Milaana 20700 / 21700 Conversion (get extended battery life)

[KeroZen]

WARNING / DISCLAIMER:
By performing this conversion, there is a small risk of damaging your Milaana. But if you are careful and take your time, chances will be very low. You are more likely if you screw up to end up with cosmetic defects rather than a broken non-functional device anyway.


Introduction
The goal of this very simple conversion is to make your Milaana accept the new Lithium-Ion cell format(s) coming into the market. By marginally increasing the cell dimensions over our now classic 18650 ones, manufacturers are able to considerably increase their capacity.

This new trend is spearheaded mostly by the partnership between Tesla Automobiles and Panasonic. The first two cells hitting the market were released by Panasonic under the Sanyo name and are called NCR20700A and NCR20700B. Other major manufacturers (LG and Samsung) already announced their respective products but they are not available for sale at the time of this writing.

There is still some uncertainty about which format will become the new standard. Some say 20700, others say 21700 but it's basically the same. 18650 cells are 18mm diameter and 650mm long, while the new ones are between 20mm and 21mm diameter for a length of 700mm (meaning 2-3mm larger and 5mm longer) Note that the 20700 are already not precisely 20mm they are slightly larger, so in the end the two might be the same, depending if you round up or down.

The advantages in a nutshell are: either you can considerably increase your battery life (more bowls per cell) or you can get the same battery life but get a hotter running device (as if you were using a cell that remained like fresh out of the charger for a longer time)

I will show you how I did, but there has to be a better way and it's still a work in progress. I invite you to post your own conversions and share your method as well as any improvement you can think of. The more people do the conversion, the more likely Ryan will realize that it's both viable and easy, and eventually in the end he might update the production Milaana to natively support these new cells (and this guide will then become obsolete, yeah!)


Pros
- Either increase your battery life by 1/3 over the current largest capacity 18650 (+33% by using the NCR20700B cell for instance, which was tested at 4000mAh vs 3000mAh for the HG2/30Q/VTC6)
- Or get more punch by having a very good 30A cell (vs 20A or less for the ones we use) with the same large capacity that we have (3000mAh for NCR20700A, when the best 30A 18650 are only 1500mAh)
- It's only the beginning, new cells to be released might be even better
- You can revert to 18650 at any time and very easily


Cons
- I won't lie to you: filing and sanding the wood with the inappropriate tools I used was tedious
- I don't have a definitive and elegant solution for the contact tab replacement but I'm searching
- If you screw up, your battery hole will not be perfectly round anymore
- If you really screw up... well, please don't!

 

[GreenHopper]

Nice guide bud, everyone loves MORE POWER!

I assume this would void the warranty?

 

[Alegre]

Following!

 

[KeroZen]

Step 1: get some 20700 cells
You will need to have at least one cell in your hands. You could do it all by measuring but nothing beats having the real deal to test the fit.

You can get them on your regular reputed dealer, although demand is currently pretty high due to the novelty and also because they are so promising! I got mine from Fasttech and I'm still waiting for my A sample, which they delayed several times already, so I only got a single B to test.

Here are a couple of pictures for size comparison with 18650:

I assume this would void the warranty?

Only Ryan could tell. Any damage you do to the wood by for instance removing too much material is basically irreversible and would obviously not be covered. But that's the only part you need to modify so as long as you don't damage the bottom contact, or the contact post, or the glass... but I don't know, the heater is fragile after all.

 

[KeroZen]

Step 2: get yourself a compatible charger while you are it
To my dismay, none of my chargers could accept the new cell dimensions. My Nitecore is close but not enough, and all the others including my box mods are clearly too small.

I ordered myself a cheap BASEN BO1 for less than $6 shipped again from Fasttech:

https://www.fasttech.com/products/0/10029259/8065300-authentic-basen-bo1-single-slot-battery-charger

But you can also get the BASEN B02 with two slots for slightly more:

https://www.fasttech.com/products/1421/10029259/8092900-authentic-basen-bo2-2-slot-battery-charger

Or this fancy universal Olight Magnetic one:

https://www.fasttech.com/products/0/10027642/6041700-authentic-olight-universal-magnetic-usb-charger

Meanwhile I've been charging my cell with crocodile clips and magnets on my higher end charger, but it's far from optimal...

 

[KeroZen]

Step3: mark cell outline to use as a guide
Remove the nut and the copper contact tab. Put the cell on top of the empty battery hole and use an erasable pen to mark its outline on the wood:

I tried to offset the cell as on the picture as I thought there was less matter towards the exterior side compared to the interior, but in retrospect this was more hassle than anything else. So you can put the cell centered instead, this wood is pretty hard and it won't get too thin to worry about.

The circle is just a rough guide and you will likely have to enlarge it more than that in the end. But it's important to have it: it's our safety net that will tell us our progress and if we've gone too far or are about to.

 

[TeeJay1952]

Aftermarket 3rd party conversion company?

 

[KeroZen]

Step3B: errata
Having slept since I posted step 3, I remembered that new Milaanas are somewhat slimmer. I don't know by how much nor in which locations.

I looked again at mine and finally it was maybe not that bad of an idea to draw the circle outline offset towards the center of the device as I did on the picture. The external facing wall at the end is only 2mm thick at it's thinnest point.

But you can't go very far in that direction either, as there's the air intake hole and also the contact post. I ended very close to the intake with about 1.2mm at the thinnest point.

I think it might be tight with some Milaana versions, so please double-check that you will have enough clearance before even starting anything.


Step 4: elbow grease is all you need!

** CAUTION GRAPHICAL MATERIAL: the following picture might hurt your sensibility! **​

(gross picture of a Milaana vomiting its guts)​

This is the hard part. In fact it's the only step of this entire guide where you have real work to provide, and it's not that trivial when you lack experience and/or the correct tools (as I shamelessly did)

I'm not claiming that I did it the right way, but it worked and the result is rather nice. My battery hole is not as perfectly round as it was, but you have to look closely to notice it. From a distance it's perfectly fine, plus when the cell is inside and the contact in place it's partly hidden from view.

I would advise against doing it with power tools for several reasons:

• it's way too easy to overdo and remove too much material or depart in the wrong direction or end up completely uneven
• you would need a rather long shaft to reach to the bottom (and most of my dremel bits are silly short)
• there is a battery contact at the bottom and the tool could damage it easily

That being said, if you open your device bottom and unscrew temporarily the bottom contact to move it out of the way, then use a good jig to hold the body and a press to move your tool perfectly on the vertical axis, it's the way to go!

I didn't have access to a press and I didn't plan to open my device so I went the hard manual way. I thought it would be easier I must admit, but it was a bit of chore. It took me several hours spread over a few days as I didn't have enough time to do it in one go.

I used cheapo Chinese diamond files. As you can see on the picture the cheap bastards didn't dip the tools in the abrasive solution all the way down, every cent is worth sparing, the useful part is only 2/3 of the tool length. Well this proved to be a good thing in the end! (by the way the entire files set was under $5 shipped from BangGood IIRC)

Files made specially for wood would most probably be a better choice. With a coarser grit it would have been faster. I didn't expect that maple to be so hard but it is.

I started with the round file but in the end most of the work was done with the triangular one as it has one side that is completely flat down to the tip, whereas the round one tapers down to a point. The flat file proved relatively useless.

From this point on, I can only give you a few but important advices:

• focus from the beginning on filing the bottom of the hole as deep as you can
• the natural movement will always tend to create a cone or funnel instead of a cylinder, and that's what you need to avoid at all costs
• getting the bottom part of the hole done took me exponentially more time than the upper part
• getting the top opening round should be your last priority not your first, you'll have all time to perfect the round shape once the bottom is done
• if you start by the opening, you'll inevitably end up enlarging it too much (yes I'm saying the same thing since the beginning but using different sentences so it's really clear haha)
• what's inside the tube is hidden from view, you don't care if it's smooth or perfect or not, nobody will see it and I never stuck my finger in that hole prior to that
• use a flash-light and your finger to see/feel how you are progressing down inside
• at regular intervals use the 20700 cell to test if it fits and see where it touches the walls, insert the cell with the negative down so it grinds on the non important part of the heatshrink cover
• the file will tend to create grooves / channels near the bottom, always following the same path, you need to avoid creating them as much as possible
• when grooves happen usually it creates a bump between two adjacent ones, focus on filing those bumps before they start developing too much and get out of control, those are the parts where the cell will touch
• removing the device bottom gives you partial access to the very bottom of the tube, it helped me a lot to finish the last centimeter but it's not necessary
• beware of the second smaller hole that goes even deeper down the battery hole (where the leg of the contact is) your file can go deeper in that part and it can grind the wire(s) and their insulation, try to stop at the same depth as the rest

That's all I can think of, now good luck for that part, afterwards it's almost done!

PS: my cheap files with smaller useful surface proved to be a good thing as when I spent more and more time finishing the bottom, they weren't filing the top anymore.

 

[KeroZen]

Step5: optional interlude
I don't know if it was about to happen anyway, or if (more likely) by not being careful enough, the tip of my file rammed into the bottom cap through the second hole at the end of the battery hole that I mentioned earlier, but...

It happened, the bottom cap got lose. Apparently this was unit #159.

Now this was a good thing for several reasons:

• Firstly and as I said in the previous post, having access to the end of the battery hole helped me a lot. I could look at the butt of the 20700 cell and see where it was grinding and where I needed to work. I was also able to file through the bottom hole and reach two locations that were hard to get to (but movement range is limited)
• It allowed me to fix the problem that I had where my contact post (the protruding screw where you put the copper tab and the washers etc) was getting unscrewed on a regular basis. When it happened my device became completely anemic. I knew it was having an intermittent contact that created extra resistance and it was pretty bad. My previous solution was to screw the post counter-clockwise as much as possible before every session, but it kept undoing itself. When I saw the device internals it became clear: the wire is just crimped between the head of the post (which in fact is just a long screw) and the wood. When the post unscrewed, the wire was basically free-floating, doh! I took the opportunity to put a generous dab of solder on that connection and now it's solid.
• Note that recent Milaanas are supposedly fixed, I imagine using a nut to crimp the wire between the post screw head and the nut itself. Another solution would be to put a nut at the top of the post in place of the washers but it would have to be thin.
• It was the occasion to see the device internals, how it's built and dis-spell any doubts about the air-path isolation. I took a couple of pictures for you to see:

In this one you can see the (red) butt of the 20700 peeking through the second hole in fully inserted position. The black wire is crimped to the battery terminal with a screw and goes to the trigger button first leg. Here again only screws are used, no solder anywhere.

Then from that angle, the screw at the bottom right is the head of the contact post that kept getting undone on mine, releasing the shiny bare wire which is the first heater electrode. The second electrode is connected to the second leg of the trigger button and the circuit is complete.

As you can see it's pretty safe in there and the two heater wires pass through very thin holes in the wood. I couldn't detect any gap. This means that this bottom section is almost fully isolated from the air path on the other side. I would even consider it completely isolated but people will argue that by creating a vacuum some minute amount of air could be sucked in from this section through the two tiny holes where the wires pass... Let's say it's 99% isolated, and there's nothing worrying in this place anyway.

PS: careful when you remove the previous glue, the two wood parts need to be very precisely flat otherwise the interface will not be perfect when you re-assemble. I thought I was, but now it's not as smooth as before...

 

[KeroZen]

Step 6: replacement battery contact tab
We're almost done! Now that the cell fits, you'll notice how much more it protrudes (5mm) You'll be able to almost screw the original copper contact tab, but it takes a weird angle and it creates a dicky connection, so that's not the way to go.

(yes my female GonG is broken but that happened a while ago already and it's fully functional so I don't care)


We need to find an elegant solution to replace that tab. Bonus points if it works for both 18650 and 2x700 as it would mean we wouldn't have to switch contacts when going from one format to another (the idea of this conversion is to still retain 18650 compatibility)

In the above picture you can see several solutions that I envisaged, from left to right: 18650 contacts from Keystone Electronics which were way too small, then two Chinese 18650 battery holders than had larger contacts that could be looted but also proved inadequate.

This model might be better but I didn't test it yet >> http://www.mouser.com/ProductDetail/Keystone-Electronics/5231/?qs=U32tdPngY/zD9hIzRVKITw==

My temporary solution is a super fat heavy duty folded bit of what looks like stainless steel wire. I salvaged it from a keyring in fact (and I have plenty others if you want) I reshaped it and voila, not the prettiest but does the job!

Now it's you turn to be creative and tell me what better and more elegant solution you have in mind! And above all, I expect to see pictures of your own conversions!

 

[ZC]

I know I kinda brushed off the need for these bigger cells in the Nomad thread but this is tempting, especially since it doesn't really add to the footprint of the Mi.

Trying to think through better ways to enlarge the hole, but enlarging holes is always a difficult task. I'm not sure if my CNC has enough clearance, but it might be able to align and START the new hole, precisely get the top 18mm~ to the right size, and then the rest could be drilled out with a drill press and forstner bit as long as you align and clamp down everything properly. Certainly not an easy task.

If you take the bottom cap off early you can remove the screw holding the bottom spring on, and drill all the way down to that platform, you can even drill a little into that platform so the battery doesn't stick out as much when you're done.

I have 3 mii's so maybe I'll try this out, for the greater good.

 

[KeroZen]

you can even drill a little into that platform so the battery doesn't stick out as much when you're done

But only so far if you want to keep 18650 compatibility (as those don't stick out too much, at least on my device)

PS: for the Nomad it would have required a larger device and last-minute changes that are never a good thing, so it's probably better to keep that for the Nomad v2

 

[ZC]

I honestly didn't really consider keeping 18650 compatibility, but yeah you're right.

Really I'd like to see Dan take the modular heaters from the nomad and make a version with two of these bigger batteries and regulation like the Zion. But I'm getting way off topic there.

 

[cannabis.pro]

I honestly didn't really consider keeping 18650 compatibility, but yeah you're right.

Really I'd like to see Dan take the modular heaters from the nomad and make a version with two of these bigger batteries and regulation like the Zion. But I'm getting way off topic there.

Wonder if RBT could be convinced of doing something like that? Milaana meets Zion...