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HP Forum Archive 11

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A couple of simple questions on the hp 45
Message #1 Posted by Jeremy on 16 Mar 2003, 12:48 a.m.

I just got one in the mail today from an eBay auction I won about a week ago. It is very well used, the sides are all shiny, and some keys don't bounce back as well as others, but the thing still feels very solid. It had the nameplate of some engineering firm on it, which is gone now.

While hanging out here, I learned that HPs of this era were designed for HPs proprietary battery pack. However, I didn't know they put the contacts on the bottom instead of the end. So I'm going to have to figure out how to wire this baby up properly. I don't care much for athenticity or collectibility; I just wanted an old-school LED RPN HP. So now the barrage of questions begin. ;)

1. What voltage is the input, 3.6? 4.5? (the battery input, that is..)

2. As you look at the open battery compartment from behind, which terminal is positive? the upper or the lower one?

3. Lastly, what is a good way to jury rig this to hold AAs or AAAs. I'm thinking that if it is 4.5 volts (or 3.6 for Ni-Cads) a three cell holder from Radio Shack might be just the thing to hardwire in there...

What are your thoughts? Thanks.


PS- the next step will be to tear this baby down and clean the keypad contacts. Some of them are a bit sticky. It is obvious to me that whoever used this, didn't not treat it gently. Maybe some chucklehead even did some durability demos on it... ;)

Re: A couple of simple questions on the hp 45
Message #2 Posted by Nenad Vulic (Croatia) on 16 Mar 2003, 5:24 a.m.,
in response to message #1 by Jeremy

1. 3 ENTER 1.2 X gives 3.6 V

2. The lower one is positive

3. Three NiCd's preconnected together (intended for wireless honme phones) would be OK.

It is not a big issue to open the battery pack with Exacto knife, replace the NiCd set and glue it back together by super glue, but, be carefull not to cut yourself.

Thanks, and more questions.
Message #3 Posted by Jeremy on 16 Mar 2003, 9:14 a.m.,
in response to message #2 by Nenad Vulic (Croatia)

Yeah, I didn't know if it took 2,3, or 4 1.2V cells. Now I know. I had forgotten the part about cordless phone batteries.

I don't have the original batter pack to cut open, replace the cells and super glue back together. I think what I will do is open it up, find the terminals where the spring connections are made and solder leads there so I don't have to mess up the spring clips. Then, if I can find a cell holder from Radio Shack or something that will hold Alkaline cells, I will just hardwire that in. I really don't like the idea of having rechargable batteries in a calc, because they die on you when you least expect it. As a student, the stakes are too high.

However, I will assume for now that I won't be able to find something to fit and do the cordless phone battery pack idea. Assuming that, I will need to know the ratings of the stock battery charger:

1. What are the voltage and current or power output on it? 2. Was the original a simple linear transformer charger, or did it have some sort of logic built into it? (switch-mode)

Thanks for all your help! -Jeremy

Re: A couple of simple questions on the hp 45
Message #4 Posted by Dan M (Vermont, USA) on 16 Mar 2003, 2:06 p.m.,
in response to message #1 by Jeremy


Help can be found not too far away... Check out the following sites for hp battery information:

Battery Pack with Polarity Marked:

Battery Compartment with Polarity Marked:

I've found good prices on 3-pack NiCds at the clearance bins at Staples, Office Depot, etc. Good Luck!


Re: A couple of simple questions on the hp 45
Message #5 Posted by Richard Parfitt (UK) on 17 Mar 2003, 5:22 a.m.,
in response to message #4 by Dan M (Vermont, USA)

Jeremy, I have sent this info to many people I have seen on MoHP concerning batteries in the "Classic series, eg 35,45,55,65,67,80 etc). The batteries I have found are normally used in Cordless handset phones, and I obtained them in the UK from RS Components, ( stock No.595-491 and cost 7-20 plus local tax. They are Ni-Cad 3.6V/700mAh, and I have used them in three of my HP35's and a HP45 with no problems. They come as a unit with two tags and I just solder on flying leads (very thin wire is best) which I then solder to the battery terminals in the back of the calculator, I solder them halfway down the terminal so as not to modify the ends that might want to be used in the future. As they are shrink wrapped with insulator I just let them rest in the battery compartment. It might be possible to take the three cells and incorporate them into the HP battery pack after cuting around the joint on the plastic. The other thing I do is to take 3 AA Alkaline cells and put them into a HP battery pack again after cutting around the joint to separate the two halves. This is a solution I have used very succesfully in my HP25, just take 2AA's and place them in the battery pack from your HP25,21,27,29 etc. I have enclosed some pictures to show you what I have done. RS Components has a place in the USA called "Allied Electronics in Texas, their web address is, I found this from the RS catalogue I receive regularly. I hope this is of some help, let me know if it's helpful or makes sense, please feel free to let others know and call me if you want more info if I can provide it. Regards Richard.

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