Jump to content

Duo Li-ion Battery


Recommended Posts

I see a few threads where this has been discussed, but not any that seem to have resulted in a fully-functional Li-ion pack. Now that my 280c is re-capped and functional, the next step is to make it portable! It's OE NiMh is long dead, so an upgrade is in order. I want the pack to charge and operate properly in-situ (no janky discharge only, remove to recharge arrangement), have as much capacity as possible within the limited space available, and be safe to operate.

Given those parameters, I first considered Lipo, which I have quite a bit of experience with professionally, but their lack of internal regulation and penchant for expansion make me nervous--even if they'd be the most volumetrically efficient. LiFePO would be my preferred option from a stability standpoint, but the cell voltages don't align very nicely with the original output of the 10-cell NiMH pack. Using that chemistry would require regulation in and out wasting energy / creating unnecessary heat, so it's off the island. That leaves the tried-and-true 18650--specifically 3 x Samsung 3,500mAh cells. That'll provide over 200% more capacity than the original battery, which should provide a very satisfactory runtime in conjunction with the installed SCSI2SD :) 

Choosing cells is really the easy part though. Aligning the voltages and addressing Lithium batteries' specific sensitivities is the trick. If it weren't for the need to add some additional electronics for regulation and charging, I might have been able to stuff 6 cells into the available space, but c'est la vie... I'm measuring 20v coming from the +/- leads of the notebook when plugged in, which I'm sure drops to a suitable level for the NiMH under the load of charging, but an unregulated circuit certainly won't serve for a Lithium battery. Some form of variable input, regulated 3S Li-ion charger is needed. Also necessary is a BMS (battery management system) to keep the cells balanced and disable the input / output if any cell gets too low, too high, or the current demands exceed reasonable thresholds.


Here's what I have mocked up so far. The little PCB on the left is a 3S Li-ion charger that accepts an input voltage up to 24vdc. The 3S BMS is on the right.

IMG_20200714_084731.thumb.jpg.6bcf5f915a262abd8a2681a1fb784d57.jpg


Another challenge will be steering current through the charger when charging, but bypassing it when discharging. I'm planning to address that with a pair of P-channel FETs vs. diodes (much lower forward voltage drop). I'll post updates with success / failures as it starts to come together...

Link to post
Share on other sites

At the risk of hijacking your thread (which looks awesome by the way), I am an extreme amateur who has been trying for a long time with no success to get my Duo to run off of a custom battery...


Lacking your technical know-how, I have simply replaced the original cells with 1700 mAh NiMH cells and fit the whole thing back together. The laptop detects the battery (software is 7.5.3 rev 2), but does not seem to want to run off of it, ever. I get a charging icon, but it dies the second I unplug it. Multimeter shows 12 volts (proper voltage) on the contacts and it is making contact with the board.  
 

Can you think of an obvious problem with this setup that would be causing this? Sorry to bother you and I can’t wait to see how yours turns out! 

image.jpg

Link to post
Share on other sites

Interesting... I can't tell for sure from your pic, but did you retain the little TO-92 packaged (looks like a transistor but with 2 legs) ID chip when you rebuilt it? I guess it wouldn't be recognized if you hadn't. My experience with a duo running on battery is thus far non-existent, but maybe a subject matter expert will chime in.

I will say that my initial attempt to run the 280c from my bench power supply were unsuccessful. I didn't try very hard and chalked it up to a bad connection with the ID chip, but maybe there's more to this than I thought. My assumption has been that as long as it sees something in the range of 13.5 - 9.5v on the outer 2 pads, and gets a reading from the thermister and ID chip from the middle 3, it should work.

More testing required...

Edited by sutekh
Link to post
Share on other sites
  • 2 weeks later...

Made a bit of progress on the battery front yesterday and today. I wired up the Li-Ion cells, BMS, and charger, and was able to get it to charge from the Duo. I still need to do more thermal testing and wire in the FETs (they just arrived today!) before trying to go both directions.

Try as I might though, I just couldn't get the larger diameter 18650s into the original battery enclosure as originally hoped so a custom case was ultimately necessary. I drew up and printed the bottom half pictured below, and it looks like version 1 is going to work (that's somewhat rare!).

The top half is printing now, and I'll report back once the remaining wiring is completed and tested. Fingers crossed...
 

Duo 280c Battery Schematic.png

Duo 280c Battery Bottom.png

IMG_20200724_233218.jpg

Edited by sutekh
Link to post
Share on other sites
10 hours ago, TimHD said:

Are those small boards custom, relatively easy to source or originals (retained)?

They're both modern and readily / inexpensively available:

Assuming this ends up working, I'll summarize the entire BOM.

Edited by sutekh
Link to post
Share on other sites

Well, shame on me for making bad assumptions about the sophistication of the charging circuitry in the Duo. It appears to be software controlled and current limited. Unless it detects a valid battery in the voltage range of a depleted NiMH pack, it doesn't engage. Probably also has some other fancy algorithms for bulk / float charging and "learning" pack characteristics. The Duo 280c service manual actually details much of this and provides the function calls to query the charge status had I bothered to look. I'm by no means giving up though! I just have to trick the charger into thinking it's looking at a discharged NiMH...

Edited by sutekh
Link to post
Share on other sites

Some progress this weekend, if measured. I ordered an external charger off the auction site for bench testing and reverse engineering (I really don't want to wreck my Duo), only to discover when it wouldn't charge that there are apparently two versions of said unit. Come to discover that P/N M7778, which is what I ordered, will only charge Type I batteries :/ M1812 is what you apparently need for Type II & III (mine is type II). All of this is outlined in a service bulletin, which I of course didn't find until after running into this problem, found here: https://www.macrepaircentral.us/powerbook-200-series-duo-210-duo-230-250-270c/battery-recharger.html

Thankfully, someone had the updated version listed inexpensively, and so after another untenable delay, my testing will continue. I hate waiting...

 

IMG_20200802_120806.jpg

Edited by sutekh
Link to post
Share on other sites
  • 3 weeks later...

With my new PB 180c distraction out of the way (because it's 100% functional!), I had a chance to get back to this project. My M1812 charger arrived and I've been able to test a lot of different scenarios. As I surmised, it's current regulated, and must see the following before engaging a charge cycle:

  • A valid response from the ID chip
  • A reading from the thermister  (haven't tested where this cuts off due to heat, but it can't be open)
  • A voltage from the battery within a range that would require charging. Haven't tested below 9v, but it seems to cut out around 13.8v, which is perfect as the charger I'm using needs an input of at least ~1v above the fully-charged pack voltage of 12.6v.

All of those conditions met, it starts feeding ~600ma to the pack.

Point of clarification from above, the FET steering circuit in my schematic is flawed. Using a FET as a cheap "ideal diode" (very little leakage or voltage drop) in 3rd quadrant more works great with a single transistor, but with 2 of them in an "or" arrangement as I depicted, even after the current reverses, the gate of the previously active FET remains energized across their common grounds and current can flow both directions. I should have caught that :) For now, I've just simplified the circuit with a pair of 1N5401 diodes and accepted the 0.7v loss, although I'm going to revisit with a pair of actual ideal diodes because a charged pack (12.6v) minus 0.7v is low enough that the Duo thinks the battery is dangerously discharged and pops up warnings.

Anyway, I've buried the lead here. The pack is working! Charging and discharging as expected, both in the duo and external charger. Here are a few pics of the finished article. The little li-ion charge board I used has an SMD LED indicating charge status that I removed and routed to be externally visible through the small hole where the release button was on the original pack. I didn't attempt to re-create the delicate sliding lock rail geometry of the original (that wouldn't have 3D printed well), and instead am locking the pack to the retained external slide lock portion of the original pack via a screw once it's slid into the locked position. It's secure and cosmetically adequate (if not perfect).

I have one more OE Type-II Duo battery, and when I rebuild that one I'm going to use 6x 14300 cells (vs. the 3x 18650 used here), which I believe should fit easily within the original case and provide similar capacity. Before I get to that though, I'm going to build a similar battery for my PB 180c. That should be much easier, as it only has +/- and its 7.5v input is right next door to a 2S Li-Ion's 7.4v :) No more cord tethers!!!
 

IMG_20200823_111504.jpg

IMG_20200823_111222.jpg

IMG_20200823_110521.jpg

Link to post
Share on other sites
11 hours ago, Johanncerecke said:

this is genius. Beyond my level of expertise or understanding, but should you find time to create a tutorial, I would certainly have a go at trying to make my own.

Thanks! The above posts provide most of the bullet points, but I'll add a bill of materials. I also forgot the two most important photos!


Look Ma, no wires!

 

IMG_20200823_191950.thumb.jpg.8e336b3577a44222611bc0df4cb6c22f.jpg

 

Plugged in and charging...

 

IMG_20200823_192114.thumb.jpg.f97cf11bd7094c58b6ad78067d9f1a93.jpg

Edited by sutekh
Link to post
Share on other sites
  • 2 weeks later...
  • 3 weeks later...

I am super interested in this, and would love to get every detail, from parts info to what PLA/color used for 3d printing the case, to how to open the original battery case without cracking it etc etc.

 

I will follow with a lot of attention, and thank you for what you did so far!

 

Edited by micheledipaola
Link to post
Share on other sites
  • 2 weeks later...

Alright, I promised an update...

The ideal diodes arrived and they work nicely! Under full load, I'm only seeing a ~.2v drop, but (because of course there's a but) I'm still getting low-power alerts from the OS throughout much of the discharge cycle. The OE pack contains 10 NiMH cells in series, which should measure from ~1.5vdc per cell charged to 900mv discharged (15v - 9v overall), and I'd surmised that a Li-Ion replacement outputting 12.6v - 10.5v should fall nicely within that range. I think the problem lies in the fact that NiMH cells spend most of their discharge cycle at ~1.2v, and only drop off rapidly toward .9v at the very end of their useful life. Even with the ideal diodes, under load my Li-Ion pack is measuring in the elevens throughout much of its discharge cycle, which the power manager is interpreting as a mostly discharged battery.

 

That "but" notwithstanding though, the pack works quite well! E.g., I ran the 280c for a few hours this afternoon with the added draw of an Etherdock and my wifi-module. I'm not really interested in trying to boost the output voltage with more internal electronics since it'd just waste energy, but I wonder if there might be a potential software solution? I suspect the acceptable voltage ranges are flashed onto the ROM or Power Manager (can anyone confirm?), and this passage from the Power Manager Developer Note is particularly interesting:

 

  • Reading the Status of the Battery and the Battery Charger 6: The Power Manager monitors the voltage level of the internal battery and warns the user when the voltage drops below a threshold value stored in parameter RAM. If the voltage continues to drop and falls below another, lower value stored in parameter RAM, the Power Manager puts the computer into the sleep state. The Power Manager provides a function that allows you to read the state of charge of the battery and the status of the battery charger.

 

Infuriatingly, neither that Developer Note, nor the Duo's, indicate WHAT those values are, or WHERE they originate from, but I'd bet an extension could override them. There is, for instance, an existing "Type III Battery" extension for Duo type III NiMH packs that ostensibly does something similar to make the OS / Power Manager play nicely with those higher-capacity batteries. I pulled that extension into ResEdit and HEX dumped it, but haven't made heads or tails of the instructions yet. I'd welcome assistance from someone with more experience in that arena than I have. I think all this hypothetical extension would need to do is update the value of "batteryLow" in PRAM to a slightly lower value.


Anyway, that annoying but mostly cosmetic wrinkle aside, here's an updated, accurate circuit diagram and BOM. I've also attached the STLs for any who want to 3D print the enclosure I designed. I printed mine using ABS (Octave's Gray) on my MakerBot 2X with 2 shells at 20% infill.

 

1303175756_Duo280cBattery-Schematicv2.png.cc0d9611f20dc755d3bb902d1a4d43aa.png

 

Quote

 

Bill of Materials - PowerBook Duo 280c Battery          
               
Name Qty P/N MFG Vendor Unit Cost Total Cost URL / Notes
Apple OEM Duo Battery 1 M1499 Apple (Other?) eBay $15.00 $15.00 Needed for ID chip, thermistor, & contact pads. Wild guess on the price :)
Samsung 3500mAh Li-Ion 3 INR18650-35E Samsung Various $8.04 $24.12 https://ebay.com/p/2155089627
Li-Ion CC/CV Charger 1 DD23CRTA Eletechsup AliExpress $4.45 $4.45 https://aliexpress.com/item/32993044945.html
Li-Ion 3S BMS (10A) 1 HX-3S-01 Generic Amazon $2.33 $2.33 https://amazon.com/gp/product/B07T2P5XHS/ref=ppx_yo_dt_b_asin_title_o00_s01
Ideal Diode 2 YH11040A-2 ??? AliExpress $3.90 $7.80 https://aliexpress.com/item/1005001367556002.html
3D Printed Enclosure 1 N/A Sutekh N/A -- $0.00 See attached Top / Bottom STL files
#4 x 3/4in Flat Head Screws 5 N/A Various Various $0.06 $0.30 4 to hold the case together, one to secure it to the sliding lock
Misc 18 AWG wire, solder, etc. N/A N/A Various Various $1.00 $1.00 I'm not going to itemize ever little thing, but you get the idea…
               
Total           $40.00  

 

 

Duo 280c Battery Top.stl

Duo 280c Battery Bottom.stl

Edited by sutekh
Link to post
Share on other sites
  • 4 weeks later...
22 hours ago, aladds said:

Have you tried using the Insomnia extension from various Mac OS CD-ROM System Folders? I don't know how it does it, but I know it prevents PowerBooks from sleeping, even if the battery is low.

 

The way I understand it, the OS via Power Manager references values stored in PRAM (how they get there initially I don't know. OS? ROM?) to determine how it responds to various voltage conditions. After further observation, in the case of my Duo 280c, it warns at 11.4v, indicates the pack is critically low at 11.2v, and goes sleep at 11.0v.

Further reading has suggested that the voltage is measured by an ADC and assigned an 8-bit value, with 0 being the lowest (in this Duo's case, 11.0v), but the scale is apparently fixed (probably defined in ROM). While an extension could modify the warn and critical thresholds values in PRAM (setting both to 0 would, I think, suppress alerts completely), I don't believe the zero point can be moved to allow the laptop to remain on at a voltage below 11.0v.

I've played with a few different extensions, Insomnia included, but it just prevents the notebook from going into a timeout induced sleep (i.e., if configured to sleep after X minutes), but doesn't prevent the Duo from powering off when it reaches 11.0v :/

Without being able to draw below 11.0 volts, I can only access ~50% of the pack's capacity, so I think the only answer from here is an internal boost converter immediately behind D2. I'd really hoped to avoid that because a) complexity, b) inefficiency, and c) the pack output voltage is then fixed vs. variable depending upon capacity remaining. I'll have no indication that pack is nearing depletion until the BMS unceremoniously powers down at LVC. I suppose I could use a variable output boost converter and find a way to reference the output from the input voltage, but still less than ideal...

Edited by sutekh
Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
×
×
  • Create New...