Author Topic: MAHA MH-C800S Charger teardown  (Read 11741 times)

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Offline pgross

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MAHA MH-C800S Charger teardown
« on: June 21, 2014, 01:56:02 pm »
Hi,

Just purchased a MAHA MH-C800S Powerex Ni-Mh / Ni-Cd charger and want to share some teardown photos of the unit.

My charger is the smallest model in the 800 series. It will charge 8 pcs. AA or AAA batteries in 1-2 hours and it incorporates a “conditional” feature where the batteries are charged lightly at first – then discharged slowly and finally charged to full power. This feature can breathe new life in older and infrequently used batteries – and it really works!   

With just four rounds of charging on the milage I think it is time for a teardown – lets go - enjoy.

/Peter
« Last Edit: June 21, 2014, 02:00:50 pm by pgross »
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Offline DJ

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Re: MAHA MH-C800S Charger teardown
« Reply #1 on: June 21, 2014, 02:01:42 pm »
 Have one of those,  works well but the rightmost two batteries get warm. Your pictures show why.

Maybe some hack to bump the heatsink efficiency - larger + some better thermal coupling to the outside world.
 

Offline pgross

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Re: MAHA MH-C800S Charger teardown
« Reply #2 on: June 21, 2014, 02:27:14 pm »
Hi DJ,

You're absolutely right about the rightmost batteries gets pretty warm. Thats exactly why I have created a little L shaped heatsink to replace the original tiny heatsink. See the attached picture.

Also to my surprise, the big inductor "L1" gets very warm during charging.

In general I'm happy with the charger, and the build quality is actually pretty decent to say at least - especially with respect to the relative low price of the charger.

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Offline DJ

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Re: MAHA MH-C800S Charger teardown
« Reply #3 on: June 21, 2014, 06:06:30 pm »
Nicely done!

 :-+
 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #4 on: June 22, 2014, 12:33:21 pm »
Thanks for the good tear down.  Instructions:

http://www.powerex.es/descargas/MH-C800S_manual_EN.pdf

This is a good charger for a non-tech person. 

Its most helpful to be able to set each charge slot individually and independently; for example you can charge slot #1 at 1A, Slot #2 at 0.5A, Slot #3 conditioning, slot #4 discharging etc., which is offered by the Maha C-9000.  NiMH cells do not age at the same rate, some will need to be reconditioned sooner, some not; as it ages, some will require a lower maximum charge rate, some not.  The first indication of aging is the affected cell gets warmer than the others at the same charge rate, thus that particularly cell needs to have a lower charge rate or be reconditioned so it can work like new.   If the instructions posted are true, the charge rate or reconditioning mode is set for all the bays equally once it is set.

The C-9000 is the same price [at least by Amazon USA], and will keep NiMH cells in like new condition for many years, but only has 4 charge slots.  With LSD NiMH cells you can stock up on charged batteries, but if you use a lot of batteries quickly [ say with children's toys] having one multi-bay charger is better to get charging done quickly, and maybe one C-9000 to repair and characterize the batteries for later.




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Offline Rick Law

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Re: MAHA MH-C800S Charger teardown
« Reply #5 on: June 25, 2014, 05:21:03 am »
When I was shopping for a charger, I read a bunch of reviews.  I saw 3 or 4 reviews claiming that this one is weak at detecting negative delta v.

In your experience, is that true?
 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #6 on: June 25, 2014, 03:22:45 pm »
Which charger, the C800S or the C-9000?

When I was shopping for a charger, I read a bunch of reviews.  I saw 3 or 4 reviews claiming that this one is weak at detecting negative delta v.

In your experience, is that true?
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Offline Rick Law

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Re: MAHA MH-C800S Charger teardown
« Reply #7 on: June 26, 2014, 03:01:53 am »
Which charger, the C800S or the C-9000?

When I was shopping for a charger, I read a bunch of reviews.  I saw 3 or 4 reviews claiming that this one is weak at detecting negative delta v.

In your experience, is that true?

The C-9000.

Just curious if that was true.  The turning point for me was a review of the UI, it appears that the LaCross has a more intuitive UI, so I went with a lacross BC700, so I am no longer in the market for a charger.
 

Offline pgross

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Re: MAHA MH-C800S Charger teardown
« Reply #8 on: June 26, 2014, 07:31:33 am »
The C-9000 was on my list before I went with the C800S. I can see some advantages on the C-9000 that may become helpful if I want to analyze or “restore” some Ni-Mh’s, but for plain and hassle free charging the C800S is fulfilling the task – primary for charging batteries for my Speedlight flashes, and I utilize the Slow charging mode most of the time.

I recently discovered some older Panasonic 1800 mAh Ni-Mh batteries that went pretty warm during the Conditional charging. I did not measure the temp on the batteries but to my touch I felt like it was in the 40-50 °C range. One or more batteries actually produced some popping/farting noise for some minuts.

I really don’t know if this is a normal behavior, as I haven’t observed this on some of my relatively new Eneloops.

I don’t know if the C800S have issues with the -?V feature.

Best Regards

Peter
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Offline HKJ

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Re: MAHA MH-C800S Charger teardown
« Reply #9 on: June 26, 2014, 11:04:02 am »
I don’t know if the C800S have issues with the -?V feature.

It is fairly common for NiMH chargers (Even C-9000) to terminate on voltage, instead of -dv/dt.
They terminate at around 1.45 to 1.50 volt (Measured with current off) and reports battery charged.
Some chargers (Like C-9000) will then apply a top off charge, other chargers only uses a trickle charge.
 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #10 on: June 26, 2014, 03:47:39 pm »
Yes, the C-9000 can terminate early.  It uses a combination of Negative Delta V, Zero Delta V, Peak Voltage, time and temperature to determine the end-of-charge.  It also has some unsaid end of charge terminating algorithms, aka proprietary.  What it actually uses depends on the health of the battery being charged and the mode you select, the main indicator of its health is the impedance test, the voltage slope at the time of the charge, then lastly temperature. 

Effectively I've never seen the batteries overheat in a C9000.   Oveheat is defined as >45oC, the temperature cutoff of the C9000 is 50oC.  The typical battery temp in a C9000 is 35-40oC.  All the above assume room temperature is 25oC.

http://www.mahaenergy.com/FAQ-C9000/

http://www.amazon.com/review/RZCMBYAN3QKN3

Key to any charging is to preserve battery life [e.g. total charge cycles or calendar working life] and its mAh rating.  As the batteries a C-9000 charges remain like new now over 5 years old, and its prevented deterioration of cells I still have in use from 2006, it would seem from practical purposes Maha method, is a better method.  Also, the battery Ah at end of charge is within specifications, e.g. a 2000mAh eneloop specifies that its provides a minimum of 1900mAh based on the IEC test curve, after a 'proper' charge.

A cautious word.  I own one working Lacrosse charger and had to troubleshoot 2 others that burned. 

Insufficient cooling: The BC700 runs above 40oC at maximum current, the BC9009, 900 and BC700 use the same chassis, it easily overheat over 50oC at 1C charge current; it worse if all the bays are used.  They simply up-spec'd the components without properly ventilating the units, which was marginal with the BC700.  failure ranges from burned cells or charger components burn internally without destroying the cells, or both, either are fire hazards. 

That photo is from a BC700 from 2013 we had on a expedition, ruining brand new sets of eneloops and itself.  The money was one thing, that we were in a remote island was worse as replacing the lost equipment was impossible.




IMHO Lacrosse gets away with their design because the default charge current is 200mA on their units; this is far underneath its rated capacity.  To program the Lacrosse incurs a >0.5sec delay between each key press, whereas on the Maha each key press is instant; so while the Lacrosse shows multiple values on demand versus the cycling of the Maha, it takes longer to custom set a Lacrosse making it more cumbersome to use.  Thus, I've rarely seen a LaCrosse charger owner who use the advance functions; its often on the defaults.

The BC700 is the best of their units as its unlikely to self destruct, but it can overheat the batteries it charges at its 700mA charge current, but its not likely to burn.  On the other units, if you own one use a fan on high when using 500mA or higher.

Note the unit that fried the eneloops above did so at default charge current 200mA.


The C-9000.

Just curious if that was true.  The turning point for me was a review of the UI, it appears that the LaCross has a more intuitive UI, so I went with a lacross BC700, so I am no longer in the market for a charger.
« Last Edit: June 26, 2014, 06:01:28 pm by saturation »
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Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #11 on: June 26, 2014, 04:01:10 pm »
Those are not normal, and those cells are likely at or near end of life, noises are likely vented gas.  One thing the C9000 does is the 'impedance' test so it does not charge cells that could react this way.  Essentially its a test of internal resistance.  After a few seconds of this test, it either begins charging or refuses to charge it.  Cells the C9000 rejects can be charged elsewhere, or used in the break-in mode at user programmable currents; you could also try reconditioning them to see if it reduces heating later on.  Given better NiMH chemistry around its better to retire older cells to prevent accidents once such symptoms occur or it fails the C9000 impedance test.


I recently discovered some older Panasonic 1800 mAh Ni-Mh batteries that went pretty warm during the Conditional charging. I did not measure the temp on the batteries but to my touch I felt like it was in the 40-50 °C range. One or more batteries actually produced some popping/farting noise for some minuts.

I really don’t know if this is a normal behavior, as I haven’t observed this on some of my relatively new Eneloops.

I don’t know if the C800S have issues with the -?V feature.

Best Regards

Peter

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Offline HKJ

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Re: MAHA MH-C800S Charger teardown
« Reply #12 on: June 26, 2014, 04:04:31 pm »
Yes, the C-9000 can terminate early.  It uses a combination of Negative Delta V, Zero Delta V, Peak Voltage, time and temperature to determine the end-of-charge.  It also has some unsaid end of charge terminating algorithms, aka proprietary.  What it actually uses depends on the health of the battery being charged and the mode you select, the main indicator of its health is the impedance test, the voltage slope at the time of the charge, then lastly temperature.

I have been running a couple of tests on it and I did not see a -dv/dt or 0 dv/dt termination, all termination was on maximum voltage and before the battery was full.

When testing capacity there is two ways, the break-in mode that charges for 16 hours with C/10 and the battery will always reach with maximum capacity. There is also the refresh mode, where it add 200mAh after the regular charge, this does also usual mean a AA battery will be full.
When doing a normal charge you have to leave the batteries in the charger for two hours after it says full, to get the extra 200mAh.

Charging 4 AA at full current will get above 40C, a more normal charge will not:

The charger says "done" at the yellow line.


 

Online dunkemhigh

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Re: MAHA MH-C800S Charger teardown
« Reply #13 on: June 26, 2014, 04:15:33 pm »
Quote from: saturation
Effectively I've never seen the batteries overheat in a C9000.   Oveheat is defined as >45oC, the temperature cutoff of the C9000 is 50oC.

I have. I sent photos, to Maha support, of a battery being charged at 0.75C despite the battery being at 68C. I was asking if I had a faulty charger since I understood, as you do, that charging would be terminated if the battery got to 50C.

A Maha engineer replied:
Quote
C9000 sets OTP at 45C. This is not the battery temperature. This is the
temperature at the sensor. The internal temperature of battery will be
much higher. Heat will pass through battery case, negative contact
terminal and metal plat to the sensor. When temperature reaches the
limit, C9000 controller will reduce charging current 50%. It does not
shut down.

The C9000 doesn't actually match up with the hype, although it is still a pretty decent charger (albeit with a rather poor UI).

Edit: the particular battery was an Ansmann with 2100mA capacity, so 1500mA was being shoved into it. When, or if, the charger finally figures it is a bit hot, that would be reduced to 1000mA, which is still a bit high for my liking. Note that this was during battery capacity testing so the charger would be expected to be left on for 2 or 3 days continuously...
« Last Edit: June 26, 2014, 04:21:15 pm by dunkemhigh »
 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #14 on: June 26, 2014, 04:34:32 pm »
HKJ a most excellent revue review, I've never seen it before.  Will compare notes and report back.

http://lygte-info.dk/review/Review%20Charger%20Powerex%20MH-C9000%20UK.html

dunkemhigh I'm surprised as I have 3 units purchased in 2010, 11, 13.  Will revisit what the units do at 0.75C or more.  Your temps appear close to HKJ thermgraphs.


I have been running a couple of tests on it and I did not see a -dv/dt or 0 dv/dt termination, all termination was on maximum voltage and before the battery was full.
Quote from: saturation
Effectively I've never seen the batteries overheat in a C9000.   Oveheat is defined as >45oC, the temperature cutoff of the C9000 is 50oC.

I have. I sent photos, to Maha support, of a battery being charged at 0.75C despite the battery being at 68C. I was asking if I had a faulty charger since I understood, as you do, that charging would be terminated if the battery got to 50C.

« Last Edit: June 26, 2014, 09:10:49 pm by saturation »
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Offline HKJ

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Re: MAHA MH-C800S Charger teardown
« Reply #15 on: June 26, 2014, 04:55:45 pm »
HKJ a most excellent revue, I've never seen it before.

That review is very recent, but I have been doing charger (Mostly LiIon) and battery reviews for a few years: http://www.lygte-info.dk/info/indexBatteriesAndChargers%20UK.html

 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #16 on: June 26, 2014, 09:10:14 pm »
That's great, I'd like to discuss these results as I get more data of my own and check the old studies from candlepower forum.  Mods feel free to break this thread into a Maha C-9000 thread if you so choose.


HKJ a most excellent revue, I've never seen it before.

That review is very recent, but I have been doing charger (Mostly LiIon) and battery reviews for a few years: http://www.lygte-info.dk/info/indexBatteriesAndChargers%20UK.html


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Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #17 on: June 27, 2014, 08:06:43 pm »
HKJ, kudos to your methods, gear and presentation  :clap:, it is very comprehensive and clear.  I would only comment on your conclusions.

http://lygte-info.dk/review/Review%20Charger%20Powerex%20MH-C9000%20UK.html

Regardless how a charge algorithm terminates, the final result must be to provide the rated cell Ah and to charge without overheating [< 45oC].  If the cells are undercharged one never gets the Ah one paid for even if not overheated, and if a charger charges a cell to 100% of its rated Ah but overheats, it reduces the lifespan of the cell, further reducing the available Ah over time.



Your chart summarizes my experience with 2A rated NiMH cells charged in the C9000 since 2007, eneloop or otherwise.  The final output capacity by various charge methods is between 95-98% of the rated Ah without raising the cell's surface temperature over 40oC, as many of your graphs show, i.e., black line.  The eneloops in particular are labeled that the final Ah is no less than 1900mAh for a 2000mAh rated cell, and can also be seen in the graph of the eneloop spec sheet, attached.







By contrast, my BC9009 at 0.5C causes the cells to rise  > 50oC and while likely terminated by -dV/dt still provides the same Ah as the Maha similar to this post from Candlepower:

http://www.candlepowerforums.com/vb/showthread.php?188349-AA-fast-chargers-Delta-V&p=2363047&viewfull=1#post2363047


@dunkemhigh

At room temperature, 25oC, at charge currents of 1A or less with all bays full, I've not seen the Maha overheat cells.  I do not have a thermal imager, but to compensate I scanned the surface of the charger with the IR thermometer than is calibrated against a thermocouple, see photo, to identify hot spots.  Cells were charged at 1C and 0.5C.  Thermocouple is located near the Maha thermal sensor on the charge bay, i.e., negative terminal.

I have also just tested the C9000 on all bays at 2C or 2A, with temps reaching 57oC.  I need to double check the results before I post as my 2 units terminated charging, it did not reduce current 50% and continue the charge.



HKJ a most excellent revue, I've never seen it before.

That review is very recent, but I have been doing charger (Mostly LiIon) and battery reviews for a few years: http://www.lygte-info.dk/info/indexBatteriesAndChargers%20UK.html
« Last Edit: June 27, 2014, 08:16:03 pm by saturation »
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Offline HKJ

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Re: MAHA MH-C800S Charger teardown
« Reply #18 on: June 27, 2014, 08:27:46 pm »
The problem is that the charger needs the 2 hours top-off charge, after it has reported done, to charge the cell "full".
Here is a charger where the top-off charger does fill the battery (There is a temperature increase):


That charger can also do true dv/dt, but I did not have temperature probe on when I did that track:
 

Online dunkemhigh

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Re: MAHA MH-C800S Charger teardown
« Reply #19 on: June 27, 2014, 11:57:07 pm »
Quote
At room temperature, 25oC, at charge currents of 1A or less with all bays full, I've not seen the Maha overheat cells.

It gets barely warm with good Eneloops. I got the charger because my existing cells seemed to be flaky and I wanted a fuss-free way to properly charge and test them. I wound up throwing most of them out (they'd been fried by a crap fast charger), and the high temperatures were seen when charging these cells.

The issue, to me, is not that good cells reach that temperature (they don't) but that the charger didn't recognise when it had bad cells. Could it burn my office down? I really don't want to find out...
 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #20 on: July 01, 2014, 04:01:15 pm »
I did some tests over the weekend. 

For a quick check on how chargers respond to heat just point a hair dryer, or heat gun on low setting, to the thermal sensor port, while the charger is charging; it will force it to trip prematurely.  You can then examine the programmed response. 

The actual cutoff point, for both LaCrosse BC9009 and Maha C9000 is  ~57oC.  I used the hair dryer method and I confirmed this by charging old 1A NiMH cells at 2A to force it to overheat.  The LaCrosse is no longer made and replaced by the BC1000.

On both my C9000, the charger terminates charging and goes into trickle mode, despite what the Maha folks say.  I checked all charger bays for a total of 8 bays on 2 chargers.  Each port has its own sensor.

The BC9009 zeroes output current and resumes charging at 45oC.  See photo marked B.  The charger was set at 700mA.  Bay #1 is 'FULL' while #3 continues to charge.

So at least with these chargers, even with my bad cells and treated badly, the thermal cutoff work and should not cause your office or home to burn, but the C9000 will allow a long cool down period should a cell overheat.  NiMH do not flash or burn when overheated, they bubble out and melt like boiling water.

However, that model LaCrosse overheats cells.  Because it resumes charging at a high temperature, the final temperature of cells hover between 45-57oC.   In the photo note the IR thermometer detects the center of the test cell is 59oC while the tip of the battery on the Agilent thermocouple in 51oC.

However, you can use the LaCrosse if you use active cooling it to keep the temps below 45oC or do not exceed 500mA charge current for each bay with passive cooling.

Quote
At room temperature, 25oC, at charge currents of 1A or less with all bays full, I've not seen the Maha overheat cells.

It gets barely warm with good Eneloops. I got the charger because my existing cells seemed to be flaky and I wanted a fuss-free way to properly charge and test them. I wound up throwing most of them out (they'd been fried by a crap fast charger), and the high temperatures were seen when charging these cells.

The issue, to me, is not that good cells reach that temperature (they don't) but that the charger didn't recognise when it had bad cells. Could it burn my office down? I really don't want to find out...

« Last Edit: July 01, 2014, 04:05:07 pm by saturation »
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Online dunkemhigh

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Re: MAHA MH-C800S Charger teardown
« Reply #21 on: July 01, 2014, 06:29:26 pm »
Quote
just point a hair dryer, or heat gun on low setting, to the thermal sensor port

If you'll pardon my French, that's a fairly useless test. Sure, it will tell you that the sensors do indeed sense, and it does indeed got into trickle when the sensors are hot. But in real life they are getting heat conducted along the charge pins. The battery can get really seriously hot (as I note, I've seen 68C) without that heat all making its way to the sensors via conduction. When batteries come with hair dryers attached, your test may be more reasonable.

A better test is to put heat a bad battery (or fake battery) with a soldering iron or something, and then see how long it takes for the sensors to catch up.
 

Offline saturation

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Re: MAHA MH-C800S Charger teardown
« Reply #22 on: July 01, 2014, 08:45:00 pm »
Yes, did so, as posted on my message.  The hair dryers simply insures the thermal circuits are functional, why risk the batteries bursting if it did not work?

Quote
just point a hair dryer, or heat gun on low setting, to the thermal sensor port

If you'll pardon my French, that's a fairly useless test. Sure, it will tell you that the sensors do indeed sense, and it does indeed got into trickle when the sensors are hot. But in real life they are getting heat conducted along the charge pins. The battery can get really seriously hot (as I note, I've seen 68C) without that heat all making its way to the sensors via conduction. When batteries come with hair dryers attached, your test may be more reasonable.

A better test is to put heat a bad battery (or fake battery) with a soldering iron or something, and then see how long it takes for the sensors to catch up.


@ HKJ:

Yes, 2 more hours are needed to take the battery from 90-95% to 95-100%, but the price compared to dV/dt termination is near absence of overheating.  As you clearly point out in many of your graphs,  +dT occurs with -dV so clearly one can expect  >45oC to happen nearly always using -dV charge termination.

Is having 10% more mAH worth risking reducing cycle life?  It is clear heat during charging is the enemy of NiMH but its not clear for how long a cell can sustain > 45oC before damage occurs internally.  In most of your graphs, the C9000 does not overheat during charge cycles.

I repeated some of your tests to confirm the charge algorithm and sequence, and indeed the Maha never does go beyond voltage cutoff.  However, I could not replicate the overheating you have on the thermogram except once, by charging 4 1A NiMH cells at 2A.  It reached 51oC but did not trip the thermal sensors [ sensors pre-tested to be working. ]



I think the NC2500 you post maybe part of the answer for those looking for the most in a charger, a user customizable charge termination.


The problem is that the charger needs the 2 hours top-off charge, after it has reported done, to charge the cell "full".
« Last Edit: July 01, 2014, 08:46:35 pm by saturation »
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Online dunkemhigh

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Re: MAHA MH-C800S Charger teardown
« Reply #23 on: July 01, 2014, 10:59:04 pm »
Quote
Yes, did so, as posted on my message

Sorry, it wasn't clear to me when I read it, but I am kind of pre-occupied today. I would expect some controlled  heat injection rather than relying on duff cells. As you can see from my picture, the heat is all in the battery and little is leaking into the charger:



My understanding is that the sensor is at the bottom end, and that's just within spec:



These are after some time left on charge, not after a short while warming up. All I can say is that they are not the results I'd expect from reading your post.
 

Offline HKJ

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Re: MAHA MH-C800S Charger teardown
« Reply #24 on: July 02, 2014, 06:16:18 am »
Is having 10% more mAH worth risking reducing cycle life?  It is clear heat during charging is the enemy of NiMH but its not clear for how long a cell can sustain > 45oC before damage occurs internally.  In most of your graphs, the C9000 does not overheat during charge cycles.

Even if it cost 50% in cycle life, it is not really a problem with good cells (Eneloop is rated at 1800 cycles).
But I do not have any information about how much damage temperature does to the cell.

I repeated some of your tests to confirm the charge algorithm and sequence, and indeed the Maha never does go beyond voltage cutoff.  However, I could not replicate the overheating you have on the thermogram except once, by charging 4 1A NiMH cells at 2A.  It reached 51oC but did not trip the thermal sensors [ sensors pre-tested to be working.

When I do the thermograph it is with maximum current on all channels.
 

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Re: MAHA MH-C800S Charger teardown
« Reply #25 on: July 02, 2014, 08:36:59 pm »
dunkemhigh, thanks for providing added details; those are very concerning thermographs.

I don't think such evidence has been shown in most any Internet site for this charger.  I wouldn't expect cells to reach that temperature without triggering the thermal sensor, now I see I am in error.    If the charger you have is not faulty, then the Maha C9000 as designed cannot pick up a potentially dangerous condition.  Even if the cells you used were faulty, the Maha should have shut down by now. 



These are after some time left on charge, not after a short while warming up. All I can say is that they are not the results I'd expect from reading your post.
Best Wishes,

 Saturation
 

Online dunkemhigh

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Re: MAHA MH-C800S Charger teardown
« Reply #26 on: July 02, 2014, 09:35:13 pm »
Quote
Even if the cells you used were faulty, the Maha should have shut down by now.

Indeed, that was my concern when contacting support. Their response was somewhat disappointing (in acknowledging that the charger isn't faulty) but I am at least aware of it now.
 


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