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Dieter · (This post was last modified: 09-25-2017 12:00 PM by Dieter.)

(09-25-2017 09:50 AM)Sadsilence Wrote: Details of charge curcuit within HP41 rechargeable battery pack are perfectly explained here.

Yes, I had already linked to Kees van der Sanden's site in post #9. This is the later version of the 82120A, earlier ones had a 78L05 regulator and an additional contact at the center pin of the charger connector. The newer design avoids some problems of the earlier version.

(09-25-2017 09:50 AM)Sadsilence Wrote: There is a 1/3 AAA NiMH C=170 mAh datasheet from GP, that states an overcharge time of one year for 0.1C charging current (=17mA) does no harm to the cell.

...if "no conspicuous deformation and/or leakage" occurs. Yes, I also linked to that data sheet in post #17. ;-)

Many, if not most NiCds and NiMHs are designed to handle a permanent charging current of about 0,03...0,05 C, and most of them should even withstand 0,1 C without major harm. So a 0,1 C charge with full 12...14 hours every now and then (if you don't know if the battery is nearly empty or almost fully charged) should do no harm either.

(09-25-2017 09:50 AM)Sadsilence Wrote: Looking at HP82120A curcuit actual charging current Ic depends on voltage of cells.
Formula is ( 12V - 0.7V - battery voltage )/ 365 Ohm.

Empty pack @ 4*1V = 4V -> Ic = 12V - 0.7V - 4V / 365 Ohm = 20 mA
Loaded pack @ 4*1.4V = 5.6V -> Ic = 12V - 0.7V - 5.6V / 365 = 15.6 mA

That perfectly matches 17 mA standard charge current of mentioned 170 mAh 1/3 AAA cells.

So that's 12 hours for an empty pack.

(09-25-2017 09:50 AM)Sadsilence Wrote: To get a completely empty battery fully loaded you need around 16 hours (typical formula is 15-16h @ charge current C/10 as there are energy transforming losses).

The actual efficiency factor for NiCds and NiMHs and currents around 0,1...0,3 C usually is given as 0,83, leading to a factor of 1,2x for the charging time. Nevertheless, often a time of 14...16 hours is given for 0,1 C. This is because the actual capacity of new cells may be higher than the nominal value (e.g. for the GP17AAAH the manufacturer states 180 instead of 170 mAh) and at charging rates this low a bit of overcharge does not hurt. But if you look at the respective diagrams in the data sheets you will notice that the point of full charge indeed is reached at about 120% the capacity. You can also see this in the mentioned GP data sheet for higher rates: Here the factor for 0,5 C is about 1,2 and for 1 C even lower at 1,1.

Anyway, we are talking about low charging currents near 0,1 C here, so about 15...17 mA for 12 hours or maybe 14 should be fine for an empty 170 mAh battery pack. And it most probably won't do any harm if a fully charged pack is charged this long once in a while.

Let's not forget: the original 1/2N cells in the 82120A had around 60...80 mAh so the new cells will provide more than twice the operation time. And the correct charging time was around 6 hours back then while HP suggested much more, leading to overcharge. So the rebuilt 82120A now finally meets the original specification of a 12 hour charge. ;-)

Dieter

Dieter · (This post was last modified: 09-25-2017 11:05 AM by Dieter.)

(09-25-2017 10:43 AM)Neve Wrote: Charging did not reduce the output, repeated use of the calculator and card reader did. I just can seem to bring it back to it’s original output value of 5.8v. I am positive it was 5.8v. I even checked the next day after extensive use of the card reader and the DVM read 5.0v or 5.1v.

Sounds reasonable.

(09-25-2017 10:43 AM)Neve Wrote: Worthy to note that my power adapter specifies an output of 3VA/8V.
I have no way of measuring the current, but the AC output of mine is 12V!
It’s a 82066B Eurocharger.

I have the same version here. The stated output on the AC-adapter is merely a nominal value, usually rated at full load. So at 375 mA the output should be close to 8 V AC. On the other hand you are measuring the open circuit voltage (no load), or maybe the voltage with just a few mA current. Here the voltage can and will be much higher. This is perfectly normal, I seem to remember even values like 14 V and more. Essentially this is just a transformer, not a regulated power supply, so the lower the applied load, the higher the output voltage.

(09-25-2017 10:43 AM)Neve Wrote: Although I can’t read German, I can tell you that my battery pack is the one from your first link with the 2-prong outlet. Not the 3-prong one seen on the second link.

Fine, that's the newer version. It should contain a 78L12 regulator and a 365 Ohm resistor.

Dieter

Dieter · (This post was last modified: 09-25-2017 11:57 AM by Dieter.)

(09-25-2017 10:48 AM)Neve Wrote: Where do you get your 12V and your other figures? The charger is supposed to be delivering 8VAC (at least that’s what written on it). Although mine does deliver 12VAC!

The "charger" (actually a simple AC-adapter) provides about 8 V under full load at 375 mA, but significantly more with no or no substantial load applied, like in our case (we are talking about ~20 mA here). So an open circuit voltage of 12 V or even more is normal. This has been discussed several times here, even back in 1999.

Edit: I just found a 2011 post by myself, saying that both of my 82066B provide 11,5 V AC with no load. Others have reported values between 11 and 12,5 V, so your 12 Volts are perfectly OK.

Take a look at the circuit diagram. The input provided by the 82059/82066 is first rectified by the four diodes D1...D4. Assuming 12 V AC, due to C1 the output should be somewhere near 16 V DC or a bit more (√2 · 12V). This is fed to a 78L12 regulator which delivers exactly 12 V. Diode D6 reduces this by approx. 0,7 V. So the voltage between the 78L12's output and GND is 0,7 V + the voltage across R1 + Vbat (or the Zener, if the battery is not connected). This leads to 11,3 V – Vbat for R1. If we assume a battery voltage of 5,3 V during charge this means about 6 V across R1 and thus 6 V / 365 Ohm ≈ 16 mA charging current. Or, as Sadsilence already said, near 20 mA for a completely empty pack and about 15 mA as it approaches full charge.

But... if you have opened the pack and installed new NiMH cells, why don't you just use your meter and see what you get ?-) You could directly measure the input voltage of the 78L12, confirm its output to be exactly 12 V, and you could measure the voltage across R1 as well as the actual charging current.

Dieter

Sadsilence · 09-25-2017, 01:58 PM

Perfectly explained ;-).

Neve · (This post was last modified: 09-25-2017 03:25 PM by Neve.)

Yes Dieter, well explained.
Mine gives actually exactly 12.5VAC at only 2mA according to the DVM I have!
That seems kind of very low.

Dieter · (This post was last modified: 09-25-2017 05:27 PM by Dieter.)

(09-25-2017 03:20 PM)Neve Wrote: Yes Dieter, well explained.
Mine gives actually exactly 12.5VAC at only 2mA according to the DVM I have!
That seems kind of very low.

?!? – what exactly have you measured, and how?
As already said, 12,5 V is perfectly OK. But how did you get these 2 mA? Please explain in detail how you determined this.
Is your meter able to measure AC current?

Dieter

Neve · 09-25-2017, 07:41 PM

(09-25-2017 05:25 PM)Dieter Wrote:
(09-25-2017 03:20 PM)Neve Wrote: Yes Dieter, well explained.
Mine gives actually exactly 12.5VAC at only 2mA according to the DVM I have!
That seems kind of very low.

?!? – what exactly have you measured, and how?
As already said, 12,5 V is perfectly OK. But how did you get these 2 mA? Please explain in detail how you determined this.
Is your meter able to measure AC current?

Dieter

Yes I know 12.5VAC is fine. I just wanted to be more precise.
Yes, my DVM can apparently measure AC and DC currents up to 10A.
That’s how I measured it.

Dieter · (This post was last modified: 09-25-2017 07:48 PM by Dieter.)

(09-25-2017 07:41 PM)Neve Wrote: Yes I know 12.5VAC is fine. I just wanted to be more precise.
Yes, my DVM can apparently measure AC and DC currents up to 10A.
That’s how I measured it.

OK, obviously I was not clear enough, so let me try once again.
You said:

Quote:Mine gives actually exactly 12.5VAC at only 2mA according to the DVM I have!
That seems kind of very low.

How did you measure these 2 mA, what exactly did you do here? How exactly did you connect the meter?
What are these 2 mA supposed to mean and why do you think this is kind of very low?

Dieter

Neve · (This post was last modified: 09-25-2017 07:57 PM by Neve.)

(09-25-2017 07:48 PM)Dieter Wrote: How did you measure these 2 mA, what exactly did you do here? How exactly did you connect the meter?
What are these 2 mA supposed to mean and why do you think this is kind of very low?

Dieter

I connected the meter according to the quick ref. guide it came with, I guess.
I don’t know, isn’t it low?

Neve

Dieter · (This post was last modified: 09-25-2017 08:10 PM by Dieter.)

(09-25-2017 07:54 PM)Neve Wrote: I connected the meter according to the quick ref. guide it came with, I guess.

Sorry, obviously I am not able to express what I want to know.
Maybe others can help and/or have an idea what you may have measured here.

Dieter

Neve · 09-25-2017, 08:33 PM

(09-25-2017 08:02 PM)Dieter Wrote:
(09-25-2017 07:54 PM)Neve Wrote: I connected the meter according to the quick ref. guide it came with, I guess.

Sorry, obviously I am not able to express what I want to know.
Maybe others can help and/or have an idea what you may have measured here.

Dieter

I set the meter to 4mA (I also tried 400mA), connected one end of the leads to the DVM Amp inputs, and measured the output of the cord from the charger.
Isn’t it how it’s supposed to be done?

Dieter · (This post was last modified: 09-25-2017 09:07 PM by Dieter.)

(09-25-2017 08:33 PM)Neve Wrote: I set the meter to 4mA (I also tried 400mA), connected one end of the leads to the DVM Amp inputs, and measured the output of the cord from the charger.
Isn’t it how it’s supposed to be done?

There are two leads.
One end of each usually plugs into the meter.
The other two ends usually have tips that you connect to two specific points in the electronic circuit.

Do you want to say that you placed the two tips right into the two contacts of the "charger" plug while the meter was set to 4 or 400 mA? No, this is not how it works.

Code:

Voltage:

    +---o  <===== meter tip 1

====|  <

    +---o  <===== meter tip 2

Current:                                           +--------+

                                                   |        |

    +---o  <===== meter tip 1                      |        |

====|  <                      meter tip 2 =====> O)|        |

    +---o  <----- short cable -----------------> O)| 82120A |

                  maybe with alligator clips       |        |

                                                   |        |

                                                   +--------+

Voltage: place the two tips at the two points between which you want to measure the voltage, i.e. parallel to the circuit.

Current: place the two tips in series (!) with the circuit within which you want to measure the current.

Dieter

Neve · 09-25-2017, 10:37 PM

(09-25-2017 09:00 PM)Dieter Wrote: There are two leads.
One end of each usually plugs into the meter.
The other two ends usually have tips that you connect to two specific points in the electronic circuit.

Do you want to say that you placed the two tips right into the two contacts of the "charger" plug while the meter was set to 4 or 400 mA? No, this is not how it works.

Yes, this is what I did. I guess I got it all wrong...

Code:

Voltage:

    +---o  <===== meter tip 1

====|  <

    +---o  <===== meter tip 2

Current:                                           +--------+

                                                   |        |

    +---o  <===== meter tip 1                      |        |

====|  <                      meter tip 2 =====> O)|        |

    +---o  <----- short cable -----------------> O)| 82120A |

                  maybe with alligator clips       |        |

                                                   |        |

                                                   +--------+

Quote:Voltage: place the two tips at the two points between which you want to measure the voltage, i.e. parallel to the circuit.

I did that for both voltage and current. All wrong then... Sad

Quote:Current: place the two tips in series (!) with the circuit within which you want to measure the current.

Dieter

I don’t know how to do that. Oh well.... I’ll try to figure it out.... I hope I will. I’ll post what I’ll find when I do. At least I’ve learned something! Smile

Thank you Dieter! (And everyone who has contributed)

Dieter · (This post was last modified: 09-26-2017 05:56 AM by Dieter.)

(09-25-2017 10:37 PM)Neve Wrote: Yes, this is what I did. I guess I got it all wrong...

Definitely. I just wonder why you got 2 mA – you have shorted the charger output which should lead to a very high value or even overload. But you may have connected the meter incorrectly, see below.

(09-25-2017 10:37 PM)Neve Wrote: I don’t know how to do that. Oh well.... I’ll try to figure it out.... I hope I will.

Take a look at the ASCII-picture I posted (the bottom part for measuring currents). The left side is the "charger" plug, and on the right you can see the battery pack. You will need a short connection cable, maybe with small alligator clips, to connect one of the charger contacts with one of the prongs on the battery pack.

Also be sure to connect the leads to the meter correctly. Usually there is one common GND socket and then one for voltage readings an another one (!) for currents.
If still in doubt you may post a picture of your meter.

Dieter

Neve · 09-26-2017, 06:45 AM

(09-26-2017 05:51 AM)Dieter Wrote: Take a look at the ASCII-picture I posted (the bottom part for measuring currents). The left side is the "charger" plug, and on the right you can see the battery pack. You will need a short connection cable, maybe with small alligator clips, to connect one of the charger contacts with one of the prongs on the battery pack.

Also be sure to connect the leads to the meter correctly. Usually there is one common GND socket and then one for voltage readings an another one (!) for currents.
If still in doubt you may post a picture of your meter.

Dieter

Hi Dieter,

I will try that and post the results.
Thank you.

PS: I was using the correct DVM output for current. But I was using it like I do with the voltage readings, in parallel.
As to why I got 2mA, I have no clue.

Dave Frederickson · 09-26-2017, 07:30 AM

Was the DVM set to AC AMPS rather than DC AMPS? I get about 1A AC when I measure the current from the adapter without a battery connected.

Expect the AC current measured with the battery connected as described by Dieter to be different than the expected 16 mA DC current measured at the battery.

Dave

Dieter · (This post was last modified: 09-26-2017 07:50 PM by Dieter.)

(09-26-2017 07:30 AM)Dave Frederickson Wrote: Was the DVM set to AC AMPS rather than DC AMPS? I get about 1A AC when I measure the current from the adapter without a battery connected.

I suspect the current in this setup is only limited by the adapter's internal resistance. Something like 1 A is about 3x the specified max. load, so I'd say "don't try this at home". #-)

(09-26-2017 07:30 AM)Dave Frederickson Wrote: Expect the AC current measured with the battery connected as described by Dieter to be different than the expected 16 mA DC current measured at the battery.

I think here the actual charging current is more intesting, i.e. the current through R1. Maybe Neve should measure this instead of the total current the circuit draws from the adapter.

@Neve: Locate the resistor on the PCB in the battery pack. Place the two meter tips at its two ends and measure the voltage (!). Should be something around 6 V. Divide this voltage by 0,365 to get the charging current in mA.

Alternate method: open one of the two connections between the NiMH cell pack and the PCB (leave the other one connected). Set the meter to DC Amps and place its two tips at the two ends of opened connection, i.e. these two points are now connected by the meter. Now you can measure the charging current directly.

Dieter

Neve · 09-26-2017, 08:15 PM

(09-26-2017 07:44 PM)Dieter Wrote: I think here the actual charging current is more intesting, i.e. the current through R1. Maybe Neve should measure this instead of the total current the circuit draws from the adapter.

@Neve: Locate the resistor on the PCB in the battery pack. Place the two meter tips at its two ends and measure the voltage (!). Should be something around 6 V. Divide this voltage by 0,365 to get the charging current in mA.

Alternate method: open one of the two connections between the NiMH cell pack and the PCB (leave the other one connected). Set the meter to DC Amps and place its two tips at the two ends of opened connection, i.e. these two points are now connected by the meter. Now you can measure the charging current directly.

Dieter

Dieter, I would if I could. But I partially sealed back the pack after rebuilding it. I don’t really feel like reopening in again unless I really have to.

But thank you for the idea.

**Gene** · 09-26-2017, 09:55 PM

Anyone have a link to someone selling these 82162A compatible batteries on the USA TAS ?

I don't recall having seen them. Of course having stated that... I'm sure there must be dozens of sellers! :-)

TIA

**rprosperi** · 09-26-2017, 10:33 PM

(09-26-2017 09:55 PM)Gene Wrote: Anyone have a link to someone selling these 82162A compatible batteries on the USA TAS ?

Here's a couple from the 2 most consistent sellers of these type batteries; these sellers always have them available and are reliable sellers, but note they do not use the original battery case:

http://www.ebay.com/itm/Battery-pack-for-Hewlett-Packard-HP91-HP97-and-HP82143A-printers-/222657312787

http://www.ebay.com/itm/Battery-for-HP91...2270869464

And here is 1-off that does use the original case, which would need new cells installed:

http://www.ebay.com/itm/HP-82033A-BATTER...2076178405