeksll]

sounds good, I wouldn't be quite so cavalier about drilling that hole, but it sounds like you are and its your bike

The hole is going to need to be big enough to allow some play as its going to have to have the cable already poking out when you tighten up the stem cap. You might also need some taller spacers so you can cleanly drill a hole through 1 spacer. Although I wonder if a short spacer with a gap top to bottom would make life easier.

Regarding the batteries, I am mainly sourcing 18650 as quality ones seem easier to find. However if there is enough space in the steerer tube, there are fatter ones with potentially longer run time since this isnt the sort of thing I would want to swap batteries out too often.

I have no holes in my frame so i can't mount inside the seat tube or seat post, but I can see the OP has a hole for mechanical cables, so if you wimp out drilling that hole you might have another option.

[Discodan]

If I can be confident on how the charging board works it would open up lots of options for using different/bigger cells but I'm not there yet. It's a 1.5" steerer so there's lots of room there. I'm no guru on that so unless someone knows any better about the charging logic then I'll have to play safe and just repackage the existing cells and charging board.

A hole in the steerer is certainly not one to approach lightly and eeksll raises good points about spacers etc. I do have some 10mm spacers on the stack which could be drillable but the gap option works as well and adds flexibility.

I've got a much shorter Hope compression plug on another bike that might allow some better options for exiting the cable. I'll have proper look tomorrow and keep on mulling this.

I'm not keen on using the vacant mechanical ports on the headtube as they're too low down and would defeat the purpose of keeping it clean. If I was to put the battery in the seat-tube (I wonder what voltage a Di2 battery is?) I'd piggy back off the port under the top tube where the Di2 cables enter the frame, it's already in a heatshrink so I could put a second cable in there without too much drama

[eeksll]

regarding the existing circuit on the batteries, it could be just a charging circuit, then your options become rather easy e.g I am using one of these skyrc e3 all the circuitry is in the charger and its a direct wire up to the batteries (just get the pins right) you would need 3 wires coming off the battery and out of the bike though.

But your circuit board may also be a LED driver for the light, in that case things start to get difficult.

I looked at the di2 battery route a while ago, from memory they are 2 very small batteries <1000 mAh so unlikely to have enough capacity for your light. Also there is circuitry in a di2 battery which will control the current/voltage that comes out of it. plus they are ridiculously expensive compared to just getting the cells.

[Discodan]

@find_bruce: Unfortunately it's a carbon Giant OD2 headtube so options are a little more limited in terms of star-nuts etc. There's easily the 140mm under the compression nut for two cells and the bottom of the steerer is closed in so they won't drop onto the wheel and send me over the bars. The option of the seattube could work with some clever routing, I think that may be my backup option.

@eeksll: I'm pretty sure it's just a charging circuit rather than a LED driver on the battery pack. I can use that battery pack to drive another LED and visa versa so it just seems to be a power source. That does open the option of an external charger. I wouldn't want to use the Di2 battery either; as you say it's too expensive and I wouldn't want to share a battery and have the scenario where you forget to turn off your light and suddenly have no shifting.

[Nate]

whoa... steady on.

Different battery chemistry's require VERY different charging parameters. DONT mix or substitute!!! Ni-CD, NI-MH, LiPo have very different requirements to charging - and are NOT compatible.
You'd be crazy to change it, stick with 2 18650 cells in parallel & you've got everything working & it becomes a packaging problem.

I consider myself a master DIY guy & went with off the shelf...
ebay "Waterproof 4x18650 Battery Storage Case"
its $10, straps to the top tube & done with it.

You need to be VERY careful with these things too, when Lithium batteries go bad... they go bang!
you're now putting a bang into a sealed metal tube... THINK VERY CAREFULLY about that. at LEAST put some vent holes in... or ways to extract gas... then you're drilling holes in a structure... ummm yeah.
also very very careful putting wires through holes, you MUST at least use grommets & a decent quality wire (i used Tefzel coated wires on my car restoration, insanely abrasion resistant - used in aeronautical applications)

I DIY everything, re-wired an entire car from scratch without a diagram... i went off the shelf.

[eeksll]

Different battery chemistry's require VERY different charging parameters. DONT mix or substitute!!! Ni-CD, NI-MH, LiPo have very different requirements to charging - and are NOT compatible.

yes stick with correct charger for your batteries. Li-po and Li-Ion battery and chargers are cross compatible. With the exception that Li-Ions generally can't be charged at a current as high as the Li-Po. Keep to the cheaper end of town ie no fast chargers and that should be fine there.

... 2 18650 cells in parallel ...

I got excited and forgot about the parallel issue. You will need fancy controller circuit to be able to balance these (never seen one off the shelf). The purpose of balancing is safety reasons. Is OP sure it is in parrallel?

You need to be VERY careful with these things too, when Lithium batteries go bad... they go bang!

This happens when unbalanced batteries are charged without the correct circuit, worth thinking about given the above (ie 2 batteries in parrallel). The "easiest" way around this is to buy 18650 batteries which have protection circuit on them (both low voltage cut off and over charge protection)

you're now putting a bang into a sealed metal tube... THINK VERY CAREFULLY about that. at LEAST put some vent holes in... or ways to extract gas...

I doubt a fork would be sealed well enough to make this a concern. Not to mention there is a fair amount of space in a fork. When these batteries go bad they can bulge a bit, so just don't make the batteries a perfect fit.

[Discodan]

I think we're on the same page here, I know what I don't know and I will be out of my depth if I start screwing with battery types, voltages, chargers etc. The most adventurous I'm willing to go is to swap out the 2200 mAh 18650 cells for some higher quality 2800 or 3000 mAh 18650 units but that may be Mk2 of this adventure. As Nate says I'll keep the original configuration and just change the physical config so they can fit in the steerer tube. eeksll, the two cells are definitely in parallel to give the 3.7V output.

Nate, good point about using quality abrasion resistant wire so I'll look into that. At least the design will have a removable power lead so in the worst case I can easily replace it.

Re the battery being in a confined space: it will be in a foam sleeve so will have room to bulge but if it does go up in smoke it will be a problem as I won't be able to get it out quickly, unlike if it's just strapped to the bars where you can dump it on the road. That kind of heat would kill the steerer so I'd be down a set of forks in that worst case scenario. Now it becomes a likelihood and consequence game, is that a risk I'm willing to accept?

[find_bruce]

... 2 18650 cells in parallel ...

I got excited and forgot about the parallel issue. You will need fancy controller circuit to be able to balance these (never seen one off the shelf). The purpose of balancing is safety reasons. Is OP sure it is in parrallel?

You need to be VERY careful with these things too, when Lithium batteries go bad... they go bang!

This happens when unbalanced batteries are charged without the correct circuit, worth thinking about given the above (ie 2 batteries in parrallel). The "easiest" way around this is to buy 18650 batteries which have protection circuit on them (both low voltage cut off and over charge protection)

Don't get too excited eeksl - parallel is good, it is cells in series you need to be concerned about. Once cells are connected in parallel they will remain balanced - it is why when you are putting them together you want to check they are the same voltage, otherwise the high voltage will immediately start charging the low. Individual protection circuits are not much use in series & won't help at all in parallel. The reason is that they have a reset feature - add a suitable charge to the cell & the protection circuit resets - if one cell drops out, the other conveniently keeps resetting the protection until the protection circuit is fried. If you're lucky it fries open & all that has happened is that you have lost half your capacity.

What you actually want is a protection circuit that controls both cells - they are similar to the individual cell versions but also usually have a maximum discharge current

[eeksll]

Don't get too excited eeksl - parallel is good, it is cells in series you need to be concerned about. Once cells are connected in parallel they will remain balanced

that is interesting and good to know, thanks! Gives me an option to play with (4 smaller batteries in the bars)

@Discodan I have come across these things called fireproof lipo charging bags in my wanderings, might be able to cut one up for padding. With the correct charge/discharge circuits, I am fairly confident the fire risk is negligable, most lipos dont have the protection circuits, relies on the RC vehicle to have them, where as its pretty easy to get 18650 with protections circuits already part of the unit.

[Trevtassie]

If you really wanted to go the whole hog, a hub dynamo with a Forumslader in the steerer would be the go, you could even charge your mobile and run a 12V light! Jens does a nice USB stem cap....

[Nate]

Re the battery being in a confined space: it will be in a foam sleeve so will have room to bulge but if it does go up in smoke it will be a problem as I won't be able to get it out quickly, unlike if it's just strapped to the bars where you can dump it on the road. That kind of heat would kill the steerer so I'd be down a set of forks in that worst case scenario. Now it becomes a likelihood and consequence game, is that a risk I'm willing to accept?

ummmm careful...
its a flat cell & not a 18650... BUT... keep in mind the energy...
[shareyoutube]https://www.youtube.com/watch?v=bqcX1AjdxSw[/shareyoutube]

have a look on candlepower forums, search for "candlepower explode" for some interesting reads.
is it worth the risk to put it in there?
its a "big space" if it swells... but what happens when it releases gases?
I dare say a steerer hasnt been designed to take those loads - how will it respond? predictably?

Lipo bags - fibreglass... looks scratchy, if you jam it in there (i.e. NOT bolted/secured in place positively) - i'd put money on it either rubbing through the steerer (carbon/alloy) or the battery itself.