ThinkJet batteries from Ebay

[Ellis Easley]

My batteries arrived the other day. I opened one up to see what condition it was in. The year on the cells in 1984. There is a little coating of rust around the button on some of the positive terminals and one of the negative terminals has a little blue corrosion creeping out under the shrink tubing. All the cells had a little voltage. I started charging the pack and measured the voltage every few minutes for a while. I measured the voltages across the three pairs of cells and they were very close to each other every time I measured. I also monitored the voltage across the current limiting resistor (BTW, the 4.7 ohm 5% resistor measured 5.3 ohms with my pretty good meter) I calculated 340 mA at the beginning. It fell quickly to 200 mA as the cell voltages started to rise. After about 10 hours the current had dropped to 188 mA and the cells were about 1.48V each and a little warm. I never noticed the voltage dropping but I wasn't monitoring them that frequently, it might have peaked between my readings. Also, I re-read my Sanyo manual and the temperature rise is only particularly acute when using the 0.3C fast charge rate - that might apply to the voltage drop as well.

I was beginning to worry because I sent my money order on April 4 and the package didn't arrive until the 29th or 30th. Also there was a local news story about an Ebay scam involving HP monitors! The seller who listed the auction said he did so for a friend and handed me off to him - after three weeks I was beginning to smell a rat! - but then the package arrived.

I wonder how these batteries would run a 9114, maybe after removing one cell (7.2V -> 6V) and changing the current limit resistor and adding the 2 pin Jones connector? The pack fits in the opening of the 9114 with room above - the wire for the Jones connector could loop in there - of course, it doesn't latch in place, but there's always the handyman's secret weapon!

[Bill Smith]

regarding your last paragraph; if you find a way to make this work in the 9114, i'd really like to hear about it. i was able to get a 9114B recently, though without a battery and charger. there were a few of these offered recently, so i'm probably not alone. i have the 82059D from some other component, actually the 2225B, i think.

should you get a workable solution, consider writing it up so that an electronic ignoramous like myself could follow the instructions. thanks,

bill

[Ellis Easley]

I sure will. I've just taken another look and I'm more hopeful than before. Regarding the physical size, I think shimming the battery pack could make it fit snugly and done correctly, the latch might even work! Regarding the connector, there is enough clearance between the frontmost surface of the battery pack and the innermost wall of the drive cabinet that an electrical adapter completely external to the battery pack and the drive might be possible. Regarding the voltage, instead of removing a cell, the extra voltage could be dropped by one or two diodes in the adapter wiring. Also, it is possible that the drive will allow the extra voltage and, if it has a switching converter inside, it will actually use the extra power rather than just waste it. I'm not going to just try it with my precious 9114B, I'm going to do some research on the power supply in the drive. Finally, the sub-C cells in the pack are rated at 1.3A-H, I think - certainly contemporary sub-C NiCads are - and that is only about half of what the original 9114 battery's capacity is (2.4 A-H). But NiMH sub-C cells are rated at 3 A-H. However, even using only 5 of those is nearly a $50 rebuild! DigiKey lists them at $9.55 for the tabbed cells, $8.60 each for 10. If we could put together an order for a case of 480, the price drops to $5.77 each! Makes you think about living with a smaller capacity for $4 total! Actually, those NiMH prices are from my 2000 paper catalog. The online catalog shows $8.10, $7.29/10, $4.86/480. Only ten times as much for twice the capacity!

[David Ramsey]

Why would you even think that 20 year old NiCads would be viable?

[David Smith]

I have some 30 year old nicad pacs that still work fine. Capacity is about 60% of stated value.

[Ellis Easley]

It's my understanding that unless the pressure relief valve has been activated by extreme temperature, NiCads don't deteriorate in storage, although it can take two or three charge/discharge cylcles to get them back to where they were.

[Glynn]

Except where moisture/humidity or temp extremes are involved. Once the battery gets furry on top, don't trust it.

ALSO: packs are subject to things that individual cells aren't. There is such a thing as "cell reversal", which comes about because cells can't be made all perfect and with exactly the same capacity.

If you string three cells, say, in series, and the actual capacity of each is, say, 502mA, 499mA, 501mA-- as the cell self-discharges, the middle one empties first. Then cell one and cell three have a differential to equalize between them. In practice, the tolerances on cell capacities vary much more than my little example, and sometimes the differential between cells is enough to cause a backwards flow through the middle cell, killing it with a "short". Then once you've lost a cell, charging the pack as a 3.6v unit is wrong, because now it is a 2.4v pack.

For reasons above, pack manufacturers usually ship the packs "unformed", meaning they don't charge the whole to its fullest extent. This reduces reversal problems on the shelf. 1-3 charge cycles "form" the pack to its fullest capacity.