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HP-28S battery door
09-06-2018, 03:02 AM (This post was last modified: 09-06-2018 03:06 PM by burkhard.)
Post: #15
RE: HP-28S battery door
(09-04-2018 09:17 PM)burkhard Wrote:  
(09-04-2018 07:30 PM)jonese Wrote:  Ideas on how do I can avoid the battery door issue?

I had considered (but haven't tried it yet) trying either a flat top N or possibly even a flat top 2/3 AAA instead of the normal N. The normal "N" battery should be slightly shorter (better) than a normal "2/3 AAA", but a flatop "2/3 AAA" might be slightly shorter (better) than the normal "N", helping to reduce the static loading of the door:body interface. I haven't confirmed the measurements yet, though.

OK, I just did confirm it. The "regular" alkaline Energizer N batteries HP expected you to use in the calculator I have measure 29.45 mm long. The "flat top" Chinese generic 2/3 AAA batteries I have measure 28.35 mm. So, each of the "flat top" 2/3 AAA is more than a millimeter shorter than the specified N batteries.

I tried out some of these "flat top" 2/3 AAA in a 28C just now and indeed there is noticably less pressure on the battery springs. Remember, the clamshells use 3 batteries, a stack of two and a single in parallel. So the stack of two side is ≈ 2.2mm shorter than a stack of two regular N batteries. That's noticeably less preload on the spring. I'm not sure if that substantially reduces the risk of side door area breakage, but it couldn't hurt.

They are a little smaller in diameter than N batteries as well, so no risk of getting stuck.

Oh yeah... as a bonus they seem to work OK as well. Everything seems to make contact... the calculator turns on and looks like it operates properly.

These are the exact batteries I have, purchased off eBay from a Canadian battery seller. They are *cheap*, only about $1US each *including* Canada → US shipping. They are NiMH as well, so rechargeable with the right adapters rigged up to get them to AAA length and preferably the charging current reduced somewhat.

"Flat Top" 2/3 AAA batteries as replacement for type N.
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Messages In This Thread
HP-28S battery door - jonese - 09-04-2018, 07:30 PM
RE: HP-28S battery door - Zaphod - 09-04-2018, 08:05 PM
RE: HP-28S battery door - burkhard - 09-04-2018, 09:17 PM
RE: HP-28S battery door - burkhard - 09-06-2018 03:02 AM
RE: HP-28S battery door - SlideRule - 09-04-2018, 09:20 PM
RE: HP-28S battery door - Jlouis - 09-05-2018, 01:53 AM
RE: HP-28S battery door - burkhard - 09-05-2018, 01:07 PM
RE: HP-28S battery door - rprosperi - 09-05-2018, 02:35 PM
RE: HP-28S battery door - ijabbott - 09-05-2018, 04:03 PM
RE: HP-28S battery door - rprosperi - 09-05-2018, 06:11 PM
RE: HP-28S battery door - Jlouis - 09-06-2018, 01:26 AM
RE: HP-28S battery door - jonese - 09-05-2018, 10:01 PM

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