HP 67: charging of battery pack

[Dr. Mabuse]

Gentlemen:

Are there any concerns to recharge my HP 67 battery pack using the standard HP 67 wall power supply device !? I'm not sure whether the battery pack is in good conditions or not. I know about the problems regarding to the HP Woodstock models by using wall power supply on bad batteries and/or battery contacts. Therefore I wanna kindly ask the forum experts, if this is a similar problem with the HP 67 series.

Kind regards from Germany and many thanks for your feedback in advance !

[d b]

The 67 is susceptible to this problem. I don't even trust clean contacts. Contacts are usually the problem; batteries have to be pretty bad off to cause this. There are several anti-corrosion, conductive grease products on the market. Every manufacturer of aluminum wire & cable has one as do most breaker suppliers. No Lox brand can be bought in about a one ounce tube here in the states. As they said about Brylcreem; a little dab'll do ya.

Or you could just charge your battery in your 35, 45, 70, or 80. They're impervious to this by design.

[Geoff Quickfall]

As Don stated the 67 is susceptible to damage. It is a woodstock, which is why the Panamatik chip can be used to ressurect a damaged ACT on the 67.

Get an HP classic external charger or charge using a clsssic 35, 45, 55, 65, 70 or 80.

Geoff

[Dr. Mabuse]

Hello Den and Geoff,

Many thanx for your fast reply - I'm looking for a external charger for while but these items are quite seldom here in Europe. Maybe the recharging by a classic HP calculator is best solution.

P.S.
Which kind of batteries is your recommodation - I've just found a supplier in Germany, who offer NiMH and NiCd both.


Kind regards,

Dr. Mabuse

[Dave Frederickson]

I use a AAA battery pack from Mark Hoskins (Waterhosko) and some Eneloops.

http://www.hpmuseum.org/forum/thread-6339.html

And obviously a BC-700 to charge the batteries.

Dave

[Dr. Mabuse]

Hi Dave,

Thank you for your reply and the related link to your proposed solution !

Best regards,

Thomas

[PANAMATIK]

(04-22-2017 04:04 PM)Den Belillo (Martinez Ca.) Wrote:  The 67 is susceptible to this problem. I don't even trust clean contacts. Contacts are usually the problem; batteries have to be pretty bad off to cause this. There are several anti-corrosion, conductive grease products on the market. Every manufacturer of aluminum wire & cable has one as do most breaker suppliers. No Lox brand can be bought in about a one ounce tube here in the states. As they said about Brylcreem; a little dab'll do ya.

Or you could just charge your battery in your 35, 45, 70, or 80. They're impervious to this by design.

I have to disagree. The HP-67 is not susceptible to this problem. When calling it a "Woodstock" calculator, this belongs only to the chip set but not to the charger. This will become clear when you have a look to the charger slot. Like the "Classic" calculators, it has three contacts. If you insert the charger plug pins 1 and 3 will be interrupted and the battery plus will become completely disconnected from the circuit, the high charging voltage is applied only to the battery, thus it is irrelevant to have a battery pack inside while charging and working with it while charging.

Because the HP-67 was a more expensive model, the charger was designed more costly to deliver two voltages, one regulated voltage for the circuit and one unregulated for charging. Only the cheaper "Woodstocks" used a charger with only two contacts and only one voltage for working and charging, this design requires the batteries inserted while charging and having switched on the calculator.

The HP-67 is save to charge and work without batteries like the HP-35,45,55,65,70,80.

Bernhard

[rprosperi]

(04-25-2017 12:34 PM)PANAMATIK Wrote:  I have to disagree. The HP-67 is not susceptible to this problem. When calling it a "Woodstock" calculator, this belongs only to the chip set but not to the charger. This will become clear when you have a look to the charger slot. Like the "Classic" calculators, it has three contacts. If you insert the charger plug pins 1 and 3 will be interrupted and the battery plus will become completely disconnected from the circuit, the high charging voltage is applied only to the battery, thus it is irrelevant to have a battery pack inside while charging and working with it while charging.

Because the HP-67 was a more expensive model, the charger was designed more costly to deliver two voltages, one regulated voltage for the circuit and one unregulated for charging. Only the cheaper "Woodstocks" used a charger with only two contacts and only one voltage for working and charging, this design requires the batteries inserted while charging and having switched on the calculator.

The HP-67 is save to charge and work without batteries like the HP-35,45,55,65,70,80.

Bernhard

Thank you for clarifying this Bernhard. I have read several past threads on this exact topic, and each time there seem to be folks arguing for each view. Your simple explanation is convincing, but if someone else can explain the damage mechanism given the '67 design, please do so. I prefer to simply charge my '67 battery in the machine, and have done so for many years, but don't want to risk it if there is some confirmed failure mode that has not yet been explained.

[Dr. Mabuse]

(04-25-2017 12:34 PM)PANAMATIK Wrote:  

(04-22-2017 04:04 PM)Den Belillo (Martinez Ca.) Wrote:  The 67 is susceptible to this problem. I don't even trust clean contacts. Contacts are usually the problem; batteries have to be pretty bad off to cause this. There are several anti-corrosion, conductive grease products on the market. Every manufacturer of aluminum wire & cable has one as do most breaker suppliers. No Lox brand can be bought in about a one ounce tube here in the states. As they said about Brylcreem; a little dab'll do ya.

Or you could just charge your battery in your 35, 45, 70, or 80. They're impervious to this by design.

I have to disagree. The HP-67 is not susceptible to this problem. When calling it a "Woodstock" calculator, this belongs only to the chip set but not to the charger. This will become clear when you have a look to the charger slot. Like the "Classic" calculators, it has three contacts. If you insert the charger plug pins 1 and 3 will be interrupted and the battery plus will become completely disconnected from the circuit, the high charging voltage is applied only to the battery, thus it is irrelevant to have a battery pack inside while charging and working with it while charging.

Because the HP-67 was a more expensive model, the charger was designed more costly to deliver two voltages, one regulated voltage for the circuit and one unregulated for charging. Only the cheaper "Woodstocks" used a charger with only two contacts and only one voltage for working and charging, this design requires the batteries inserted while charging and having switched on the calculator.

The HP-67 is save to charge and work without batteries like the HP-35,45,55,65,70,80.

Bernhard

Hi there Bernhard,

Many thanks for your statement and the telecon today !

Best regards from the neighborhood,

Thomas alias Dr. Mabuse

[d b]

RE: "The HP-67 is save to charge and work without batteries like the HP-35,45,55,65,70,80."

Bernhard;
You may well be correct. If so that's good news, with a clear explanation.
However; I've read the opposite here for probably 15 years from other knowledgeable people. So until I'm sure, I'll err on the safe side and urge "new" members with that question to err on the conservative side too. IF there is any greater chance of frying the ACT in powering it that way; I'd rather avoid the penance of buying another of your chips, the couple of hours changing it out, and the peeling and re-sticking of the backplate. I always hate that part.
I admit that charging the battery outside is an extra step. Probably everyone, except one of us, who has a working 67 also has a classic charging cradle or a relatively cheap 35, 45, or 80 though. So the hardware part of this is already taken care of. Even another classic with keyboard, display or other problems should work.

[Dr. Mabuse]

Hi all,

Just found the real recharging unit for my HP 67 on ebay : )

http://www.ebay.de/itm/HP-35-Hewlett-Pac...Swj85YOY5w

Whadday think !?

[PANAMATIK]

(04-25-2017 05:47 PM)Den Belillo (Martinez Ca.) Wrote:  RE: "The HP-67 is save to charge and work without batteries like the HP-35,45,55,65,70,80."

Bernhard;
You may well be correct. If so that's good news, with a clear explanation.
However; I've read the opposite here for probably 15 years from other knowledgeable people. So until I'm sure, I'll err on the safe side and urge "new" members with that question to err on the conservative side too. IF there is any greater chance of frying the ACT in powering it that way; I'd rather avoid the penance of buying another of your chips, the couple of hours changing it out, and the peeling and re-sticking of the backplate. I always hate that part.
I admit that charging the battery outside is an extra step. Probably everyone, except one of us, who has a working 67 also has a classic charging cradle or a relatively cheap 35, 45, or 80 though. So the hardware part of this is already taken care of. Even another classic with keyboard, display or other problems should work.

Hi Dennis,
I met with this problem, when I once got an HP-67 which was running only with charger and not with batteries. I found out that the metal strip at the charger slot was missing. This metal strip connects Pin 1 and 3 when no charger is plugged in.

The original HP-67 manual lists the HP 82002A as charger, which is the same as for the classics (HP 82010A for EU version). Here is a description with schematic.

Charger HP 82002A

You can see the three pins of the charger slot in the charger circuit with 4,7V zener diode at Q1, which delivers about 4,5V to the calculator circuit while the battery plus is connected to the other part of the charger circuit, which delivers a constant current and potentially higher voltage by Q2 Q3. If the two outer pins are connected by the metal strip when the charger is not plugged in, the battery delivers its voltage to the circuit.

But you are right, you may be safer than safe when you always charge the batteries externally, because the charger circuit could be defective and could deliver a higher voltage than normal. Or the charger could be set to 110Volt accidentally which could potentially destroy a HP-67 in europe. On the other side, when charging externally, you could accidentally reverse the battery polarity, when reinserting them into the battery case. There is always space for making a mistake somehow.

My conclusion: When you state that the "Classics" are safe to operate without batteries inserted then also the HP-67 is safe.

Bernhard

[d b]

Yes. If one handles loose batteries singly enough times; at least one will get put back in wrong. That IS a good thing to avoid. I marked red and black ends for both batteries on one of my Woodstock battery boxes for that reason, because I use alkalines in it. I charge the rechargeables in an hp external cradle.

[Paul Dale]

The advice I received here recently, for my first 67, was that using the card reader required the battery but otherwise it was fine from the adaptor. I'm using an USB adaptor and it works fine. I've got to look into the card reader still.

[BobVA]

In this interesting thread Tony Duell states:

Quote:It is _NOT_ safe to operate a 65 or 67 from the AC adapter without a good battery installed.

On these machines, the chips on the CPU board run off the regulated voltage output of the charger (as in all other classics) but the card reader sense amplifier chip runs off the battery pack directly (in order to supply enough current to run the motor) and if the battery pack is open-circuit or missing, this chip can be damaged, since the voltage across this chip then rises to about 16V

The 65 user manual contains an explicit warning about this. The chip was re-designed for the 67 (the new version is used in the 97 and 41 card readers too), and the new version is claimed to be able to withstand the charging voltage, but I don't like to risk it. It's an HP custom chip, and spares are not trivial to obtain. I charge the batteries either in a classic without a card reader, or in a 'reserve power pack'

(That thread has some other cool details, too.)

The HP-67 manual I've got (later printing, maybe?) also has a warning about not operating the calculator without a battery pack.

[Geoff Quickfall]

You beat me to it Bob.

It's more of a charger-no-battery-card-reader problem versus a charger-no battery-ACT problem. No battery can also be substituted by dead battery pack (infinite resistance).

So use with a charger and no battery pack for calculator operations but NOT card reader ops.

Geoff

[PANAMATIK]

(04-26-2017 05:34 PM)BobVA Wrote:  The HP-67 manual I've got (later printing, maybe?) also has a warning about not operating the calculator without a battery pack.

Maybe Tony Duell is right about the HP-65, I don't know its connection scheme, but not about the HP-67.

I just tried following with my HP-67.

1.) I removed the battery pack, plugged in the charger and switched On. OK calculator works well.
2.) I inserted the battery pack, plugged in the charger and swicthed On. OK calculator works well.
3.) I removed the charger from the mains, while calculator is still swicthed On. The calculator gets dark, has no voltage, because the battery is disconnected.
4.) I removed the plug from the charger slot, while calculator is still swicthed On. The calculator starts up, because now the battery is connected again.

This proves that the battery is not connected while charging. How can a battery influence the voltage, if it is disconnected?

The warning not to use the calculator without batteries should nevertheless be followed. Maybe it is just a warning, that the current for the card reader is not strong enough without batteries but there will be no circuit damage.

Bernhard

[BobVA]

(04-26-2017 05:59 PM)PANAMATIK Wrote:  3.) I removed the charger from the mains, while calculator is still swicthed On. The calculator gets dark, has no voltage, because the battery is disconnected.

Oh yes! That's what would happen, but it's just the logic PCB that is disconnected from the battery by the leaf switch in the charger jack, not the card reader electronics. Further down in the thread, Tony said:

Quote:...BUT in the 65 and 67, the sense amplifier chip is connected directly to the battery terminals. Not even the on/off switch is between them. If you connect an adapter to one of these machines, it relies on the battery pack acting as a shunt regulator to pull the voltage down. If the battery is missing or open-circuit, it won't do this, and the sense amplifer chip will get 15V across it. Even if the machine is switched off.

The original HP65 sense amplifier can be damaged by this. The later one, used in the 67, is supposed to stand it, but I don't want to risk it....

That makes some sense, as there must be an electrical path from the battery (and hence the battery charger when it's connected) to the card reader that bypasses the leaf switch, otherwise it couldn't provide current to "help" the card reader when the calculator is running on AC power.

This seems to pose a more perilous danger than that faced by the Woodstocks, since they have to be turned on without a battery for the damage to occur. (And they can be fixed by your ACT chip!) The ACT in the 67 would be protected by the leaf switch, but the failure would be a difficult to replace chip on the card reader.

[PANAMATIK]

Thanks for sharing this information. It changed indeed my view, I didn't know, that the card reader electronics is connected to the constant current source of the charger.

I apologize and agree, that it is not safe to run the HP-67 without batteries. And it is also not safe to run it with batteries, because you could have placed them wrong inside.

My conclusion: The only safe way is to run it without batteries and without charger.

Bernhard

[BobVA]

(04-26-2017 10:12 PM)PANAMATIK Wrote:  My conclusion: The only safe way is to run it without batteries and without charger.

Bernhard

But only when switched off! :-)

Certainly no apologies necessary! That circuit arrangement is a bit counter-intuitive and was a surprise to me as well. Thanks for your logical questions that helped me learn something!

I guess I can understand the design decision to re-use the existing AC adapter and consequently use the battery as a "jump starter" for the card reader but, as with speculation about the Woodstocks, it seems odd they didn't at least put some kind of clamping circuit across the card reader, as a bad/missing battery is a likely event.

Is it possible this wasn't much of a problem 40 years ago? Did the ACT get more fragile as it aged? I recall more than one episode of accidentally powering on my trusty HP-25 in college with a bad battery contact while on AC power and living to tell the tale. It seems they are a lot less forgiving of that today, but perhaps that's just my imagination.