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HP 67 Battery charger not working - any alternatives
04-07-2021, 07:15 PM
Post: #1
HP 67 Battery charger not working - any alternatives
Hi,

I have a non working 67 charger, not sure when it stopped working but now I cant charge the batteries! I do have the external battery holder to use and to avoid any risk to the calculator.

Apart from getting a new charger, what options are there to make up a charger that could be used with the external holder to charge the batteries? Has anyone done this, or maybe used a USB cable with a custom cable to connect to the batteries directly?

Short of that what are the options for determining what's wrong with the charger. I am not experienced at electrical repairs, but I can check voltages etc. I also noticed on the US spec charger I have that there is a slider type switch which seems to indicate it can operate at either US spec (110v) or European voltage.

Any advice would be welcomed!

dbhp67
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04-07-2021, 07:22 PM
Post: #2
RE: HP 67 Battery charger not working - any alternatives
Maybe something like taht?
http://davidreaton.com/hp-calculators/hp...-chargers/
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04-07-2021, 07:31 PM
Post: #3
RE: HP 67 Battery charger not working - any alternatives
Hello!

Throw away the defective charger and never connect another charger to that wonderful calculator ever again. See this recent thread about the subject: https://www.hpmuseum.org/forum/thread-16502.html

Regards
Max
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04-07-2021, 07:45 PM
Post: #4
RE: HP 67 Battery charger not working - any alternatives
USB charger cable.

By Mark Hoskins.

Greetings,
    Massimo

-+×÷ ↔ left is right and right is wrong
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04-07-2021, 09:48 PM
Post: #5
RE: HP 67 Battery charger not working - any alternatives
I would recommend buying one of the AAA holders from Mark Hoskins via ebay, and getting a couple sets of NiMH AAAs (Eneloop, EBL, etc.) and a decent outboard charger. Don't attempt to charge NiMHs inside the calculator, as they can overheat quite dramatically if overcharged.
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04-07-2021, 10:38 PM
Post: #6
RE: HP 67 Battery charger not working - any alternatives
Thanks - I have an external battery holder for the 67 and would only use it in that. I don't have one for the 97. Does one of those exist? If not I might have to find one from somewhere.

I have contacted the vendor by email to order one of those cables for the 67 and the 97!

Again, thanks for the pointers!
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04-07-2021, 11:01 PM
Post: #7
RE: HP 67 Battery charger not working - any alternatives
(04-07-2021 10:38 PM)dbhp67 Wrote:  Thanks - I have an external battery holder for the 67 and would only use it in that. I don't have one for the 97. Does one of those exist? If not I might have to find one from somewhere.

Yes, there is a "Reserve Power Pack" (external charger) for the 97/TopCat products, Product Number 82037A. They show up on eBay from time to time, and though relatively rare, they often sell for fairly reasonable prices, well under $100. This charger uses the same AC adapter the 97 itself uses (Seen here)

--Bob Prosperi
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04-07-2021, 11:13 PM
Post: #8
RE: HP 67 Battery charger not working - any alternatives
(04-07-2021 10:38 PM)dbhp67 Wrote:  Thanks - I have an external battery holder for the 67 and would only use it in that. I don't have one for the 97. Does one of those exist? If not I might have to find one from somewhere.

I have contacted the vendor by email to order one of those cables for the 67 and the 97!

Again, thanks for the pointers!

The HP-97 has charger overvoltage protection, but it only works properly if the original charger is used (or one that has the same specs as the original). If you use a different charger with higher current capability, then you can risk overheating and damaging the protection circuit if something goes wrong.

cheers

Tony
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04-08-2021, 05:56 AM
Post: #9
RE: HP 67 Battery charger not working - any alternatives
(04-07-2021 07:22 PM)AndiGer Wrote:  Maybe something like taht?
http://davidreaton.com/hp-calculators/hp...-chargers/

that circuit with the LED looks odd. seems that emitter and collector of the transistor got accidentally swapped.
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04-08-2021, 07:27 AM (This post was last modified: 04-08-2021 07:30 AM by ThomasF.)
Post: #10
RE: HP 67 Battery charger not working - any alternatives
(04-08-2021 05:56 AM)Hans Brueggemann Wrote:  
(04-07-2021 07:22 PM)AndiGer Wrote:  Maybe something like taht?
http://davidreaton.com/hp-calculators/hp...-chargers/

that circuit with the LED looks odd. seems that emitter and collector of the transistor got accidentally swapped.

Hi Hans!

Yes, you are observant and probably right!
Compare with the drawing by Tony Duel:

https://www.hpmuseum.org/forum/attachment.php?aid=8320

That will probably explain why my breadboard charger doesn't finish charging ... Big Grin

Thanks!

Best regards,
Thomas

[35/45/55/65/67/97/21/25/29C/31E/32E/33E|C/38E/41C|CV|CX/71B/10C/11C/12C/15C/16C/32SII/42S/28S/48GX/49G/35S/DM41X]
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04-08-2021, 02:42 PM
Post: #11
RE: HP 67 Battery charger not working - any alternatives
Hi,

I have a Universal Charger which I used for the my RC models. That has every battery option known to man.

Looking at the 67 spare batteries I was thinking of using this in the meantime.

So, the spec on the batteries is:

NiCd (3 AAs)
1000 mAh

I have set the charger to NiCd and the current to be 400mA (.4C) and the charger has a delta peak voltage detection. Its a bit crude, but so far seems to be working. It hasn't finished charging yet. By my calculations it should take 1000/400 = 2.5 hrs.

Since I can't find an external battery holder to charge my 97 batteries I will probably use this method for them too!

Has anyone used these type of chargers for their calculators. Is there anything to be mindful of when doing this?

Thanks
db67
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04-08-2021, 03:11 PM
Post: #12
RE: HP 67 Battery charger not working - any alternatives
Hello!

(04-08-2021 02:42 PM)dbhp67 Wrote:  Has anyone used these type of chargers for their calculators.

Yes, this is how I usually do it.

(04-08-2021 02:42 PM)dbhp67 Wrote:  Is there anything to be mindful of when doing this?

One thing to consider is that normal NiCd Batteries must be charged at 1/10 of their capacity for 14 hours. There are "quick charge" variants, but unless you are sure that yours are of that type you should stay low on the charging current. Otherwise they may last only a few cycles.

Regards
Max
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04-08-2021, 03:27 PM
Post: #13
RE: HP 67 Battery charger not working - any alternatives
OK - thanks - so in this case that would be 100mA for a 1000mAh battery. Is my understanding correct?
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04-08-2021, 03:31 PM
Post: #14
RE: HP 67 Battery charger not working - any alternatives
(04-08-2021 02:42 PM)dbhp67 Wrote:  Since I can't find an external battery holder to charge my 97 batteries I will probably use this method for them too!

Has anyone used these type of chargers for their calculators. Is there anything to be mindful of when doing this?

I've modified my Topcat Power Pack to plug into a Tenergy 01006 Universal Smart Charger. The same charger is used to charge my 2225B printer battery packs.

For Classic battery packs I use the adapters from Mark Hoskins and a smart charger like the BC-700.

Be aware of the charging current and pack temperature. Both of the above chargers detect overtemperature.
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04-08-2021, 03:34 PM (This post was last modified: 04-08-2021 03:36 PM by dbhp67.)
Post: #15
RE: HP 67 Battery charger not working - any alternatives
Hi,

So for the Topcat batteries what charge current do you recommend?

The NiCads don't seem to get hot on charging. Is your experience different?
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04-08-2021, 03:47 PM
Post: #16
RE: HP 67 Battery charger not working - any alternatives
(04-08-2021 03:34 PM)dbhp67 Wrote:  Hi,

So for the Topcat batteries what charge current do you recommend?

The NiCads don't seem to get hot on charging. Is your experience different?

All my NiCd packs, except one, have been rebuilt with NiMH cells and are charged at 0.5C or less. I haven't noticed the packs getting hot on charging, but I use the temp sensor just to be safe.

For serious battery cell maintenance, find a charger that can perform a "Forming Charge", like the Powerex MH-C9000PRO.

Dave
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05-09-2021, 03:59 PM (This post was last modified: 05-09-2021 07:15 PM by tuxfan.)
Post: #17
RE: HP 67 Battery charger not working - any alternatives
I have built a AA-batteryholder for my HP67. I can swap the battery-set at any time against a 2nd set. I charge the batteries in an external charger for NiMH batteries. Eneloop AA-batteries have a capacity of 1900 mAh. The runtime at continuous operation of the HP67 is about 10 hours. Another advantage of eneloops is the very low self-discharge rate (about -10% after 1 year).

see here
and here
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