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HP-34C external battery charging
12-06-2017, 03:23 AM
Post: #1
HP-34C external battery charging
I have an HP-34C calculator and battery pack (aftermarket) but no wall adapter to plug into the calculator to charge the battery. Short of finding an HP-34c adapter or 82103a external battery charger, what other solutions are there to charge the batteries?

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12-06-2017, 04:20 AM
Post: #2
RE: HP-34C external battery charging
(12-06-2017 03:23 AM)Craig Bladow Wrote:  I have an HP-34C calculator and battery pack (aftermarket) but no wall adapter to plug into the calculator to charge the battery. Short of finding an HP-34c adapter or 82103a external battery charger, what other solutions are there to charge the batteries?

If you have access to a bench power supply, you can fabricate a pretty simple set of contacts to insert. Another page on the same site shows the connector and lists the power settings (oddly, it's 9V AC). This is probably the easiest of all HP power cords to replicate due to the exposed contacts.

http://www.keesvandersanden.nl/calculato...e_chargers

Also: Note that the 82103A power pack requires the same AC adapter as the Spice series machines use.

If you are planning to acquire one sooner or later, I can loan you one for the interim, contact me off-list to arrange.

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12-06-2017, 09:16 AM
Post: #3
RE: HP-34C external battery charging
I've changed the original, now useless NiCd batteries with AA-type rechargeables with a low self-discharge rate (e.g. eneloop from Panasonic).
They really hold the power for a long period if you use the calculator only sporadically. If necessary, you can load them outside the calculator.
To my knowledge, the Spice series is not critical to be operated without batteries that buffer the power coming from an adapter, as it was the case in the Woodstock series. However, I personally favor the workaround of a transplant with an up-to-date battery pack because you are more flexible without the power cord being attached all time.
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12-06-2017, 06:38 PM
Post: #4
RE: HP-34C external battery charging
I "recycled" a worn out hair cutting machine that had 2 AA shaped rechargeables inside, positioned parallel and is fed from a 3V DC charger. This way I can put a battery pack (cells connected permanently) inside for recharging.
Operating a spice from the original charger without a battery installed is no good idea in Spices.
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12-06-2017, 08:06 PM
Post: #5
RE: HP-34C external battery charging
(12-06-2017 09:16 AM)Frido Bohn Wrote:  To my knowledge, the Spice series is not critical to be operated without batteries that buffer the power coming from an adapter, as it was the case in the Woodstock series. However, I personally favor the workaround of a transplant with an up-to-date battery pack because you are more flexible without the power cord being attached all time.

No, I believe the Spice series has the same type of charging circuit design as the Woodstock series so it shares the same problem of potential damage to the calculator if using the changer without batteries installed.
My HP-33E/33C Owner's Handbook (April 1979) has the following warning on Page 76.

"Note: Do not attempt to operate the calculator from the ac line with the battery pack removed."
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12-07-2017, 03:51 AM
Post: #6
RE: HP-34C external battery charging
The advice and cautions are all good to know. I'm in the process of trickle charging the pack using a two-cell AA battery holder that I modified to hold the 34c nicad pack. I'm using a bench power supply to input a DC voltage.

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12-07-2017, 11:44 AM
Post: #7
RE: HP-34C external battery charging
(12-06-2017 09:16 AM)Frido Bohn Wrote:  I've changed the original, now useless NiCd batteries with AA-type rechargeables with a low self-discharge rate (e.g. eneloop from Panasonic).
They really hold the power for a long period if you use the calculator only sporadically.

I think that's definitely the way to go. Current Eneloops have about four times the capacity of the original NiCd pack, and they hold their charge extremely well when not in use. Connecting the two batteries can be done with a thin piece of metal, I even use folded aluminum foil in my 34C.

Charging should be done in an external "smart" processor controlled charger, as recommended several times in this forum, e.g. the BC700 series and its siblings.

Dieter
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12-07-2017, 06:55 PM
Post: #8
RE: HP-34C external battery charging
In older discussions there were concerns with using AA rechargeable that are physically longer and compress the battery contacts more, potentially fatiguing the metal and resulting in the contact breaking off. One solution was to ‘tap’ the button flatter on the rechargeable battery, does anyone have personal experience with this solution?

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12-07-2017, 11:35 PM
Post: #9
RE: HP-34C external battery charging
(12-07-2017 06:55 PM)Craig Bladow Wrote:  In older discussions there were concerns with using AA rechargeable that are physically longer and compress the battery contacts more, potentially fatiguing the metal and resulting in the contact breaking off. One solution was to ‘tap’ the button flatter on the rechargeable battery, does anyone have personal experience with this solution?

I have never done this, so cannot say from personal experience, however I've read many reports that doing so can easily damage the battery interior leading to poor life (best case) to explosion (worst case).

I suggest you instead simply use 'flat-top' NiCd cells, that don't cost much more, for example here. These are the same cells as in the original Spice battery pack (you can charge them externally in the smart charger), and insert them into the orginal Spice battery pack frame (held with scotch tape) and simply use a folded aluminim foil conductor for the far end as Dieter noted. Sounds silly, but works perfectly. This is better than jamming stuff in the battery bay to keep the loose batteries tight.

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12-08-2017, 07:58 PM
Post: #10
RE: HP-34C external battery charging
(12-07-2017 11:35 PM)rprosperi Wrote:  I suggest you instead simply use 'flat-top' NiCd cells, that don't cost much more, for example here.

I agree that flat top cells probably are a good solution. But why do you recommend NiCds instead of NiMHs with 2x or 3x the capacity and virtually no self discharge?

(12-07-2017 11:35 PM)rprosperi Wrote:  These are the same cells as in the original Spice battery pack (you can charge them externally in the smart charger),

If NiCds are used be sure to get a charger with sufficiently low charging current. The mentioned BC700 charger has a lowest (default) current setting of 200 mA which is perfect for 800 mAh NiCds.

(12-07-2017 11:35 PM)rprosperi Wrote:  and insert them into the orginal Spice battery pack frame (held with scotch tape) and simply use a folded aluminim foil conductor for the far end as Dieter noted.

For the record: I do not use the original battery pack frame, just two standard Sanyo/Panasonic AA Eneloops and a piece of folded aluminum foil. Works fine here.

Dieter
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12-08-2017, 11:05 PM
Post: #11
RE: HP-34C external battery charging
(12-08-2017 07:58 PM)Dieter Wrote:  I agree that flat top cells probably are a good solution. But why do you recommend NiCds instead of NiMHs with 2x or 3x the capacity and virtually no self discharge?

Not recommending them over NiMH, I prefer Eneloops too, I'm just pointing out some cells in the same range as the NiCd currently in use.

(12-08-2017 07:58 PM)Dieter Wrote:  If NiCds are used be sure to get a charger with sufficiently low charging current. The mentioned BC700 charger has a lowest (default) current setting of 200 mA which is perfect for 800 mAh NiCds.

I agree, I have the same BC700, it is easy to use, reliable and inexpensive.

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12-08-2017, 11:23 PM
Post: #12
RE: HP-34C external battery charging
Thanks for the great discussion! I have a Nicad pack from TAS on the way, I found a 34C wall adapter (long story) and have ordered the BC700 and eneloops. The 34C I received this week first powered up (off of a bench supply) with missing led segments, slight (very slight) twisting of the case brought them back to life. That reminds me that I need to weigh it to see if it is the soldered or press fit version.

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12-09-2017, 02:15 AM
Post: #13
RE: HP-34C external battery charging
(12-08-2017 11:23 PM)Craig Bladow Wrote:  ...
That reminds me that I need to weigh it to see if it is the soldered or press fit version.

With the batteries installed the original press-fit version weighs about 220-230 g. The newer soldered version is lighter and weighs around 170-180 g.

Another member writes the following:
"Pick one key (calculator ON or OFF), perhaps [ENTER] key and slowly press it till it "clicks" and stops. If the key's upper face (not the top of the key) hides itself in a way the top face almost reaches the keyboard level, then it is a solderless unit. If the key moves just a little bit and the upper face keeps half of it hidden and half appearing, then it is a soldered unit. This is because the solderless units have a single flex circuit that "plays the role" of keyboard contacts, circuit trails and IC's connectors, and the bubble caps for each key are somehow "far" from the keys contacts. The soldered units use metal caps almost like the ones used in the HP41 (and HP75C/D and HP71B) for each key, and their "moving range" is a lot smaller."
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12-09-2017, 04:51 AM
Post: #14
RE: HP-34C external battery charging
220 Grams == press fit, but it is working!

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12-17-2017, 04:32 AM
Post: #15
RE: HP-34C external battery charging
I have tried both the Eneloops and the Ebay 34c NiCad replacement battery, and the Nicad is definitely the better fit in the HP-34c. The BC700 is a very nice charger with many good features.

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