[Test-Equipment] MAHA battery cooker

[Brooke Clarke]

Hi Dick:

I too had that problem with the Maha C777 and sent it back because it was not 
properly figuring out the number of cells in a pack.  For example if you 
connect 4 AA cells in a series string and put them on the charger it should do 
the initial conditioning charge which takes a few minutes then the voltage 
should be about 4 * 1.0 if the pack was dead to 4 * 1.4 if the pack was 
charged, i.e. the pack voltage should be between 4 and 5.6 Volts.  In my case 
the pack voltage was 6.6 V meaning the the 777 did not correctly count the 
number of cells.  They have sent me a new 777Plus-II but I haven't taken it out 
of the box yet.  I did pull the II manual out of the box to see what the II can 
do.  You should do a similar check to see if the 777 can figure out the number 
of cells properly.

Note that the Ni-Cad charge chemistry is endothermic.  That's why a Ni-Cad 
charger typically does not use a temperature sensor.  BUT, Ni-MH charge 
chemistry is exothermic so they get very hot when over charged, hence the need 
for temperature sensors.  With the C777Plus the charge termination was almost 
always an overheat error message.  I was not then paying attention to the pack 
voltage so it may have been miscalculating the number of cells all along.

I have just got going on measuring the shelf life of the Sanyo eneloop 
Ready-To-Use Ni-MH AA cells.  These are supposed to loose only 15% of their 
charge after sitting for a year on the shelf.  It was the Maha C777 that I 
started with but was getting very strange readings.  After a phone consultation 
and running some tests while on the phone they asked to have it back.

In the mean time I got the Maha C9000 AA charger/Analyzer/Conditioner, see:
http://www.prc68.com/I/MHC9000.shtml
It has 4 independent slots that can be doing completely different things.  So I 
tried using it for the eneloop testing, but the consistency of the battery 
capacities was less than I'd hoped for.  Note the C9000 uses delta V/delta V 
charge termination which is the common method for fast chargers, BUT when you 
do that the battery is not being filled completely.

I got the Maha MH-C401FS with the eneloop cells which is just a charger and so 
tried using it for charging the enelopps and the C9000 to analyze them and WOW, 
it's great, see: http://www.prc68.com/I/MHC401FS.shtml
 From what I can tell the C401FS uses the delta V/delta V charge termination, 
then waits a short while, then adds a topping charge at a low current.  This 
has the effect of filling the battery but not over heating it.

Look at the preliminary test data on the Ready-To-Use web page, see:
http://www.prc68.com/I/RTU-Batt.shtml#PCT
you can see that prior to using the C401FS the capacity data on the exact same 
cell was quite different, but after using the C401FS for charging the data is 
repeating better than 1%.  In addition to the Ready-To_use cells, two different 
brands of Ni-MH and some Ni-Cads also will be tested for shelf life.

The Triton2 also has the topping charge function and it's programmable in terms 
of mAh.  But it's a single channel charger so would be much slower when testing 
4 batteries at a time.  For more on the Triton2 see:
http://www.prc68.com/I/Triton2.shtml
For me the great thing about the Triton2 is that it can charge a string of 20 
Ni-MH cells allowing for simple charging of a battery pack for my 5590BA 
battery adapter, see: http://www.prc68.com/I/5590BAv2.html

Have Fun,

Brooke Clarke, N6GCE
http://www.PRC68.com
http://www.precisionclock.com
http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Cam


Dick KF4NS wrote:
> Hope this is the right forum for this, could not find any other more 
> appropriate.
> 
> I have the Maha MH-C777PLUS-II which Maha gave me as a replacement for 
> my failed original PLUS version. I have tried several times to query 
> them about the problem with it cooking my NIMH batteries of various mah 
> values. They get so hot that they cannot be touched. Sometimes the temp 
> sensor brings on the error code but mostly not.
> 
> I asked them if there is a mod to cure this trouble. They do not seem to 
> be willing to answer any questions by email. All the NICAD charge great 
> at normal charge as well as in the discharge mode which I use after 
> several normal charges. Never had a problem with the NICADs, jus the NIMH.
> 
> Any help/advice would be greatly appreciated.
> 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!