Author Topic: [Fixed] Keysight U1252B battery charging behavior (hot battery!)  (Read 6017 times)

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Offline bitseeker

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I picked up a new U1252B DMM last week. It was manufactured in 2015. After unwrapping the included NiMH 8.4V 250mAh battery, I checked how much power was in it using the DMM's bar graph battery level checker and it was around 60%. So, I plugged in the included charger and let it do its thing.

The charging system in the DMM has a maximum charge time limit of 220 minutes. The battery should be full before that time and the meter should indicate when charging has been completed.

However, in my case, the DMM never indicated it was done. Instead, as the countdown timer got down to about half an hour remaining, I noticed that the case of the meter around the battery compartment was quite warm to the touch. Taking the battery cover off and touching the battery itself, it was hot. Not good.

In order to see if this might have just been an anomaly with a battery that has been in storage for a year, I let the meter run the battery down until its battery icon started flashing. The battery level showed 0% on the bar graph. Checking the voltage on the battery terminals, it read about 6.5V. That seems rather low. With 7 cells inside an 8.4V battery, 1V per cell would be 7V for "empty".

Anyway, I plugged the charger back in, with my bench DMM reading the current to the battery. When the charger engaged, the battery terminals started off at about 8.5V. Charging current was about 156mA.

Over the course of a couple of hours, the current slowly dropped to about 148mA and the battery came up to 11V. That's when the battery started to heat up again. I pulled the plug on the charger before it overheated the battery again.

The documentation isn't very clear, but it seems that the bar graph is supposed to indicate the state of charge as it's charging. In my case, the bar was always at 76% from empty to the point the battery started to heat up. After removing the charger and letting the battery settle for half an hour, checking the battery level showed 100% on the bar graph.

So, what's going on?

Bad battery? The DMM's pre-charge test passes. The battery holds a good charge, requiring many hours to fully drain it by running the DMM. However, I didn't measure its actual capacity.

Bad charger in the DMM? Could it be failing to correctly sense the state of charge and overcharging the battery as a result?

The meter is under warranty, of course, but I like to have a reasonably good sense of what a problem is before sending anything (electronics, car, myself) in for service.

Searching the interwebs didn't turn up any info about known charging issues like this with the U1251B or U1252B. The U1253B had a charging problem, but it was undercharging and a firmware update was released to correct the battery charging time. I could not find a service note for the U1252B about charging the battery.

Has anyone encountered this behavior with their U125xA or U125xB, or even some other battery charger to shed some light on what's going on?
« Last Edit: October 12, 2016, 11:21:13 pm by bitseeker »
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Offline ArcticGeek

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #1 on: August 15, 2016, 06:49:47 pm »
I have both a U1252A and a U1252B, and I have not experience the problem you have described.  It sounds to me like you might have a bad battery though.  What you might want to try is to buy a different battery to see if the problem goes away.  I would recommend the Ray-O-Vac rechargeable 9V battery that Best Buy sells - it only cost $8.99 and is sold in most of their stores.  While this is only a 200mA-hr battery (vs. the 250ma-hr battery that comes with the U1252B), it is a low-self-discharge type of battery and I have found that it works better for my use because of that.  I purchased my U1252A without any battery, and decided to buy this Ray-O-Vac battery for my U1252A.  The price was right and I could buy it at my local store, so I gave it a whirl.  I was pleasantly surprised on how well it worked.

For $9 it's probably worth a try to see if this fixes your problem, as it might save you the hassle of returning the meter.
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #2 on: August 15, 2016, 09:32:00 pm »
Hi AG. Thanks for the confirmation on the behavior of your DMMs and the battery recommendation. I'll give another battery a try. A low self-discharge battery is a good thing to use regardless.
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Offline TheSteve

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #3 on: August 15, 2016, 10:35:45 pm »
With such a high charge rate I don't see how the battery wouldn't get hot. Unless of course it has a thermal sensor(doubtful) or is using a peak detect(negative delta V) charge circuit. A timer only based charger with such a high charge rate will always cook the battery.
If a NiMH battery sits for a long time or is over discharged it will tend to give false peaks when charging instead of not giving a detectable peak at all.
More then anything it sounds like the default charge rate is too high.
It will be interesting to hear the results of a new battery.
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #4 on: August 15, 2016, 10:51:35 pm »
@TheSteve

Yeah, it's puzzling, so I figured I'd make this thread about it. It seemed out of the ordinary, but I wasn't sure. NiMH doesn't get hot at this rate until it's full, which is why some chargers trigger based on the sudden temp change to know when to shut off.  The negative delta V tends to be fairly small, so that's why I initially suspected a potential problem with the charger, but a bad battery is as much a possibility. The timer, as far as I can tell, is simply a fail safe to prevent grossly overcharging. At ~0.6C charge rate, a completely flat 250mAh battery will be full in approximately half the duration of the 220-minute charge timer.

@ArcticGeek

If you have the opportunity to measure the initial charge rate on your U1252B, that'd be a useful bit of comparison data. Thanks.
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Offline VK5RC

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #5 on: August 15, 2016, 11:00:14 pm »
I have a U1253B and I recall a firmware update (on the u1235b at least) that resolved a charging issue. Certainly worth a look into firmware version and Keysight update pages
Whoah! Watch where that landed we might need it later.
 

Offline nanofrog

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #6 on: August 16, 2016, 01:35:17 am »
I have a U1253B and I recall a firmware update (on the u1235b at least) that resolved a charging issue. Certainly worth a look into firmware version and Keysight update pages
FWIW, there's no new firmware for the LCD versions in the U125xB series; just the logging software is available in the downloads section.
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #7 on: August 16, 2016, 03:39:20 am »
Correct. No firmware updates for U1252B. The charging problem with the U1253B was undercharging due to the charging timer value being incorrect.
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Offline VK5RC

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #8 on: August 16, 2016, 11:22:51 am »
A long shot re the update, Bugger.

Here is a shot of what came in my U1253B about 5yo now.
Whoah! Watch where that landed we might need it later.
 

Offline nanofrog

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #9 on: August 16, 2016, 02:53:54 pm »
A long shot re the update, Bugger.

Here is a shot of what came in my U1253B about 5yo now.
Same came in my U1252B, which is about 7yo and still holds a charge.

Since all my meters to date use 9V batteries, using a 3rd party charger and LSD rechargeable batteries is convenient (+ reduced risk of battery leakage).
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #10 on: August 16, 2016, 09:54:09 pm »
Mine came with a PowerEx also, but a 250mAh version with black housing instead of the 300mAh white ones you guys got. There's a new 300mAh PowerEx with low self-discharge, also in a black housing.

For testing, I ordered the 200mAh Ray-o-Vac that Arctic Geek had good results with it. I'll update this thread again after I've cycled the battery a time or two.
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Offline amitchell

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #11 on: August 17, 2016, 12:42:27 am »
Is it worth getting the rechargeable battery for these meters?

I purchased a Demo stock U1252A that came with all accessories and extra bits, but did not come with a rechargeable battery. I have thought about picking one up when my last 9v is used up.
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #12 on: August 17, 2016, 12:54:08 am »
Is it worth getting the rechargeable battery for these meters?

Yes. I wish non-rechargeable batteries would disappear. They're wasteful, expensive, and cost even more when they leak into and damage the device they're powering. I hate single-use batteries. Grrr.
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Offline ArcticGeek

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #13 on: August 17, 2016, 04:45:14 am »
Hi bitseeker,

As luck would have it, my U1252B meter was in need of a battery recharge.  Pressing the "bat" button showed only 1 or 2 bars on the fuel guage, so I pulled the battery cover off and probed the battery.  The battery voltage measured 8.547V.  After installing the charger, the current into the battery starts out initially at only about 6mA during the very first part of the self test (for about 5 sec), then jumps up to 157mA.  The self test then takes a minute or so to complete, and then the actual battery charging begins with the meter switching to the "220 minute" display.  At this point the battery charge current remained steady at about 159mA, nearly identical to what you measured on your unit.  I can't tell you much more than that because I just started the unit charging and I don't plan to stay up to monitor it - its amost midnight here - must sleep!

I too have have black & gray PowerEx 8.4V battery rated at 250ma-hr in my U1252B.  I think the white batteries that other people mention on the older units are 7.2V batteries - Keysight still shows them on their Find-A-Part website but they have been obsoleted by the newer 8.4V batteries.

Although this PowerEX battery is rated at 250ma-hr, I like the Ray-O-Vac 200ma-hr battery better that is in my U1252A because it has a lower self discharge.  My U1252B almost always needs a charge after about 3-4 months of light use whereas my U1252A is still going strong with about the same amount of use, but your mileage my vary.  But the thing that really motivated me to initially buy the Ray-O-Vac battery is because I could walk into the BestBuy store and buy it over the counter - I guess I'm still old school because I prefer buying something in a real store than ordering online if I can.

Let me know how things turn out.
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #14 on: August 17, 2016, 05:00:59 am »
Thanks for the update AG. That all sounds good. More updates in time.
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Offline nanofrog

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #15 on: August 17, 2016, 05:59:23 am »
Is it worth getting the rechargeable battery for these meters?
Definitely.

It's convenient if you keep the batteries charged (i.e. 3rd party charger), no disposables ending up as landfill, and is much less likely to leak and corrode the terminals on the battery connector.

I think the white batteries that other people mention on the older units are 7.2V batteries.
Yep.
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #16 on: August 29, 2016, 05:53:16 am »
Update: I got a Ray-o-Vac 8.4V 200mAh battery, like ArcticGeek. After draining it to nearly 50%, I plugged in the charger. The behavior was similar. The charging current started at 164 mA, the bar graph slowly came up to 75% and stayed there for approximately half an hour, the current dropping to around 158 mA, until the battery started to warm up. The voltage at this point was 10.2V. I disconnected the charger at this point in order not to overheat the cells and then turned on the DMM to check the battery level. The DMM indicated that it was 100%.

So, when your U125xB is on the charger, does the bar graph go to 100% and then display "End" when the battery is full? Is the battery warm or hot when it ends or at/near room temperature? What is the final voltage?
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #17 on: August 31, 2016, 08:29:54 pm »
Contacted Keysight and explained the situation. They agree it sounds defective and handed it off to the appropriate department to address it. I'll post again when it's resolved in order to wrap up the thread.
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #18 on: September 08, 2016, 11:01:21 pm »
Still trying to get an RMA. They're checking with engineering in Malaysia to find out whether the fault is in the power adapter (which they call the Battery Charging Adapter), which has a 3-month warranty, or the DMM, which has a 3-year warranty.

As far as I can tell, the power adapter is nothing more than a switching power supply. The charge controller should be in the DMM.  ???
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #19 on: September 09, 2016, 05:50:54 pm »
Well, since one of my batteries was at 75%, I decided to confirm that the so-called charging adapter is nothing more than an SMPS (as it should be). So, I hooked up an Agilent E3631A to the charging jacks and fed the DMM 24V, just as the charging adapter does. Same result.

Side note: As one would expect, the DMM only draws 124-126 mA @ 24 V from the power supply while charging the battery. The 2.5 A maximum output of the charging adapter is quite over rated for this purpose. Does Keysight have some other devices that also use this adapter and need much more current?
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Offline TheSteve

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #20 on: September 09, 2016, 07:07:11 pm »
I was looking at the data sheet for your meter and think I figured out the problem. I am not sure they realize they are supposed to charge the battery. The data sheet says "Built-in battery charging for optimum capacitance"
So hopefully your meters capacitance is at least working correctly... :)

http://literature.cdn.keysight.com/litweb/pdf/5989-5509EN.pdf?id=835490
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #21 on: September 09, 2016, 07:19:16 pm »
 :-DD Good one, Steve. When I got it, I checked it with a decade capacitance box and it's looking good there. :-DMM
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #22 on: September 28, 2016, 05:05:19 pm »
Got an RMA and sent in the meter. It'll be a couple of weeks until I get the repaired/replaced device.
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #23 on: October 06, 2016, 01:44:27 am »
Replacement arrived. Thanks, Keysight. :-+

After the battery goes down some, I'll give it a recharge for verification.
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Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #24 on: October 06, 2016, 03:35:38 am »
It's amazing that the charge on your battery lasts so long. Granted, I've intentionally been running mine down for testing, but that's great runtime you're getting. It certainly helps having the LCD screen instead of the OLED one.

When you eventually do recharge your battery via the DMM, guesstimate the time required for it to complete based on the charge current given earlier in this thread. Then, as it approaches that time, watch for the status to change to "done" while monitoring the temperature of the battery or battery compartment.

I also like the meter so far, with what little time I've had it. If I could make changes, some things that I would like to have are (1) faster continuity in auto mode, (2) Low Z mode, (3) non-contact voltage detector, (4) higher maximum signal generator frequency (e.g., 1 MHz or 10 MHz) and (5) lower or adjustable continuity voltage to avoid triggering semiconductor junctions.
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Offline nanofrog

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #25 on: October 06, 2016, 05:06:10 pm »
Ansmann 300mAH 8.4V LSD batteries
Those are very good batteries.  :-+
 

Offline bitseeker

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Re: Keysight U1252B battery charging behavior (hot battery!)
« Reply #26 on: October 12, 2016, 11:20:36 pm »
Recharged two batteries in the new meter and all is well now. The display shows the correct level in the bar graph as it charges and the graph goes to 100% before C-End is displayed at charge termination. :-DMM :-+
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