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Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I cleaned up the mess.
The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH ().
Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome your help.

Best regards

On 21/07/18 19:40, anotherlin@... wrote:

Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I cleaned up the mess.
The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH ().
Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome your help.

One point to be aware of is how it is charged. If a cell is charged too fast or for too long, it will be damaged.

An "intelligent" charger will determine when a cell is fully charged, and stop charging. Frequently a backup battery does not have an intelligent charger, but simply "trickle charges" the cells all the time it is connected to the mains.

So you probably need to determine the trickle charging current in the circuit, and compare that with the datasheet's spec. In the absence of more specific information, it is usual to assume than trickle charging at "C/10" is OK, which would be 11mA for a 110mAh cell.

On Sat, 21 Jul 2018 11:40:14 -0700, you wrote:

Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I cleaned up the mess.
The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH ().
Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome your help.

I'd suggest a different approach. The backup battery will leak again,
sooner or later. In addition, even with 150 mah, if it's in storage,
it will go below the point where the cal constants are valid. You
will have to provide various (highly accurate) voltages, including 250
or so and 700 VAC to calibrate this.

Calibration, unless you have the equipment, is a pain. (there are
ways of working around the accuracy requirement, but you still need
the 700 volts AC and 1000 volts DC).

I'd put in a lithium battery, I'd suggest a Tadiran TL-2155, which
will fit in the slot. You MUST put a diode in series to prevent the
battery from being charged, however.

Before you go to the trouble, I'd suggest temporarily wiring in two
small NiCd batteries, capacity not super important. Let them charge
up. Then go through and attempt to calibrate the unit as best you
can. What you're looking for is bad calibration constants, indicating
that the battery corrosion has damaged part of the backup circuitry.

At that point, if you can fix it, good, if not, then you'll have to
figure out a workaround.

One workaround is to rebuild/remake the CPU board with a more modern
processor, an AVR mega (a big one) would work. However, you'll want
to know how the insides interact with the processor, and I do not have
anywhere near complete information on that.

Given that information, a more modern board can be made, the functions
may be expanded, and you can restore the DMM to full service.

I put the battery in, and the memory storage was still not working, so
rebuilding is going to be what I do, for now, unless I find one that
is still working.

Harvey

Best regards

Hi everyone,

My plan is only to fix this unit back to working condition, and hopefully
have fun in the process.
So there's no plan to re-make the CPU board, that's just to much work,
especially for a 4.5 digit only meter.

The DM5010 uses a "simple" trickle charger for the battery. However, the
charge current may seem too high.
Original battery specifcation is 150mA so trickle charge current should be
0.1 x capacity = 15mA.
However, the replacement battery specifies a trickle charge at 4mA, so I
may have to tweek the current limiting resistor.

I've noticed there is already a subject on eevblog regarding the battery
replacement.
May be I should move there (would be easier to post photos).
Or would guys prefer to continue here?


Best regards,


On Sat, Jul 21, 2018 at 9:13 PM, Harvey White <madyn@...>
wrote:

On Sat, 21 Jul 2018 11:40:14 -0700, you wrote:

Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I

cleaned up the mess.

The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH (

complete_11_Jan_25-21018.pdf).

Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome

your help.

I'd suggest a different approach. The backup battery will leak again,
sooner or later. In addition, even with 150 mah, if it's in storage,
it will go below the point where the cal constants are valid. You
will have to provide various (highly accurate) voltages, including 250
or so and 700 VAC to calibrate this.

Calibration, unless you have the equipment, is a pain. (there are
ways of working around the accuracy requirement, but you still need
the 700 volts AC and 1000 volts DC).

I'd put in a lithium battery, I'd suggest a Tadiran TL-2155, which
will fit in the slot. You MUST put a diode in series to prevent the
battery from being charged, however.

Before you go to the trouble, I'd suggest temporarily wiring in two
small NiCd batteries, capacity not super important. Let them charge
up. Then go through and attempt to calibrate the unit as best you
can. What you're looking for is bad calibration constants, indicating
that the battery corrosion has damaged part of the backup circuitry.

At that point, if you can fix it, good, if not, then you'll have to
figure out a workaround.

One workaround is to rebuild/remake the CPU board with a more modern
processor, an AVR mega (a big one) would work. However, you'll want
to know how the insides interact with the processor, and I do not have
anywhere near complete information on that.

Given that information, a more modern board can be made, the functions
may be expanded, and you can restore the DMM to full service.

I put the battery in, and the memory storage was still not working, so
rebuilding is going to be what I do, for now, unless I find one that
is still working.

Harvey

Best regards

--
/* Lin Ke-Fong
* anotherlin@...
* I always do what I say, especially if it's something stupid.
*/

On Sat, 21 Jul 2018 19:56:27 +0100, you wrote:

On 21/07/18 19:40, anotherlin@... wrote:

Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I cleaned up the mess.
The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH ().
Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome your help.

One point to be aware of is how it is charged. If a cell is charged too fast or
for too long, it will be damaged.

Quite true.

An "intelligent" charger will determine when a cell is fully charged, and stop
charging. Frequently a backup battery does not have an intelligent charger, but
simply "trickle charges" the cells all the time it is connected to the mains.

At that time of development, there was really no such thing as a smart
charger, and it would have been about as complicated as the existing
CPU board. All they did was to trickle charge it. The "use" senario
was to have the unit plugged in and on most of the time, certainly
enough (averaged over a week) to keep the battery charged when
considering the power needed to keep the CMOS RAM alive.

So you probably need to determine the trickle charging current in the circuit,
and compare that with the datasheet's spec. In the absence of more specific
information, it is usual to assume than trickle charging at "C/10" is OK, which
would be 11mA for a 110mAh cell.

I think it was more like 1/20th C, but that's what I've remembered.

All that was really needed was to put in more (use the 66% rule) than
got taken out when the meter was turned off.

Harvey

On Sat, 21 Jul 2018 23:28:34 +0200, you wrote:

Hi everyone,

My plan is only to fix this unit back to working condition, and hopefully
have fun in the process.
So there's no plan to re-make the CPU board, that's just to much work,
especially for a 4.5 digit only meter.

Agreed, you don't have *three* of them and no TM5000 DMMS.

The DM5010 uses a "simple" trickle charger for the battery. However, the
charge current may seem too high.
Original battery specifcation is 150mA so trickle charge current should be
0.1 x capacity = 15mA.
However, the replacement battery specifies a trickle charge at 4mA, so I
may have to tweek the current limiting resistor.

Not necessarily so, has more to do with the "how long it's used and
how long it's plugged in" vs. "how long the thing remains off."

For normal use, I suspect there's not a problem with this, but when
it's set on the shelf for two or three years, well, the CPU is toast.

I've noticed there is already a subject on eevblog regarding the battery
replacement.
May be I should move there (would be easier to post photos).
Or would guys prefer to continue here?

For my opinion, here is better. Photos could be put in the photo
section.

Harvey

Best regards,


On Sat, Jul 21, 2018 at 9:13 PM, Harvey White <madyn@...>
wrote:

On Sat, 21 Jul 2018 11:40:14 -0700, you wrote:

Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I

cleaned up the mess.

The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH (

complete_11_Jan_25-21018.pdf).

Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome

your help.

I'd suggest a different approach. The backup battery will leak again,
sooner or later. In addition, even with 150 mah, if it's in storage,
it will go below the point where the cal constants are valid. You
will have to provide various (highly accurate) voltages, including 250
or so and 700 VAC to calibrate this.

Calibration, unless you have the equipment, is a pain. (there are
ways of working around the accuracy requirement, but you still need
the 700 volts AC and 1000 volts DC).

I'd put in a lithium battery, I'd suggest a Tadiran TL-2155, which
will fit in the slot. You MUST put a diode in series to prevent the
battery from being charged, however.

Before you go to the trouble, I'd suggest temporarily wiring in two
small NiCd batteries, capacity not super important. Let them charge
up. Then go through and attempt to calibrate the unit as best you
can. What you're looking for is bad calibration constants, indicating
that the battery corrosion has damaged part of the backup circuitry.

At that point, if you can fix it, good, if not, then you'll have to
figure out a workaround.

One workaround is to rebuild/remake the CPU board with a more modern
processor, an AVR mega (a big one) would work. However, you'll want
to know how the insides interact with the processor, and I do not have
anywhere near complete information on that.

Given that information, a more modern board can be made, the functions
may be expanded, and you can restore the DMM to full service.

I put the battery in, and the memory storage was still not working, so
rebuilding is going to be what I do, for now, unless I find one that
is still working.

Harvey

Best regards

You can still buy Ni-Cad replacements for cordless phones, but I always extend the leads and mount them away from anything they can damage. You may have to buy a three cell package and remove one cell, but some are easily reworked and cheap. They are sold by many places, and on Ebay.


Michael A. Terrell

On Sat, 21 Jul 2018 18:36:42 -0400 (GMT-04:00), you wrote:

You can still buy Ni-Cad replacements for cordless phones, but I always extend the leads and mount them away from anything they can damage. You may have to buy a three cell package and remove one cell, but some are easily reworked and cheap. They are sold by many places, and on Ebay.

Agreed. There are two cell packages (somewhere) as well. The main
problem with the NiCds is twofold. One is the amount of time between
use/charge and loss of calibration data. The second one, (of more
interest once you finally have the calibration equipment) is the
damage a leaking NiCd will cause. Hopefully, the Lithium primary
cells don't do that. IIRC, such cells were not included in the
design, although I do remember one in the AWG series.


Harvey

Michael A. Terrell


-----Original Message-----

From: Harvey White <madyn@...>
Sent: Jul 21, 2018 3:13 PM
To: [email protected]
Subject: Re: [TekScopes] Tektronix DM5010 NiCa 2.4V battery replacement

On Sat, 21 Jul 2018 11:40:14 -0700, you wrote:

Hi everyone,

I need to replace the backup battery of a DM5010. It has leaked but I cleaned up the mess.
The service manual specifies a Nickel Cadnium 2.4V 150mAH at 14mA.

So far, I was able to find (on Mouser) a 2.4V 110mAH ().
Does it meet specification? In particular, we have 0.11AH vs 0.15AH.

I've absolutely no experience with rechargeable batteries. So I welcome your help.

I'd suggest a different approach. The backup battery will leak again,
sooner or later. In addition, even with 150 mah, if it's in storage,
it will go below the point where the cal constants are valid. You
will have to provide various (highly accurate) voltages, including 250
or so and 700 VAC to calibrate this.

Calibration, unless you have the equipment, is a pain. (there are
ways of working around the accuracy requirement, but you still need
the 700 volts AC and 1000 volts DC).

I'd put in a lithium battery, I'd suggest a Tadiran TL-2155, which
will fit in the slot. You MUST put a diode in series to prevent the
battery from being charged, however.

Before you go to the trouble, I'd suggest temporarily wiring in two
small NiCd batteries, capacity not super important. Let them charge
up. Then go through and attempt to calibrate the unit as best you
can. What you're looking for is bad calibration constants, indicating
that the battery corrosion has damaged part of the backup circuitry.

At that point, if you can fix it, good, if not, then you'll have to
figure out a workaround.

One workaround is to rebuild/remake the CPU board with a more modern
processor, an AVR mega (a big one) would work. However, you'll want
to know how the insides interact with the processor, and I do not have
anywhere near complete information on that.

Given that information, a more modern board can be made, the functions
may be expanded, and you can restore the DMM to full service.

I put the battery in, and the memory storage was still not working, so
rebuilding is going to be what I do, for now, unless I find one that
is still working.

Harvey

I have a couple control panels from a machine tool where the design was for the Varta 3.6V 70mAh batteries that were common on computer motherboards. When they became NLA, the company started using NiMh batteries without a redesign. They leak in under a year, and badly damage the interface board. I just received some rechargable Li-ion batteries to try, when I repair the boards.



12-pcs-LIR2032-Li-ion-Button-Coin-3-6V-Rechargeable-Cell-Battery-w-Tab-US-Stock/
Michael A. Terrell

My (limited) understanding is that NiMH cells really don't like more than C/20 - and in many cases the definition of C is, um, very optimistic. I'd restrict trickle charging to C/40 or C/50 - but that is finger in the wind.

From what I've read, you should never trickle charge Ni-Mh batteries. I just replaced the Ni-Mh batteries in two of a set of three cordless phones. The phones have a controlled charging system, and these battery packs were about 12 years old. They were used when I got them, and I've used them for more than 10 years, plus they were in storage for almost a year between users.

The machine tools is never shut down between uses. It is a commercial pipe bender, used by a local canopy manufacturer. The charge current was below C-1/40, yet the boards all failed in under a year.

Michael A. Terrell

On Sun, 22 Jul 2018 08:40:54 +0100, you wrote:

My (limited) understanding is that NiMH cells really don't like more than C/20 -
and in many cases the definition of C is, um, very optimistic. I'd restrict
trickle charging to C/40 or C/50 - but that is finger in the wind.

As I remember it, NiCd cells can be left on trickle charge
indefinitely, NiMh cells do require a lower trickle charge current.
NiMh charging is intended to be C/4, C/2, or C (depending on the
cell), but that is for a limited time with end of charge detection
(either delta V, or temperature rise) with failsafe timers, etc. Look
up the TI BQ series for examples of chargers.

So for NiMh the trickle charge is a very low rate. The actual rating
in MAH is dependent on age, manufacturer, etc. Chinese MAH, like the
motors rated in Chinese horses on their lathes and mills, tend to be a
bit smaller than we think.

I did find some Raytheon 2400 MAH NiMh cells that measured just about
2400 MAH.

Harvey

On 22/07/18 00:52, Michael A. Terrell wrote:

I have a couple control panels from a machine tool where the design was for the Varta 3.6V 70mAh batteries that were common on computer motherboards. When they became NLA, the company started using NiMh batteries without a redesign. They leak in under a year, and badly damage the interface board. I just received some rechargable Li-ion batteries to try, when I repair the boards.



12-pcs-LIR2032-Li-ion-Button-Coin-3-6V-Rechargeable-Cell-Battery-w-Tab-US-Stock/
Michael A. Terrell


-----Original Message-----

From: Harvey White <madyn@...>
Sent: Jul 21, 2018 7:02 PM
To: [email protected]
Subject: Re: [TekScopes] Tektronix DM5010 NiCa 2.4V battery replacement

On Sat, 21 Jul 2018 18:36:42 -0400 (GMT-04:00), you wrote:

You can still buy Ni-Cad replacements for cordless phones, but I always extend the leads and mount them away from anything they can damage. You may have to buy a three cell package and remove one cell, but some are easily reworked and cheap. They are sold by many places, and on Ebay.

Agreed. There are two cell packages (somewhere) as well. The main
problem with the NiCds is twofold. One is the amount of time between
use/charge and loss of calibration data. The second one, (of more
interest once you finally have the calibration equipment) is the
damage a leaking NiCd will cause. Hopefully, the Lithium primary
cells don't do that. IIRC, such cells were not included in the
design, although I do remember one in the AWG series.


Harvey

Hi everyone,

Ok, I've created a photo album ("DM5010 NiCad battery replacement info") with the battery schematic part and spec of the CMOS RAM.

According to the DM5010 manual, the battery is to be replaced every 2 years.
Procedure is to let the DM5010 running 24h for the battery to fully charge, and then do the calibration.

The CMOS RAM (U1220) that is battery backed, is a HMI-6562-9 (Harris).
According to the specification, the data retention supply current is 10uA max.
For a 110mAH, that would be (110 / .01) = 11000 hours (458 days) for full discharge?
At least, the battery should handle a month or two, I guess?
Correct me if I'm wrong.

Also, according to the schematic, we have a current limit of around 24mA (R1135 limiter resistor at 100R for around 2.3-2.4V) for the trickle charger.
But the trickle charge would be quite high as R1131 is only 100R. Let's say BT1121 is 2.4V and CR1133 cathode is 5V, that would be around 24mA.
Even for the original battery spec'ed at 150mA, trickle charge should be C/10 = 15mA.

My planned replacement battery is spec'ed at 4mA for trickle charge, should I replace R1131 by a 680R resistor? This would give around 3.5mA max.

Thank you for your comments.

Best regards,

You can certainly trickle charge some NiMH cells depending on the mfgr. I’ve used Panasonic cells that have a trickle charge spec. The trick is that the trickle charge level can’t generate more evolved oxygen than can be absorbed at operating temps. That is the upper bound on trickle charging.
There is also a lower bound on trickle charging that is often overlooked. You have about 15-20 hrs max to recharge to full capacity. The reasoning by mfgrs is vague but true and likely related to temp rise and gas evolution. If you trickle charge at a rate less than that which will fully recharge in 15-20 hrs you will never fully restore full capacity.

Kjo

Sent from kjo iPhone

Half a century after men walked on the moon, can anyone please explain why
batteries still leak? Or why engineers capable of designing incredible
electronics can't at least protect the circuits from leak caused damage?
I'm sure that I'm not the only one who has lost often irreplaceable
electronics to this pitfall.

Russ

--
Good judgement comes from experience; experience comes from bad judgement.

99 times out of 10 a blown fuse is not due to a bad fuse.....

On Mon, 23 Jul 2018 23:45:15 -0500, you wrote:

Half a century after men walked on the moon, can anyone please explain why
batteries still leak?

Because the batteries don't cost $20,000 each. They're made (for
primary cells) as throwaways. For secondary cells, it's the cost.

Or why engineers capable of designing incredible
electronics can't at least protect the circuits from leak caused damage?

They've all been laid off because they are too old, those that did not
retire.

You could protect the circuits, just put the battery in a hermeticly
sealed enclosure.

Look at the original post, though. The DM5010 had a VERY leaky
battery (don't ask how I know) and as such, the battery was to be
replaced every two to three years. This was well within the point
where the battery would leak, so no problem.

What the equipment was NOT designed to do was to sit idle on a shelf
for five to fifteen years, not being used, not being charged, while
the innards of the 5 dollar battery merrily ate away at the seals, or
the shell, way after the point at which the battery would have been
replaced.

Lithium primary cells don't seem to be so badly behaved, although if
you charge the secondary cells wrongly, or short either one; well,
overheating as well as realize that lithium IS very fond of oxygen.

We don't have a good cell chemistry yet, not one that can be charged
thousands of times, has a good power to weight ratio, and so on. Still
looking at the electron valence voltages between something
electropositive and electronegative, and hoping that it's stable,
light weight, and hopefully part of a reversible chemical action.

How to store charge/power WELL is something we don't really know yet.

Harvey

I'm sure that I'm not the only one who has lost often irreplaceable
electronics to this pitfall.

Russ

On Monday, July 23, 2018, Kevin Oconnor <kjo@...> wrote:

You can certainly trickle charge some NiMH cells depending on the mfgr.
I’ve used Panasonic cells that have a trickle charge spec. The trick is
that the trickle charge level can’t generate more evolved oxygen than can
be absorbed at operating temps. That is the upper bound on trickle
charging.
There is also a lower bound on trickle charging that is often overlooked.
You have about 15-20 hrs max to recharge to full capacity. The reasoning by
mfgrs is vague but true and likely related to temp rise and gas evolution.
If you trickle charge at a rate less than that which will fully recharge in
15-20 hrs you will never fully restore full capacity.

Kjo

Sent from kjo iPhone

Hi Russ:

You have a very valid point concerning corrosion due to batteries leaking.? It is probably a matter of economics that makes the manufacturer
continue to provide super thin casings.? Also, the casing cannot encompass the entire battery, there must be electrical isolation between the
terminals which is a natural source of leaking.? If the manufacturer were to encompass the battery in a leak proof shell the weight, cost and
size would go up dramatically.? It all boils down to the almighty buck!

Reed Dickinson

Hi everyone,

Please keep in mind that this DMM has been available since the very beginning of the eighties, if not late seventies.
It has been designed about ten or less years after man walked on moon.
We should now be able to replace the entire CPU board with a single $2-3 micro-controller.

Best regards,

On Tue, 24 Jul 2018 00:26:58 -0700, you wrote:

Hi everyone,

Please keep in mind that this DMM has been available since the very beginning of the eighties, if not late seventies.
It has been designed about ten or less years after man walked on moon.
We should now be able to replace the entire CPU board with a single $2-3 micro-controller.

You can, within limits. The 488 bus is a difficulty, and may be more
happily replaced with a chip or an FPGA, your choice, although there
are 488 simulators. The front panel had a separate chip that did LED
output scanning and keypad decoding. That can be replaced with a CPLD
if you want. The rest of it is custom interface to the remainder of
the boards and the EEPROM (the CMOS battery backed up RAM being the
main source of the problems).

I would design with an ARM processor (yes, overkill), and an FPGA (I'd
prefer a Xilinx Spartan 6 in a 144 pin TQFP package, which can be done
at home). Then you'd have to have a number of level converters, some
to the 5 volt front panel, and the rest to the 5 volt system boards.

I'd rather overengineer and have capability left over than to get 3/4
of the way through and not have the capability left.

You'd probably do well with a MEGA 64 (64K flash, and I think 8K RAM,
2K EEPROM) which would do for the 5 volt processor (if you wanted),
then you'd need an interface to the 3.3 volt FPGA. Alternative is the
XMEGA series (runs on 3.3 volts) replacing the ARM processor. I ran
out of capability in the MEGA/XMEGA lines a while back and switched to
ARM.


The main problem is not the circuit design, but the replication of the
original program in C. Mostly you want to know what the interface to
the existing hardware happens to be (program wise). The 488 stuff is
better defined.

Harvey

Best regards,