On Sun, Mar 13, 2016 at 9:41 AM, Rick Bensene <[email protected]> wrote:
> Michael Thompson wrote: > > > > The NiCad batteries for emergency head retract are toast. These look like > > standard 1.2V 2/3AA 400mAh cells. It looks like some cordless phones use > the > > same batteries so I can buy an assembled 4.8V battery pack. > > > > Any other suggestions for replacement batteries for the RK05? > > > > > I've used those 4.8V rechargeable battery packs for cordless phones as the > emergency retract batteries in a few RK05 drives, and they seem to work > just fine. Just make sure you get a NiCd pack rather than NiMH as there > are charging differences and I'm not sure if NiMH batteries would be happy > in the charging circuit of an RK05 (but, who knows, they may work, I just > haven't tried it). > > -Rick > The Old Calculator Museum > http://oldcalculatormuseum.com > The only difference in NiMH and NiCd charging schemes occurs when rapid charging them. When rapid charging both types would use a DV/DT technique coupled with a temperature sensor. The DV/DT is much smaller for NiMH than NiCd. So if they went to the effort to recharge fast after an event (why since you could probably do several retracts on a charge) you would not want to use NiMH replacement batteries. It is unlikely that anything other than a trickle charge was used with these batteries since it is cheap, simple and reliable. The trickle current would have been 30 to 50 ma. I would not use the low self discharge NiMH cells (Panasonic Eneloop or Energizer Recharge) as they would convert more of the trickle current to heat and suffer a short life in this application. Non low self discharge NiMH should work fine. I think I have a box of unused Sanyo 500-AR cells. If you need some I could do a quick test and see if any are still good enough to use. The 500-AR are about 1/2 A size. I am sure you can find the dimensions online. -- Doug Ingraham PDP-8 SN 1175
