Powerbook 100 Battery Rebuild

[electricmonk]

I understood you - it just strikes me that you would have to either have a cable travelling from the battery bay to the outside of the computer and snaking round the back to the power plug... or you’d have to cobble together some means of switching between the “Internal thinpack” and the mains power adapter. I suppose if you just disconnected the internal battery cells you could run off mains but if the battery and the AC were connected at the same time would that be bad? I suppose they’d be running in parallel.

 

[electricmonk]

Anyway good news for anyone following this saga - sat down with a multimeter to investigate tonight and it was actually a mechanical problem. My disembowelled dummy battery wasn’t making contact with the positive and negative terminals at the same time - only one or the other depending on which way it was nudged. Because the end with the terminals was physically separate to the rest of the battery (just basically free floating) and there’s a bit of spare height up that end of the battery bay it just wasn’t pressing down hard enough.

So that error message was, needless to say, coming up regardless of what kind of power source was connected to the dummy battery - the tech docs say the powerbook goes to sleep when the battery drops past 5.74v and it looks like you get the same error message whether it’s zero volts or 5.7v. The computer knows that the battery is inserted because it presses on a switch and if the voltage is below the lower threshold you get the error and it goes to sleep.

So I’ve done a quick and dirty job of rebuilding the battery pack by tacking the end back on with superglue and then filling in the jagged cut with epoxy putty. That should be nice and solid when it dries and the battery should exert sufficient force on the terminals to make good contact.

 

[electricmonk]

Hmm so this doesn’t appear to have fixed the problem. I can now read 6.73v across the battery terminals on the logic board with my 5 x AAA cells attached but it still won’t boot without the mains power adapter, and if I attach my benchtop power supply to the dummy battery it delivers zero current.

The logic board can obviously READ the battery voltage because I no longer get the “No battery reserve power remains” error with my dummy battery, but if I pull the DC plug from the back it just turns off instantly rather than running off battery.

I’m not entirely sure where to start measuring voltages on the board as I don’t want to short something out.

I read 5.8v across the fuse. With no cells attached and with the power brick plugged in and battery bay switch pushed in I read 4.62v (jumps around a bit) across the battery terminals. Same reading with a dead battery attached. That seems very low for a charging voltage but I’m hesitant to draw too many conclusions from this because I ain’t no EE.

Incidentally I get infinite ohms across the speaker so I think that explains why there is no sound. Audio works fine through the headphones.

I’ve attached an image of the dummy battery brutally patched together with epoxy putty. As you can see the computer runs reasonably well off mains.

 

[electricmonk]

Hi everyone, it seems to be working now but the plot thickens!

The other day I found there was a capacitor that had fallen off from its perch atop some kind of mysterious regulator thing near the DC jack so I soldered it back on (I created another thread about it because it wasn't battery-related). Tried to boot from dummy battery after fixing this, still no joy.

So today I was poking around checking voltages and I discovered that the only reason it wasn't booting off the dummy battery at this point was that the bloody fuse was blown! I had the benchtop power supply attached to the dummy battery leads, I had had the black probe hooked up to the -ve battery terminal and then on a whim decided to connect it to the GND pin of the SCSI socket instead and this possibly enabled me to notice that for some reason there was a drop from 7V to 0.7V across the fuse, and this was why certain components were only getting a miserable 0.7V. I would've expected a 100% drop rather than a 90% drop - and I wouldn't have expected it to boot off the rear DC jack with a blown fuse - but then I'm really only starting out with this stuff and having a bit of fun with trial and error so I shouldn't be surprised by all these little revelations.

Removed fuse, tested it: blown. Swapped it for a length of wire (in lieu of a replacement quick-blow 5A fuse) and the Powerbook works perfectly off the benchtop power supply via the dummy battery!!! Powered off but wired up it draws about 70mA. When you boot it up the current draw rises to 700mA, jumps around a lot, briefly rises to just over 900mA as the boot sequence continues and then it settles down to 700mA again once you've arrived at the desktop. I'll test it under different conditions later on to see what kind of current draw you get from various operations. So far this all seems perfectly logical and quite promising!



However, as I said, from here the plot thickens. When I hook up my 5 x AAA 900mAh Ni-Cad battery pack it starts up but doesn't complete the boot sequence. It usually gets to the "welcome to Macintosh" screen and then shuts down. I hooked up my multimeter to the battery pack which was reading about 6.5V. When I pressed space bar to boot the Powerbook the voltage dropped to 6V or so and then as the boot sequence progressed the voltage steadily plummeted to 5.8v and beyond and the machine powered down. I read in some tech doc somewhere that it cuts out at about 5.74V. Hmm!

I tried a fresh set of charged Ni-Cad AAAs which started off at 6.65v and it got a bit further with the boot sequence before shutting down. The voltage still drops precipitously during the boot sequence. I then put my meter in series and monitored the current draw and discovered that when it's trying to boot off the AAAs it never gets up to the dizzying heights of 700mA, let alone 900mA. It gets up to just below 500mA and then the system shuts down.

Not sure what to think of this. Is it the Ni-Cad AAAs? The battery harness? The attachment of the alligator clips holding it all together for testing purposes? If I had a spare 6V motorcycle battery lying around I could test it with that. Theoretically the AAAs should be able to output almost an amp each at least from my random googling but then maybe I misunderstood what I was reading. If anyone has any insight they can share I'd be very pleased to hear. I'll be doing more testing later on of course.

 

[electricmonk]

Well, with 6 x AAA NiMh batteries, which I incorrectly described in my previous post as Ni-Cad, the battery works perfectly. So 5 x AAA NiMh batteries simply couldn't provide a high enough voltage under load. With no load the voltage of this pack of 6 cells is 8V which is a tad high, however as we now know that's irrelevant because the voltage drops under load. Once the powerbook has started up the voltage of the 6 cells in series settles at 6.6V. It ranges between 6.4V and 6.6V depending on what you're doing with the Powerbook. So NiMh definitely works! If I just mount these battery holders in the hole I cut in the PB100 battery it'll be a usable daily driver. I still need to recap the display though so I won't use it extensively until I have done that.

It only occurred to me tonight, however, that because all these little 1.2v (nominal) 900mAh NiMh batteries are in series I had basically made one 7.2v (nominal) 900mAh NiMh Powerbook 100 battery. Oops! This compares extremely poorly to the original SLA battery which was 2.5Ah, and was also able to be charged by the Powerbook itself. I really should've just refilled, charged and desulfated the lead-acid batteries instead of hacking one open to install cells of a different chemistry. Even if they'd only regained half of their original capacity they would have been ahead of the dummy battery full of AAAs. techknight suggests in another thread that this desulfation will probably have good results. Any thoughts @techknight?

So my next project will be to refill and recover my other dead Powerbook 100 battery and see if it compares favourably with my hacked NiMh battery.

It's pretty clear that swapping out the SCSI drive for a SCSI2SD has reduced the power consumption of the Powerbook so either way it might not be too bad. Although when I metered the 6.4-6.6v 6 x AAA NiMh battery pack it was drawing more like 900mA than 700mA, so you would possibly get less than an hour out of this pack.

So apart from the plan to recover my other PB100 battery, as I have this dummy battery to play with for the moment I could try to improve it. I could squeeze in another six NiMh AAAs in order to create an 1800mAh battery pack but that is a lot of batteries to periodically remove and charge. Something else that only occurred to me tonight is that if I install several series pairs of 600mAh 3.6v 10440 lithium batteries (same form factor as AAA) in parallel then I could make better use of the space I've carved out of the battery. I could install 3 x pairs in parallel and produce an 1800mAh 7.2v Li-ion battery pack. This would mean I would only need to remove and charge six batteries, and I already have a universal four-channel Li-ion charger so this wouldn't be any more inconvenient.

It's possible that I could also try to build a charging circuit into the battery pack. There are plenty of Li-ion charging controller ICs you can buy for like $5. I suspect most of them are not designed to be used in a device which both draws from and charges its battery through the same two contacts but with a bit of research something could probably be done.

 

[electricmonk]

I'm aware that this has become something of a monologue but I wonder if a cheap and sensible solution might not be to put a powerbank in the battery bay, then I could just remove it and charge it by USB. The laptop could probably even charge the powerbank as modern powerbanks can both charge and receive charge from a USB-C port. There are plenty of USB-C to barrel adapters out there so one could just wire a barrel plug to the battery terminals of the powerbook.

The DC barrel cable would want to be long enough so you could remove the power bank and then just unplug it. I could put a little bit of adhesive foam in there to stop the powerbank from sliding around - there are plenty of powerbanks which are of similar height to a PB100 battery - 13mm apparently. A snug fit would probably be good.

QC3.0 powerbanks can deliver between 5v (2.5A) and 12v (2A) which means it could certainly spit out the requisite 7.2V & 1.6A but I wonder if there would need to be some kind of voltage limiter between it and the terminals to stop it delivering more than 7.2v.

 

[cheesestraws]

become something of a monologue

I, at least, am following this with interest, even if I can't contribute.  So please monologue away .

 

[GregorHouse]

I'm aware that this has become something of a monologue but I wonder if a cheap and sensible solution might not be to put a powerbank in the battery bay, then I could just remove it and charge it by USB. The laptop could probably even charge the powerbank as modern powerbanks can both charge and receive charge from a USB-C port. There are plenty of USB-C to barrel adapters out there so one could just wire a barrel plug to the battery terminals of the powerbook.

The DC barrel cable would want to be long enough so you could remove the power bank and then just unplug it. I could put a little bit of adhesive foam in there to stop the powerbank from sliding around - there are plenty of powerbanks which are of similar height to a PB100 battery - 13mm apparently. A snug fit would probably be good.

QC3.0 powerbanks can deliver between 5v (2.5A) and 12v (2A) which means it could certainly spit out the requisite 7.2V & 1.6A but I wonder if there would need to be some kind of voltage limiter between it and the terminals to stop it delivering more than 7.2v.

Maybe you could use a linear voltage regulator like L78S75CV for example. Using a 12V powerbank it would limit the voltage to 7.5V up to 2A. I'm not an expert though, I'm just giving the idea.

https://www.mouser.es/datasheet/2/389/cd00000449-1795347.pdf

 

[Trash80toHP_Mini]

Overvoltage protection shouldn't be difficult?

Sorry I haven't chimed in more. This is fascinating research. Hadn't thought about doing banks of batteries, that's brilliant. Gotta think that one over. I'm all but sure you can find ICs to detect the lack of draw across the contacts when it's removed. Use the circuit in order to charge the banks separately from the same USB power source?

 

[leopard]

I found a blog post where a man has successfully rebuilt PowerBook 100 battery using 6 of cells (compatible Sony NH-14WM). He writes that it works but when the battery charge goes low, he has to take them out and charge them using the charger (not through PB 100's circuitry). Their shape is the key to fitting 6 of them in thin case. 

1.2 V and typically rated 1,400 mAh

What do you think? Has anybody tried this method?